RFC7325
Internet Engineering Task Force (IETF) C. Villamizar, Ed. Request for Comments: 7325 OCCNC Category: Informational K. Kompella ISSN: 2070-1721 Juniper Networks
S. Amante
Apple Inc.
A. Malis
Huawei
C. Pignataro
Cisco
August 2014
MPLS Forwarding Compliance and Performance Requirements
Abstract
This document provides guidelines for implementers regarding MPLS forwarding and a basis for evaluations of forwarding implementations. Guidelines cover many aspects of MPLS forwarding. Topics are highlighted where implementers might otherwise overlook practical requirements that are unstated or underemphasized, or that are optional for conformance to RFCs but often considered mandatory by providers.
Status of This Memo
This document is not an Internet Standards Track specification; it is published for informational purposes.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7325.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Contents
- 1 Introduction and Document Scope
- 2 Forwarding Issues
- 2.1 Forwarding Basics
- 2.2 MPLS Multicast
- 2.3 Packet Rates
- 2.4 MPLS Multipath Techniques
- 2.5 MPLS-TP and UHP
- 2.6 Local Delivery of Packets
- 2.7 Number and Size of Flows
- 3 Questions for Suppliers
- 4 Forwarding Compliance and Performance Testing
- 5 Security Considerations
- 6 Organization of References Section
- 7 References
Introduction and Document Scope
The initial purpose of this document was to address concerns raised on the MPLS WG mailing list about shortcomings in implementations of MPLS forwarding. Documenting existing misconceptions and potential pitfalls might potentially avoid repeating past mistakes. The document has grown to address a broad set of forwarding requirements.
The focus of this document is MPLS forwarding, base pseudowire forwarding, and MPLS Operations, Administration, and Maintenance (OAM). The use of pseudowire Control Word and the use of pseudowire Sequence Number are discussed. Specific pseudowire Attachment Circuit (AC) and Native Service Processing (NSP) are out of scope. Specific pseudowire applications, such as various forms of Virtual Private Network (VPN), are out of scope.
MPLS support for multipath techniques is considered essential by many service providers and is useful for other high-capacity networks. In order to obtain sufficient entropy from MPLS, traffic service providers and others find it essential for the MPLS implementation to interpret the MPLS payload as IPv4 or IPv6 based on the contents of the first nibble of payload. The use of IP addresses, the IP protocol field, and UDP and TCP port number fields in multipath load balancing are considered within scope. The use of any other IP protocol fields, such as tunneling protocols carried within IP, are out of scope.
Implementation details are a local matter and are out of scope. Most interfaces today operate at 1 Gb/s or greater. It is assumed that all forwarding operations are implemented in specialized forwarding hardware rather than on a general-purpose processor. This is often referred to as "fast path" and "slow path" processing. Some recommendations are made regarding implementing control or management-plane functionality in specialized hardware or with limited assistance from specialized hardware. This advice is based on expected control or management protocol loads and on the need for denial of service (DoS) protection.
Abbreviations
The following abbreviations are used.
AC Attachment Circuit (RFC3985)
ACH Associated Channel Header (pseudowires)
ACK Acknowledgement (TCP flag and type of TCP packet)
AIS Alarm Indication Signal (MPLS-TP OAM)
ATM Asynchronous Transfer Mode (legacy switched circuits)
BFD Bidirectional Forwarding Detection
BGP Border Gateway Protocol
CC-CV Continuity Check and Connectivity Verification
CE Customer Edge (RFC4364)
CPU Central Processing Unit (computer or microprocessor)
CT Class Type (RFC4124)
CW Control Word (RFC4385)
DCCP Datagram Congestion Control Protocol
DDoS Distributed Denial of Service
DM Delay Measurement (MPLS-TP OAM)
DSCP Differentiated Services Code Point (RFC2474)
DWDM Dense Wave Division Multiplexing
DoS Denial of Service
E-LSP Explicitly TC-encoded-PSC LSP (RFC5462)
EBGP External BGP
ECMP Equal-Cost Multipath
ECN Explicit Congestion Notification (RFC3168 and RFC5129)
EL Entropy Label (RFC6790)
ELI Entropy Label Indicator (RFC6790)
EXP Experimental (field in MPLS renamed to "TC" in RFC5462)
FEC Forwarding Equivalence Classes (RFC3031); also Forward Error
Correction in other context
FR Frame Relay (legacy switched circuits)
FRR Fast Reroute (RFC4090)
G-ACh Generic Associated Channel (RFC5586)
GAL Generic Associated Channel Label (RFC5586)
GFP Generic Framing Procedure (used in OTN)
GMPLS Generalized MPLS (RFC3471)
GTSM Generalized TTL Security Mechanism (RFC5082)
Gb/s Gigabits per second (billion bits per second)
IANA Internet Assigned Numbers Authority
ILM Incoming Label Map (RFC3031)
IP Internet Protocol
IPVPN Internet Protocol VPN
IPv4 Internet Protocol version 4
IPv6 Internet Protocol version 6
L-LSP Label-Only-Inferred-PSC LSP (RFC3270)
L2VPN Layer 2 VPN
LDP Label Distribution Protocol (RFC5036)
LER Label Edge Router (RFC3031)
LM Loss Measurement (MPLS-TP OAM)
LSP Label Switched Path (RFC3031)
LSR Label Switching Router (RFC3031)
MP2MP Multipoint to Multipoint
MPLS Multiprotocol Label Switching (RFC3031)
MPLS-TP MPLS Transport Profile (RFC5317)
Mb/s Megabits per second (million bits per second)
NSP Native Service Processing (RFC3985)
NTP Network Time Protocol
OAM Operations, Administration, and Maintenance (RFC6291)
OOB Out-of-band (not carried within a data channel)
OTN Optical Transport Network
P Provider router (RFC4364)
P2MP Point to Multipoint
PE Provider Edge router (RFC4364)
PHB Per-Hop Behavior (RFC2475)
PHP Penultimate Hop Popping (RFC3443)
POS PPP over SONET
PSC This abbreviation has multiple interpretations.
1. Packet Switch Capable (RFC3471
2. PHB Scheduling Class (RFC3270)
3. Protection State Coordination (RFC6378)
PTP Precision Time Protocol
PW Pseudowire
QoS Quality of Service
RA Router Alert (RFC3032)
RDI Remote Defect Indication (MPLS-TP OAM)
RSVP-TE RSVP Traffic Engineering
RTP Real-time Transport Protocol
SCTP Stream Control Transmission Protocol
SDH Synchronous Data Hierarchy (European SONET, a form of TDM)
SONET Synchronous Optical Network (US SDH, a form of TDM)
T-LDP Targeted LDP (LDP sessions over more than one hop)
TC Traffic Class (RFC5462)
TCP Transmission Control Protocol
TDM Time-Division Multiplexing (legacy encapsulations)
TOS Type of Service (see RFC2474)
TTL Time-to-live (a field in IP and MPLS headers)
UDP User Datagram Protocol
UHP Ultimate Hop Popping (opposite of PHP)
VCCV Virtual Circuit Connectivity Verification (RFC5085)
VLAN Virtual Local Area Network (Ethernet)
VOQ Virtual Output Queuing (switch fabric design)
VPN Virtual Private Network
WG Working Group
Use of Requirements Language
This document is Informational. The uppercase RFC2119 key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY" are used in this document in the following cases.
1. RFC 2119 keywords are used where requirements stated in this
document are called for in referenced RFCs. In most cases, the RFC containing the requirement is cited within the statement using an RFC 2119 keyword.
2. RFC 2119 keywords are used where explicitly noted that the
keywords indicate that operator experiences indicate a requirement, but there are no existing RFC requirements.
Advice provided by this document may be ignored by implementations. Similarly, implementations not claiming conformance to specific RFCs may ignore the requirements of those RFCs. In both cases, implementers should consider the risk of doing so.
Apparent Misconceptions
In early generations of forwarding silicon (which might now be behind us), there apparently were some misconceptions about MPLS. The following statements provide clarifications.
1. There are practical reasons to have more than one or two labels
in an MPLS label stack. Under some circumstances, the label stack can become quite deep. See Section 2.1.
2. The label stack MUST be considered to be arbitrarily deep.
Section 3.27.4 ("Hierarchy: LSP Tunnels within LSPs") of RFC 3031
states "The label stack mechanism allows LSP tunneling to nest to
any depth" RFC3031. If a bottom of the label stack cannot be
found, but sufficient number of labels exist to forward, an LSR
MUST forward the packet. An LSR MUST NOT assume the packet is
malformed unless the end of packet is found before the bottom of
the stack. See Section 2.1.
3. In networks where deep label stacks are encountered, they are not
rare. Full packet rate performance is required regardless of label stack depth, except where multiple pop operations are required. See Section 2.1.
4. Research has shown that long bursts of short packets with 40-byte
or 44-byte IP payload sizes in these bursts are quite common. This is due to TCP ACK compression [ACK-compression]. The following two sub-bullets constitute advice that reflects very common nonnegotiable requirements of providers. Implementers may ignore this advice but should consider the risk of doing so.
A. A forwarding engine SHOULD, if practical, be able to sustain
an arbitrarily long sequence of small packets arriving at
full interface rate.
B. If indefinitely sustained full packet rate for small packets
is not practical, a forwarding engine MUST be able to buffer
a long sequence of small packets inbound to the on-chip
decision engine and sustain full interface rate for some
reasonable average packet rate. Absent this small on-chip
buffering, QoS-agnostic packet drops can occur.
See Section 2.3.
5. The implementations and system designs MUST support pseudowire
Control Word (CW) if MPLS-TP is supported or if ACH RFC5586 is being used on a pseudowire. The implementation and system designs SHOULD support pseudowire CW even if MPLS-TP and ACH
RFC5586 are not used, using instead CW and VCCV Type 1 RFC5085 to allow the use of multipath in the underlying network topology without impacting the PW traffic. RFC7079 does note that there are still some deployments where the CW is not always used. It also notes that many service providers do enable the CW. See Section 2.4.1 for more discussion on why deployments SHOULD enable the pseudowire CW.
The following statements provide clarification regarding more recent requirements that are often missed.
1. The implementer and system designer SHOULD support adding a
pseudowire Flow Label RFC6391. Deployments MAY enable this feature for appropriate pseudowire types. See Section 2.4.3.
2. The implementer and system designer SHOULD support adding an MPLS
Entropy Label RFC6790. Deployments MAY enable this feature. See Section 2.4.4.
Non-IETF definitions of MPLS exist, and these should not be used as normative texts in place of the relevant IETF RFCs. RFC5704 documents incompatibilities between the IETF definition of MPLS and one such alternative MPLS definition, which led to significant issues in the resulting non-IETF specification.
Target Audience
This document is intended for multiple audiences: implementer (implementing MPLS forwarding in silicon or in software); systems designer (putting together a MPLS forwarding systems); deployer (running an MPLS network). These guidelines are intended to serve the following purposes:
1. Explain what to do and what not to do when a deep label stack is
encountered. (audience: implementer)
2. Highlight pitfalls to look for when implementing an MPLS
forwarding chip. (audience: implementer)
3. Provide a checklist of features and performance specifications to
request. (audience: systems designer, deployer)
4. Provide a set of tests to perform. (audience: systems designer,
deployer).
The implementer, systems designer, and deployer have a transitive supplier-customer relationship. It is in the best interest of the supplier to review their product against their customer's checklist and secondary customer's checklist if applicable.
This document identifies and explains many details and potential pitfalls of MPLS forwarding. It is likely that the identified set of potential pitfalls will later prove to be an incomplete set.
Forwarding Issues
A brief review of forwarding issues is provided in the subsections that follow. This section provides some background on why some of these requirements exist. The questions to ask of suppliers is covered in Section 3. Some guidelines for testing are provided in Section 4.
Forwarding Basics
Basic MPLS architecture and MPLS encapsulation, and therefore packet forwarding, are defined in RFC3031 and RFC3032. RFC 3031 and RFC 3032 are somewhat LDP centric. RSVP-TE supports traffic engineering (TE) and fast reroute, features that LDP lacks. The base document for MPLS RSVP-TE is RFC3209.
A few RFCs update RFC 3032. Those with impact on forwarding include the following.
1. TTL processing is clarified in RFC3443.
2. The use of MPLS Explicit NULL is modified in RFC4182.
3. Differentiated Services is supported by RFC3270 and RFC4124.
The "EXP" field is renamed to "Traffic Class" in RFC5462, removing any misconception that it was available for experimentation or could be ignored.
4. ECN is supported by RFC5129.
5. The MPLS G-ACh and GAL are defined in RFC5586.
6. RFC5332 redefines the two data link layer codepoints for MPLS
packets.
Tunneling encapsulations carrying MPLS, such as MPLS in IP RFC4023, MPLS in GRE RFC4023, MPLS in L2TPv3 RFC4817, or MPLS in UDP [MPLS-IN-UDP], are out of scope.
Other RFCs have implications to MPLS Forwarding and do not update RFC 3032 or RFC 3209, including:
1. The pseudowire (PW) Associated Channel Header (ACH) is defined by
RFC5085 and was later generalized by the MPLS G-ACh RFC5586.
2. The Entropy Label Indicator (ELI) and Entropy Label (EL) are
defined by RFC6790.
A few RFCs update RFC 3209. Those that are listed as updating RFC 3209 generally impact only RSVP-TE signaling. Forwarding is modified by major extensions built upon RFC 3209.
RFCs that impact forwarding are discussed in the following subsections.
MPLS Special-Purpose Labels
RFC3032 specifies that label values 0-15 are special-purpose labels with special meanings. RFC7274 renamed these from the term "reserved labels" used in RFC3032 to "special-purpose labels". Three values of NULL label are defined (two of which are later updated by RFC4182) and a Router Alert Label is defined. The original intent was that special-purpose labels, except the NULL labels, could be sent to the routing engine CPU rather than be processed in forwarding hardware. Hardware support is required by new RFCs such as those defining Entropy Label and OAM processed as a result of receiving a GAL. For new special-purpose labels, some accommodation is needed for LSRs that will send the labels to a general-purpose CPU or other highly programmable hardware. For example, ELI will only be sent to LSRs that have signaled support for RFC6790, and a high OAM packet rate must be negotiated among endpoints.
RFC3429 reserves a label for ITU-T Y.1711; however, Y.1711 does not work with multipath and its use is strongly discouraged.
The current list of special-purpose labels can be found on the "Multiprotocol Label Switching Architecture (MPLS) Label Values" registry reachable at IANA's pages at <http://www.iana.org>.
RFC7274 introduces an IANA "Extended Special-Purpose MPLS Label Values" registry and makes use of the "extension" label, label 15, to indicate that the next label is an extended special-purpose label and requires special handling. The range of only 16 values for special- purpose labels allows a table to be used. The range of extended special-purpose labels with 20 bits available for use may have to be handled in some other way in the unlikely event that in the future
the range of currently reserved values 256-1048575 is used. If only the Standards Action range, 16-239, and the Experimental range, 240-255, are used, then a table of 256 entries can be used.
Unknown special-purpose labels and unknown extended special-purpose labels are handled the same. When an unknown special-purpose label is encountered or a special purpose label not directly handled in forwarding hardware is encountered, the packet should be sent to a general-purpose CPU by default. If this capability is supported, there must be an option to either drop or rate limit such packets based on the value of each special-purpose label.
MPLS Differentiated Services
RFC2474 deprecates the IP Type of Service (TOS) and IP Precedence (Prec) fields and replaces them with the Differentiated Services Field more commonly known as the Differentiated Services Code Point (DSCP) field. RFC2475 defines the Differentiated Services architecture, which in other forums, is often called a Quality of Service (QoS) architecture.
MPLS uses the Traffic Class (TC) field to support Differentiated Services RFC5462. There are two primary documents describing how DSCP is mapped into TC.
1. RFC3270 defines E-LSP and L-LSP. E-LSP uses a static mapping
of DSCP into TC. L-LSP uses a per-LSP mapping of DSCP into TC, with one PHB Scheduling Class (PSC) per L-LSP. Each PSC can use multiple Per-Hop Behavior (PHB) values. For example, the Assured Forwarding service defines three PSCs, each with three PHB RFC2597.
2. RFC4124 defines assignment of a class-type (CT) to an LSP,
where a per-CT static mapping of TC to PHB is used. RFC4124 provides a means to support up to eight E-LSP-like mappings of DSCP to TC.
To meet Differentiated Services requirements specified in RFC3270, the following forwarding requirements must be met. An ingress LER MUST be able to select an LSP and then apply a per-LSP map of DSCP into TC. A midpoint LSR MUST be able to apply a per-LSP map of TC to PHB. The number of mappings supported will be far less than the number of LSPs supported.
To meet Differentiated Services requirements specified in RFC4124, the following forwarding requirements must be met. An ingress LER MUST be able to select an LSP and then apply a per-LSP map of DSCP into TC. A midpoint LSR MUST be able to map LSP number to Class Type
(CT), then use a per-CT map to map TC to PHB. Since there are only eight allowed values of CT, only eight maps of TC to PHB need to be supported. The LSP label can be used directly to find the TC-to-PHB mapping, as is needed to support L-LSPs as defined by RFC3270.
While support for RFC4124 and not RFC3270 would allow support for only eight mappings of TC to PHB, it is common to support both and simply state a limit on the number of unique TC-to-PHB mappings that can be supported.
Time Synchronization
PTP or NTP may be carried over MPLS [TIMING-OVER-MPLS]. Generally, NTP will be carried within IP, and IP will be carried in MPLS RFC5905. Both PTP and NTP benefit from accurate timestamping of incoming packets and the ability to insert accurate timestamps in outgoing packets. PTP correction that occurs when forwarding requires updating a timestamp compensation field based on the difference between packet arrival at an LSR and packet transmit time at that same LSR.
Since the label stack depth may vary, hardware should allow a timestamp to be placed in an outgoing packet at any specified byte position. It may be necessary to modify Layer 2 checksums or frame check sequences after insertion. PTP and NTP timestamp formats differ in such a way as to require different implementations of the timestamp correction. If NTP or PTP is carried over UDP/IP or UDP/IP/MPLS, the UDP checksum will also have to be updated.
Accurate time synchronization, in addition to being generally useful, is required for MPLS-TP Delay Measurement (DM) OAM. See Section 2.6.4.
Uses of Multiple Label Stack Entries
MPLS deployments in the early part of the prior decade (circa 2000) tended to support either LDP or RSVP-TE. LDP was favored by some for its ability to scale to a very large number of PE devices at the edge of the network, without adding deployment complexity. RSVP-TE was favored, generally in the network core, where traffic engineering and/or fast reroute were considered important.
Both LDP and RSVP-TE are used simultaneously within major service provider networks using a technique known as "LDP over RSVP-TE Tunneling". This technique allows service providers to carry LDP tunnels inside RSVP-TE tunnels. This makes it possible to take advantage of the traffic engineering and fast reroute on more expensive intercity and intercontinental transport paths. The
ingress RSVP-TE PE places many LDP tunnels on a single RSVP-TE LSP and carries it to the egress RSVP-TE PE. The LDP PEs are situated further from the core, for example, within a metro network. LDP over RSVP-TE tunneling requires a minimum of two MPLS labels: one each for LDP and RSVP-TE.
The use of MPLS FRR RFC4090 might add one more label to MPLS traffic but only when FRR protection is in use (active). If LDP over RSVP-TE is in use, and FRR protection is in use, then at least three MPLS labels are present on the label stack on the links through which the Bypass LSP traverses. FRR is covered in Section 2.1.7.
LDP L2VPN, LDP IPVPN, BGP L2VPN, and BGP IPVPN added support for VPN services that are deployed by the vast majority of service providers. These VPN services added yet another label, bringing the label stack depth (when FRR is active) to four.
Pseudowires and VPN are discussed in further detail in Sections 2.1.8 and 2.1.9.
MPLS hierarchy as described in RFC4206 and updated by RFC7074 can in principle add at least one additional label. MPLS hierarchy is discussed in Section 2.1.6.
Other features such as Entropy Label (discussed in Section 2.4.4) and Flow Label (discussed in Section 2.4.3) can add additional labels to the label stack.
Although theoretical scenarios can easily result in eight or more labels, such cases are rare if they occur at all today. For the purpose of forwarding, only the top label needs to be examined if PHP is used, and a few more if UHP is used (see Section 2.5). For deep label stacks, quite a few labels may have to be examined for the purpose of load balancing across parallel links (see Section 2.4); however, this depth can be bounded by a provider through use of Entropy Label.
Other creative uses of MPLS within the IETF, such as the use of MPLS label stack in source routing, may result in label stacks that are considerably deeper than those encountered today.
MPLS Link Bundling
MPLS Link Bundling was the first RFC to address the need for multiple parallel links between nodes RFC4201. MPLS Link Bundling is notable in that it tried not to change MPLS forwarding, except in
specifying the "all-ones" component link. MPLS Link Bundling is seldom if ever deployed. Instead, multipath techniques described in Section 2.4 are used.
MPLS Hierarchy
MPLS hierarchy is defined in RFC4206 and updated by RFC7074. Although RFC 4206 is considered part of GMPLS, the Packet Switching Capable (PSC) portion of the MPLS hierarchy is applicable to MPLS and may be supported in an otherwise GMPLS-free implementation. The MPLS PSC hierarchy remains the most likely means of providing further scaling in an RSVP-TE MPLS network, particularly where the network is designed to provide RSVP-TE connectivity to the edges. This is the case for envisioned MPLS-TP networks. The use of the MPLS PSC hierarchy can add at least one additional label to a label stack, though it is likely that only one layer of PSC will be used in the near future.
MPLS Fast Reroute (FRR)
Fast reroute is defined by RFC4090. Two significantly different methods are defined in RFC 4090: the "One-to-One Backup" method, which uses the "Detour LSP", and the "Facility Backup", which uses a "bypass tunnel". These are commonly referred to as the detour and bypass methods, respectively.
The detour method makes use of a presignaled LSP. Hardware assistance may be needed for detour FRR in order to accomplish local repair of a large number of LSPs within the target of tens of milliseconds. For each affected LSP, a swap operation must be reprogrammed or otherwise switched over. The use of detour FRR doubles the number of LSPs terminating at any given hop and will increase the number of LSPs within a network by a factor dependent on the average detour path length.
The bypass method makes use of a tunnel that is unused when no fault exists but may carry many LSPs when a local repair is required. There is no presignaling indicating which working LSP will be diverted into any specific bypass LSP. If interface label space is used, the bypass LSP MUST extend one hop beyond the merge point, except if the merge point is the egress and PHP is used. If the bypass LSPs are not extended in this way, then the merge LSR (egress LSR of the bypass LSP) MUST use platform label space (as defined in RFC3031) so that an LSP working path on any given interface can be backed up using a bypass LSP terminating on any other interface. Hardware assistance may be needed to accomplish local repair of a large number of LSPs within the target of tens of milliseconds. For each affected LSP a swap operation must be reprogrammed or otherwise
switched over with an additional push of the bypass LSP label. The use of platform label space impacts the size of the LSR ILM for an LSR with a very large number of interfaces.
IP/LDP Fast Reroute (IP/LDP FRR) RFC5714 is also applicable in MPLS networks. ECMP and Loop-Free Alternates (LFAs) RFC5286 are well- established IP/LDP FRR techniques and were the first methods to be widely deployed. Work on IP/LDP FRR is ongoing within the IETF RTGWG. Two topics actively discussed in RTGWG are microloops and partial coverage of the established techniques in some network topologies. RFC5715 covers the topic of IP/LDP Fast Reroute microloops and microloop prevention. RTGWG has developed additional IP/LDP FRR techniques to handle coverage concerns. RTGWG is extending LFA through the use of remote LFA [REMOTE-LFA]. Other techniques that require new forwarding paths to be established are also under consideration, including the IPFRR "not-via" technique defined in RFC6981 and maximally redundant trees (MRT) [MRT]. ECMP, LFA (but not remote LFA), and MRT swap the top label to an alternate MPLS label. The other methods operate in a similar manner to the facility backup described in RFC 4090 and push an additional label. IP/LDP FRR methods that push more than one label have been suggested but are in early discussion.
Pseudowire Encapsulation
The pseudowire (PW) architecture is defined in RFC3985. A pseudowire, when carried over MPLS, adds one or more additional label entries to the MPLS label stack. A PW Control Word is defined in RFC4385 with motivation for defining the Control Word in RFC4928. The PW Associated Channel defined in RFC4385 is used for OAM in RFC5085. The PW Flow Label is defined in RFC6391 and is discussed further in this document in Section 2.4.3.
There are numerous pseudowire encapsulations, supporting emulation of services such as Frame Relay, ATM, Ethernet, TDM, and SONET/SDH over packet switched networks (PSNs) using IP or MPLS.
The pseudowire encapsulation is out of scope for this document. Pseudowire impact on MPLS forwarding at the midpoint LSR is within scope. The impact on ingress MPLS push and egress MPLS UHP pop are within scope. While pseudowire encapsulation is out of scope, some advice is given on Sequence Number support.
Pseudowire Sequence Number
Pseudowire (PW) Sequence Number support is most important for PW payload types with a high expectation of lossless and/or in-order delivery. Identifying lost PW packets and the exact amount of lost
payload is critical for PW services that maintain bit timing, such as Time Division Multiplexing (TDM) services since these services MUST compensate lost payload on a bit-for-bit basis.
With PW services that maintain bit timing, packets that have been received out of order also MUST be identified and MAY be either reordered or dropped. Resequencing requires, in addition to sequence numbering, a "reorder buffer" in the egress PE, and the ability to reorder is limited by the depth of this buffer. The down side of maintaining a large reorder buffer is added end-to-end service delay.
For PW services that maintain bit timing or any other service where jitter must be bounded, a jitter buffer is always necessary. The jitter buffer is needed regardless of whether reordering is done. In order to be effective, a reorder buffer must often be larger than a jitter buffer needs to be, thus creating a tradeoff between reducing loss and minimizing delay.
PW services that are not timing critical bit streams in nature are cell oriented or frame oriented. Though resequencing support may be beneficial to PW cell- and frame-oriented payloads such as ATM, FR, and Ethernet, this support is desirable but not required. Requirements to handle out-of-order packets at all vary among services and deployments. For example, for Ethernet PW, occasional (very rare) reordering is usually acceptable. If the Ethernet PW is carrying MPLS-TP, then this reordering may be acceptable.
Reducing jitter is best done by an end-system, given that the tradeoff of loss vs. delay varies among services. For example, with interactive real-time services, low delay is preferred, while with non-interactive (one-way) real-time services, low loss is preferred. The same end-site may be receiving both types of traffic. Regardless of this, bounded jitter is sometimes a requirement for specific deployments.
Packet reordering should be rare except in a small number of circumstances, most of which are due to network design or equipment design errors:
1. The most common case is where reordering is rare, occurring only
when a network or equipment fault forces traffic on a new path with different delay. The packet loss that accompanies a network or equipment fault is generally more disruptive than any reordering that may occur.
2. A path change can be caused by reasons other than a network or
equipment fault, such as an administrative routing change. This may result in packet reordering but generally without any packet loss.
3. If the edge is not using pseudowire Control Word (CW) and the
core is using multipath, reordering will be far more common. If this is occurring, using CW on the edge will solve the problem. Without CW, resequencing is not possible since the Sequence Number is contained in the CW.
4. Another avoidable case is where some core equipment has multipath
and for some reason insists on periodically installing a new random number as the multipath hash seed. If supporting MPLS-TP, equipment MUST provide a means to disable periodic hash reseeding, and deployments MUST disable periodic hash reseeding. Operator experience dictates that even if not supporting MPLS-TP, equipment SHOULD provide a means to disable periodic hash reseeding, and deployments SHOULD disable periodic hash reseeding.
In provider networks that use multipath techniques and that may occasionally rebalance traffic or that may change PW paths occasionally for other reasons, reordering may be far more common than loss. Where reordering is more common than loss, resequencing packets is beneficial, rather than dropping packets at egress when out-of-order arrival occurs. Resequencing is most important for PW payload types with a high expectation of lossless delivery since in such cases out-of-order delivery within the network results in PW loss.
Layer 2 and Layer 3 VPN
Layer 2 VPN RFC4664 and Layer 3 VPN RFC4110 add one or more label entry to the MPLS label stack. VPN encapsulations are out of scope for this document. Their impact on forwarding at the midpoint LSR are within scope.
Any of these services may be used on an ingress and egress that are MPLS Entropy Label enabled (see Section 2.4.4 for discussion of Entropy Label); this would add an additional two labels to the MPLS label stack. The need to provide a useful Entropy Label value impacts the requirements of the VPN ingress LER but is out of scope for this document.
MPLS Multicast
MPLS Multicast encapsulation is clarified in RFC5332. MPLS Multicast may be signaled using RSVP-TE RFC4875 or LDP RFC6388.
RFC4875 defines a root-initiated RSVP-TE LSP setup rather than the leaf-initiated join used in IP multicast. RFC6388 defines a leaf- initiated LDP setup. Both RFC4875 and RFC6388 define point-to- multipoint (P2MP) LSP setup. RFC6388 also defined multipoint-to- multipoint (MP2MP) LSP setup.
The P2MP LSPs have a single source. An LSR may be a leaf node, an intermediate node, or a "bud" node. A bud serves as both a leaf and intermediate. At a leaf, an MPLS pop is performed. The payload may be an IP multicast packet that requires further replication. At an intermediate node, an MPLS swap operation is performed. The bud requires that both a pop operation and a swap operation be performed for the same incoming packet.
One strategy to support P2MP functionality is to pop at the LSR interface serving as ingress to the P2MP traffic and then optionally push labels at each LSR interface serving as egress to the P2MP traffic at that same LSR. A given LSR egress chip may support multiple egress interfaces, each of which requires a copy, but each with a different set of added labels and Layer 2 encapsulation. Some physical interfaces may have multiple sub-interfaces (such as Ethernet VLAN or channelized interfaces), each requiring a copy.
If packet replication is performed at LSR ingress, then the ingress interface performance may suffer. If the packet replication is performed within a LSR switching fabric and at LSR egress, congestion of egress interfaces cannot make use of backpressure to ingress interfaces using techniques such as virtual output queuing (VOQ). If buffering is primarily supported at egress, then the need for backpressure is minimized. There may be no good solution for high volumes of multicast traffic if VOQ is used.
Careful consideration should be given to the performance characteristics of high-fanout multicast for equipment that is intended to be used in such a role.
MP2MP LSPs differ in that any branch may provide an input, including a leaf. Packets must be replicated onto all other branches. This forwarding is often implemented as multiple P2MP forwarding trees, one for each potential input interface at a given LSR.
Packet Rates
While average packet size of Internet traffic may be large, long sequences of small packets have both been predicted in theory and observed in practice. Traffic compression and TCP ACK compression can conspire to create long sequences of packets of 40-44 bytes in payload length. If carried over Ethernet, the 64-byte minimum payload applies, yielding a packet rate of approximately 150 Mpps (million packets per second) for the duration of the burst on a nominal 100 Gb/s link. The peak rate for other encapsulations can be as high as 250 Mpps (for example, when IP or MPLS is encapsulated using GFP over OTN ODU4).
It is possible that the packet rates achieved by a specific implementation are acceptable for a minimum payload size, such as a 64-byte (64B) payload for Ethernet, but the achieved rate declines to an unacceptable level for other packet sizes, such as a 65B payload. There are other packet rates of interest besides TCP ACK. For example, a TCP ACK carried over an Ethernet PW over MPLS over Ethernet may occupy 82B or 82B plus an increment of 4B if additional MPLS labels are present.
A graph of packet rate vs. packet size often displays a sawtooth. The sawtooth is commonly due to a memory bottleneck and memory widths, sometimes an internal cache, but often a very wide external buffer memory interface. In some cases, it may be due to a fabric transfer width. A fine packing, rounding up to the nearest 8B or 16B will result in a fine sawtooth with small degradation for 65B, and even less for 82B packets. A coarse packing, rounding up to 64B can yield a sharper drop in performance for 65B packets, or perhaps more important, a larger drop for 82B packets.
The loss of some TCP ACK packets are not the primary concern when such a burst occurs. When a burst occurs, any other packets, regardless of packet length and packet QoS are dropped once on-chip input buffers prior to the decision engine are exceeded. Buffers in front of the packet decision engine are often very small or nonexistent (less than one packet of buffer) causing significant QoS- agnostic packet drop.
Internet service providers and content providers at one time specified full rate forwarding with 40-byte payload packets as a requirement. Today, this requirement often can be waived if the provider can be convinced that when long sequences of short packets occur no packets will be dropped.
Many equipment suppliers have pointed out that the extra cost in designing hardware capable of processing the minimum size packets at full line rate is significant for very-high-speed interfaces. If hardware is not capable of processing the minimum size packets at full line rate, then that hardware MUST be capable of handling large bursts of small packets, a condition that is often observed. This level of performance is necessary to meet Differentiated Services RFC2475 requirements; without it, packets are lost prior to inspection of the IP DSCP field RFC2474 or MPLS TC field RFC5462.
With adequate on-chip buffers before the packet decision engine, an LSR can absorb a long sequence of short packets. Even if the output is slowed to the point where light congestion occurs, the packets, having cleared the decision process, can make use of larger VOQ or output side buffers and be dealt with according to configured QoS treatment, rather than dropped completely at random.
The buffering before the packet decision engine should be arranged such that 1) it can hold a relatively large number of small packets, 2) it can hold a small number of large packets, and 3) it can hold a mix of packets of different sizes.
These on-chip buffers need not contribute significant delay since they are only used when the packet decision engine is unable to keep up, not in response to congestion, plus these buffers are quite small. For example, an on-chip buffer capable of handling 4K packets of 64 bytes in length, or 256KB, corresponds to 200 microseconds on a 10 Gb/s link and 20 microseconds on a 100 Gb/s link. If the packet decision engine is capable of handling packets at 90% of the full rate for small packets, then the maximum added delay is 20 microseconds and 2 microseconds, respectively, and this delay only applies if a 4K burst of short packets occurs. When no burst of short packets was being processed, no delay is added. These buffers are only needed on high-speed interfaces where it is difficult to process small packets at full line rate.
Packet rate requirements apply regardless of which network tier the equipment is deployed in. Whether deployed in the network core or near the network edges, one of the two conditions MUST be met if Differentiated Services requirements are to be met:
1. Packets must be processed at full line rate with minimum-sized
packets. -OR-
2. Packets must be processed at a rate well under generally accepted
average packet sizes, with sufficient buffering prior to the packet decision engine to accommodate long bursts of small packets.
MPLS Multipath Techniques
In any large provider, service providers, and content providers, hash-based multipath techniques are used in the core and in the edge. In many of these providers, hash-based multipath is also used in the larger metro networks.
For good reason, the Differentiated Services requirements dictate that packets within a common microflow SHOULD NOT be reordered RFC2474. Service providers generally impose stronger requirements, commonly requiring that packets within a microflow MUST NOT be reordered except in rare circumstances such as load balancing across multiple links, path change for load balancing, or path change for other reason.
The most common multipath techniques are ECMP applied at the IP forwarding level, Ethernet Link Aggregation Group (LAG) with inspection of the IP payload, and multipath on links carrying both IP and MPLS, where the IP header is inspected below the MPLS label stack. In most core networks, the vast majority of traffic is MPLS encapsulated.
In order to support an adequately balanced load distribution across multiple links, IP header information must be used. Common practice today is to reinspect the IP headers at each LSR and use the label stack and IP header information in a hash performed at each LSR. Further details are provided in Section 2.4.5.
The use of this technique is so ubiquitous in provider networks that lack of support for multipath makes any product unsuitable for use in large core networks. This will continue to be the case in the near future, even as deployment of the MPLS Entropy Label begins to relax the core LSR multipath performance requirements given the existing deployed base of edge equipment without the ability to add an Entropy Label.
A generation of edge equipment supporting the ability to add an MPLS Entropy Label is needed before the performance requirements for core LSRs can be relaxed. However, it is likely that two generations of deployment in the future will allow core LSRs to support full packet rate only when a relatively small number of MPLS labels need to be inspected before hashing. For now, don't count on it.
Common practice today is to reinspect the packet at each LSR and use information from the packet combined with a hash seed that is selected by each LSR. Where Flow Labels or Entropy Labels are used, a hash seed must be used when creating these labels.
Pseudowire Control Word
Within the core of a network, some form of multipath is almost certain to be used. Multipath techniques deployed today are likely to be looking beneath the label stack for an opportunity to hash on IP addresses.
A pseudowire encapsulated at a network edge must have a means to prevent reordering within the core if the pseudowire will be crossing a network core, or any part of a network topology where multipath is used (see RFC4385 and RFC4928).
Not supporting the ability to encapsulate a pseudowire with a Control Word may lock a product out from consideration. A pseudowire capability without Control Word support might be sufficient for applications that are strictly both intra-metro and low bandwidth. However, a provider with other applications will very likely not tolerate having equipment that can only support a subset of their pseudowire needs.
Large Microflows
Where multipath makes use of a simple hash and simple load balance such as modulo or other fixed allocation (see Section 2.4), there can be the presence of large microflows that each consume 10% of the capacity of a component link of a potentially congested composite link. One such microflow can upset the traffic balance, and more than one can reduce the effective capacity of the entire composite link by more than 10%.
When even a very small number of large microflows are present, there is a significant probability that more than one of these large microflows could fall on the same component link. If the traffic contribution from large microflows is small, the probability for three or more large microflows on the same component link drops significantly. Therefore, in a network where a significant number of parallel 10 Gb/s links exists, even a 1 Gb/s pseudowire or other large microflow that could not otherwise be subdivided into smaller flows should carry a Flow Label or Entropy Label if possible.
Active management of the hash space to better accommodate large microflows has been implemented and deployed in the past; however, such techniques are out of scope for this document.
Pseudowire Flow Label
Unlike a pseudowire Control Word, a pseudowire Flow Label RFC6391 is required only for pseudowires that have a relatively large capacity. There are many cases where a pseudowire Flow Label makes sense. Any service such as a VPN that carries IP traffic within a pseudowire can make use of a pseudowire Flow Label.
Any pseudowire carried over MPLS that makes use of the pseudowire Control Word and does not carry a Flow Label is in effect a single microflow (in the terms defined in RFC2475) and may result in the types of problems described in Section 2.4.2.
MPLS Entropy Label
The MPLS Entropy Label simplifies flow group identification RFC6790 at midpoint LSRs. Prior to the MPLS Entropy Label, midpoint LSRs needed to inspect the entire label stack and often the IP headers to provide an adequate distribution of traffic when using multipath techniques (see Section 2.4.5). With the use of the MPLS Entropy Label, a hash can be performed closer to network edges, placed in the label stack, and used by midpoint LSRs without fully reinspecting the label stack and inspecting the payload.
The MPLS Entropy Label is capable of avoiding full label stack and payload inspection within the core where performance levels are most difficult to achieve (see Section 2.3). The label stack inspection can be terminated as soon as the first Entropy Label is encountered, which is generally after a small number of labels are inspected.
In order to provide these benefits in the core, an LSR closer to the edge must be capable of adding an Entropy Label. This support may not be required in the access tier, the tier closest to the customer, but is likely to be required in the edge or the border to the network core. An LSR peering with external networks will also need to be able to add an Entropy Label on incoming traffic.
Fields Used for Multipath Load Balance
The most common multipath techniques are based on a hash over a set of fields. Regardless of whether a hash is used or some other method is used, there is a limited set of fields that can safely be used for multipath.
MPLS Fields in Multipath
If the "outer" or "first" layer of encapsulation is MPLS, then label stack entries are used in the hash. Within a finite amount of time (and for small packets arriving at high speed, that time can be quite limited), only a finite number of label entries can be inspected. Pipelined or parallel architectures improve this, but the limit is still finite.
The following guidelines are provided for use of MPLS fields in multipath load balancing.
1. Only the 20-bit label field SHOULD be used. The TTL field SHOULD
NOT be used. The S bit MUST NOT be used. The TC field (formerly EXP) MUST NOT be used. See text following this list for reasons.
2. If an ELI label is found, then if the LSR supports Entropy
Labels, the EL label field in the next label entry (the EL) SHOULD be used, label entries below that label SHOULD NOT be used, and the MPLS payload SHOULD NOT be used. See below this list for reasons.
3. Special-purpose labels (label values 0-15) MUST NOT be used.
Extended special-purpose labels (any label following label 15) MUST NOT be used. In particular, GAL and RA MUST NOT be used so that OAM traffic follows the same path as payload packets with the same label stack.
4. If a new special-purpose label or extended special-purpose label
is defined that requires special load-balance processing, then, as is the case for the ELI label, a special action may be needed rather than skipping the special-purpose label or extended special-purpose label.
5. The most entropy is generally found in the label stack entries
near the bottom of the label stack (innermost label, closest to S=1 bit). If the entire label stack cannot be used (or entire stack up to an EL), then it is better to use as many labels as possible closest to the bottom of stack.
6. If no ELI is encountered, and the first nibble of payload
contains a 4 (IPv4) or 6 (IPv6), an implementation SHOULD support the ability to interpret the payload as IPv4 or IPv6 and extract and use appropriate fields from the IP headers. This feature is considered a nonnegotiable requirement by many service providers. If supported, there MUST be a way to disable it (if, for example, PW without CW are used). This ability to disable this feature is considered a nonnegotiable requirement by many service providers.
Therefore, an implementation has a very strong incentive to support both options.
7. A label that is popped at egress (UHP pop) SHOULD NOT be used. A
label that is popped at the penultimate hop (PHP pop) SHOULD be used.
Apparently, some chips have made use of the TC (formerly EXP) bits as a source of entropy. This is very harmful since it will reorder Assured Forwarding (AF) traffic RFC2597 when a subset does not conform to the configured rates and is remarked but not dropped at a prior LSR. Traffic that uses MPLS ECN RFC5129 can also be reordered if TC is used for entropy. Therefore, as stated in the guidelines above, the TC field (formerly EXP) MUST NOT be used in multipath load balancing as it violates Differentiated Services Ordered Aggregate (OA) requirements in these two instances.
Use of the MPLS label entry S bit would result in putting OAM traffic on a different path if the addition of a GAL at the bottom of stack removed the S bit from the prior label.
If an ELI label is found, then if the LSR supports Entropy Labels, the EL label field in the next label entry (the EL) SHOULD be used, and the search for additional entropy within the packet SHOULD be terminated. Failure to terminate the search will impact client MPLS- TP LSPs carried within server MPLS LSPs. A network operator has the option to use administrative attributes as a means to identify LSRs that do not terminate the entropy search at the first EL. Administrative attributes are defined in RFC3209. Some configuration is required to support this.
If the label removed by a PHP pop is not used, then for any PW for which CW is used, there is no basis for multipath load split. In some networks, it is infeasible to put all PW traffic on one component link. Any PW that does not use CW will be improperly split, regardless of whether the label removed by a PHP pop is used. Therefore, the PHP pop label SHOULD be used as recommended above.
IP Fields in Multipath
Inspecting the IP payload provides the most entropy in provider networks. The practice of looking past the bottom of stack label for an IP payload is well accepted and documented in RFC4928 and in other RFCs.
Where IP is mentioned in the document, both IPv4 and IPv6 apply. All LSRs MUST fully support IPv6.
When information in the IP header is used, the following guidelines apply:
1. Both the IP source address and IP destination address SHOULD be
used. There MAY be an option to reverse the order of these addresses, improving the ability to provide symmetric paths in some cases. Many service providers require that both addresses be used.
2. Implementations SHOULD allow inspection of the IP protocol field
and use of the UDP or TCP port numbers. For many service providers, this feature is considered mandatory, particularly for enterprise, data center, or edge equipment. If this feature is provided, it SHOULD be possible to disable use of TCP and UDP ports. Many service providers consider it a nonnegotiable requirement that use of UDP and TCP ports can be disabled. Therefore, there is a strong incentive for implementations to provide both options.
3. Equipment suppliers MUST NOT make assumptions that because the IP
version field is equal to 4 (an IPv4 packet) that the IP protocol will either be TCP (IP protocol 6) or UDP (IP protocol 17) and blindly fetch the data at the offset where the TCP or UDP ports would be found. With IPv6, TCP and UDP port numbers are not at fixed offsets. With IPv4 packets carrying IP options, TCP and UDP port numbers are not at fixed offsets.
4. The IPv6 header flow field SHOULD be used. This is the explicit
purpose of the IPv6 flow field; however, observed flow fields rarely contain a non-zero value. Some uses of the flow field have been defined, such as RFC6438. In the absence of MPLS encapsulation, the IPv6 flow field can serve a role equivalent to the Entropy Label.
5. Support for other protocols that share a common Layer 4 header
such as RTP RFC3550, UDP-Lite RFC3828, SCTP RFC4960, and DCCP RFC4340 SHOULD be provided, particularly for edge or access equipment where additional entropy may be needed. Equipment SHOULD also use RTP, UDP-lite, SCTP, and DCCP headers when creating an Entropy Label.
6. The following IP header fields should not or must not be used:
A. Similar to avoiding TC in MPLS, the IP DSCP, and ECN bits
MUST NOT be used.
B. The IPv4 TTL or IPv6 Hop Count SHOULD NOT be used.
C. Note that the IP TOS field was deprecated. (RFC0791 was updated by RFC2474.) No part of the IP DSCP field can be used (formerly IP PREC and IP TOS bits).
7. Some IP encapsulations support tunneling, such as IP-in-IP, GRE,
L2TPv3, and IPsec. These provide a greater source of entropy that some provider networks carrying large amounts of tunneled traffic may need, for example, as used in RFC5640 for GRE and L2TPv3. The use of tunneling header information is out of scope for this document.
This document makes the following recommendations. These recommendations are not required to claim compliance to any existing RFC; therefore, implementers are free to ignore them, but due to service provider requirements should consider the risk of doing so. The use of IP addresses MUST be supported, and TCP and UDP ports (conditional on the protocol field and properly located) MUST be supported. The ability to disable use of UDP and TCP ports MUST be available.
Though potentially very useful in some networks, it is uncommon to support using payloads of tunneling protocols carried over IP. Though the use of tunneling protocol header information is out of scope for this document, it is not discouraged.
Fields Used in Flow Label
The ingress to a pseudowire (PW) can extract information from the payload being encapsulated to create a Flow Label. RFC6391 references IP carried in Ethernet as an example. The Native Service Processing (NSP) function defined in RFC3985 differs with pseudowire type. It is in the NSP function where information for a specific type of PW can be extracted for use in a Flow Label. Determining which fields to use for any given PW NSP is out of scope for this document.
Fields Used in Entropy Label
An Entropy Label is added at the ingress to an LSP. The payload being encapsulated is most often MPLS, a PW, or IP. The payload type is identified by the Layer 2 encapsulation (Ethernet, GFP, POS, etc.).
If the payload is MPLS, then the information used to create an Entropy Label is the same information used for local load balancing (see Section 2.4.5.1). This information MUST be extracted for use in generating an Entropy Label even if the LSR local egress interface is not a multipath.
Of the non-MPLS payload types, only payloads that are forwarded are of interest. For example, payloads using the Address Resolution Protocol (ARP) are not forwarded, and payloads using the Connectionless-mode Network Protocol (CLNP), which is used only for IS-IS, are not forwarded.
The non-MPLS payload types of greatest interest are IPv4 and IPv6. The guidelines in Section 2.4.5.2 apply to fields used to create an Entropy Label.
The IP tunneling protocols mentioned in Section 2.4.5.2 may be more applicable to generation of an Entropy Label at the edge or access where deep packet inspection is practical due to lower interface speeds than in the core where deep packet inspection may be impractical.
MPLS-TP and UHP
MPLS-TP introduces forwarding demands that will be extremely difficult to meet in a core network. Most troublesome is the requirement for Ultimate Hop Popping (UHP), the opposite of Penultimate Hop Popping (PHP). Using UHP opens the possibility of one or more MPLS pop operations plus an MPLS swap operation for each packet. The potential for multiple lookups and multiple counter instances per packet exists.
As networks grow and tunneling of LDP LSPs into RSVP-TE LSPs is used, and/or RSVP-TE hierarchy is used, the requirement to perform one or more MPLS pop operations plus an MPLS swap operation (and possibly a push or two) increases. If MPLS-TP LM (link monitoring) OAM is enabled at each layer, then a packet and byte count MUST be maintained for each pop and swap operation so as to offer OAM for each layer.
Local Delivery of Packets
There are a number of situations in which packets are destined to a local address or where a return packet must be generated. There is a need to mitigate the potential for outage as a result of either attacks on network infrastructure, or in some cases unintentional misconfiguration resulting in processor overload. Some hardware assistance is needed for all traffic destined to the general-purpose CPU that is used in processing of the MPLS control protocol or the network management protocol and in most cases to other general- purpose CPUs residing on an LSR. This is due to the ease of overwhelming such a processor with traffic arriving on LSR high-speed interfaces, whether the traffic is malicious or not.
Denial of service (DoS) protection is an area requiring hardware support that is often overlooked or inadequately considered. Hardware assists are also needed for OAM, particularly the more demanding MPLS-TP OAM.
DoS Protection
Modern equipment supports a number of control-plane and management- plane protocols. Generally, no single means of protecting network equipment from DoS attacks is sufficient, particularly for high-speed interfaces. This problem is not specific to MPLS but is a topic that cannot be ignored when implementing or evaluating MPLS implementations.
Two types of protections are often cited as the primary means of protecting against attacks of all kinds.
Isolated Control/Management Traffic
Control and management traffic can be carried out-of-band (OOB), meaning not intermixed with payload. For MPLS, use of G-ACh and GAL to carry control and management traffic provides a means of isolation from potentially malicious payloads. Used alone, the compromise of a single node, including a small computer at a network operations center, could compromise an entire network. Implementations that send all G-ACh/GAL traffic directly to a routing engine CPU are subject to DoS attack as a result of such a compromise.
Cryptographic Authentication
Cryptographic authentication can very effectively prevent malicious injection of control or management traffic. Cryptographic authentication can in some circumstances be subject to DoS attack by overwhelming the capacity of the decryption with a high volume of malicious traffic. For very-low-speed interfaces, cryptographic authentication can be performed by the general-purpose CPU used as a routing engine. For all other cases, cryptographic hardware may be needed. For very-high-speed interfaces, even cryptographic hardware can be overwhelmed.
Some control and management protocols are often carried with payload traffic. This is commonly the case with BGP, T-LDP, and SNMP. It is often the case with RSVP-TE. Even when carried over G-ACh/GAL, additional measures can reduce the potential for a minor breach to be leveraged to a full network attack.
Some of the additional protections are supported by hardware packet filtering.
GTSM
RFC5082 defines a mechanism that uses the IPv4 TTL or IPv6 Hop Limit fields to ensure control traffic that can only originate from an immediate neighbor is not forged and is not originating from a distant source. GTSM can be applied to many control protocols that are routable, for example, LDP RFC6720.
IP Filtering
At the very minimum, packet filtering plus classification and use of multiple queues supporting rate limiting is needed for traffic that could potentially be sent to a general-purpose CPU used as a routing engine. The first level of filtering only allows connections to be initiated from specific IP prefixes to specific destination ports and then preferably passes traffic directly to a cryptographic engine and/or rate limits. The second level of filtering passes connected traffic, such as TCP connections having received at least one authenticated SYN or having been locally initiated. The second level of filtering only passes traffic to specific address and port pairs to be checked for cryptographic authentication.
The cryptographic authentication is generally the last resort in DoS attack mitigation. If a packet must be first sent to a general- purpose CPU, then sent to a cryptographic engine, a DoS attack is possible on high-speed interfaces. Only where hardware can fully process a cryptographic authentication without intervention from a general-purpose CPU (to find the authentication field and to identify the portion of packet to run the cryptographic algorithm over) is cryptographic authentication beneficial in protecting against DoS attacks.
For chips supporting multiple 100 Gb/s interfaces, only a very large number of parallel cryptographic engines can provide the processing capacity to handle a large-scale DoS or distributed DoS (DDoS) attack. For many forwarding chips, this much processing power requires significant chip real estate and power, and therefore reduces system space and power density. For this reason, cryptographic authentication is not considered a viable first line of defense.
For some networks, the first line of defense is some means of supporting OOB control and management traffic. In the past, this OOB channel might make use of overhead bits in SONET or OTN or a dedicated DWDM wavelength. G-ACh and GAL provide an alternative OOB mechanism that is independent of underlying layers. In other networks, including most IP/MPLS networks, perimeter filtering serves a similar purpose, though it is less effective without extreme vigilance.
A second line of defense is filtering, including GTSM. For protocols such as EBGP, GTSM and other filtering are often the first line of defense. Cryptographic authentication is usually the last line of defense and insufficient by itself to mitigate DoS or DDoS attacks.
MPLS OAM
RFC4377 defines requirements for MPLS OAM that predate MPLS-TP. RFC4379 defines what is commonly referred to as LSP Ping and LSP Traceroute. RFC4379 is updated by RFC6424, which supports MPLS tunnels and stitched LSP and P2MP LSP. RFC4379 is updated by RFC6425, which supports P2MP LSP. RFC4379 is updated by RFC6426 to support MPLS-TP connectivity verification (CV) and route tracing.
RFC4950 extends the ICMP format to support TTL expiration that may occur when using IP Traceroute within an MPLS tunnel. The ICMP message generation can be implemented in forwarding hardware, but if the ICMP packets are sent to a general-purpose CPU, this packet flow must be rate limited to avoid a potential DoS attack.
RFC5880 defines Bidirectional Forwarding Detection (BFD), a protocol intended to detect faults in the bidirectional path between two forwarding engines. RFC5884 and RFC5885 define BFD for MPLS. BFD can provide failure detection on any kind of path between systems, including direct physical links, virtual circuits, tunnels, MPLS Label Switched Paths (LSPs), multihop routed paths, and unidirectional links as long as there is some return path.
The processing requirements for BFD are less than for LSP Ping, making BFD somewhat better suited for relatively high-rate proactive monitoring. BFD does not verify that the data plane matches the control plane, where LSP Ping does. LSP Ping is somewhat better suited for on-demand monitoring including relatively low-rate periodic verification of the data plane and as a diagnostic tool.
Hardware assistance is often provided for BFD response where BFD setup or parameter change is not involved and may be necessary for relatively high-rate proactive monitoring. If both BFD and LSP Ping are recognized in filtering prior to passing traffic to a general- purpose CPU, appropriate DoS protection can be applied (see Section 2.6.1). Failure to recognize BFD and LSP Ping and at least to rate limit creates the potential for misconfiguration to cause outages rather than cause errors in the misconfigured OAM.
Pseudowire OAM
Pseudowire OAM makes use of the control channel provided by Virtual Circuit Connectivity Verification (VCCV) RFC5085. VCCV makes use of the pseudowire Control Word. BFD support over VCCV is defined by RFC5885. RFC5885 is updated by RFC6478 in support of static pseudowires. RFC4379 is updated by RFC6829 to support LSP Ping for Pseudowire FEC advertised over IPv6.
G-ACh/GAL (defined in RFC5586) is the preferred MPLS-TP OAM control channel and applies to any MPLS-TP endpoints, including pseudowire. See Section 2.6.4 for an overview of MPLS-TP OAM.
MPLS-TP OAM
RFC6669 summarizes the MPLS-TP OAM toolset, the set of protocols supporting the MPLS-TP OAM requirements specified in RFC5860 and supported by the MPLS-TP OAM framework defined in RFC6371.
The MPLS-TP OAM toolset includes:
CC-CV
RFC6428 defines BFD extensions to support proactive Continuity Check and Connectivity Verification (CC-CV) applications. RFC6426 provides LSP Ping extensions that are used to implement on-demand connectivity verification.
RDI
Remote Defect Indication (RDI) is triggered by failure of proactive CC-CV, which is BFD based. For fast RDI, RDI SHOULD be initiated and handled by hardware if BFD is handled in forwarding hardware. RFC6428 provides an extension for BFD that includes the RDI in the BFD format and a specification of how this indication is to be used.
Route Tracing
RFC6426 specifies that the LSP Ping enhancements for MPLS-TP on-demand connectivity verification include information on the use of LSP Ping for route tracing of an MPLS-TP path.
Alarm Reporting
RFC6427 describes the details of a new protocol supporting Alarm Indication Signal (AIS), Link Down Indication (LDI), and fault management. Failure to support this functionality in forwarding hardware can potentially result in failure to meet protection recovery time requirements; therefore, support of this functionality is strongly recommended.
Lock Instruct
Lock instruct is initiated on demand and therefore need not be implemented in forwarding hardware. RFC6435 defines a lock instruct protocol.
Lock Reporting
RFC6427 covers lock reporting. Lock reporting need not be implemented in forwarding hardware.
Diagnostic
RFC6435 defines protocol support for loopback. Loopback initiation is on demand and therefore need not be implemented in forwarding hardware. Loopback of packet traffic SHOULD be implemented in forwarding hardware on high-speed interfaces.
Packet Loss and Delay Measurement
RFC6374 and RFC6375 define a protocol and profile for Packet Loss Measurement (LM) and Delay Measurement (DM). LM requires a very accurate capture and insertion of packet and byte counters when a packet is transmitted and capture of packet and byte counters when a packet is received. This capture and insertion MUST be implemented in forwarding hardware for LM OAM if high accuracy is needed. DM requires very accurate capture and insertion of a timestamp on transmission and capture of timestamp when a packet is received. This timestamp capture and insertion MUST be implemented in forwarding hardware for DM OAM if high accuracy is needed.
See Section 2.6.2 for discussion of hardware support necessary for BFD and LSP Ping.
CC-CV and alarm reporting is tied to protection and therefore SHOULD be supported in forwarding hardware in order to provide protection for a large number of affected LSPs within target response intervals. When using MPLS-TP, since CC-CV is supported by BFD, providing hardware assistance for BFD processing helps ensure that protection recovery time requirements can be met even for faults affecting a large number of LSPs.
MPLS-TP Protection State Coordination (PSC) is defined by RFC6378 and updated by RFC7324, which corrects some errors in RFC6378.
MPLS OAM and Layer 2 OAM Interworking
RFC6670 provides the reasons for selecting a single MPLS-TP OAM solution and examines the consequences were ITU-T to develop a second OAM solution that is based on Ethernet encodings and mechanisms.
RFC6310 and RFC7023 specify the mapping of defect states between many types of hardware Attachment Circuits (ACs) and associated pseudowires (PWs). This functionality SHOULD be supported in forwarding hardware.
It is beneficial if an MPLS OAM implementation can interwork with the underlying server layer and provide a means to interwork with a client layer. For example, RFC6427 specifies an inter-layer propagation of AIS and LDI from MPLS server layer to client MPLS layers. Where the server layer uses a Layer 2 mechanism, such as Ethernet, PPP over SONET/SDH, or GFP over OTN, interwork among layers is also beneficial. For high-speed interfaces, supporting this interworking in forwarding hardware helps ensure that protection based on this interworking can meet recovery time requirements even for faults affecting a large number of LSPs.
Extent of OAM Support by Hardware
Where certain requirements must be met, such as relatively high CC-CV rates and a large number of interfaces, or strict protection recovery time requirements and a moderate number of affected LSPs, some OAM functionality must be supported by forwarding hardware. In other cases, such as highly accurate LM and DM OAM or strict protection recovery time requirements with a large number of affected LSPs, OAM functionality must be entirely implemented in forwarding hardware.
Where possible, implementation in forwarding hardware should be in programmable hardware such that if standards are later changed or extended these changes are likely to be accommodated with hardware reprogramming rather than replacement.
For some functionality, there is a strong case for an implementation in dedicated forwarding hardware. Examples include packet and byte counters needed for LM OAM as well as needed for management protocols. Similarly, the capture and insertion of packet and byte counts or timestamps needed for transmitted LM or DM or time synchronization packets MUST be implemented in forwarding hardware if high accuracy is required.
For some functions, there is a strong case to provide limited support in forwarding hardware, but an external general-purpose processor may be used if performance criteria can be met. For example, origination of RDI triggered by CC-CV, response to RDI, and Protection State Coordination (PSC) functionality may be supported by hardware, but expansion to a large number of client LSPs and transmission of AIS or RDI to the client LSPs may occur in a general-purpose processor. Some forwarding hardware supports one or more on-chip general-purpose processors that may be well suited for such a role. RFC7324, being
a very recent document that affects a protection state machine that requires hardware support, underscores the importance of having a degree of programmability in forwarding hardware.
The customer (system supplier or provider) should not dictate design, but should independently validate target functionality and performance. However, it is not uncommon for service providers and system implementers to insist on reviewing design details (under a non-disclosure agreement) due to past experiences with suppliers and to reject suppliers who are unwilling to provide details.
Support for IPFIX in Hardware
The IPFIX architecture is defined by RFC5470. IPFIX supports per- flow statistics. IPFIX information elements (IEs) are defined in RFC7012 and include IEs for MPLS.
The forwarding chips used in core routers are not optimized for high- touch applications like IPFIX. Often, support for IPFIX in core routers is limited to optional IPFIX metering, which involves a 1-in-N packet sampling, limited filtering support, and redirection to either an internal CPU or an external interface. The CPU or device at the other end of the external interface then implements the full IPFIX filtering and IPFIX collector functionality.
LSRs that are intended to be deployed further from the core may support lower-capacity interfaces but support higher-touch applications on the forwarding hardware and may provide dedicated hardware to support a greater subset of IPFIX functionality before handing off to a general-purpose CPU. In some cases, far from the core the entire IPFIX functionality up to and including the collector may be implemented in hardware and firmware in the forwarding silicon. It is also worth noting that at lower speeds a general- purpose CPU may become adequate to implement IPFIX, particularly if metering is used.
Number and Size of Flows
Service provider networks may carry up to hundreds of millions of flows on 10 Gb/s links. Most flows are very short lived, many under a second. A subset of the flows are low capacity and somewhat long lived. When Internet traffic dominates capacity, a very small subset of flows are high capacity and/or very long lived.
Two types of limitations with regard to number and size of flows have been observed.
1. Some hardware cannot handle some high-capacity flows because of
internal paths that are limited, such as per-packet backplane paths or paths internal or external to chips such as buffer memory paths. Such designs can handle aggregates of smaller flows. Some hardware with acknowledged limitations has been successfully deployed but may be increasingly problematic if the capacity of large microflows in deployed networks continues to grow.
2. Some hardware approaches cannot handle a large number of flows,
or a large number of large flows, due to attempting to count per flow, rather than deal with aggregates of flows. Hash techniques scale with regard to number of flows due to a fixed hash size with many flows falling into the same hash bucket. Techniques that identify individual flows have been implemented but have never successfully deployed for Internet traffic.
Questions for Suppliers
The following questions should be asked of a supplier. These questions are grouped into broad categories and are intended to be open-ended questions to the supplier. The tests in Section 4 are intended to verify whether the supplier disclosed any compliance or performance limitations completely and accurately.
Basic Compliance
Q#1 Can the implementation forward packets with an arbitrarily
large stack depth? What limitations exist, and under what
circumstances do further limitations come into play (such as
high packet rate or specific features enabled or specific types
of packet processing)? See Section 2.1.
Q#2 Is the entire set of basic MPLS functionality described in
Section 2.1 supported?
Q#3 Is the set of MPLS special-purpose labels handled correctly and
with adequate performance? Are extended special-purpose labels
handled correctly and with adequate performance? See
Section 2.1.1.
Q#4 Are mappings of label value and TC to PHB handled correctly,
including L-LSP mappings (RFC 3270) and CT mappings (RFC 4124) to PHB? See Section 2.1.2.
Q#5 Is time synchronization adequately supported in forwarding
hardware?
A. Are both PTP and NTP formats supported?
B. Is the accuracy of timestamp insertion and incoming
stamping sufficient?
See Section 2.1.3.
Q#6 Is link bundling supported?
A. Can an LSP be pinned to specific components?
B. Is the "all-ones" component link supported?
See Section 2.1.5.
Q#7 Is MPLS hierarchy supported?
A. Are both PHP and UHP supported? What limitations exist on
the number of pop operations with UHP?
B. Are the pipe, short-pipe, and uniform models supported?
Are TTL and TC values updated correctly at egress where
applicable?
See Section 2.1.6 regarding MPLS hierarchy. See RFC3443 regarding PHP, UHP, and pipe, short-pipe, and uniform models.
Q#8 Is FRR supported?
A. Are both "One-to-One Backup" and "Facility Backup"
supported?
B. What forms of IP/LDP FRR are supported?
C. How quickly does protection recovery occur?
D. Does protection recovery speed increase when a fault
affects a large number of protected LSPs? And if so, by
how much?
See Section 2.1.7.
Q#9 Are pseudowire Sequence Numbers handled correctly? See
Section 2.1.8.1.
Q#10 Is VPN LER functionality handled correctly and without
performance issues? See Section 2.1.9.
Q#11 Is MPLS multicast (P2MP and MP2MP) handled correctly?
A. Are packets dropped on uncongested outputs if some outputs
are congested?
B. Is performance limited in high-fanout situations?
See Section 2.2.
Basic Performance
Q#12 Can very small packets be forwarded at full line rate on all
interfaces indefinitely? What limitations exist? And under
what circumstances do further limitations come into play (such
as specific features enabled or specific types of packet
processing)?
Q#13 Customers must decide whether to relax the prior requirement and
to what extent. If the answer to the prior question indicates
that limitations exist, then:
A. What is the smallest packet size where full line rate
forwarding can be supported?
B. What is the longest burst of full-rate small packets that
can be supported?
Specify circumstances (such as specific features enabled or
specific types of packet processing) that often impact these
rates and burst sizes.
Q#14 How many pop operations can be supported along with a swap
operation at full line rate while maintaining per-LSP packet and
byte counts for each pop and swap? This requirement is
particularly relevant for MPLS-TP.
Q#15 How many label push operations can be supported. While this
limitation is rarely an issue, it applies to both PHP and UHP,
unlike the pop limit that applies to UHP.
Q#16 For a worst case where all packets arrive on one LSP, what is
the counter overflow time? Are any means provided to avoid
polling all counters at short intervals? This applies to both
MPLS and MPLS-TP.
Multipath Capabilities and Performance
Multipath capabilities and performance do not apply to MPLS-TP, but they apply to MPLS and apply if MPLS-TP is carried in MPLS.
Q#17 How are large microflows accommodated? Is there active
management of the hash space mapping to output ports? See
Section 2.4.2.
Q#18 How many MPLS labels can be included in a hash based on the MPLS
label stack?
Q#19 Is packet rate performance decreased beyond some number of
labels?
Q#20 Can the IP header and payload information below the MPLS stack
be used in the hash? If so, which IP fields, payload types, and
payload fields are supported?
Q#21 At what maximum MPLS label stack depth can Bottom of Stack and
an IP header appear without impacting packet rate performance?
Q#22 Are special-purpose labels excluded from the label stack hash?
Are extended special-purpose labels excluded from the label
stack hash? See Section 2.4.5.1.
Q#23 How is multipath performance affected by high-capacity flows, an
extremely large number of flows, or very short-lived flows? See
Section 2.7.
Pseudowire Capabilities and Performance
Q#24 Is the pseudowire Control Word supported?
Q#25 What is the maximum rate of pseudowire encapsulation and
decapsulation? Apply the same questions as in Section 3.2
("Basic Performance") for any packet-based pseudowire, such as
IP VPN or Ethernet.
Q#26 Does inclusion of a pseudowire Control Word impact performance?
Q#27 Are Flow Labels supported?
Q#28 If so, what fields are hashed on for the Flow Label for
different types of pseudowires?
Q#29 Does inclusion of a Flow Label impact performance?
Entropy Label Support and Performance
Q#30 Can an Entropy Label be added when acting as an ingress LER, and
can it be removed when acting as an egress LER?
Q#31 If an Entropy Label can be added, what fields are hashed on for
the Entropy Label?
Q#32 Does adding or removing an Entropy Label impact packet rate
performance?
Q#33 Can an Entropy Label be detected in the label stack, used in the
hash, and properly terminate the search for further information
to hash on?
Q#34 Does using an Entropy Label have any negative impact on
performance? It should have no impact or a positive impact.
DoS Protection
Q#35 For each control- and management-plane protocol in use, what
measures are taken to provide DoS attack hardening?
Q#36 Have DoS attack tests been performed?
Q#37 Can compromise of an internal computer on a management subnet be
leveraged for any form of attack including DoS attack?
OAM Capabilities and Performance
Q#38 What OAM proactive and on-demand mechanisms are supported?
Q#39 What performance limits exist under high proactive monitoring
rates?
Q#40 Can excessively high proactive monitoring rates impact control-
plane performance or cause control-plane instability?
Q#41 Ask the prior questions for each of the following.
A. MPLS OAM
B. Pseudowire OAM
C. MPLS-TP OAM
D. Layer 2 OAM Interworking
See Section 2.6.
Forwarding Compliance and Performance Testing
Packet rate performance of equipment supporting a large number of 10 Gb/s or 100 Gb/s links is not possible using desktop computers or workstations. The use of high-end workstations as a source of test traffic was barely viable 20 years ago but is no longer at all viable. Though custom microcode has been used on specialized router forwarding cards to serve the purpose of generating test traffic and measuring it, for the most part, performance testing will require specialized test equipment. There are multiple sources of suitable equipment.
The set of tests listed here do not correspond one-to-one to the set of questions in Section 3. The same categorization is used, and these tests largely serve to validate answers provided to the prior questions. They can also provide answers where a supplier is unwilling to disclose compliance or performance.
Performance testing is the domain of the IETF Benchmark Methodology Working Group (BMWG). Below are brief descriptions of conformance and performance tests. Some very basic tests, specified in RFC5695, partially cover only the basic performance test T#3.
The following tests should be performed by the systems designer or deployer; or, if it is not practical for the potential customer to perform the tests directly, they may be performed by the supplier on their behalf. These tests are grouped into broad categories.
The tests in Section 4.1 should be repeated under various conditions to retest basic performance when critical capabilities are enabled. Complete repetition of the performance tests enabling each capability and combinations of capabilities would be very time intensive; therefore, a reduced set of performance tests can be used to gauge the impact of enabling specific capabilities.
Basic Compliance
T#1 Test forwarding at a high rate for packets with varying number
of label entries. While packets with more than a dozen label
entries are unlikely to be used in any practical scenario today,
it is useful to know if limitations exists.
T#2 For each of the questions listed under "Basic Compliance" in
Section 3, verify the claimed compliance. For any functionality
considered critical to a deployment, the applicable performance
using each capability under load should be verified in addition
to basic compliance.
Basic Performance
T#3 Test packet forwarding at full line rate with small packets.
See RFC5695. The most likely case to fail is the smallest packet size. Also, test with packet sizes in 4-byte increments ranging from payload sizes of 40 to 128 bytes.
T#4 If the prior tests did not succeed for all packet sizes, then
perform the following tests.
A. Increase the packet size by 4 bytes until a size is found
that can be forwarded at full rate.
B. Inject bursts of consecutive small packets into a stream of
larger packets. Allow some time for recovery between
bursts. Increase the number of packets in the burst until
packets are dropped.
T#5 Send test traffic where a swap operation is required. Also set
up multiple LSPs carried over other LSPs where the device under
test (DUT) is the egress of these LSPs. Create test packets
such that the swap operation is performed after pop operations,
increasing the number of pop operations until forwarding of
small packets at full line rate can no longer be supported.
Also, check to see how many pop operations can be supported
before the full set of counters can no longer be maintained.
This requirement is particularly relevant for MPLS-TP.
T#6 Send all traffic on one LSP and see if the counters become
inaccurate. Often, counters on silicon are much smaller than
the 64-bit packet and byte counters in various IETF MIBs.
System developers should consider what counter polling rate is
necessary to maintain accurate counters and whether those
polling rates are practical. Relevant MIBs for MPLS are
discussed in RFC4221 and RFC6639.
T#7 RFC6894 provides a good basis for MPLS FRR testing. Similar
testing should be performed to determine restoration times;
however, this testing is far more difficult to perform due to
the need for a simulated test topology that is capable of
simulating the signaling used in restoration. The simulated
topology should be comparable with the target deployment in the
number of nodes and links and in resource usage flooding and
setup delays. Some commercial test equipment can support this
type of testing.
Multipath Capabilities and Performance
Multipath capabilities do not apply to MPLS-TP but apply to MPLS and apply if MPLS-TP is carried in MPLS.
T#8 Send traffic at a rate well exceeding the capacity of a single
multipath component link, and where entropy exists only below
the top of stack. If only the top label is used, this test will
fail immediately.
T#9 Move the labels with entropy down in the stack until either the
full forwarding rate can no longer be supported or most or all
packets try to use the same component link.
T#10 Repeat the two tests above with the entropy contained in IP
headers or IP payload fields below the label stack rather than
in the label stack. Test with the set of IP headers or IP
payload fields considered relevant to the deployment or to the
target market.
T#11 Determine whether traffic that contains a pseudowire Control
Word is interpreted as IP traffic. Information in the payload
MUST NOT be used in the load balancing if the first nibble of
the packet is not 4 or 6 (IPv4 or IPv6).
T#12 Determine whether special-purpose labels and extended special-
purpose labels are excluded from the label stack hash. They
MUST be excluded.
T#13 Perform testing in the presence of combinations of:
A. Very large microflows.
B. Relatively short-lived high-capacity flows.
C. Extremely large numbers of flows.
D. Very short-lived small flows.
Pseudowire Capabilities and Performance
T#14 Ensure that pseudowire can be set up with a pseudowire label and
pseudowire Control Word added at ingress and the pseudowire
label and pseudowire Control Word removed at egress.
T#15 For pseudowire that contains variable-length payload packets,
repeat performance tests listed under "Basic Performance" for
pseudowire ingress and egress functions.
T#16 Repeat pseudowire performance tests with and without a
pseudowire Control Word.
T#17 Determine whether pseudowire can be set up with a pseudowire
label, Flow Label, and pseudowire Control Word added at ingress
and the pseudowire label, Flow Label, and pseudowire Control
Word removed at egress.
T#18 Determine which payload fields are used to create the Flow Label
and whether the set of fields and algorithm provide sufficient
entropy for load balancing.
T#19 Repeat pseudowire performance tests with Flow Labels included.
Entropy Label Support and Performance
T#20 Determine whether Entropy Labels can be added at ingress and
removed at egress.
T#21 Determine which fields are used to create an Entropy Label.
Labels further down in the stack, including Entropy Labels
further down and IP headers or IP payload fields where
applicable, should be used. Determine whether the set of fields
and algorithm provide sufficient entropy for load balancing.
T#22 Repeat performance tests under "Basic Performance" when Entropy
Labels are used, where ingress or egress is the device under
test (DUT).
T#23 Determine whether an ELI is detected when acting as a midpoint
LSR and whether the search for further information on which to
base the load balancing is used. Information below the Entropy
Label SHOULD NOT be used.
T#24 Ensure that the Entropy Label indicator and Entropy Label (ELI
and EL) are removed from the label stack during UHP and PHP
operations.
T#25 Ensure that operations on the TC field when adding and removing
Entropy Label are correctly carried out. If TC is changed
during a swap operation, the ability to transfer that change
MUST be provided. The ability to suppress the transfer of TC
MUST also be provided. See the pipe, short-pipe, and uniform
models in RFC3443.
T#26 Repeat performance tests for a midpoint LSR with Entropy Labels
found at various label stack depths.
DoS Protection
T#27 Actively attack LSRs under high protocol churn load and
determine control-plane performance impact or successful DoS
under test conditions. Specifically, test for the following.
A. TCP SYN attack against control-plane and management-plane
protocols using TCP, including CLI access (typically SSH-
protected login), NETCONF, etc.
B. High traffic volume attack against control-plane and
management-plane protocols not using TCP.
C. Attacks that can be performed from a compromised management
subnet computer, but not one with authentication keys.
D. Attacks that can be performed from a compromised peer within
the control plane (internal domain and external domain).
Assume that keys that are per peering and keys that are per
router ID, rather than network-wide keys, are in use.
See Section 2.6.1.
OAM Capabilities and Performance
T#28 Determine maximum sustainable rates of BFD traffic. If BFD
requires CPU intervention, determine both maximum rates and CPU
loading when multiple interfaces are active.
T#29 Verify LSP Ping and LSP Traceroute capability.
T#30 Determine maximum rates of MPLS-TP CC-CV traffic. If CC-CV
requires CPU intervention, determine both maximum rates and CPU
loading when multiple interfaces are active.
T#31 Determine MPLS-TP DM precision.
T#32 Determine MPLS-TP LM accuracy.
T#33 Verify MPLS-TP AIS/RDI and Protection State Coordination (PSC)
functionality, protection speed, and AIS/RDI notification speed
when a large number of Maintenance Entities (MEs) must be
notified with AIS/RDI.
Security Considerations
This document reviews forwarding behavior specified elsewhere and points out compliance and performance requirements. As such, it introduces no new security requirements or concerns.
Discussion of hardware support and other equipment hardening against DoS attack can be found in Section 2.6.1. Section 3.6 provides a list of questions regarding DoS to be asked of suppliers. Section 4.6 suggests types of testing that can provide some assurance of the effectiveness of a supplier's claims about DoS hardening.
Knowledge of potential performance shortcomings may serve to help new implementations avoid pitfalls. It is unlikely that such knowledge could be the basis of new denial of service, as these pitfalls are already widely known in the service provider community and among leading equipment suppliers. In practice, extreme data and packet rates are needed to affect existing equipment and to affect networks that may be still vulnerable due to failure to implement adequate protection. The extreme data and packet rates make this type of denial of service unlikely and make undetectable denial of service of this type impossible.
Each normative reference contains security considerations. A brief summarization of MPLS security considerations applicable to forwarding follows:
1. MPLS encapsulation does not support an authentication extension.
This is reflected in the security section of RFC3032. Documents that clarify MPLS header fields such as TTL RFC3443, the explicit null label RFC4182, renaming EXP to TC RFC5462, ECN for MPLS RFC5129, and MPLS Ethernet encapsulation RFC5332 make no changes to security considerations in RFC3032.
2. Some cited RFCs are related to Diffserv forwarding. RFC3270
refers to MPLS and Diffserv security. RFC2474 mentions theft of service and denial of service due to mismarking. RFC2474 mentions IPsec interaction, but with MPLS, not being carried by IP, the type of interaction in RFC2474 is not relevant.
3. RFC3209 is cited here due only to make-before-break forwarding
requirements. This is related to resource sharing and the
theft-of-service and denial-of-service concerns in RFC2474
apply.
4. RFC4090 defines FRR, which provides protection but does not
add security concerns. RFC 4201 defines link bundling but raises no additional security concerns.
5. Various OAM control channels are defined in RFC4385 (PW CW),
RFC5085 (VCCV), and RFC5586 (G-Ach and GAL). These documents describe potential abuse of these OAM control channels.
6. RFC4950 defines ICMP extensions when MPLS TTL expires and the
payload is IP. This provides MPLS header information that is of
no use to an IP attacker, but sending this information can be
suppressed through configuration.
7. GTSM RFC5082 provides a means to improve protection against
high traffic volume spoofing as a form of DoS attack.
8. BFD RFC5880 RFC5884 RFC5885 provides a form of OAM used in
MPLS and MPLS-TP. The security considerations related to the
OAM control channel are relevant. The BFD payload supports
authentication. The MPLS encapsulation, the MPLS control
channel, or the PW control channel, which BFD may be carried in,
do not support authentication. Where an IP return OAM path is
used, IPsec is suggested as a means of securing the return path.
9. Other forms of OAM are supported by RFC6374 RFC6375 (Loss
and Delay Measurement), RFC6428 (Continuity Check/Verification based on BFD), and RFC6427 (Fault Management). The security considerations related to the OAM control channel are relevant. IP return paths, where used, can be secured with IPsec.
10. Linear protection is defined by RFC6378 and updated by
RFC7324. Security concerns related to MPLS encapsulation and OAM control channels apply. Security concerns reiterate RFC5920 as applied to protection switching.
11. The PW Flow Label RFC6391 and MPLS Entropy Label RFC6790
affect multipath load balancing. Security concerns reiterate
RFC5920. Security impacts would be limited to load
distribution.
MPLS security including data-plane security is discussed in greater detail in RFC5920 (MPLS/GMPLS Security Framework). The MPLS-TP security framework RFC6941 builds upon this, focusing largely on the MPLS-TP OAM additions and OAM channels with some attention given to using network management in place of control-plane setup. In both security framework documents, MPLS is assumed to run within a "trusted zone", defined as being where a single service provider has total operational control over that part of the network.
If control-plane security and management-plane security are sufficiently robust, compromise of a single network element may result in chaos in the data plane anywhere in the network through denial-of-service attacks, but not a Byzantine security failure in which other network elements are fully compromised.
MPLS security, or lack thereof, can affect whether traffic can be misrouted and lost, or intercepted, or intercepted and reinserted (a man-in-the-middle attack), or spoofed. End-user applications, including control-plane and management-plane protocols used by the service provider, are expected to make use of appropriate end-to-end authentication and, where appropriate, end-to-end encryption.
Organization of References Section
The References section is split into Normative and Informative subsections. References that directly specify forwarding encapsulations or behaviors are listed as normative. References that describe signaling only, though normative with respect to signaling, are listed as informative. They are informative with respect to MPLS forwarding.
References
Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC3032 Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
RFC3209 Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
RFC3270 Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, May 2002.
RFC3443 Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
in Multi-Protocol Label Switching (MPLS) Networks", RFC
3443, January 2003.
RFC4090 Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.
RFC4182 Rosen, E., "Removing a Restriction on the use of MPLS
Explicit NULL", RFC 4182, September 2005.
RFC4201 Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
RFC4385 Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
RFC4950 Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
Extensions for Multiprotocol Label Switching", RFC 4950, August 2007.
RFC5082 Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
RFC5085 Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007.
RFC5129 Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
Marking in MPLS", RFC 5129, January 2008.
RFC5332 Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.
RFC5586 Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
RFC5880 Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
RFC5884 Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010.
RFC5885 Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", RFC 5885, June 2010.
RFC6374 Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374, September 2011.
RFC6375 Frost, D. and S. Bryant, "A Packet Loss and Delay
Measurement Profile for MPLS-Based Transport Networks",
RFC 6375, September 2011.
RFC6378 Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
Protection", RFC 6378, October 2011.
RFC6391 Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow-Aware Transport of Pseudowires
over an MPLS Packet Switched Network", RFC 6391, November
2011.
RFC6427 Swallow, G., Fulignoli, A., Vigoureux, M., Boutros, S.,
and D. Ward, "MPLS Fault Management Operations,
Administration, and Maintenance (OAM)", RFC 6427, November
2011.
RFC6428 Allan, D., Swallow Ed. , G., and J. Drake Ed. , "Proactive
Connectivity Verification, Continuity Check, and Remote
Defect Indication for the MPLS Transport Profile", RFC
6428, November 2011.
RFC6790 Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012.
RFC7324 Osborne, E., "Updates to MPLS Transport Profile Linear
Protection", RFC 7324, July 2014.
Informative References
[ACK-compression]
Zhang, L., Shenker, S., and D. Clark, "Observations and
Dynamics of a Congestion Control Algorithm: The Effects of
Two-Way Traffic", Proc. ACM SIGCOMM, ACM Computer
Communications Review (CCR) Vol. 21, No. 4, pp. 133-147.,
1991.
[MPLS-IN-UDP]
Xu, X., Sheth, N., Yong, L., Pignataro, C., and F.
Yongbing, "Encapsulating MPLS in UDP", Work in Progress,
January 2014.
[MRT] Atlas, A., Kebler, R., Bowers, C., Envedi, G., Csaszar,
A., Tantsura, J., Konstantynowicz, M., and R. White, "An
Architecture for IP/LDP Fast-Reroute Using Maximally
Redundant Trees", Work in Progress, July 2014.
[REMOTE-LFA]
Bryant, S., Filsfils, C., Previdi, S., Shand, M., and S.
Ning, "Remote LFA FRR", Work in Progress, May 2014.
RFC0791 Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
RFC2474 Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
RFC2475 Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
RFC2597 Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, June 1999.
RFC3031 Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
RFC3168 Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, September 2001.
RFC3429 Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS)
Operation and Maintenance (OAM) Functions", RFC 3429,
November 2002.
RFC3471 Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471, January 2003.
RFC3550 Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
RFC3828 Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and
G. Fairhurst, "The Lightweight User Datagram Protocol
(UDP-Lite)", RFC 3828, July 2004.
RFC3985 Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
RFC4023 Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating
MPLS in IP or Generic Routing Encapsulation (GRE)", RFC
4023, March 2005.
RFC4110 Callon, R. and M. Suzuki, "A Framework for Layer 3
Provider-Provisioned Virtual Private Networks (PPVPNs)",
RFC 4110, July 2005.
RFC4124 Le Faucheur, F., "Protocol Extensions for Support of
Diffserv-aware MPLS Traffic Engineering", RFC 4124, June 2005.
RFC4206 Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
RFC4221 Nadeau, T., Srinivasan, C., and A. Farrel, "Multiprotocol
Label Switching (MPLS) Management Overview", RFC 4221, November 2005.
RFC4340 Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
RFC4364 Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
RFC4377 Nadeau, T., Morrow, M., Swallow, G., Allan, D., and S.
Matsushima, "Operations and Management (OAM) Requirements
for Multi-Protocol Label Switched (MPLS) Networks", RFC
4377, February 2006.
RFC4379 Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
RFC4664 Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
RFC4817 Townsley, M., Pignataro, C., Wainner, S., Seely, T., and
J. Young, "Encapsulation of MPLS over Layer 2 Tunneling
Protocol Version 3", RFC 4817, March 2007.
RFC4875 Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
RFC4928 Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128, RFC 4928, June 2007.
RFC4960 Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
RFC5036 Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.
RFC5286 Atlas, A. and A. Zinin, "Basic Specification for IP Fast
Reroute: Loop-Free Alternates", RFC 5286, September 2008.
RFC5317 Bryant, S. and L. Andersson, "Joint Working Team (JWT)
Report on MPLS Architectural Considerations for a
Transport Profile", RFC 5317, February 2009.
RFC5462 Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
RFC5470 Sadasivan, G., Brownlee, N., Claise, B., and J. Quittek,
"Architecture for IP Flow Information Export", RFC 5470, March 2009.
RFC5640 Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
Balancing for Mesh Softwires", RFC 5640, August 2009.
RFC5695 Akhter, A., Asati, R., and C. Pignataro, "MPLS Forwarding
Benchmarking Methodology for IP Flows", RFC 5695, November 2009.
RFC5704 Bryant, S., Morrow, M., and IAB, "Uncoordinated Protocol
Development Considered Harmful", RFC 5704, November 2009.
RFC5714 Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC
5714, January 2010.
RFC5715 Shand, M. and S. Bryant, "A Framework for Loop-Free
Convergence", RFC 5715, January 2010.
RFC5860 Vigoureux, M., Ward, D., and M. Betts, "Requirements for
Operations, Administration, and Maintenance (OAM) in MPLS
Transport Networks", RFC 5860, May 2010.
RFC5905 Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
RFC5920 Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
RFC6291 Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
D., and S. Mansfield, "Guidelines for the Use of the "OAM"
Acronym in the IETF", BCP 161, RFC 6291, June 2011.
RFC6310 Aissaoui, M., Busschbach, P., Martini, L., Morrow, M.,
Nadeau, T., and Y(J). Stein, "Pseudowire (PW) Operations,
Administration, and Maintenance (OAM) Message Mapping",
RFC 6310, July 2011.
RFC6371 Busi, I. and D. Allan, "Operations, Administration, and
Maintenance Framework for MPLS-Based Transport Networks",
RFC 6371, September 2011.
RFC6388 Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
"Label Distribution Protocol Extensions for Point-to-
Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, November 2011.
RFC6424 Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
Performing Label Switched Path Ping (LSP Ping) over MPLS
Tunnels", RFC 6424, November 2011.
RFC6425 Saxena, S., Swallow, G., Ali, Z., Farrel, A., Yasukawa,
S., and T. Nadeau, "Detecting Data-Plane Failures in
Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC
6425, November 2011.
RFC6426 Gray, E., Bahadur, N., Boutros, S., and R. Aggarwal, "MPLS
On-Demand Connectivity Verification and Route Tracing",
RFC 6426, November 2011.
RFC6435 Boutros, S., Sivabalan, S., Aggarwal, R., Vigoureux, M.,
and X. Dai, "MPLS Transport Profile Lock Instruct and
Loopback Functions", RFC 6435, November 2011.
RFC6438 Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, November 2011.
RFC6478 Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", RFC 6478, May 2012.
RFC6639 King, D. and M. Venkatesan, "Multiprotocol Label Switching
Transport Profile (MPLS-TP) MIB-Based Management
Overview", RFC 6639, June 2012.
RFC6669 Sprecher, N. and L. Fang, "An Overview of the Operations,
Administration, and Maintenance (OAM) Toolset for MPLS-
Based Transport Networks", RFC 6669, July 2012.
RFC6670 Sprecher, N. and KY. Hong, "The Reasons for Selecting a
Single Solution for MPLS Transport Profile (MPLS-TP)
Operations, Administration, and Maintenance (OAM)", RFC
6670, July 2012.
RFC6720 Pignataro, C. and R. Asati, "The Generalized TTL Security
Mechanism (GTSM) for the Label Distribution Protocol
(LDP)", RFC 6720, August 2012.
RFC6829 Chen, M., Pan, P., Pignataro, C., and R. Asati, "Label
Switched Path (LSP) Ping for Pseudowire Forwarding
Equivalence Classes (FECs) Advertised over IPv6", RFC
6829, January 2013.
RFC6894 Papneja, R., Vapiwala, S., Karthik, J., Poretsky, S., Rao,
S., and JL. Le Roux, "Methodology for Benchmarking MPLS
Traffic Engineered (MPLS-TE) Fast Reroute Protection", RFC
6894, March 2013.
RFC6941 Fang, L., Niven-Jenkins, B., Mansfield, S., and R.
Graveman, "MPLS Transport Profile (MPLS-TP) Security
Framework", RFC 6941, April 2013.
RFC6981 Bryant, S., Previdi, S., and M. Shand, "A Framework for IP
and MPLS Fast Reroute Using Not-Via Addresses", RFC 6981, August 2013.
RFC7012 Claise, B. and B. Trammell, "Information Model for IP Flow
Information Export (IPFIX)", RFC 7012, September 2013.
RFC7023 Mohan, D., Bitar, N., Sajassi, A., DeLord, S., Niger, P.,
and R. Qiu, "MPLS and Ethernet Operations, Administration,
and Maintenance (OAM) Interworking", RFC 7023, October
2013.
RFC7074 Berger, L. and J. Meuric, "Revised Definition of the GMPLS
Switching Capability and Type Fields", RFC 7074, November 2013.
RFC7079 Del Regno, N. and A. Malis, "The Pseudowire (PW) and
Virtual Circuit Connectivity Verification (VCCV)
Implementation Survey Results", RFC 7079, November 2013.
RFC7274 Kompella, K., Andersson, L., and A. Farrel, "Allocating
and Retiring Special-Purpose MPLS Labels", RFC 7274, June 2014.
[TIMING-OVER-MPLS]
Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
Montini, "Transporting Timing messages over MPLS
Networks", Work in Progress, April 2014.
Appendix A. Acknowledgements
Numerous very useful comments have been received in private email. Some of these contributions are acknowledged here, approximately in chronologic order.
Paul Doolan provided a brief review resulting in a number of clarifications, most notably regarding on-chip vs. system buffering, 100 Gb/s link speed assumptions in the 150 Mpps figure, and handling of large microflows. Pablo Frank reminded us of the sawtooth effect in PPS vs. packet-size graphs, prompting the addition of a few paragraphs on this. Comments from Lou Berger at IETF 85 prompted the addition of Section 2.7.
Valuable comments were received on the BMWG mailing list. Jay Karthik pointed out testing methodology hints that after discussion were deemed out of scope and were removed but may benefit later work in BMWG.
Nabil Bitar pointed out the need to cover QoS (Differentiated Services), MPLS multicast (P2MP and MP2MP), and MPLS-TP OAM. Nabil also provided a number of clarifications to the questions and tests in Sections 3 and 4.
Mark Szczesniak provided a thorough review and a number of useful comments and suggestions that improved the document.
Gregory Mirsky and Thomas Beckhaus provided useful comments during the review by the MPLS Review Team.
Tal Mizrahi provided comments that prompted clarifications regarding timestamp processing, local delivery of packets, and the need for hardware assistance in processing OAM traffic.
Alexander (Sasha) Vainshtein pointed out errors in Section 2.1.8.1 and suggested new text that, after lengthy discussion, resulted in restating the summarization of requirements from PWE3 RFCs and more clearly stating the benefits and drawbacks of packet resequencing based on PW Sequence Number.
Loa Anderson provided useful comments and corrections prior to WGLC. Adrian Farrel provided useful comments and corrections prior as part of the AD review.
Discussion with Steve Kent during SecDir review resulted in expansion of Section 5, briefly summarizing security considerations related to forwarding in normative references. Tom Petch pointed out some editorial errors in private email plus an important math error. Al
Morton during OpsDir review prompted clarification in the section about the target audience, suggested more clear wording in places, and found numerous editorial errors.
Discussion with Stewart Bryant and Alia Atlas as part of IESG review resulted in coverage of IPFIX and improvements to document coverage of MPLS FRR, and IP/LDP FRR, plus some corrections to the text elsewhere.
Authors' Addresses
Curtis Villamizar (editor) Outer Cape Cod Network Consulting, LLC
EMail: [email protected]
Kireeti Kompella Juniper Networks
EMail: [email protected]
Shane Amante Apple Inc. 1 Infinite Loop Cupertino, California 95014
EMail: [email protected]
Andrew Malis Huawei Technologies
EMail: [email protected]
Carlos Pignataro Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC 27709 US
EMail: [email protected]
