RFC2851
Network Working Group M. Daniele Request for Comments: 2851 Compaq Computer Corporation Category: Standards Track B. Haberman
Nortel Networks
S. Routhier
Wind River Systems, Inc.
J. Schoenwaelder
TU Braunschweig
June 2000
Textual Conventions for Internet Network Addresses
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
This MIB module defines textual conventions to represent commonly used Internet network layer addressing information. The intent is that these definitions will be imported and used in MIBs that would otherwise define their own representations.
This work is output from the Operations and Management Area "IPv6MIB" design team.
Contents
Introduction
Several standard-track MIB modules use the IpAddress SMIv2 base type. This limits the applicability of these MIB modules to IP Version 4 (IPv4) since the IpAddress SMIv2 base type can only contain 4 byte IPv4 addresses. The IpAddress SMIv2 base type has become problematic with the introduction of IP Version 6 (IPv6) addresses [21].
This document defines multiple textual conventions as a mechanism to express generic Internet network layer addresses within MIB module specifications. The solution is compatible with SMIv2 (STD 58) and SMIv1 (STD 16). New MIB definitions which need to express network layer Internet addresses SHOULD use the textual conventions defined in this memo. New MIBs SHOULD NOT use the SMIv2 IpAddress base type anymore.
A generic Internet address consists of two objects, one whose syntax is InetAddressType, and another whose syntax is InetAddress. The value of the first object determines how the value of the second object is encoded. The InetAddress textual convention represents an opaque Internet address value. The InetAddressType enumeration is used to "cast" the InetAddress value into a concrete textual convention for the address type. This usage of multiple textual conventions allows expression of the display characteristics of each address type and makes the set of defined Internet address types extensible.
The textual conventions defined in this document can be used to define Internet addresses by using DNS domain names in addition to IPv4 and IPv6 addresses. A MIB designer can write compliance statements to express that only a subset of the possible address types must be supported by a compliant implementation.
MIB developers who need to represent Internet addresses SHOULD use these definitions whenever applicable, as opposed to defining their own constructs. Even MIBs that only need to represent IPv4 or IPv6 addresses SHOULD use the textual conventions defined in this memo.
In order to make existing widely-deployed IPv4-only MIBs fit for IPv6, it might be a valid approach to define separate tables for different address types. This is a decision for the MIB designer. For example, the tcpConnTable of the TCP-MIB [18] was left intact
and a new table was added for TCP connections over IPv6 in the IPV6- TCP-MIB [19]. Note that even in this case, the MIBs SHOULD use the textual conventions defined in this memo.
Note that MIB developers SHOULD NOT use the textual conventions defined in this document to represent transport layer addresses.
Instead the SMIv2 TAddress textual convention and associated definitions should be used for transport layer addresses.
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT" and "MAY" in this document are to be interpreted as described in RFC 2119 [1].
The SNMP Management Framework
The SNMP Management Framework presently consists of five major components:
o An overall architecture, described in RFC 2571 [2]. o Mechanisms for describing and naming objects and events for the
purpose of management. The first version of this Structure of Management Information (SMI) is called SMIv1 and described in STD 16, RFC 1155 [3], STD 16, RFC 1212 [4] and RFC 1215 [5]. The second version, called SMIv2, is described in STD 58, RFC 2578 [6], STD 58, RFC 2579 [7] and STD 58, RFC 2580 [8].
o Message protocols for transferring management information. The
first version of the SNMP message protocol is called SNMPv1 and described in STD 15, RFC 1157 [9]. A second version of the SNMP message protocol, which is not an Internet standards track protocol, is called SNMPv2c and described in RFC 1901 [10] and RFC 1906 [11]. The third version of the message protocol is called SNMPv3 and described in RFC 1906 [11], RFC 2572 [12] and RFC 2574 [13].
o Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats is described in STD 15, RFC 1157 [9]. A second set of protocol operations and associated PDU formats is described in RFC 1905 [14].
o A set of fundamental applications described in RFC 2573 [15] and
the view-based access control mechanism described in RFC 2575 [16].
A more detailed introduction to the current SNMP Management Framework can be found in RFC 2570 [17].
Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the mechanisms defined in the SMI.
This memo specifies a MIB module that is compliant to the SMIv2. A MIB conforming to the SMIv1 can be produced through the appropriate translations. The resulting translated MIB must be semantically equivalent, except where objects or events are omitted because no translation is possible (use of Counter64). Some machine readable information in SMIv2 will be converted into textual descriptions in SMIv1 during the translation process. However, this loss of machine readable information is not considered to change the semantics of the MIB.
Definitions
INET-ADDRESS-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, mib-2 FROM SNMPv2-SMI TEXTUAL-CONVENTION FROM SNMPv2-TC;
inetAddressMIB MODULE-IDENTITY
LAST-UPDATED "200006080000Z"
ORGANIZATION
"IETF Operations and Management Area"
CONTACT-INFO
"Mike Daniele
Compaq Computer Corporation
110 Spit Brook Rd
Nashua, NH 03062, USA
Phone: +1 603 884-1423
EMail: [email protected]
Brian Haberman
Nortel Networks
4039 Emperor Blvd., Suite 200
Durham, NC 27703, USA
Phone: +1 919 992-4439
EMail: [email protected]
Shawn A. Routhier
Wind River Systems, Inc.
1 Tara Blvd, Suite 403
Nashua, NH 03062, USA
Phone: +1 603 897-2000
EMail: [email protected]
Juergen Schoenwaelder
TU Braunschweig
Bueltenweg 74/75
38106 Braunschweig, Germany
Phone: +49 531 391-3289
EMail: [email protected]
Send comments to [email protected]."
DESCRIPTION
"This MIB module defines textual conventions for representing Internet addresses. An Internet address can be an IPv4 address, an IPv6 address or a DNS domain name."
REVISION "200006080000Z" DESCRIPTION
"Initial version, published as RFC 2851."
- = { mib-2 76 }
InetAddressType ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"A value that represents a type of Internet address.
unknown(0) An unknown address type. This value MUST
be used if the value of the corresponding
InetAddress object is a zero-length string.
It may also be used to indicate an IP address
which is not in one of the formats defined
below.
ipv4(1) An IPv4 address as defined by the
InetAddressIPv4 textual convention.
ipv6(2) An IPv6 address as defined by the
InetAddressIPv6 textual convention.
dns(16) A DNS domain name as defined by the
InetAddressDNS textual convention.
Each definition of a concrete InetAddressType value must be
accompanied by a definition of a textual convention for use
with that InetAddressType.
The InetAddressType textual convention SHOULD NOT be subtyped
in object type definitions to support future extensions. It
MAY be subtyped in compliance statements in order to require
only a subset of these address types for a compliant
implementation."
SYNTAX INTEGER {
unknown(0),
ipv4(1), -- these named numbers are aligned
ipv6(2), -- with AddressFamilyNumbers from
dns(16) -- IANA-ADDRESS-FAMILY-NUMBERS-MIB
}
InetAddress ::= TEXTUAL-CONVENTION
STATUS current
DESCRIPTION
"Denotes a generic Internet address.
An InetAddress value is always interpreted within the
context of an InetAddressType value. The InetAddressType
object which defines the context must be registered
immediately before the object which uses the InetAddress
textual convention. In other words, the object identifiers
for the InetAddressType object and the InetAddress object
MUST have the same length and the last sub-identifier of
the InetAddressType object MUST be 1 less than the last
sub-identifier of the InetAddress object.
When this textual convention is used as the syntax of an
index object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2, STD 58. In this case,
the OBJECT-TYPE declaration MUST include a 'SIZE' clause
to limit the number of potential instance sub-identifiers."
SYNTAX OCTET STRING (SIZE (0..255))
InetAddressIPv4 ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1d.1d.1d.1d"
STATUS current
DESCRIPTION
"Represents an IPv4 network address:
octets contents encoding
1-4 IP address network-byte order
The corresponding InetAddressType value is ipv4(1)." SYNTAX OCTET STRING (SIZE (4))
InetAddressIPv6 ::= TEXTUAL-CONVENTION
DISPLAY-HINT "2x:2x:2x:2x:2x:2x:2x:2x%4d" STATUS current DESCRIPTION
"Represents an IPv6 network address:
octets contents encoding
1-16 IPv6 address network-byte order
17-20 scope identifier network-byte order
The corresponding InetAddressType value is ipv6(2).
The scope identifier (bytes 17-20) MUST NOT be present
for global IPv6 addresses. For non-global IPv6 addresses
(e.g. link-local or site-local addresses), the scope
identifier MUST always be present. It contains a link
identifier for link-local and a site identifier for
site-local IPv6 addresses.
The scope identifier MUST disambiguate identical address
values. For link-local addresses, the scope identifier will
typically be the interface index (ifIndex as defined in the
IF-MIB, RFC 2233) of the interface on which the address is
configured.
The scope identifier may contain the special value 0
which refers to the default scope. The default scope
may be used in cases where the valid scope identifier
is not known (e.g., a management application needs to
write a site-local InetAddressIPv6 address without
knowing the site identifier value). The default scope
SHOULD NOT be used as an easy way out in cases where
the scope identifier for a non-global IPv6 is known."
SYNTAX OCTET STRING (SIZE (16|20))
InetAddressDNS ::= TEXTUAL-CONVENTION
DISPLAY-HINT "255a"
STATUS current
DESCRIPTION
"Represents a DNS domain name. The name SHOULD be
fully qualified whenever possible.
The corresponding InetAddressType is dns(16).
The DESCRIPTION clause of InetAddress objects that
may have InetAddressDNS values must fully describe
how (and when) such names are to be resolved to IP
addresses."
SYNTAX OCTET STRING (SIZE (1..255))
END
Usage Hints
One particular usage of InetAddressType/InetAddress pairs is to avoid over-constraining an object definition by the use of the IpAddress SMI base type. An InetAddressType/InetAddress pair allows to represent IP addresses in various formats.
The InetAddressType and InetAddress objects SHOULD NOT be subtyped. Subtyping binds the MIB module to specific address formats, which may cause serious problems if new address formats need to be introduced. Note that it is possible to write compliance statements in order to express that only a subset of the defined address types must be implemented to be compliant.
Internet addresses MUST always be represented by a pair of InetAddressType/InetAddress objects. It is not allowed to "share" an InetAddressType between multiple InetAddress objects. Furthermore, the InetAddressType object must be registered immediately before the InetAddress object. In other words, the object identifiers for the InetAddressType object and the InetAddress object MUST have the same length and the last sub-identifier of the InetAddressType object MUST be 1 less than the last sub-identifier of the InetAddress object.
Table Indexing
When a generic Internet address is used as an index, both the InetAddressType and InetAddress objects MUST be used. The InetAddressType object MUST come immediately before the InetAddress object in the INDEX clause. If multiple Internet addresses are used in the INDEX clause, then every Internet address must be represented by a pair of InetAddressType and InetAddress objects.
The IMPLIED keyword MUST NOT be used for an object of type InetAddress in an INDEX clause. Instance sub-identifiers are then of the form T.N.O1.O2...On, where T is the value of the InetAddressType object, O1...On are the octets in the InetAddress object, and N is the number of those octets.
There is a meaningful lexicographical ordering to tables indexed in this fashion. Command generator applications may lookup specific addresses of known type and value, issue GetNext requests for addresses of a single type, or issue GetNext requests for a specific type and address prefix.
Uniqueness of Addresses
IPv4 addresses were intended to be globally unique, current usage notwithstanding. IPv6 addresses were architected to have different scopes and hence uniqueness [21]. In particular, IPv6 "link-local" and "site-local" addresses are not guaranteed to be unique on any particular node. In such cases, the duplicate addresses must be configured on different interfaces. So the combination of an IPv6 address and an interface number is unique. The interface number may therefore be used as a scope identifier.
The InetAddressIPv6 textual convention has been defined to represent global and non-global IPv6 addresses. MIB designers who use InetAddressType/InetAddress pairs therefore do not need define additional objects in order to support link-local or site-local addresses.
The size of the scope identifier has been chosen so that it matches the sin6_scope_id field of the sockaddr_in6 structure defined in RFC 2553 [22].
Multiple InetAddresses per Host
A single host system may be configured with multiple addresses (IPv4 or IPv6), and possibly with multiple DNS names. Thus it is possible for a single host system to be represented by multiple InetAddressType/InetAddress pairs.
If this could be an implementation or usage issue, then the DESCRIPTION clause of the relevant objects MUST fully describe required behavior.
Resolving DNS Names
DNS names must be resolved to IP addresses when communication with the named host is required. This raises a temporal aspect to defining MIB objects whose value is a DNS name: When is the name translated to an address?
For example, consider an object defined to indicate a forwarding destination, and whose value is a DNS name. When does the forwarding entity resolve the DNS name? Each time forwarding occurs? Once, when the object was instantiated?
The DESCRIPTION clause of such objects SHOULD precisely define how and when any required name to address resolution is done.
Similarly, the DESCRIPTION clause of such objects SHOULD precisely define how and when a reverse lookup is being done if an agent has accessed instrumentation that knows about an IP address and the MIB or implementation requires to map the address to a name.
Table Indexing Example
This example shows a table listing communication peers that are identified by either an IPv4 address, an IPv6 address or a DNS name. The table definition also prohibits entries with an empty address (whose type would be "unknown"). The size of a DNS name is limited to 64 characters.
peerTable OBJECT-TYPE
SYNTAX SEQUENCE OF PeerEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A list of communication peers."
::= { somewhere 1 }
peerEntry OBJECT-TYPE
SYNTAX PeerEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry containing information about a particular peer."
INDEX { peerAddressType, peerAddress }
::= { peerTable 1 }
PeerEntry ::= SEQUENCE {
peerAddressType InetAddressType, peerAddress InetAddress, peerStatus INTEGER }
peerAddressType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The type of Internet address by which the peer
is reachable."
::= { peerEntry 1 }
peerAddress OBJECT-TYPE
SYNTAX InetAddress (SIZE (1..64)) MAX-ACCESS not-accessible STATUS current
DESCRIPTION
"The Internet address for the peer. Note that
implementations must limit themselves to a single
entry in this table per reachable peer.
The peerAddress may not be empty due to the SIZE
restriction.
If a row is created administratively by an SNMP
operation and the address type value is dns(16), then
the agent stores the DNS name internally. A DNS name
lookup must be performed on the internally stored DNS
name whenever it is being used to contact the peer.
If a row is created by the managed entity itself and
the address type value is dns(16), then the agent
stores the IP address internally. A DNS reverse lookup
must be performed on the internally stored IP address
whenever the value is retrieved via SNMP."
::= { peerEntry 2 }
The following compliance statement specifies that implementations need only support IPv4 addresses and globally unique IPv6 addresses to be compliant. Support for DNS names or scoped IPv6 addresses is not required.
peerCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement the peer MIB."
MODULE -- this module
MANDATORY-GROUPS { peerGroup }
OBJECT peerAddressType
SYNTAX InetAddressType { ipv4(1), ipv6(2) }
DESCRIPTION
"An implementation is only required to support IPv4
and IPv6 addresses."
OBJECT peerAddress
SYNTAX InetAddress (SIZE(4|16))
DESCRIPTION
"An implementation is only required to support IPv4
and globally unique IPv6 addresses."
::= { somewhere 2 }
Note that the SMIv2 does not permit inclusion of not-accessible objects in an object group (see section 3.1 in STD 58, RFC 2580 [8]). It is therefore not possible to formally refine the syntax of auxiliary objects which are not-accessible. In such a case, it is suggested to express the refinement informally in the DESCRIPTION clause of the MODULE-COMPLIANCE macro invocation.
Security Considerations
This module does not define any management objects. Instead, it defines a set of textual conventions which may be used by other MIB modules to define management objects.
Meaningful security considerations can only be written in the modules that define management objects.
Acknowledgments
The authors would like to thank Randy Bush, Richard Draves, Mark Ellison, Bill Fenner, Jun-ichiro Hagino, Tim Jenkins, Glenn Mansfield, Keith McCloghrie, Thomas Narten, Erik Nordmark, Peder Chr. Norgaard, Randy Presuhn, Andrew Smith, Dave Thaler, Kenneth White, Bert Wijnen, and Brian Zill for their comments and suggestions.
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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Harrington, D., Presuhn, R. and B. Wijnen, "An Architecture for
Describing SNMP Management Frameworks", RFC 2571, April 1999.
[3] Rose, M. and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16, RFC 1155, May 1990.
[4] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16,
RFC 1212, March 1991.
[5] Rose, M., "A Convention for Defining Traps for use with the
SNMP", RFC 1215, March 1991.
[6] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[7] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[8] McCloghrie, K., Perkins, D., Schoenwaelder, J., Case, J., Rose,
M. and S. Waldbusser, "Conformance Statements for SMIv2", STD
58, RFC 2580, April 1999.
[9] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "A Simple
Network Management Protocol (SNMP)", STD 15, RFC 1157, May 1990.
[10] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901, January 1996.
[11] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Transport Mappings for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1906, January 1996.
[12] Case, J., Harrington, D., Presuhn, R. and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", RFC 2572, April 1999.
[13] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM)
for version 3 of the Simple Network Management Protocol
(SNMPv3)", RFC 2574, April 1999.
[14] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1905, January 1996.
[15] Levi, D., Meyer, P. and B. Stewart, "SNMP Applications", RFC
2573, April 1999.
[16] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access
Control Model (VACM) for the Simple Network Management
Protocol (SNMP)", RFC 2575, April 1999.
[17] Case, J., Mundy, R., Partain, D. and B. Stewart, "Introduction
to Version 3 of the Internet-standard Network Management
Framework", RFC 2570, April 1999.
[18] McCloghrie, K., "SNMPv2 Management Information Base for the
Transmission Control Protocol using SMIv2", RFC 2012, November 1996.
[19] Daniele, M., "IP Version 6 Management Information Base for the
Transmission Control Protocol", RFC 2452, December 1998.
[20] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB
using SMIv2", RFC 2233, November 1997.
[21] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[22] Gilligan, R., Thomson, S., Bound, J. and W. Stevens, "Basic
Socket Interface Extensions for IPv6", RFC 2553, March 1999.
Authors' Addresses
Mike Daniele Compaq Computer Corporation 110 Spit Brook Rd Nashua, NH 03062 USA
Phone: +1 603 884-1423 EMail: [email protected]
Brian Haberman Nortel Networks 4039 Emperor Blvd., Suite 200 Durham, NC 27703 USA
Phone: +1 919 992-4439 EMail: [email protected]
Shawn A. Routhier Wind River Systems, Inc. 1 Tara Blvd, Suite 403 Nashua, NH 03062 USA
Phone: +1 603 897-2000 EMail: [email protected]
Juergen Schoenwaelder TU Braunschweig Bueltenweg 74/75 38106 Braunschweig Germany
Phone: +49 531 391-3289 EMail: [email protected]
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