RFC5223
Network Working Group H. Schulzrinne Request for Comments: 5223 Columbia University Category: Standards Track J. Polk
Cisco
H. Tschofenig
Nokia Siemens Networks
August 2008
Discovering Location-to-Service Translation (LoST) Servers Using the
Dynamic Host Configuration Protocol (DHCP)
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.
Abstract
The Location-to-Service Translation (LoST) Protocol describes an XML- based protocol for mapping service identifiers and geospatial or civic location information to service contact Uniform Resource Locators (URLs). LoST servers can be located anywhere, but a placement closer to the end host, e.g., in the access network, is desirable. In disaster situations with intermittent network connectivity, such a LoST server placement provides benefits regarding the resiliency of emergency service communication.
This document describes how a LoST client can discover a LoST server using the Dynamic Host Configuration Protocol (DHCP).
Contents
Introduction
The Location-to-Service Translation (LoST) Protocol RFC5222 describes an XML-based protocol for mapping service identifiers and geospatial or civic location information to service contact Uniform Resource Locators (URLs).
In order to interact with a LoST server, the LoST client needs to discover the server's IP address. Several mechanisms can be used to learn this address, including manual configuration. In environments where the access network itself either deploys a LoST server or knows a third party that operates a LoST server, DHCP can provide the end host with a domain name. This domain name is then used as input to the DNS-based resolution mechanism described in LoST RFC5222 that reuses the URI-enabled NAPTR specification (see RFC4848).
This document specifies a DHCPv4 and a DHCPv6 option that allows LoST clients to discover local LoST servers.
Section 2 provides terminology. Section 3 shows the encoding of the domain name. Section 4 describes the DHCPv4 option while Section 5 describes the DHCPv6 option, with the same functionality. IANA and Security Considerations complete the document in Sections 7 and 8.
Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 RFC2119.
Within this document, we use terminology from RFC5012 and RFC5222.
Domain Name Encoding
This section describes the encoding of the domain name used in the DHCPv4 option shown in Section 4 and also used in the DHCPv6 option shown in Section 5.
The domain name is encoded according to Section 3.1 of RFC 1035 RFC1035 whereby each label is represented as a one-octet length field followed by that number of octets. Since every domain name ends with the null label of the root, a domain name is terminated by a length byte of zero. The high-order two bits of every length octet MUST be zero, and the remaining six bits of the length field limit the label to 63 octets or less. To simplify implementations, the total length of a domain name (i.e., label octets and label length octets) is restricted to 255 octets or less.
LoST Server DHCPv4 Option
The LoST server DHCPv4 option carries a DNS (RFC 1035 RFC1035) fully-qualified domain name (FQDN) to be used by the LoST client to locate a LoST server.
The DHCP option for this encoding has the following format:
Code Len LoST Server Domain Name
+-----+-----+-----+-----+-----+-----+-----+----
| 137 | n | s1 | s2 | s3 | s4 | s5 | ...
+-----+-----+-----+-----+-----+-----+-----+----
Figure 1: LoST FQDN DHCPv4 Option
The values s1, s2, s3, etc. represent the domain name labels in the domain name encoding. Note that the length field in the DHCPv4 option represents the length of the entire domain name encoding, whereas the length fields in the domain name encoding (see Section 3) is the length of a single domain name label.
Code: OPTION_V4_LOST (137)
Len: Length of the 'LoST Server Domain Name' field
in octets; variable.
LoST Server Domain Name: The domain name of the LoST
server for the client to use.
A DHCPv4 client MAY request a LoST server domain name in a Parameter Request List option, as described in RFC2131.
The encoding of the domain name is described in Section 3.
This option contains a single domain name and, as such, MUST contain precisely one root label.
LoST Server DHCPv6 Option
This section defines a DHCPv6 option to carry a domain name.
The DHCPv6 option has the format shown in Figure 2.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_V6_LOST | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LoST Server Domain Name | | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_V6_LOST (51)
option-length: Length of the 'LoST Server Domain Name' field
in octets; variable.
LoST Server Domain Name: The domain name of the LoST
server for the client to use.
Figure 2: DHCPv6 Option for LoST Server Domain Name List
A DHCPv6 client MAY request a LoST server domain name in an Options Request Option (ORO), as described in RFC3315.
The encoding of the domain name is described in Section 3.
This option contains a single domain name and, as such, MUST contain precisely one root label.
Example
This section shows an example of a DHCPv4 option where the DHCP server wants to offer the "example.com" domain name to the client as input to the U-NAPTR LoST discovery procedure. This domain name would be encoded as follows:
+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |137 |13 | 7 | e | x | a | m | p | l | e | 3 | c | o | m | 0 | +----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 3: Example for a LoST FQDN DHCPv4 Option
IANA Considerations
DHCPv4 Option
The following DHCPv4 option code for the Location-to-Service Translation (LoST) Protocol server option has been assigned by IANA:
Option Name Value Described in ----------------------------------------------- OPTION_V4_LOST 137 Section 4
DHCPv6 Option
IANA has assigned the following DHCPv6 option code for the Location- to-Service Translation (LoST) Protocol option:
Option Name Value Described in ------------------------------------------------ OPTION_V6_LOST 51 Section 5
Security Considerations
If an adversary manages to modify the response from a DHCP server or insert its own response, a LoST client could be led to contact a rogue LoST server under the control of the adversary or be given an invalid address. These threats are documented in RFC5069. The security considerations in RFC2131, RFC2132, and RFC3315 are applicable to this document.
RFC5222 enumerates the LoST security mechanisms.
Acknowledgements
Andrew Newton reviewed the document and helped simplify the mechanism. Other helpful input was provided by Jari Arkko, Leslie Daigle, Vijay K. Gurbani (Gen-ART Review), David W. Hankins, Russ Housley, Tim Polk, Mark Stapp, and Christian Vogt.
10. References
10.1. Normative References
RFC1035 Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
RFC2131 Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
RFC2132 Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
RFC3315 Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
10.2. Informative References
RFC4848 Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
RFC5012 Schulzrinne, H. and R. Marshall, "Requirements for
Emergency Context Resolution with Internet Technologies",
RFC 5012, January 2008.
RFC5069 Taylor, T., Tschofenig, H., Schulzrinne, H., and M.
Shanmugam, "Security Threats and Requirements for
Emergency Call Marking and Mapping", RFC 5069,
January 2008.
RFC5222 Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
Authors' Addresses
Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US
EMail: [email protected] URI: http://www.cs.columbia.edu
James Polk Cisco 2200 East President George Bush Turnpike Richardson, TX 75082 US
EMail: [email protected]
Hannes Tschofenig Nokia Siemens Networks Linnoitustie 6 Espoo 02600 Finland
Phone: +358 (50) 4871445 EMail: [email protected] URI: http://www.tschofenig.priv.at
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