Network Working Group H. Schulzrinne

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).

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Domain Name Encoding . . . . . . . . . . . . . . . . . . . . . 3
4. LoST Server DHCPv4 Option . . . . . . . . . . . . . . . . . . . 3
5. LoST Server DHCPv6 Option . . . . . . . . . . . . . . . . . . . 4
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7.1. DHCPv4 Option . . . . . . . . . . . . . . . . . . . . . . . 5
7.2. DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . . 6

1. 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.

2. 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].

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RFC 5223 DHCP-Based LoST Discovery August 2008

Within this document, we use terminology from [RFC5012] and
[RFC5222].

3. 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.

4. 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.

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RFC 5223 DHCP-Based LoST Discovery August 2008

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.

5. 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.

6. 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:

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RFC 5223 DHCP-Based LoST Discovery August 2008

+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|137 |13 | 7 | e | x | a | m | p | l | e | 3 | c | o | m | 0 |
+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

Figure 3: Example for a LoST FQDN DHCPv4 Option

7. IANA Considerations

7.1. 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

7.2. 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

8. 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.

9. 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.

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RFC 5223 DHCP-Based LoST Discovery August 2008

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.

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RFC 5223 DHCP-Based LoST Discovery 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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RFC 5223 DHCP-Based LoST Discovery August 2008

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