Link Selection sub-option for the Relay Agent Information Option for DHCPv4
RFC 3527
Document | Type | RFC - Proposed Standard (April 2003; No errata) | |
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Authors | Richard Johnson , Mark Stapp , Jay Kumarasamy , Jay Kumarasamy , Kim Kinnear | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3527 (Proposed Standard) | |
Action Holders |
(None)
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Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Thomas Narten | ||
IESG note | 2003-04-24: Published at RFC 3527 | ||
Send notices to | <rdroms@cisco.com> |
Network Working Group K. Kinnear Request for Comments: 3527 M. Stapp Category: Standards Track R. Johnson J. Kumarasamy Cisco Systems April 2003 Link Selection sub-option for the Relay Agent Information Option for DHCPv4 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 (2003). All Rights Reserved. Abstract This document describes the link selection sub-option of the relay- agent-information option for the Dynamic Host Configuration Protocol (DHCPv4). The giaddr specifies an IP address which determines both a subnet, and thereby a link on which a Dynamic Host Configuration Protocol (DHCP) client resides as well as an IP address that can be used to communicate with the relay agent. The subnet-selection option allows the functions of the giaddr to be split so that when one entity is performing as a DHCP proxy, it can specify the subnet/link from which to allocate an IP address, which is different from the IP address with which it desires to communicate with the DHCP server. Analogous situations exist where the relay agent needs to specify the subnet/link on which a DHCP client resides, which is different from an IP address that can be used to communicate with the relay agent. 1. Introduction In RFC 2131, the giaddr specifies an IP address which determines a subnet (and from there a link) on which a DHCP client resides as well as an IP address which can be used to communicate with the relay agent. The subnet-selection option [RFC 3011] allows these functions of the giaddr to be split, so that when one entity is performing as a Kinnear, et al. Standards Track [Page 1] RFC 3527 Link Selection sub-option April 2003 DHCP proxy, it can specify the subnet/link from which to allocate an IP address that is different from the IP address with which it desires to communicate with the DHCP server. Analogous situations exist where the relay agent needs to specify the subnet/link on which a DHCP client resides, which is different from an IP address that can be used to communicate with the relay agent. Consider the following architecture: +--------+ +---------------+ | DHCP | IP x| |IP y | Server |-.......-| Relay Agent |----+------------+ +--------+ | | | | +---------------+ | +------+ | |Modem | | +------+ | | | +-----+ +-----+ +-----+ |Host1| |Host2| |Host3| +-----+ +-----+ +-----+ In the usual approach, the relay agent would put IP address Y into the giaddr of any packets that it forwarded to the DHCP server. However, if for any reason, IP address Y is not accessible from the DHCP server, this approach will fail. There are several reasons why IP y might be inaccessible from the DHCP server: o There might be some firewall capability in the network element in which the relay agent resides that does not allow the DHCP server to access the relay agent via IP y. o There might not be an IP y. An example would be the case where there was only one host and this was a point to point link. In any of these or other cases, the relay agent needs to be able to communicate to the DHCP server the subnet/link from which to allocate an IP address. The IP address, which will communicate to the DHCP server the subnet/link information, cannot be used as a way to communicate between the DHCP server and the relay agent. Since the relay agent can modify the client's DHCP DHCPREQUEST in only two ways, the giaddr and the relay-agent-info option, there is a need to extend the relay-agent-info option with a new sub-option, the link-selection sub-option, to allow separation of the specification of the subnet/link from the IP address to use when communicating with the relay agent.Show full document text