The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4
RFC 3442
Document | Type |
RFC - Proposed Standard
(December 2002; No errata)
Updates RFC 2132
Was draft-ietf-dhc-csr (dhc WG)
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Authors | Ted Lemon , Bernie Volz , Stuart Cheshire | ||
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 3442 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Thomas Narten | ||
IESG note | . | ||
Send notices to | <rdroms@cisco.com> |
Network Working Group T. Lemon Request for Comments: 3442 Nominum, Inc. Updates: 2132 S. Cheshire Category: Standards Track Apple Computer, Inc. B. Volz Ericsson December 2002 The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4 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 (2002). All Rights Reserved. Abstract This document defines a new Dynamic Host Configuration Protocol (DHCP) option which is passed from the DHCP Server to the DHCP Client to configure a list of static routes in the client. The network destinations in these routes are classless - each routing table entry includes a subnet mask. Introduction This option obsoletes the Static Route option (option 33) defined in RFC 2132 [4]. The IP protocol [1] uses routers to transmit packets from hosts connected to one IP subnet to hosts connected to a different IP subnet. When an IP host (the source host) wishes to transmit a packet to another IP host (the destination), it consults its routing table to determine the IP address of the router that should be used to forward the packet to the destination host. The routing table on an IP host can be maintained in a variety of ways - using a routing information protocol such as RIP [8], ICMP router discovery [6,9] or using the DHCP Router option, defined in RFC 2132 [4]. Lemon, et. al. Standards Track [Page 1] RFC 3442 Classless Static Route Option for DHCPv4 December 2002 In a network that already provides DHCP service, using DHCP to update the routing table on a DHCP client has several virtues. It is efficient, since it makes use of messages that would have been sent anyway. It is convenient - the DHCP server configuration is already being maintained, so maintaining routing information, at least on a relatively stable network, requires little extra work. If DHCP service is already in use, no additional infrastructure need be deployed. The DHCP protocol as defined in RFC 2131 [3] and the options defined in RFC 2132 [4] only provide a mechanism for installing a default route or installing a table of classful routes. Classful routes are routes whose subnet mask is implicit in the subnet number - see section 3.2 of STD 5, RFC 791 [1] for details on classful routing. Classful routing is no longer in common use, so the DHCP Static Route option is no longer useful. Currently, classless routing [7, 10] is the most commonly-deployed form of routing on the Internet. In classless routing, IP addresses consist of a network number (the combination of the network number and subnet number described in RFC 950 [7]) and a host number. In classful IP, the network number and host number are derived from the IP address using a bitmask whose value is determined by the first few bits of the IP address. In classless IP, the network number and host number are derived from the IP address using a separate quantity, the subnet mask. In order to determine the network to which a given route applies, an IP host must know both the network number AND the subnet mask for that network. The Static Routes option (option 33) does not provide a subnet mask for each route - it is assumed that the subnet mask is implicit in whatever network number is specified in each route entry. The Classless Static Routes option does provide a subnet mask for each entry, so that the subnet mask can be other than what would be determined using the algorithm specified in STD 5, RFC 791 [1] and STD 5, RFC 950 [7]. Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [2]. Lemon, et. al. Standards Track [Page 2] RFC 3442 Classless Static Route Option for DHCPv4 December 2002 This document also uses the following terms: "DHCP client" DHCP client or "client" is an Internet host using DHCP to obtain configuration parameters such as a network address.Show full document text