Network Working Group W. Dec Internet-Draft R. Johnson Intended status: Informational Cisco Systems Expires: August 20, 2009 February 16, 2009 DHCPv6 Route Option draft-dec-dhcpv6-route-option-00 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 20, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes the DHCPv6 Route Option for communicating IPv6 routes to a DHCP client. This improves the ability of an Dec & Johnson Expires August 20, 2009 [Page 1] Internet-Draft DHCPv6 Route Option February 2009 operator to influence the a client host to pick an appropriate route to a destination when the client is multi-homed or where other means of route configuration may be impractical. Requirements Language 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 RFC 2119 [RFC2119]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Route Option . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Appearance of the option in DHCP messages . . . . . . . . . 4 3. DHCP Client Behavior . . . . . . . . . . . . . . . . . . . . . 5 4. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Dec & Johnson Expires August 20, 2009 [Page 2] Internet-Draft DHCPv6 Route Option February 2009 1. Introduction The Neighbor Discover protocol [RFC2461] provides a mechanism allowing hosts to discover one or more default router. Extensions to the protocol defined in [RFC4191]allow the discovery of preferences for the multiple default routers as well as more specific routes which allows network administrators to better handle multi-homed host topologies. The above cited mechanisms however fall short in network environments where the network administrator needs to dynamically configure specific routes on only a subset of clients hosts that are connected to a multi-access network segement (e.g. a shared VLAN). Similarly, the mechanisms are also not adequate in situations where administrative boundaries between network operational groups inhibit or prevent the configuration of routers that are attached to the end host network segment. In effect the above problems call for a dynamic host configuration method by that can be effected without direct manipulation of routers attached to the host's segement, in effect thus a DHCPv6 method analogous to that defined for DHCPv4 in [RFC3442]. The definition of an such a DHCPv6 extension has the added benefit of being able to provide operational simplification in networks where the DHCPv4 method is already in use and DHCPv6 is being deployed. This document describes the DHCPv6 Route Option for communicating IPv6 routes to a DHCPv6 client. This improves the ability of an operator to influence the client host to pick a route when the client is multi-homed or where other means of route discovery or configuration are impractical. The assumption carried in this document is that the next-hop address used in the route description is either an address that is well known to the operator (eg by means of static IP address configuration on a router) or one that is easily derivable from the DHCP messaging. 2. Route Option The server sends the Route Option to a client to covey one or more IPv6 routes. Each IPv6 route consists of an IPv6 prefix of a declared bit length and a next hop IPv6 address for the prefix. Multiple routes can be present in a single option. No octet alignment is done within the contents of the option, however the complete option is octet aligned by padding with 0s to the next octet boundary Dec & Johnson Expires August 20, 2009 [Page 3] Internet-Draft DHCPv6 Route Option February 2009 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_ROUTE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | Prefix (variable length) | +-+-+-+-+-+-+-+-+ . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 Next Hop Address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ option-code OPTION_ROUTE (TBD). option-len 17 + Length of the Prefix field in full octets. Prefix Length 8-bit unsigned integer. The number of leading bits in the IP Prefix that are valid. The value ranges from 0 to 128. Prefix Variable-length field containing the IP Prefix. IPv6 Next Hop Address The 128 bit IPv6 address of the next hop to be used when forwarding towards the IP Prefix. 2.1. Appearance of the option in DHCP messages The Route option MUST NOT appear in the following DHCP messages: Solicit, Request, Renew, Rebind, Information-Request and Reconfigure. A single option can be used to covey multiple routes by means of succesively inserting additional combinations of the prefix and next hop field. The example below illustrates how two routes, consisting of Prefix A and Prefix B with two different next hop addresses Next Hop 1 and Next Hop 2 respectively, can be conveyed within a single option. Dec & Johnson Expires August 20, 2009 [Page 4] Internet-Draft DHCPv6 Route Option February 2009 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_ROUTE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Prefix A Length| Prefix A (variable length) | +-+-+-+-+-+-+-+-+ . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 Next Hop Address 1 | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Prefix B Length| Prefix B (variable length) | +-+-+-+-+-+-+-+-+ . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 Next Hop Address 2 | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3. DHCP Client Behavior A client compliant with this specification SHOULD request the Route option (option value TBD) in an Options Request Option (ORO) as described in [RFC3315] by including the Route options' code in the following messages: Solicit, Request, Renew, Rebind, Information- Request and Reconfigure. In case of multiple route options being received in a single DHCP transaction, the client MUST NOT allow further occurrences of the route option to nullify the effect of previous occurrences of the option. A client receiveing in the same transaction two or more routes for the same destination prefix but with different next hop addresses should consider both routes valid and depending on the client's capability utilize all such routes. So as to facilitate the reconfiguration of routes, a client MUST be capable treating the reception of Route Options in another DHCP transaction as overriding any previous set. DHCP clients that support the Route option are expected to use the Dec & Johnson Expires August 20, 2009 [Page 5] Internet-Draft DHCPv6 Route Option February 2009 information in selecting the forwarding route by the host. The client however needs to perform some basic prefix sanity checking before using any such route(s). In particular the following prefixes and next-hop field addresses are ones for which the host MUST NOT install a route for, and consider them invalid: - A prefix or next hop address corresponding to any of the host's local node addresses (i.e. when a full /128 route option prefix is equal to a local interface address) - A destination prefix corresponding to the unspecified address (0::0/128) - A destination prefix or next hop address corresponding to the Loopback Address (::1/128) - A destination prefix that falls in the link local address or site local address range (FE::/9) - A destination prefix or next -hop address that falls in the multicast addresses range (FF::/8) When processing the Route option a client MUST substitute a 0::0 IP next hop address with the source IP address of the received DHCP message. 4. DHCP Server Behavior A server MAY send a client the Route option if the server is configured to do so. The option MAY be sent as part of other DHCP options where such a possibility exists. For example the route option may be sent as part of the IA_NA and IA_PD option set, with the semantics of the parent option unaffected. A server is allowed to use an all 0s (0::0) next-hop address to indicate that the next-hop address is to be derived by the client from the source IP address of the received DHCP message. 5. IANA Considerations IANA has assigned a DHCPv6 option number of TBD for the "Route Option" Dec & Johnson Expires August 20, 2009 [Page 6] Internet-Draft DHCPv6 Route Option February 2009 6. Security Considerations The overall security considerations discussed in [RFC3315] apply also to this document. The Route option could be used by malicious parties to misdirect traffic sent by the client either as part of a denial of service or man-in-the-middle attack. An alternative denial of service attack could also be realized by means of using the route option to overflowing any known memory limitations of the client. Neither of the above considerations are new and specific to the proposed route option. The mechanisms identified for securing DHCPv6 as well as reasonable checks performed by host implementations are deemed sufficient in addressing these problems. 7. Acknowledgements 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, 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. 8.2. Informative References [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC3442] Lemon, T., Cheshire, S., and B. Volz, "The Classless Static Route Option for Dynamic Host Configuration Protocol (DHCP) version 4", RFC 3442, December 2002. [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, November 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. Dec & Johnson Expires August 20, 2009 [Page 7] Internet-Draft DHCPv6 Route Option February 2009 Authors' Addresses Wojciech Dec Cisco Systems Haarlerbergweg 13-19 1101 CH Amsterdam The Netherlands Email: wdec@cisco.com Richard Johnson Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 USA Phone: Fax: Email: raj@cisco.com Dec & Johnson Expires August 20, 2009 [Page 8]