Network Working Group T. Boot
Internet-Draft Infinity Networks
Expires: May 21, 2009 November 17, 2008
Border Router Discovery Protocol (BRDP) Based Routing
draft-boot-brdp-based-routing-00.txt
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Abstract
This document specifies a mechanism for routing in multi-homed edge
networks. The default gateway routing mechanism is replaced with
routing to Border Routers that correspond with the source address of
the packets.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problems with default gateway routing . . . . . . . . . . . . . 3
3. Default gateway routing replaced with BRDP Based Routing . . . 4
4. Support for IPv4 . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Change Log From Previous Version . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
With the growth of the Internet, the routing table in the Internet
Default Free Zone (DFZ) is becoming unacceptably large. One of the
reasons is usage of Provider Independent (PI) Address blocks in edge
networks. A remedy is encouragement of Provider Aggregatable (PA)
Addresses. Unfortunately, PA addresses and multi-homing may
introduce some problems if not carefully planned and configured
[RFC3704].
In a stable network, multi-homing with PA addresses can be supported
by configuring routing, tunneling, filtering or other mechanisms. In
a more dynamic world, this is less practical and needs improvement.
In a MANET [RFC2501], manual configuration is infeasible.
The Border Router Discovery Protocol (BRDP) [I-D.boot-autoconf-brdp]
provides a mechanism for Address Autoconfiguration in ad hoc networks
and may support automatic renumbering. In addition, a mechanism is
needed for ensuring that traffic is directed to a Border Router that
corresponds with the source address. This will circumvent problems
with ingress filtering, as described in [RFC5220] section 2.1.2.
BRDP Based Routing provides a mechanism for packet delivery to Border
Routers that correspond with the source addresses of the packets.
This mechanism is applied for traffic that is not destined for
interior nodes of the edge network. It replaces the default route
mechanism.
The BRDP Based Routing mechanism also provides basic support for load
distribution over multiple Border Routers. More advanced load
balancing can be provided for multi-homed hosts, provisioned with
transport layer facilities that utilize multi-homing.
2. Problems with default gateway routing
Usually, the nexthop selection is based on the destination address.
In case of default gateway routing and multiple exit routers to
multiple providers, the source has no influence on what exit router
is used. In case of ingress filtering and lack of a mechanism to
redirect packets to exit routers that correspond to the source
address, packets may be dropped.
This default gateway routing behavior blocks incremental enhancement
of the Internet, e.g. through the addition of support for more
dynamic networks and / or host based load distribution mechanisms.
In a MANET, it also also prevents the use of make-before-break
[RFC3753] mechanisms.
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3. Default gateway routing replaced with BRDP Based Routing
Default gateway based routing for IPv4 is defined in [RFC1812],
section 5.2.4.3:
(5) Default Route: This is a route to all networks for which there
are no explicit routes. It is by definition the route whose
prefix length is zero.
With BRDP Based Routing, another type of route is introduced:
(6) BRDP Route: This is a route to all networks for which there
are no explicit routes, and a default route is not used.
The nexthop IP address is found by means of a Border Router
Information Cache (BRIO-Cache) lookup based on the source
address and, if a matching BRIO-Cache entry is found, a
subsequent FIB lookup based on the selected Border Router
address.
Note that route types (3) and (4) are not defined in RFC1812.
BRDP Based Routing can be turned on and off with the existence of a
default route in the IGP. This switch function might be useful in
migration scenarios towards BRDP Based Routing.
The Border Router should run the IGP on the interface with the BRDP
advertized Border Router address.
In the edge network, all interior routers should run BRDP and BRDP
Based Routing. All interior routers will have a BRIO-Cache
[I-D.boot-autoconf-brdp] with information for selecting Border
Routers as exit points to the Internet. A BRIO-Cache entry contains
a Border Router address and a summary prefix assigned to that Border
Router. BRIO-Cache lookup follows the longest-match rule.
Forwarding is solely based on FIB lookups, the nexthop IP address is
found either by a FIB lookup with the destination address or by a FIB
lookup with the address of the Border Router that corresponds with
the source address. If the nexthop IP address lookup fails, the
packet is discarded.
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4. Support for IPv4
BRDP-based Address Autoconfiguration is designed for IP version 6.
Support for IP version 4 will be taken into consideration.
5. IANA considerations
This document has no actions for IANA.
6. Security Considerations
BRDP Based Routing depends on BRDP and the IGP used. BRDP depends on
security mechanisms provided by ND [RFC4861]. ND can be secured by
SeND [RFC3971]. IGPs are assumed to have their own security
mechanisms.
More research on security issues for BRDP Based Routing is needed.
7. Acknowledgments
BRDP is inspired by MANEMO technology; thanks to all who contributed
to it. Thanks to Ran Atkinson, who guided me towards a BRDP Based
Routing mechanism that does not rely on routing headers or
encapsulation. And thanks to Ronald in 't Velt for reviewing.
8. References
8.1. Normative References
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[I-D.boot-autoconf-brdp]
Boot, T., "Border Router Discovery Protocol (BRDP) based
Address Autoconfiguration", draft-boot-autoconf-brdp-01
(work in progress), October 2008.
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8.2. Informative References
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC3753] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in Multi-
Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008.
Appendix A. Change Log From Previous Version
o 00: Initial Document.
Author's Address
Teco Boot
Infinity Networks B.V.
Elperstraat 4
Schoonloo 9443TL
The Netherlands
Email: teco@inf-net.nl
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