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Enhancing Multi-Homed Network Routing: Addressing Source-Specific Challenges

DESCRIPTION

This document explores the complexities of routing in multi-homed networks, particularly in relation to the need for source-specific routing. Early identified in BCP 38 and discussed in RFC 3704, the paper synthesizes various enhancements proposed for achieving optimal packet egress without manual configuration. It examines the requirements arising from home networks with multiple routers and upstreams, addressing common scenarios and providing insights into the challenges inherent in modern routing protocols, with a focus on the need for systematic solutions.

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Enhancing Multi-Homed Network Routing: Addressing Source-Specific Challenges

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  1. Source/Destination Routing Fred Baker Cisco Systems

  2. Problem History • Identified as a requirement soon after the deployment of BCP 38 • Discussed as an objective in shim6 context • RFC 3704 • Marcelo Bagnulo research (2003) • Various efforts centering on homenet requirements • Troan & Colitti: draft-troan-homenet-sadr • Chroboczek& Boutier: draft-boutier-homenet-source-specific-routing • Baker: draft-baker-ipv6-ospf-dst-src-routing and draft-baker-ipv6-isis-dst-src-routing • Yang & Xu: draft-xu-homenet-traffic-class, draft-xu-homenet-twod-ip-routing

  3. RFC 3704 • Savolaand Baker • Suppose a session is opened up to a remote location in a multihomed network • Suppose the default route takes it to the wrong egress • ISP A’s source address but routed to ISP B • Wouldn’t it be nice if the packet got to the right egress somehow? BCP 38 Filter ISP B ISP A Ideal Route

  4. USE Cases

  5. Homenet’s first concern • A home with • one router, • two upstreams, and • a PA Prefix from each • Is there a way to systematically have it get packets to the right upstream network? • Without manual configuration? • Might be solved from DHCPv6 IA_PD ISP B ISP A

  6. But residential routers usually have one upstream… • A home with • multiple routers, • two upstreams, and • a PA Prefix from each • Is there a way to systematically have it get packets to the right egress router? • Without manual configuration? • If there is one LAN, simple solution is for host to give packet using a source prefix to the router from which it learned a prefix ISP B ISP A

  7. Multi-LAN case • A home with • Multiple routers, • Multiple LANs • Two upstreams, and • A PA Prefix from each • Is there a way to systematically have it get packets to the right egress router? • Without manual configuration? • If there is more than one LAN, this begins to call for a routing protocol: • Separate routing for default route by source prefix ISP A ISP B

  8. NTT B-FLETS Case • What if they are not general use ISPs? • NTT B-FLETS is a video service. • It doesn’t offer general ISP services • Source Prefix: • Traffic to consumer ISP must use ISP’s source prefix • Traffic to B-FLETS must use B-FLETS-assigned source prefix • Routing: • Although B-FLETS does not provide general Internet access, it advertises a default route • Ideally, that changes to advertising a route to B-FLETS ISP B-Flets

  9. Generalizing • We need the ability to advertise and use a route • To a destination prefix (could be ::/0) • From a source prefix (could be ::/0) • Ambiguity issues • There are a number of potentially ambiguous cases • Resolution similar to longest-match rule • Use the FIB entry with the longest destination match that also matches the source

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