Subject: [v6ops] PA Address Multihoming in IPv6

From: "Fred Baker (fred)" <[email-masked]>
Date: Mon, 2 Nov 2015 05:02:59 +0000

This email is being sent in accordance with the v6ops charter, which calls for the working group to communicate operational issues and requirements to working groups that are chartered to address them.

The IETF's current primary recommendation for multihoming of midrange enterprise networks - those that cannot justify the costs and overheads of a PI address and in fact multihome - is to obtain a provider-allocated prefix from each of their upstream networks, and deploy a /64 out of each on each LAN in their networks.

https://tools.ietf.org/html/rfc4213
4213 Basic Transition Mechanisms for IPv6 Hosts and Routers. E. Nordmark,
     R. Gilligan. October 2005. (Format: TXT=58575 bytes) (Obsoletes
     RFC2893) (Status: PROPOSED STANDARD) (DOI: 10.17487/RFC4213)

This has a number of issues, not the least of which is in the back end OSS software, which needs to now scale to a much larger number of prefixes, handle multiple addresses in DNS for servers and perhaps clients, resolve reverse DNS queries, and so on. It also is obviously carrying that much more information in routing.

One outcome of v6ops' discussions this morning was that PI multihoming demonstrably works, but PA multihoming when the upstreams implement BCP 38 filtering requires the deployment of some form of egress routing - source/destination routing in which the traffic using a stated PA source prefix and directed to a remote destination is routed to the provider that allocated the prefix. The IETF currently has no such recommendation, or consensus that it should have. However, enterprise networks are known to delaying operational deployment of IPv6 in part due to the complexities visited upon them and the cost of the back end software upgrades, and this is part of that issue.

Without trying to limit the options available to the working groups in question, I'll point out that options currently on the table include the following. There are also current open source implementations of source/destination and source-specific routing in IS-IS, OSPFv3, and Babel.

https://datatracker.ietf.org/doc/draft-baker-ipv6-isis-dst-src-routing
  "IPv6 Source/Destination Routing using IS-IS", Fred Baker, David
  Lamparter, 2015-10-19

https://datatracker.ietf.org/doc/draft-boutier-babel-source-specific
  "Source-Specific Routing in Babel", Matthieu Boutier, Juliusz
  Chroboczek, 2015-05-27

https://datatracker.ietf.org/doc/draft-ietf-6man-multi-homed-host
  "Routing packets from hosts in a multi-prefix network", Fred Baker,
  Brian Carpenter, 2015-10-15

https://datatracker.ietf.org/doc/draft-ietf-ospf-ospfv3-lsa-extend
  "OSPFv3 LSA Extendibility", Acee Lindem, Sina Mirtorabi, Abhay Roy, Fred
  Baker, 2015-10-08

https://datatracker.ietf.org/doc/draft-ietf-rtgwg-dst-src-routing
  "Destination/Source Routing", David Lamparter, 2015-10-17,

https://datatracker.ietf.org/doc/draft-sarikaya-6man-sadr-overview
  "Source Address Dependent Routing and Source Address Selection for IPv6
  Hosts: Problem Space Overview", Behcet Sarikaya, Mohamed Boucadair,
  2015-08-17

https://datatracker.ietf.org/doc/draft-sarikaya-6man-sadr-ra
  "IPv6 RA Option for Source Address Dependent Routing", Behcet Sarikaya,
  2015-06-08

https://datatracker.ietf.org/doc/draft-sarikaya-dhc-6man-dhcpv6-sadr
  "DHCPv6 Solution for Source Address Dependent Routing", Behcet Sarikaya,
  2015-05-08

https://datatracker.ietf.org/doc/draft-xu-ospf-multi-homing-ipv6
  "Extending OSPFv3 to Support Multi-homing", Mingwei Xu, Shu Yang,
  Jianping Wu, Fred Baker, 2015-10-11,

https://datatracker.ietf.org/doc/draft-baker-rtgwg-src-dst-routing-use-cases