From: Jeroen Massar > Sent: Thursday, October 21, 2010 9:57 AM To: Allen Smith Cc: NANOG list Subject: Failover IPv6 with multiple PA prefixes (Was: IPv6 fc00::/7 — Unique local addresses)
[Oh wow, that subject field, so handy to indicate a topic change! ;) ]
Short answer: you announce both PA prefixes using Router Advertisement (RA) inside the network. You pull the RA when a uplink goes down/breaks.
That assumes importing some sort of routing state into your RA config. Sort of a conditional RA. Can that be done today by anyone?
Sessions break indeed, but because there is the other prefix they fall over to that and build up new sessions from there.
This still doesn’t address breakage that happens AFTER your link to your upstream. What if your upstream has a peering issue or their peer has a peering issue? How do you detect that the distant end has a route back to that prefix but doesn't to the other? You can't.