ipv6 anycast

[jan101]

Can you provide examples of how ipv6 anycast works? Thanks

[broquea]

advertise a /48 everywhere, and when one location advertising drops, the other locations are fine and the dropped location uses internal routing (ospf/ibgp) to redirect its local traffic to the correct location.

[jan101]

I am sorry but I am lost. How do you get the anycast address? I thought that routers can have the same anycast address. But when I want to send a packet to a server going through those routers. How do they process the packet from an anycast address standpoint.

[kcochran]

Same as any other packet from any other source.  There's nothing 'special' about any anycast address, aside from it existing at multiple points in a network.

Router sees traffic for a destination, and delivers it to where it knows it exists.  As broquea noted, with anycast, that just means there's alternate destinations to handle that traffic, so if one drops, another can pick it up.  Now, this is most often used with UDP based services, as then there's no real 'connection' on the service.  TCP based services would drop as the session information would be lost when one anycast point either dropped or the route from the source found a better anycast destination for that service.

[jan101]

But what mechanism the router uses to see which path to take as you have the same anycast address assigned to some specific routers?

[kcochran]

Normal routing metrics.  It may know of multiple instances, but it'll forward onto the one closest based on metrics.