RADIUS, anycast, and high availability

Phil Mayers p.mayers at imperial.ac.uk
Thu Jun 26 14:53:33 CEST 2014

On 26/06/14 13:18, Jason Healy wrote:

> annoyed if (say) multiple packets in an EAP conversation don’t go to
> the same server.

Yes, that's absolutely a problem. All packets in an EAP conversation 
must go to the same server, and ideally all future EAP sessions to allow 
you take advantage of session resumption.

However, see below.

> Basically: has anyone else tried it?  Or is this a Bad Idea and I
> just stick to regular multi-server with failover on the NAS?

A lot depends on how stable the routing is, and how many next-hops are 
present, as well as how your routers hash between multiple next-hops 
e.g. ip or ip + port.

Basically - if you're going to do this, ensure traffic to the anycast IP 
only reaches one server from every point during stable operation. During 
a routing change - which is presumably a failure event - packets will 
flow differently, but that doesn't matter because it's a failover event 

Having said all that - I personally would not use anycast for radius. 
Specify multiple servers on your NAS, and use some sort of sticky load 
balancing or active/standby failover of those IPs.

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