services on subnet-router anycast address?

Ignatios Souvatzis ignatios at
Thu Apr 26 10:25:15 CEST 2012


On Thu, Apr 26, 2012 at 08:35:03AM +0100, Brian E Carpenter wrote:

> As for the original question, I'm still looking for the harm, and

If the peer has only have *one* possible route to that subnet, or
multiple paths ending on the *same* router, there are no restrictions
- the peer will always connect to the same router.

If the peer has multiple paths that might end on *different* routers
to that subnet, stateful services (e.g. TCP) will break when the
route flaps.

So, if the subnet operator knows that only one router leads to that
subnet, it's safe to put a service on the router. Things like remote
management or statistics come to mind.

Note that I wrote "subnet", not "link". If several routers route to
a link but use seperate subnets for it, there's no possible problem.

Stateless services like ping and traceroute have no problem, of course.

All this should be obvious, so maybe I'm missing some fine point.

> I can't see any harm in having services on the RFC 2526 addresses
> either.

Those are possibly trickier. They might end up on different hosts-
e.g. if some fallback mechanism is involved. The same considerations
apply as above, but you have to look closer whether paths to multiple
instances of the specific address can coexist.


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