Anycast but for egress

Joel Jaeggli joelja at
Sun Aug 1 23:22:32 UTC 2021

On 7/27/21 10:54, Vimal wrote:
> (Unsure if this is the right forum to ask this question, but here goes:)
> From what I understand, IP Anycast can be used to steer traffic into a
> server that's close to the client.
> I am curious if anyone here has/encountered a setup where they use
> anycast IP on their gateways... to have a predictable egress IP for
> their traffic, regardless of where they are located?

Stateless outbound load-balancing setups exist.

Example you have two  or more nat44 / nat64 / cgnat boxes behind a
common ecmp path with the same destination IP(s).  this is normally so
that you have more boxes that accumulate state rather than being bound
to a single one.

> For example, a search engine crawler could in principle have the same
> IP advertised all over the world, but it looks like they don't...  I
> wonder why?

So this is a somewhat different problem...

There's  no assurance that when you initiate a connection that the
return path will return to the same instance of your anycast
announcement  when the server on the other side  replies.

Effectively the initiating party needs a unicast address or you need
some out of band path to get an errant packet back to the correct host.

> -- 
> Vimal
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