Alternatives to GSLB ?

Matthew Petach mpetach at
Tue Apr 5 20:01:54 UTC 2011

On Tue, Apr 5, 2011 at 12:17 PM, Jack Carrozzo <jack at> wrote:
> Anycast works.

...with some caveats.

> [...] we are looking for ideas on
>> how to 1) ensure clients are routed to the closest geographical server 2)
>> ensure the client hits the server(s) with the shortest path.
> No need to deal with that yourself when BGP eats that problem for breakfast
> lunch and dinner.
> -Jack Carrozzo

Note that anycast can and will bite you in the ass
repeatedly as you deploy it over wider and wider
scopes, unless you take careful steps to overcome
the differences in policies and coverage areas with
different networks.

Classic problem:

You peer with network X in the US.
You buy transit from network Y in Asia.
Network Y buys transit from network X in the US.

Network X localprefers customer routes over peer routes.

Your anycast traffic from network X in the US is
suddenly being served from your Asia nodes behind
network Y, because network X prefers the path to your
anycast subnet heard through their customer instead
of the peer-learned path directly from you.

Not saying it won't work; it just takes careful planning,
judicious use of BGP communities to limit route
propagation, and constant monitoring and adjusting
as networks change who they purchase connectivity
from over time.


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