[151031] in North American Network Operators' Group
Re: Questions about anycasting setup
daemon@ATHENA.MIT.EDU (Steve Gibbard)
Sat Mar 10 01:58:02 2012
From: Steve Gibbard <scg@gibbard.org>
In-Reply-To: <4F59C701.3090503@altadena.net>
Date: Fri, 9 Mar 2012 22:57:02 -0800
To: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Mar 9, 2012, at 1:01 AM, Pete Carah wrote:
>> Well, let's say, using Quagga/BIRD might not really be best practice =
for
>> everybody... (e.g., *we* are using Cisco equipment for this)
> Actually there is a *very* good reason why many (most?) anycast
> instances use quagga/BIRD/gated/etc
> to speak bgp (or even ospf for internal anycast) which using a Cisco =
(or
> any separate router) usually won't accomplish.
I've done this two ways.
I've used Quagga to announce routes directly from the anycast servers. =
This guarantees you that the route will go away if the server completely =
goes away, and that traffic will be directed elsewhere. It also allows =
you to run scripts on the servers that can withdraw the routes in other =
circumstances, such as if a script running on the server detects that =
the server is non-responsive (or overloaded).
I've used load balancers in front of the name servers. Like Quagga =
running directly on the server, a load balancer can withdraw routes when =
all servers behind it stop responding. It has some advantages, in that =
it can withdraw routes to non-responsive servers even in cases where the =
server may be too confused to detect its own problems and send the =
appropriate messages to Quagga. It can spread load among a larger =
collection of servers than a router would be able to on its own, sit in =
front of the servers and do rate limiting, and things like that. It =
could help with the overload issue Bill mentions by selectively sending =
some queries to other sites without the all or nothing effect you get =
from a BGP route withdrawal. On the other hand, load balancers aren't =
cheap, and and once installed in the middle of a network they become one =
more device to fail.
I have no idea what Cisco equipment Elmar is using, but I wouldn't jump =
to the conclusion that it can't withdraw routes when needed.
-Steve=
