I'm reading this post: http://blog.serverfault.com/2011/09/30/the-stack-exchange-architecture-2011-edition-episode-1/
It seems you have 2 routers sitting in front of haproxy.
Are these 2 routers hardware based on linux routers?
What do they do, I would have thought things go straight to haproxy (or are they their because you have haproxy redundancy?)