[dnsop] DNS Anycast revisited (fwd)

Wed May 4 01:58:37 UTC 2005

On May 3, 2005, at 7:38 PM, Edward B. Dreger wrote:

> PWG> Date: Tue, 3 May 2005 18:03:12 -0400
> PWG> From: Patrick W. Gilmore
>
> PWG> NB [translation, "operational content"]: Akamai does not use any
> PWG> anycast for HTTP.  I am not at all certain why Paul is telling us
> PWG> this is a bad idea, since we don't do it.  Then again, we  
> might in
> PWG> the future, I am not privy to every decision in the company.   
> (No,
> PWG> that is not a "hint", I really do not think we will do anycast  
> HTTP
> PWG> for content delivery, but I also really do not know everything we
> PWG> will do in the future.)
>
> One also should distinguish between TCP _to_ an anycasted address and
> TCP _from_ an anycasted address.  The latter is trickier, as  
> asymmetric
> routing increases the chances that the session will need to be
> transferred to another pod:

Just to make life fun, there is the whole "anycast a bunch of name  
servers, each with different zone files pointing at local HTTP  
servers".  Since the "anycast" portion is over UDP, it avoids a lot  
of the problems (real or otherwise) mentioned here, and the HTTP is  
still unicast but distributed and can be made resilient to failure.

Of course, the DNS backend is then .. uh .. "de-coherent"? :-)  But  
it works, and works well, in many currently operational configurations.

Does PPLB (or anything else) break this?  I'm certain I could find  
things that would break this if I looked hard enough.  But as I've  
said many times, reality trumps NANOG posts.  Since this is a  
_working_ configuration today, I would say that disproves any claims  
that it cannot or will not work.

-- 
TTFN,
patrick