North American Network Operators Group
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: [dnsop] DNS Anycast revisited (fwd)

  • From: Patrick W. Gilmore
  • Date: Tue May 03 21:59:44 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