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Re: Anycast reliability (was: Re: verizon.net and other email grief)

  • From: Joe Abley
  • Date: Mon Dec 13 17:26:51 2004 
On 13 Dec 2004, at 15:27, Steve Gibbard wrote:


On Mon, 13 Dec 2004, Simon Waters wrote:
Inspection suggests that the anycast announcements in the UK were
pointing to a server that wasn't accepting email.

I believe here the problem is using anycast, and not providing a backup
system not using anycast. The previous case I'm aware of was when bits
of the NE USA lost ".org" because they only had anycast DNS servers (and
still do AFAIK), and the announcement messed up.

Whilst I plead ignorant of the technical details of anycast, strikes me
that it is clearly more complex, and thus more prone to failure, and
these failures are potentially less obvious.
(for anybody reading this who doesn't know, anycast is multiple servers in
multiple locations announcing routes and accepting connections to the same
IP address).
Distribution of a service (whether by anycast or by some other means) is bound to introduce complexity over that incurred by a single instance of a service running in just one place. In some cases, the cost of that complexity is offset by reduced costs (or risk) elsewhere, and anycast makes sense.

For a discussion of some of the issues surrounding service distribution using anycast, see:

http://www.ietf.org/internet-drafts/draft-kurtis-anycast-bcp-00.txt

Flames and projectiles relating to that draft would be very gratefully received (either directly or on the GROW list, but probably not on NANOG).


Joe