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

Joe Abley jabley at isc.org
Mon Dec 13 22:24:54 UTC 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




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