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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