[dns-operations] Anycast vs. unicast NS

[Joe Abley]

On 2011-03-18, at 08:32, Jim Reid wrote:

> Well if all the DNS servers are anycast, that in itself becomes a single point of failure.

Not at all speaking for Afilias these days, but Afilias TLDs are served by two anycast clouds -- one operated by Afilias, and a second operated by a third party. Each cloud is operated by different people, according to different operational processes.

While it's philosophically feasible that there is some anycast-specific failure mode that might afflict both together, which might lead people to think that the use of anycast is a single point of failure, I'll observe that I have never heard of such a failure to date.

Whilst including unicast (by which I mean non-anycast) servers in an NS set might seem like a good idea, favouring operational diversity, it's my experience that there are many other things more likely to take an individual nameserver off-line than an anycast-specific effect and such a strategy in many cases is likely to optimise the wrong thing.


Joe