[dns-operations] anycasting axfr

Anand Buddhdev anandb at ripe.net
Tue Apr 18 13:39:48 UTC 2017

On 18/04/2017 14:22, Jim Reid wrote:

Hi Jim,

>> Anycast works well enough for HTTP, so this isn't a very convincing
>> argument against using it for AXFR. E.g.
>> https://www.nanog.org/meetings/nanog37/presentations/matt.levine.pdf
> You’re comparing apples and oranges. The characteristics of a TCP
> session for AXFR and HTTP are not the same. The slides you reference say
> anycast works OK for web sessions: fine. But there’s no equivalent
> analysis for DNS AXFRs. At least not yet AFAIK.

An analysis of actual AXFR failures caused by routing topology changes
would be great, and someone ought to do this. If I have some time, I may
even do this with K-root.

However, I would say that if HTTP works well-enough with anycast, then
AXFR should be completely fine. HTTP sessions can, and often are,
long-lived. Routing changes will hurt them. In comparison, AXFR sessions
are short and not persistent. A client makes a TCP connection, requests
the AXFR, gets the response within a few seconds at most, and closes the
connection. My conjecture is that the failure rate of AXFR, due to
routing topology changes, is so low as to be negligible.


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