[dns-operations] L-Root Maintenance 2010-01-27 1800 UTC - 2000 UTC

Rick Jones rick.jones2 at hp.com
Wed Feb 3 16:57:42 UTC 2010

Joe Abley wrote:
> On 2010-02-03, at 06:45, Paul Vixie wrote:
> Geoff Huston's recent Bad Idea regarding stateless TCP support for DNS may also be worth reading about, if you haven't already. (I'm not suggesting this is equivalent in any sense to the pointed Paul provided above, but it is somewhat relevant to the general topic of how to deal with upswings in TCP transport for DNS).
>   http://www.potaroo.net/ispcol/2009-11/stateless.html

> There is a related issue here, when looking at the use of IPv6 as the
> transport protocol for the UDP DNS query with ENDS0.

That should be "network protocol" - UDP and TCP are transports :)

> Because IPv6 UDP does not support fragmentation in flight, if the 
> path MTU between the server and the DNS client is less than the IPv6 
> interface MTU at the server, then the server will emit a large UDP 
> packet matching the local interface MTU. This will cause the packet
> to be dropped at the path MTU bottleneck, and an ICMPv6 "packet too
> big" response sent back to the server. The server has no remembered
> state of the original query, and cannot reformat its response. The
> client will not receive any response to its original query, and will
> time out. In such a case, the client turning to any other server may
> not help either. If all servers are delivering the same large
> response via UDP and there is a path MTU blackhole close to the
> client, then the client may well have a problem!

If there is such a "dumbell" (Wide at the ends, narrow in the middle) 
between the client and the server, that will affect the query carried 
over TCP as well.  Ditto with IPv4.

rick jones

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