[dns-operations] L-Root Maintenance 2010-01-27 1800 UTC - 2000 UTC
marka at isc.org
Thu Feb 4 00:05:47 UTC 2010
In message <4B69AB06.8050305 at hp.com>, Rick Jones writes:
> 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!
This issue was identified over a decade ago  and there is a standards
based solution. See RFC 3542 and IPV6_USE_MIN_MTU, which was
published May 2003.
If your OS vendor does not implement this option or your nameserver
vendor does not set this option replace the relevent part of your
> 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
> dns-operations mailing list
> dns-operations at lists.dns-oarc.net
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: marka at isc.org
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