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Broken PMTUD for . + TLD servers, was: Re: Smallest Transit MTU
- From: Iljitsch van Beijnum
- Date: Sun Jan 09 16:53:03 2005
On 5-jan-05, at 17:39, Sabri Berisha wrote:
Are there any common examples of the DF bit being set on non-TCP
This is very bad.
Here you go. A root-nameserver setting the DF-bit on its replies :)
With a 296 byte MTU I don't get answers from
(a|b|h|j).root-servers.net, *.gtld-servers.net, tld2.ultradns.net and
some lesser-known ccTLD servers.
I would have thought this impossible, but seeing is believing...
Fortunately, this problem won't present itself with regular smaller
MTUs, the MTU has to be smaller than around 500 bytes. I haven't tested
whether these servers also suffer from the "regular" PMTUD problem
where the ICMP messages are ignored, but I'm assuming they don't, so
doing all of this over TCP should still work.