[CentOS] Sendmail and pmtu discovery

David Dyer-Bennet dd-b at dd-b.net
Tue Oct 14 17:47:32 UTC 2008

On Tue, October 14, 2008 12:31, Kai Schaetzl wrote:
> Ralph Angenendt wrote on Tue, 14 Oct 2008 17:24:08 +0200:
>> If you don't know the smallest MTU on the path to the mail server, you
>> might not be able to send packets over that path, especially if DF is
>> set.
> But if it's not set? Shouldn't most devices have it not set?

Yes, most devices should fragment if necessary (DF not set).

Most devices should also pass/accept ICMP messages relating to their
connections.  Deliberately configuring them not to is asking for trouble;
those messages are part of the protocol for a reason.

(Fragmentation introduces more work and effectively many more lost packets
in most setups, so the flow will be jumpy and less efficient even if it
mostly works.)

David Dyer-Bennet, dd-b at dd-b.net; http://dd-b.net/
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