Subject: Re: MTUs
To: None <,>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
List: tech-net
Date: 01/20/2000 15:56:02
> [MTU changes on Ethernet interfaces] is necessary (AFAIK) for
> machines running behind a firewall/gatway using PPPoE/PPP combination
> to connect through ADSL.

It shouldn't be necessary.  If PMTU discovery is off, the too-large
packets should get fragmented normally; if it's on, a needs-frag ICMP
should be returned.  Either way, no problem.

Except that's clearly not what you're seeing....

> So why is it that when I set the MTU for PPP in the options file to
> 1450, it still won't pass the traffic if the ethernet frame from the
> initiating machine is 1500 bytes long?

This sounds like a bug...unless the packets have their don't-fragment
bits set.  Do they?  If so, are need-frag ICMPs being sent back in

					der Mouse

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