PPPoE over DSL, MTU problems...

Unanswered Question
Apr 3rd, 2008

I have a 1721 connected through PPPoE to a DSL connection doing NAT. I'm having MTU issues. I have several embedded devices on the network which do not allow for adjusting the MTU size. The computers work fine with the MTU adjusted down to 1492. Without manually adjusting the MTU down to 1492, connectivity to the internet does not work. Is there a way to set the 1721 up to function over a PPPoE DSL connection without having to adjust the MTU's down from 1500 on the internal network? I have ip tcp adjust-mss 1452 on the eth0 interface and ip mtu 1492 on the dialer1 interface, but that doesn't seem to be doing the trick. What am I missing here?? TIA!!


It appears that the ip tcp adjust-mss command should do what I want, but it isn't working for some reason... I'm at a loss here...

I have this problem too.
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aghaznavi Wed, 04/09/2008 - 09:36

The problem is related to either of these issues:

Maximum Transmission Unit (MTU)/Maximum Segment Size (MSS) size and Fragmentation policy during encryption

Perform a sniffer trace from the client to the server side in order to find out which is the best MTU to use.

ping -l 1400 x.x.x.x -f

x.x.x.x -- IP address of the remote machine.

Continue to reduce the value of 1400 by 20 until there is a reply


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