Thanks, for some reason I can't open that link on my blackberry, does it show a command to see if I'm getting fragmentation, if so do I set the mtu on the dialer and ethernet 0 router?

Fragmentation can be seen from the end device being affected by taking a packet trace.

It's recommended to place this command on the interface that is fragmenting the packet, often that is the tunnel interface due to GRE.

The end point is a Cisco concentrator0and on the filtered events I do are fragmentat errors every now and then, shoul I set something?

Also I don't set the mtu on the DSL dialer interface, does this default to 1500? How do I know if I should lower this?

If you are seeing fragment errors in the Cisco concentrator then configuring "ip tcp adjust-mss" will help.

Keep in mind, the commands relies on ICMP. Therefore, any ACL on the path back to the affected device must be observed and allow ICMP.

As for the DSL interface, you can find out its default IP MTU by typing show ip interface dialer x

I haven't set the mtu, should I? Its currently defaulting to 1500.

I see some sample configs set the mtu to a lower value.

leave the MTU as it is for now and just implement the "ip tcp adjust-mss" feature.