IPSec, MTU Size and different Router models and IOS

rainer.kober · ‎02-01-2008

Hi all,

hope somebody can help me with my problem. I have a cisco 7206VXR(IOS: C7200-IK9S-M 12.2(15)T1) on one site and cisco 2691(IOS: C2691-IK9S-M 12.3/17b)) on the other site. There are tunnels established on 2691 to 7206VXR through a service provider network where MTU size is 1500. MTU size on 2691 and 7206VXR are ajusted and work fine. Now we installed a cisco 2811(IOS: C2800NM-ADVIPSERVICESK9-M 12.4(9)T1) and we have to downsize the MTU size to lower size than on 2691. Can anybody tell me why? Is it the model or is there a problem with the newer IOS?

Thanks in advance for your help.

brgds

Rainer

sadbulali · ‎02-07-2008

Try with 'tunnel path-mtu-discovery' command and configure 'ip mtu 1420' on both sides of the Tunnel.

rainer.kober · ‎02-07-2008

Thanks for the answer. Thats clear for me! But what i donnot understand is that we have to configure different MTU size on the different models. We have exactly the same paths through our provider network but we have to downsize the MTU size on one model to a lower value than the other. Any answer?

thanks&brgds

Rainer