I'm having this issue with mtu size.
ip tcp adjust-mss 1338
on the LAN interface of the router, i believe that when pinging with greater packet size and DF set, the router should reply that it should be fragmented.
But on my 1841 IOS 12.4, it doesn't. I only get request timed out.
But with other routers in my network, this works fine. And the router replies that the packet needs to be fragmented. This is with a 7206vxr and a 881 router.
Why doesn't it work with the 1841 router?