Re: MTU discovery problems in the Internet?

At least one of the MTU discovery failures that Jamshid observed is an interesting artifact of the IP-over-ATM paradigm. It seems that if the two ends of a VC don't agree on the MTU, MTU discovery can persistently fail in the following way: a large packet with DF set will arrive at an ATM reassembly buffer which is to small. Since the whole packet can not be delivered, the next hop can not generate the proper ICMP message to adjust the MTU. So, If you are using PVCs in the Internet, you must verify that the upstream end generates the proper ICMP message for the down stream end. --MM--