Someone said "Think MTU," but I would say "Think IP Fragmentation and Reassembly." :) In other words, different MTUs isn't supposed to cause a problem for IP.
However, your partner company could be sending pings with the Don't Fragment bit set, in which case it would fail, if there really is an MTU issue. See additional comment below. Sean Kim wrote: > > Hello, > > My company has this 3rd party connection through ATM. The ATM > TA has an ethernet outlet which is and connected to our core > router. Our parner company is connected with anATM module on > their router. > > Recently, I was told by our partner company that they were > running ping test and they could not ping my ethernet interface > (on the core router) with datagram over 1500 byte. > > From both the router itself and my workstation, I pinged my own > interface with 1600 byte, and I was able to ping it. But when > I pinged my partner company's interface with 1600 byte, it > failed. Well, this points to your partner's interface being the problem. Ping should reply with the same payload it received. With a large payload that needs to be broken up, problems could occur with either the request or reply. It sounds like the problems occur with the request when the partner pings and with the replies when you ping the partner. The "debug ip icmp" command might help you figure out what is happening. A protocol analyzer would help too. By the way, many firewalls are set to not allow IP fragments, since there's all sorts of evil things you can do with them. Check for the existance of firewalls, including any personal firewalls on the testing machines. Good luck with it. Keep us posted! Thanks, _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com > > In general it seems that pinging from other nodes, there is no > problem, but sitting on the routers itself, pinging the other > routers interface with the datagram size of over 1500 is failing. > > There isn't any problem with connection of performance. But I > am very curious about why this is happening. > Does anybody have any idea why this would happen? Or can > anybody give me a clue as to how to approach this problem? > > Thank you in advance. > > Sean Kim > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63105&t=63085 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
