5 networks are going through a Catalyst 3550. Between two of them packets of 549 bits and up are dropped. 548 and lower are passing fine. There is a CheckPoint firewall also, running on a Nokia appliance between the two networks, on which I don't know how to change the MTU - which is 1514 to make it equal to Cisco's 1500 (which is max). Can this be an issue? Can interfereces from other devices cause this? The Nokia appliance is built in a plastic enclosure and sits in a rack, close to other devices. Thanks in advance for any ideea.
On the face of it this does sound like an MTU size problem but then again it might not be. Am I right in assuming that the firewall is effectively the router between the two networks you're having trouble with?
If so, try using the Ping command with various packet sizes (e.g. -l 1400) and the don't fragment bit set (-f) to confirm the effective MTU size of the path. Basically, start with a low value and keep increasing it until the replies stop. Once you've found it, try sending a packet bigger than the maximum size but with the -f option left unset. If it doesn't come through then the router might have the don't fragment option set which is preventing reassembly of fragmented packets
I am currently experiencing exactly the same problem as you.
Was wondering if you have managed to resolve this issue ?
I have tried looking at the various related solution at Technet, and still in vain.
Well I have found who caused my problems. It was the Nokia firewall appliance running CheckPoint FW-1 which in turn contains also whatever they call SmartDefense. It was in this module that the ICMP limit was set to 548.