MTU Limit between vlans

[karl.jones]

Hi all,

I created an additional vlan the other night (vlan 2) and configured ISL trunking using a 3662 between vlans 1 & 2. The 3662 has wan connections to other remote sites. The switches I am using are 2924's. Once I had configured the "router on a stick", I found that from vlans 1 or 2 I could ping any device on the wan at 5000 bytes using the "ping x.x.x.x -l command in dos. So connectivity and routing was ok there... but if I pinged a device on vlan 2 from vlan 1 at 5000 bytes (or vice versa) it timed out... but I could ping between the two vlans at 2500 bytes. It seemed that there was some limit when routing between the two vlans on mtu size, although I could ping other devices on the wan with the larger packet size. Am i correct in thinking this and is the restriction on the router or the switch itself. Any thoughts here would be appreciated.

[ciscomoderator]

Since there has been no response to your post, it appears to be either too complex or too rare an issue for other forum members to assist you. If you don't get a suitable response to your post, you may wish to review our resources at the online Technical Assistance Center (http://www.cisco.com/tac) or speak with a TAC engineer. You can open a TAC case online at http://www.cisco.com/tac/caseopen

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.

[amdcent]

One thing for sure is that from ethernet standard compatable NIC card you will never see packets larger than 1518 bytes. When you ping using -l option your workstation sends multiple packets to the specified destination.

amdcent