VPN functionality issues with different applications 1

[VTALsupport]

I manage a VPN WAN using Nortel COntivity 221 and 1010 routers. After moving our hub recently I have one site that pulls up the VPN but will not function normally in all applications. E-mail doesn't work at all across the VPN, and Remote Desktop works partially; it begins to load the screen but never gets to the login screen. The router gives me this message:

08/18/2008 11:02:41 0 PPPoE [02] Dropping PPPoE tx packet on devLoc 257 because the packet length 1502 exceeds the max 1494
08/18/2008 11:02:28 0 PPPoE [02] Dropping PPPoE tx packet on devLoc 257 because the packet length 1502 exceeds the max 1494
08/18/2008 11:02:21 0 PPPoE [02] Dropping PPPoE tx packet on devLoc 257 because the packet length 1502 exceeds the max 1494

The MTU and MSS settings are identical to all our other routers, which are functioning normally.

I can ping the computers at this location, and can also open the management interface on the router, but these other functions, which require different ports, don't work any more.

Any ideas?

 

[burtsbees]

They look like extra data in the IP header, like VLAN tagging. Either do an extended ping with the df bit set to determine the MTU, or adjust the mtu and mss lower than 1494 (like 1492 for mtu and 1452 for mss).

Burt

 

[VTALsupport]

THanks to Burtsbees for this suggestion. It was so simple, but when I had experimented in the past I had tried INCREASING the MTU setting, thinking that what I was doing was allowing slightly larger packets to come through. It didn't occur to me that REDUCING the packet size would allow it to process correctly through other checkpoints. Everything is running as it should!


VTALsupport

 

[burtsbees]

Well, with TCP's functionality with sequence numbers, it is able to put packets back together when fragmented, so really any size can go through. You just don't want to overload the router by setting it too low, like 8...lol.

IP is 1492, unless there's extra data. VLAN tagging is just one example. Another tool that is a free download is called TCPDoctor (I think), which you can use to tweak MTU on a pc as well.
Glad it's working!

Burt