IP MTU & Fragmentation over L2TP
Posted on 2010-01-10
We have a site router connecting over a 3G Carrier Network via L2TP/VPDN into our Cisco 7204 LNS Router to forward onto the customer network.
All sessions connecting OK and pings from site to customer data-centre OK.
However, we have found that when packets of size 1464 are sent from the the site to the data-centre, then the ping fails. Packet size 1456 work OK.
According to the customer, they can see the ping request hit the destination server in the data-centre which then replies. But the site never receives the reply from the server in the data-centre back accross the L2TP link.
All Ethernet links are default MTU 1500
We are being asked if the LNS Router is causing this, so need to prove if it is or not.
Any help would be greatly appreciated.