Panasonic NN46240-710 - Manual (Page 148)

4 MPLS L2VPN troubleshooting
Nortel Secure Router 8000 Series
_________ Troubleshooting - VPN
• Control word
• MTU
Thus, the VC status can be Up only when those parameters are consistent on both ends.
4.3.12 Large-sized packets are lost between CEs on two ends of
Layer 2 VPN
Fault symptom
After the Layer 2 VPN is set up between CEs, some large-sized packets are lost.
Fault analysis
The cause can be due to the fragmentation of the large-sized packets. The fragmentation can be
caused by the MTU on the AC interfaces or the receiving interface is smaller than the MTU of
the source interface.
Troubleshooting procedure
Step 1 Use the display interface command on the source interface to check the MTU.
Step 2 Use the display interface command on the PEs that the packet passes by to check whether AC
interfaces exist with MTU values smaller than the MTU of the source interface.
Step 3 Use the mtu command in the AC interface view on CE or PE to increase the MTU value and
ensure the packet sent by CE is not fragmented.
—End
Summary
When CEs connect through the Layer 2 VPN, the sent packet passing through PEs cannot
fragment. Otherwise, the packet cannot be received normally.
4-38 Nortel Networks Inc. Issue 5.3 (30 March2009)