Panasonic NN46240-710 - Manual (Page 97)

3 BGP/MPLS IP VPN troubleshooting
Nortel Secure Router 8000 Series
_________ Troubleshooting - VPN
Troubleshooting procedure
• Do as follows on the two PEs.
Step 1 Use the interface loopback interface-number command in the system view.
Step 2 Use the ip address ip-address 32 command to configure an IP address for the loopback
interface.
Step 3 Use the quit command to return to the system view.
Step 4 Use the bgp as-number command to enter the BGP view.
Step 5 Use the peer peer-address connect-interface loopback interface-number command to specify
the loopback interface as the outbound interface of the IBGP peer session.
Step 6 Save the configuration.
• On CE, ping the remote CE. If the ping succeeds, it indicates that the fault is isolated.
—End
Summary
When you configure PE peers, specify the local loopback interface as the outbound interface of
the local IBGP session.
3.3.3 Failure to ping large packets of the private network
Fault symptom
If the Nortel Secure Router 8000 Series router networks with a device from another vendor to
deploy Layer 3 MPLS VPN service by using the Ethernet interface, the packet larger than 1492
bytes cannot be transmitted between private network users. Users cannot access part of
websites or download files through the File Transfer Protocol (FTP).
Use the ping command, and find that the IGMP payload larger than 1464 bytes cannot be
pinged successfully.
Fault analysis
The default maximum transmission unit (MTU) of an Ethernet interface is 1500 bytes. When
forwarding data, Layer 3 MPLS VPN adds a 4-byte or 8-byte MPLS packet header between the
IP header and the Layer 2 frame header. A 4-byte label is added during the forwarding between
the penultimate hop and the tail-end hop; an 8-byte label is added in other cases.
Because MPLS processing is unknown to the link layer, it still receives a maximum of
1500-byte data packet by default. The packet is longer than 1500 bytes after adding an MPLS
packet header to a packet of 1492 to 1500 bytes. Consequently the link layer cannot receive the
packet, affecting the forwarding.
Troubleshooting procedure
Step 1 Change the MTU of the device from the other vendor. The MTU must be at least 1508 bytes.
Step 2 By default, an Ethernet interface on the Nortel Secure Router 8000 Series router can send and
receive jumbo frames. No change is needed on the Nortel Secure Router 8000 Series router.
3-18 Nortel Networks Inc. Issue 5.3 (30 March2009)