Panasonic NN46240-710 - Manual (Page 136)

4 MPLS L2VPN troubleshooting
Nortel Secure Router 8000 Series
_________ Troubleshooting - VPN
4.3.5 VC is up but the PPP session cannot establish
Fault symptom
Figure 4-15 Networking diagram
PE1 PE2
GbE2/0/0^^
GbE2/0/0
POS1/0/0
POS1/0/0
CE1
CE2
The CE and PE connect through a POS interface. The PE and PE connect through a GbE
interface.
The VC is Up, but the PPP session cannot be Up. If a POS interface connects PEs, the PPP
session between CE and PE goes Up.
Fault analysis
The VC on PE is Up because a tunnel exists between PEs and the CE-bound PE interface is Up
administratively.
To enable a PPP session to be Up, PPP negotiation must succeed.
The PPP negotiation occurs between two CE interfaces. The PE connects to the public network
through an Ethernet-type interface whose minimum packet is defined to be 64 bytes long. The
PPP control packet, LCP packet, is very small and is less than 64 bytes even after two layers of
labels are added. Consequently, the GbE interface on PE discards this negotiation packet. This
causes the failure in transmitting the negotiation packet to the remote CE over the VC.
Troubleshooting procedure
Step 1 Connect PEs by using the POS interface. Alternatively, run the mpls l2vc peer-ip-address
[ vc-id ] control-word command on the two PEs to configure a control word for Layer 2 VPN.
Padding is automatically added to Layer 2 VPN packets.
---- End
Summary
When the type of the link between CE and PE is different from that between PEs, check the
minimum MTU value.
4-26 Nortel Networks Inc. Issue 5.3 (30 March2009)