3Com Switch 8800 Configuration Guide Chapter 36 MPLS Basic Capability Configuration
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36.6 Troubleshooting MPLS Configuration Symptom: Session cannot be setup with the peer after LDP is enabled on the interface.
Troubleshooting:
Cause 1: Loop detection configuration is different at the two ends.
Solution: Check loop detection configuration at both ends to see if one end is
configured while the other end is not (this will result in session negotiation failure).
Cause 2: Local machine cannot get the route to peer LSR ID, so TCP connection
cannot be set up and session cannot be established.
Solution: The default address for session transfer is MPLS LSR ID. The local machine
should issue the LSR ID route (often the loopback address) and lean the peer LSR ID
route.