155Mpos 155M pos
NE80A, NE80B, NE40, and M20 run ISIS (NE40 and M20 run OSPF, and together with downlayer equipment form MAN) . The link between NE40 and NE80A fails, and MPLS VPN under NE40 fails also.
Enable ISIS between NE40 and M20 to ensure detailed route for Loopback ip address of NE40 exit in network.
Loopback IP Address locates in the network segment is converged; once the link fails, there is no detailed route of Loopback of NE40, so LSP cannot set up.