The service of most of network segments is normal after some MAN enables network cutover, but users of parts of network segments cannot access network and external MAN.
Change the priority of blackhole route of problematic network segment on the device of core layer lower than that of IGP. The problem is solved.
1. Check the device of whole network and it is normal. Tracert problematic network segments as source address and it is found that the traffic in core device of MAN is discarded.
2. The device is not problematic because most of network segments can access network normally.
3. Check routing table of core device and priority of the route: OSPF ASE route device is 211 and BGP route is set as 200; the priority of blackhole route is 199.
4. Analyze problematic network segment and it is found that these network segments cannot converge. It can be distributed in BGP. Compare the priority of the route. When the traffic is in core layer, the traffic is discarded because the priority of blackhole route is first chosen and the service is unreachable.
For MAN, devices on core layer and convergence layer may run many routing protocols. Notice the priority of routing protocol for network planning.