Version: MA5200G VRP3.30 release 2215 (independent of version)
Symptoms: MA5200G is connected to a device of C company through ISIS (Ethernet interfaces). Check the neighbor status, and there is no information, and the neighbor cannot set up.
1. After checkup on equipment on both sides, no problem is found.
2. The equipment could ping through nromally, without packet loss; the link works well.
3. At MA5200G, execute debugging isis adjacency command, and the following packets are captured:
*Nov 30 14:31:04 2005 Quidway RM/7/RTDBG:ISIS-ADJ: Rxed Lan L1 Hello on Ethernet4/0/7,from SNPA 00e0.fc35.88e8
*Nov 30 14:31:04 2005 Quidway RM/7/RTDBG:ISIS-ADJ: Rxed L1 LAN IIH is larger than L1 LSP buff/cir's Data link block size
*Nov 30 14:31:04 2005 Quidway RM/7/RTDBG:ISIS-ADJ: Hello PDU Dropped
Check the packets, and it is found the size of IIH packets received by MA5200G (similar to HELLO packets of ospf) is larger than that required by LSP, so MA5200G discardes IIH packets.
4. Check the parameters of equipment at both sides, and it is found that the MTU of interconnected. The MTU of Ethernet interface of C-company is 1502, but that of MA5200G is set to 1500 by default. After changing the MTU of C equipment to 1500, the problem is solved.
1. Configurations of equipment at both sides are problematic.
2. The link is problematic.
3. Parameters of equipment at both sides are problematic in matching.
The case is caused by difference in MTU value of interfaces connected, and they do not match.
ISIS has strict requirements on MTU of interface, so the MTU of interface of interconnected equipment must be identical (in the case, the MTU of the interface of MA5200G is changed to 1502, and the problem could be solved also).