Two MA5200G equipments connect through OSPF and there is transmission equipment between them. Release connection address at OSPF. Check OSPF PEER and find that the STATE is always exstart and cannot establish neighbor relation. MA5200G and other direct equipment can normally establish OSPF neighbor relation.
1. Check the link. The interface of two ports is normal. There is no false packet. Ping packet and there is no missing packet.
2. Check configuration and it is correct. Release network segment is correct, 30-byte mask. Check OSPF interface and the type is consistent and correct.
3. Check configuration and there is configuration of MTU 1600 at two ports. It is doubted that transmission equipment is not changed. Then MTU of transmission equipment is 1600.
4. Both sides send and receive OSPF HELLO packet through debug, so they are under the state of EXSTART. But when the next DD packet interacts, MA5200G-1 sends packet with the length of 1572. MA5200G-2 does not receive it.
5. Handle it with engineer of transmission equipment. Transmission MTU and MTU at the interface of MA5200G are different. Transmission MTU contains Ethernet layer 2 frame, but MA5200G not. So DD packet with 1572 adds IP head with 20, it is 1592. Ethernet layer 2 frame exceeds 1600 and is discarded by transmission equipment.
6. Change MTU of two MA5200G as 1538. Solve the problem.
The MTU of the interface of MA5200G and transmission is 1600, DD packet payload sent by MA5200G is 1572. It is 1592 with the length of IP head. For MA5200, the MTU is 1600 and the packet will not be fragmented and sent. MTU of transmission equipment not includes IP head but Ethernet head. The length of the packet exceeds MTU and DD packet is discarded. So OSPF neighborhood cannot be established.
When configuring OSPF, notice other configuration such as port type, MTU and hello time, transmission equipment and its interface configuration.