Two NE40s are connected and IS-IS protocol is established. However, neighbor relation cannot be established.
Check neighbor state and it is down.
1. Open debug is-is and it is found that both sides send hello packet, but they do not receive response packet of the peer. disp isis peer and neighbor relation is down.
2. Ping IP of opposite interface and it is normal whether pinging large packet or small packet.
3. Change tail fiber and it is still problematic. Invoke other transmission device and neighbor relation is established. Previous transmission device cannot transparent transmit the packet of link layer and they cannot receive hello packet of the peer.
4. Change transmission device and neighbor state is normally established. The problem is solved.
Physical link is problematic and the packet cannot reach.
IS-IS protocol is based on link layer, but transmission device of some corporation cannot transparent transmit the packet of link layer. Notice the problem.