4000 Router Series Interface Configuration Guide

[RouterB-Pos1/0] shutdown

[RouterB-Pos1/0] undo shutdown

Verifying the configuration

Check the interface connectivity between the POS interfaces with the display interface pos command

and test network connectivity with the ping command.

Troubleshooting POS interfaces

Symptom 1

The physical state of POS interface is down.

Solution

• Check that the transmitting and receiving fibers-optic are correctly connected to the POS interface.

If you connect the two ends of a fiber-optic to the transmitting end and the receiving end of the same

POS interface, a "loopback detected" message is displayed on the screen even if loopback is not

enabled when you execute the display interface command.

• If the two routers are directly connected back to back, check that the internal clock is enabled on

either of the two POS interfaces.

Symptom 2

The physical layer is up but the link layer is down.

Solution

Check the following items:

• The configurations of clock mode, scrambling, and other physical parameters are consistent on the

connected two POS interfaces.

• The same link layer protocol is configured on two sides.

• Both ends are assigned IP addresses.

Symptom 3

A large amount of IP packets are dropped.

Solution

Check the following items:

• The correct clock mode is configured on the POS interface. If not, a large amount of CRC errors can

be generated, which might cause IP packet drop.

• The MTU configuration is appropriate.