Troubleshooting guide

10-11
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 10 Troubleshooting Ethernet, ATM Uplink, and POS Uplink Interfaces
Troubleshooting 10/100 Ethernet Interface Modules
Step 3 Check the line protocol field to see whether the status is up.
If the interface is down, check for the following:
• The line protocol software processes might have determined that the line is unusable. Try swapping
the cable.
• The local or remote interface might be misconfigured. Check the interface configuration.
• Hardware might have failed. Try swapping the interface module.
Step 4 Check the duplex mode field. It should match the speed of the interface and be configured as
Auto-negotiation.
Step 5 Check the Last input and Last output fields. They show the number of hours, minutes, and seconds since
the last packet was successfully received or transmitted by the interface.
Step 6 Check the output hang field. It shows the number of hours, minutes, and seconds since the last reset
caused by a lengthy transmission.
Step 7 Check the CRC field. The presence of many CRC errors, but not many collisions, indicates excessive
noise. If the number of errors is too high, check the cables for damage. If you are using UTP cable, make
sure you are using category 5 cables and not another type, such as category 3.
Note Errors and the input and output difference should not exceed 0.5 to 2.0 percent of traffic on
the interface.
Step 8 Check the collisions fields. These numbers indicate packet collisions and these numbers should be very
low. The total number of collisions, with respect to the total number of output packets, should be 0.1
percent or less.
Step 9 Check the late collisions fields. Late collisions should never occur in a properly designed Ethernet
network. They usually occur when Ethernet cables are too long or when there are too many repeaters in
the network.
Step 10 Check carrier fields. These numbers indicate a lost carrier detect signal and can be caused by a
malfunctioning interface that is not supplying the transmit clock signal, or by a cable problem. If the
system notices that the carrier detect line of an interface is up, but the line protocol is down, it
periodically resets the interface in an effort to restart it. Interface resets can also occur when an interface
is looped back or shut down.
Step 11 Check the buffer fields. These numbers indicate the number of received packets discarded because there
was no buffer space. Broadcast storms on Ethernet networks, and bursts of noise on serial lines, are often
responsible for no-input buffer events.
If you determine that the physical interface is configured incorrectly, refer to the “Configuring
Interfaces” chapter in the Layer 3 Switching Software Feature and Configuration Guide.