System information

Troubleshooting Using the show interfaces serial Command
Book Title
15-322
Serial Lines: Increasing Interface Resets on Serial Link
Interface resets that appear in the output of the show interfaces serial exec command (see
Figure 15-1) are the result of missed keepalive packets.
Symptom: Increasing interface resets on serial link.
Table 15-6 outlines the possible problems that might cause this symptom and describes solutions to
those problems.
Table 15-6 Serial Lines: Increasing Interface Resets on Serial Link
Serial Lines: Increasing Carrier Transitions Count on Serial Link
Carrier transitions appear in the output of the show interfaces serial exec command whenever there
is an interruption in the carrier signal (such as an interface reset at the remote end of a link).
Symptom: Increasing carrier transitions count on serial link.
Table 15-7 outlines the possible problems that might cause this symptom and describes solutions to
those problems.
Table 15-7 Serial Lines: Increasing Carrier Transitions Count on Serial Link
Possible Problem Solution
The following problems can result in
this symptom:
• Congestion on link (typically
associated with output drops)
• Bad line causing CD transitions
• Possible hardware problem at the
CSU, DSU, or switch
When interface resets are occurring, examine other fields of the show
interfaces serial command output to determine the source of the problem.
Assuming that an increase in interface resets is being recorded, examine the
following fields:
Step 1 If there is a high number of output drops in the show interfaces
serial output, see the section “Serial Lines: Increasing Output Drops
on Serial Link” earlier in this chapter.
Step 2 Check the carrier transitions field in the show interfaces serial
display. If carrier transitions are high while interface resets are being
registered, the problem is likely to be a bad link or bad CSU or DSU.
Contact your leased-line or carrier service and swap faulty
equipment as necessary.
Step 3 Examine the input errors field in the show interfaces serial display.
If input errors are high while interface resets are increasing, the
problem is probably a bad link or bad CSU/DSU. Contact your
leased-line or other carrier service and swap faulty equipment as
necessary.