Cisco ASR 1000 Configuration Guide

20-5
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide
OL-14127-08
Chapter 20 Troubleshooting the Serial SPAs
Performing Basic Interface Troubleshooting
Serial x is up, line
protocol is down
A local or remote router is
misconfigured.
Keepalives are not being sent
by the remote router.
A leased-line or other carrier
service problem has occurred
(noisy line or misconfigured
or failed switch).
A timing problem has
occurred on the cable.
A local or remote CSU/DSU
has failed.
Router hardware (local or
remote) has failed.
1. Put the line in local loopback mode and use the
show interfaces serial command to determine
whether the line protocol comes up.
Note If the line protocol comes up, a failed
remote device is the likely problem.


This solution will only work with
High-Level Data Link Control (HDLC)
encapsulation. For Frame Relay (FR) and
Point-to-Point Protocol (PPP)
encapsulation, a looped interface will
always have the line protocol down. In
addition, you may need to change the
encapsulation to HDLC to debug this issue.
2. If the problem appears to be on the remote end,
repeat Step 1 on the remote interface.
3. Verify all cabling. Make certain that the cable is
attached to the correct interface, the correct
CSU/DSU, and the correct remote termination
point.
4. Enable the debug serial interface EXEC
command.
Note First enable per-interface debugging using
the command debug interface serial x, and
depending on the encapsulation, enable the
corresponding debug:
For HDLC: debug serial interface 
For PPP: debug ppp negotiation 
For FR: debug frame-relay lmi
Caution Because debugging output is assigned
high priority in the CPU process, it can
render the system unusable. For this
reason, use debug commands only to
troubleshoot specific problems or during
troubleshooting sessions with Cisco
technical support staff. Moreover, it is
best to use debug commands during
periods of lower network traffic and
fewer users. Debugging during these
periods decreases the likelihood that
increased debug command processing
overhead will affect system use.
Table 20-1 Serial Lines: show interfaces serial Status Line Conditions (continued)
Status Line 
Condition Possible Problem Solution

Cisco ASR 1000 Specifications

General

Brand	Cisco
Model	ASR 1000
Category	Network Router
Language	English