System information

Troubleshooting Using the show interfaces serial Command
Book Title
15-314
Figure 15-1 Output of the HDLC show interface serial Command
Table 15-1 shows the interface status conditions, possible problems associated with the conditions,
and solutions to those problems.
Table 15-1 Serial Lines: show interfaces serial Status Line Conditions
Status Line
Condition Possible Problem Solution
Serial x is up,
line protocol
is up
— This is the proper status line condition. No action
required.
Serial x is down,
line protocol is
down (DTE
1
mode)
Typically indicates that
the router is not sensing
a CD
2
signal (that is,
CD is not active).
• Telephone company
problem—Line is
down or line is not
connected to
CSU
3
/DSU
4
• Faulty or incorrect
cabling
• Hardware failure
(CSU/DSU)
Step 1 Check the LEDs on the CSU/DSU to see
whether CD is active, or insert a breakout box
on the line to check for the CD signal.
Step 2 Verify that you are using the proper cable and
interface (see your hard- ware installation
documentation).
Step 3 Insert a breakout box and check all control
leads.
Step 4 Contact your leased-line or other carrier
service to see whether there is a problem.
Step 5 Swap faulty parts.
Step 6 If you suspect faulty router hardware, change
the serial line to another port. If the connection
comes up, the previously connected interface
has a problem.
Serial 0 is up, line protocol is up
Hardware is MCI Serial
Internet address is 131.108.156.98, subnet mask is 255.255.255.240
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
Last input 0:00:00, output 0:00:00, output hang never
Last clearing of "show interface" counters never
Output queue 0/40, 5762 drops; input queue 0/75, 301 drops
Five minute input rate 9000 bits/sec, 16 packets/sec
Five minute output rate 9000 bits/sec, 17 packets/sec
5780806 packets input,785841604 bytes, 0 no buffer
Received 757 broadcasts, 0 runts, 0 giants
146124 input errors, 87243 CRC, 58857 frame, 0 overrun, 0 ignored, 3 abort
5298821 packets output, 765669598 bytes, 0 underruns
0 output errors, 0 collisions, 2941 interface resets, 0 restarts
2 carrier transitions
Input Drops
Interface resets
Carrier
transitions
Input
errors
Output
drops
Interface status line
monet>show interfaces serial 0
CRC
errors
Framing errors
Abort errors