Information Technology Reference
In-Depth Information
Table15-1 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 is required.
Serial
x
is
down, line
protocol is
down (DTE
1
mode)
The router is not
sensing a CD
2
signal
(that is, the CD is not
active).
A telephone company
problem has
occurred—line is
down or is not
connected to
CSU
3
/DSU
4
.
Cabling is faulty or
incorrect.
Hardware failure has
occurred (CSU/DSU).
1.
Check the LEDs on the CSU/DSU to see
whether the CD is active, or insert a
breakout box on the line to check for the
CD signal.
2.
Verify that you are using the proper cable
and interface (see your hardware
installation documentation).
3.
Insert a breakout box and check all control
leads.
4.
Contact your leased-line or other carrier
service to see whether there is a problem.
5.
Swap faulty parts.
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
x
is
up, line
protocol is
down (DTE
mode)
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
(SCTE
5
not set on
CSU/DSU).
A local or remote
CSU/DSU has failed.
Router hardware
(local or remote) has
failed.
1.
Put the modem, CSU, or DSU in local
loopback mode and use the
show
interfaces serial
command to determine
whether the line protocol comes up.
If the line protocol comes up, a telephone
company problem or a failed remote router is
the likely problem.
If the problem appears to be on the remote
end, repeat Step 1 on the remote modem,
CSU, or DSU.
2.
Verify all cabling. Make certain that the
cable is attached to the correct interface,
the correct CSU/DSU, and the correct
telephone company network termination
point. Use the
show controllers
exec
command to determine which cable is
attached to which interface.
3.
Enable the
debug serial interface
exec
command.mmm ,,,,
4.
