Information Technology Reference
In-Depth Information
Table15-1 Serial Lines: show interfaces serial Status Line Conditions (continued)
Status Line
Condition
Possible Problem
Solution
Serial
x
is
up, line
protocol is
down
(disabled)
A high error rate has
occurred due to a
telephone company
service problem.
A CSU or DSU
hardware problem has
occurred.
Router hardware
(interface) is bad.
Troubleshoot the line with a serial
analyzer and breakout box. Look for
toggling CTS
7
and DSR
8
signals.
1.
Loop CSU/DSU (DTE loop). If the
problem continues, it is likely that there is
a hardware problem. If the problem does
not continue, it is likely that there is a
telephone company problem.
2.
Swap out bad hardware, as required (CSU,
DSU, switch, local or remote router).
3.
Serial
x
is
administrat-
ively down,
line protocol
is down
The router
configuration includes
the
shutdown
interface
configuration
command.
A duplicate IP address
exists.
1.
Check the router configuration for the
shutdown
command.
2.
Use the
no shutdown
interface
configuration command to remove the
shutdown
command.
3.
Verify that there are no identical IP
addresses using the
show running-config
privileged exec command or the
show
interfaces
exec command.
4.
If there are duplicate addresses, resolve
the conflict by changing one of the IP
addresses.
1.
DTE = data terminal equipment
2.
CD = carrier detect
3.
CSU = channel service unit
4.
DSU = digital service unit
5.
SCTE = serial clock transmit external
6.
DCE = data circuit-terminating equipment or data communications equipment
7.
CTS = clear-to-send
8.
DSR = data-set ready
Serial Lines: Increasing Output Drops on Serial Link
Output drops appear in the output of the
show interfaces serial
command (refer to Figure 15-1) when
the system is attempting to hand off a packet to a transmit buffer but no buffers are available.
Symptom:
Increasing output drops on serial link
