System information

Troubleshooting Serial Line Problems 15-317

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.

Table 15-2 outlines the possible problem that might cause this symptom and describes solutions to

that problem.

Table 15-2 Serial Lines: Increasing Output Drops on Serial Link

Serial x is

administratively down,

line protocol is down

• Router conﬁguration includes

the shutdown interface

conﬁguration command

• Duplicate IP address

Step 1 Check the router conﬁguration for the

shutdown command.

Step 2 Use the no shutdown interface conﬁguration

command to remove the shutdown command.

Step 3 Verify that there are no identical IP addresses

using the show running-conﬁg privileged

exec command or the show interfaces exec

command.

Step 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

7 CTS = clear-to-send

8 DSR = data-set ready

Status Line

Condition Possible Problem Solution