Specifications

6-9
Cisco 1700 Series Router Software Configuration Guide
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Chapter 6 Configuring a Leased Line
Troubleshooting Problems with Leased Lines
Serial0 is up,
line protocol is
up (looped).
The possible cause is that a loop
exists in the circuit. The sequence
number in the keepalive packet
changes to a random number when a
loop is first detected. If the same
random number is returned over the
line, a loop exists.
The following are some steps you can take
to isolate the problem:
• Use the write terminal privileged
EXEC command to display any
instances of the loopback command. If
the router has been configured with the
loopback command, enter the
no loopback command to remove the
loop.
• Check to see whether the DSU/CSU is
configured in manual loopback mode.
If it is, disable manual loopback.
• Reset the DSU/CSU.
• If you are unable to isolate the problem,
contact the telephone company for help
with troubleshooting.
Serial0 is
administrativel
y down, line
protocol is up.
The possible causes for this state are
• The serial interface has been
disabled with the
shutdown interface
configuration command.
• Different interfaces on the
router are using the same IP
address.
The following are some steps you can take
to isolate the problem:
• Use the show configuration privileged
EXEC command to display the serial
port configuration. If “shutdown” is
displayed after “interface Serial0,” use
the no shutdown interface
configuration command to enable the
interface.
• Use the show interface privileged
EXEC command to display the IP
addresses for all router interfaces. Use
the ip address interface configuration
command to assign unique IP addresses
to the router interfaces.
Table 6-1 Possible Causes of and Suggested Actions for Solving Problems with Leased Lines
Line State Possible Cause Suggested Actions