Troubleshooting Leased Line Problems
Cisco 1700 Router Software Configuration Guide
4-6
Serial x 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.
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 if 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.
Serial x is
administratively 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.
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 4-1 Leased Line Problems and Suggested Actions
Line State Possible Cause Suggested Actions
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