Cisco Asr 1000 Series Aggregation Services Routers Sip And Spa Software Configuration Guide, Cisco Ios - Cisco ASR 1000 Series Software Configuration Manual

Serial Lines: show interfaces serial Status Line Conditions
Status Line Condition
Serial x is up, line protocol is up
(looped)

Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS

XE Everest 16.5
330
Possible Problem
A loop exists in the circuit. The
sequence number in the keepalive
packet changes to a random
number when a loop is initially
detected. If the same random
number is returned over the link, a
loop exists.
Troubleshooting the Serial SPAs
Solution
1 Use the show running-config
privileged EXEC command to
look for any loopback interface
configuration command entries.
2 If you find a loopback interface
configuration command entry,
use the no loopback interface
configuration command to
remove the loop.
3 If you do not find the loopback
interface configuration
command, examine the
CSU/DSU to determine
whether they are configured in
manual loopback mode. If they
are, disable manual loopback.
4 Reset the CSU or DSU, and
inspect the line status. If the
line protocol comes up, no
other action is needed.
5 If the CSU or DSU is not
configured in manual loopback
mode, contact the leased-line
or other carrier service for line
troubleshooting assistance.
OL-14127-17