Displaying Loop Detection Information

Use the show loop-detection status command to display loop detection status, as shown.

device# show loop-detection status
loop detection packets interval: 10 (unit 0.1 sec)
Number of err-disabled ports: 3
You can re-enable err-disable ports one by one by "disable" then "enable"
under interface config, re-enable all by "clear loop-detect", or
configure "errdisable recovery cause loop-detection" for automatic recovery
index port/vlan  status                         #errdis  sent-pkts recv-pkts
1     1/1/13     untag, LEARNING                0         0         0
2     1/1/15     untag, BLOCKING                0         0         0
3     1/1/17     untag, DISABLED                0         0         0
4     1/1/18     ERR-DISABLE by itself          1         6         1
5     1/1/19     ERR-DISABLE by vlan 12         0         0         0
6     vlan12     2 ERR-DISABLE ports            2         24        2

If a port is errdisabled in Strict mode, it shows "ERR-DISABLE by itself". If it is errdisabled due to its associated vlan, it shows "ERR-DISABLE by vlan ?"

The following command displays the current disabled ports, including the cause and the time.

device# show loop-detection disable
Number of err-disabled ports: 3
You can re-enable err-disable ports one by one by "disable" then "enable"
under interface config, re-enable all by "clear loop-detect", or
configure "errdisable recovery cause loop-detection" for automatic recovery
index  port         caused-by    disabled-time
1      1/1/18       itself       00:13:30
2      1/1/19       vlan 12      00:13:30
3      1/1/20       vlan 12      00:13:30

This example shows the disabled ports, the cause, and the time the port was disabled. If loop detection is configured on a physical port, the disable cause will show "itself". For VLANs configured for loop detection, the cause will be a VLAN.