Loopback Errors

CityLink recommends connecting your router/firewall directly to your CityLink port. If you have installed a switch between your router/firewall and the CityLink port, or you are using a "Layer 3" switch then you may be affected by Loopback errors.

Most Cisco switches use a feature Loopback detection to protect themselves from loops in an Ethernet network. When a large Ethernet network like CityLink's has a failure, it is possible for the Loopback detection mechanism to be triggered. Your equipment will typically err-disable the port facing CityLink and report a Loopback fault in the logs. The real issue is that the switch won't enable the port again when the fault in the network is fixed.

On a Cisco switch the following commands will cause the switch to re-enable the port automatically after 5 minutes.

errdisable recovery cause loopback 
errdisable recovery interval 300