There can only be a single path between two network devices; if there is more than one path, then the resulting loop can generate a broadcast storm that could bring down your network. If you have bridged two interfaces on your network, you should look into the possibility of looping. One way to prevent looping is to manually configure ports, so there is only one path to each device. However, the greater likelihood is that you use a spanning tree protocol such as the original Spanning Tree Protocol (STP) or Rapid Spanning Tree Protocol (RSTP).

Another situation where looping might occur is if you are running a spanning tree algorithm, but the information in the routing table is incorrect. This can happen if there is a manual misconfiguration, or if there is a failure in automatic route detection. In either case, the network will get bogged down rather quickly, so it should be easy to detect.