loop avoidance

In branched networks, the problem can arise that the routers, bridges or interface message processors( IMP) determine a route or several routes in such a way that loops are created. In primitive loop detection, as was sometimes present in early implementations, a bridge sends data packets in the Hello protocol; when a Hello data packet comes back to the bridge, it detects that a loop exists. A loop suppression algorithm is started, which leads to the deactivation of corresponding bridges or certain bridge ports.

The algorithm is in principle arbitrary, it must only transfer into an active configuration, in which between two bridges and/or net segments only one unique path exists. The suppression of loops is based on the standardized spanning tree protocol according to IEEE 802.1d. In this process, the bridges or switches send each other configuration data packets, Bridge Protocol Data Units( BPDU). If these data packets no longer arrive at the communication partner, the preferred connection between the bridges is disrupted and the spanning tree protocol must define an alternative path.