Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 155 of 669
Loop Protection Configuration
The
Configuration
>
Loop
Protection
menu path lets you view and/or change the current global and
port-level Loop Protection configuration.
Note
: If you will be using the S4224 Loop Protection function, enable Loop Protection here, both globally
and at the port level, as one of the first overall configuration steps.
Loop protection increases the efficiency of STP, RSTP, and MSTP by preventing ports from going into a
forwarding state that would result in a loop opening up in the network. In spanning tree topologies, a loop-
free network is supported by the exchange of a BPDU. Peer STP applications running on the switch
interfaces use BPDUs to communicate. The exchange of BPDUs ultimately determines which interfaces
block traffic (preventing loops) and which interfaces become root ports and forward traffic. However, a
blocking interface can transition to the forwarding state erroneously if the interface stops receiving BPDUs
from its designated port on the segment. This transition error can occur with a hardware error on the
switch or a software configuration error between the switch and its neighbor.
With loop protection enabled, the spanning tree topology detects root ports and blocked ports, and
ensures that both keep receiving BPDUs. If a loop protection enabled interface quits receiving BPDUs
from its designated port, it reacts as it would react to a problem with the physical connection on this
interface. Rather than transition the interface to a forwarding state, it instead transitions it to a 'loop
inconsistent' state. The interface recovers, and then it transitions back to the spanning tree blocking state
when it receives a BPDU.
Loop protection is most effective when enabled in the entire switched network. You should generally
enable loop protection on all switch interfaces that could become a root or designated port. If you will be
using the Loop Protection function, enable Loop Protection here, both globally and at the port level, as
one of the first overall configuration steps.
The default screen is shown below.
The Loop Protection parameters are explained below.
