More STP features?

That’s right! Can you tell I am gearing up for SWITCH? Last week I brought you a blog on UDLD and how it might of saved an integrated a lot of hassles. A comment last week Mike Kantowski on the UDLD post made me aware of a technology that I knew nothing of. Called Bridge Assurance (BA), this technology is another form of loop detection and prevention.

When enabled, BDPU’s are sent out all ports including the backup and alternate for each Hello Period. How this feature works is that it monitors the receipt of BPDUs on point to point links. If it does not hear a reply it changes the port state to an inconsistent state. This prevents any frames forwarding and a loop is avoided. The same is true of UDLD aggressive mode where a port err-disables.

Some Limitations

There are some limitations that come with BA. The biggest I have found is Rapid PVST+ and MST are the only two supported Spanning Tree version that work with BA. BA must also be configured on each end of the point to point link. If one end isn’t configured the port moves to a blocking state.


SW-1(config)# spanning-tree bridge assurance

SW-1(config-if)#spanning-tree portfast network

Ant’s perspective

After looking into the L2 Switching treats that STP has to offer it seems there could almost be no excuse for loops except, well none. Lab it. PoC it. Implement it.


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