Backbonefast is a Cisco feature that can save up to 20 seconds when a switch recovers from an indirect link failure. For backbone fast to work it must be enable on all switches of the bridge network. Backbone fast can be enabled in both the CatOS and IOS switches.  Indirect link failures casue delays when STP invalidates information deemed wrong due to a failure. How STP does this is it waits for max-age, backbone fast gets rid of the max-age delay.

In order to get rid of the delay backbone fast does two things, it introduces the ability the detect an indirect link failure as soon as possible, and it creates a mechanism to check if BPDU information stored on a port is still valid. To enable backbone fast on a CatOS switch use the Console> (enable) set spantree backbonefast enable command. To enable backbone fast on an IOS switch use the CAT-IOS# configure terminal, then CAT-IOS(config)# spanning-tree backbonefast, then CAT-IOS(config)# end, then the CAT-IOS# commands.

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Setting backbonefast on a Cisco switch