3 Reasons You Should Be Using Rapid Spanning Tree (802.1w)

Posted on in Networking

Most network administrators should be familiar with Spanning Tree Protocol (STP; IEEE 802.1D). <acronym title="Spanning Tree Protocol">STP</acronym> is tasked with ensuring there are no loops in a bridged network. Unfortunately, STP is an older protocol and doesn't quite mesh with today's high speed networks. Here are 3 reasons why you should switch from STP to Rapid Spanning Tree Protocol (RSTP; IEEE 802.1w).

#1 Rapid Convergence

Convergence in a standard STP 802.1D network takes about a minute. The transition of a port to forwarding state is based on various timers timing out. <acronym title="Rapid Spanning Tree Protocol">RSTP</acronym> uses regular (2 second, by default) hello intervals to actively poll other attached RSTP bridges. Once the network is fully converged, the protocol is able to recover from a topology change in less than a second rather than a minute. This sort of recovery time is invaluable in a fiber or radio-based metro Ethernet ring.

#2 802.1D Legacy Interoperability

The fact that RSTP works with STP means that adding a new switch doesn't mean any downtime. Although the introduction of a 802.1D STP switch means the network loses it's fast convergence benefit, the ring is still able to run in a loop-free topology since RSTP interoperates with STP. Although this may seem like a low-priority benefit, the fact of the matter is, at some time someone is going to introduce a non-compliant switch into your network. The interoperability of 802.1w with 802.1D guarantees that introduction won't cause an outage.

#3 It's a no brainer!

Finally, one big reason you should switch from STP to RSTP is it's so darn easy! The configuration change is one line per switch, and that's it. There is further tweaking that can be done to ensure top notch performance, but the benefits of rapid convergence and interoperability are available right of the chute with that one configuration change. Additionally, RSTP supports Cisco STP enhancements such as Uplink Fast, Backbone Fast, and Port Fast, so no changes are required in that regard.

Are you ready to make the change? Here's the only configuration command you have to run:

spanning-tree mode rapid-pvst


That's all it takes.

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