Its Not Your Father’s Spa ...
    13 May 09

    Its Not Your Father’s Spanning Tree

    Posted byINE

    One of the biggest challenges for CCNA students (not to mention other Certification levels) is mastering Spanning Tree Protocol (STP). And the bad news for students is the fact that you no longer must master one version, but three versions of this critical protocol. Here is a quick review of the Spanning Tree Versions you want to be well-versed in for the CCNA, and beyond.


    Classic Spanning Tree Protocol possesses a standard designation of 802.1D. You need to memorize these standard identifiers. For classic STP, just think Dog-gone Slow. The convergence delays the classic version can present are unacceptable for modern LAN uses of today, like the transmission of Voice and Video traffic. There is plenty of excellent documentation about Classic Spanning Tree Protocol out there, and that is really beneficial since most environments are still using this approach (as of the time of this writing of course). We need to study 802.1D very carefully and with intensity. This protocol prevents Layer 2 loops, and its operation is still at the heart of the enhanced versions.


    Cisco addressed the Dog-gone slowness of 802.1D by introducing proprietary enhancements to the protocol. Specifically, Cisco introduced PortFast, BackboneFast, and UplinkFast. These did a great job of improving the protocol, and were all incorporated into the enhanced version that addressed speed issues head on - Rapid Spanning Tree Protocol (RSTP). RSTP is known by 802.1w. To memorize this, just think of the classic American cartoon character - Elmer Fudd. He would call RSTP - Wapid Spanning Tree.


    Excellent! RSTP addressed the concerns of convergence delays in Classic Spanning Tree protocol. But what about the number of Spanning Tree topologies we must have in a network. Common STP (CST) has one for all VLANs, and this is certainly not flexible enough. Per VLAN STP (PVST) features a topology for every single VLAN, and this is certainly overkill. Multiple Spanning Tree Protocol (MSTP) comes to the rescue. It is known as 802.1s and it allows you to configure EXACTLY the number of topologies that you need, and map the specific VLANs you want to each topology.

    If you are interested in more information on any of the technologies, but sure to start by searching this blog site on Google. For example, go to Google and issue the following search: 802.1s

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