1-11 MSTP ConfigurationWhen configuring MSTP, go to these sections for information you are interested in:z MSTP Overviewz Configuration Task Listz Configuring the Root Bridgez Configuring Leaf Nodesz Performing mCheckz Configuring Digest Snoopingz Configuring No Agreement Checkz Configuring Protection Functionsz Displaying and Maintaining MSTPz MSTP Configuration ExampleMSTP OverviewIntroduction to STPWhy STP?The Spanning Tree Protocol (STP) was developed based on the 802.1d standard of IEEE to eliminateloops at the data link layer in a local area network (LAN). Devices running this protocol detect loops inthe network by exchanging information with one another and eliminate loops by selectively blockingcertain ports to prune the loop structure into a loop-free tree structure. This avoids proliferation andinfinite cycling of packets that would occur in a loop network and prevents decreased performance ofnetwork devices caused by duplicate packets received.In the narrow sense, STP refers to IEEE 802.1d STP; in the broad sense, STP refers to the IEEE 802.1dSTP and various enhanced spanning tree protocols derived from that protocol.Protocol Packets of STPSTP uses bridge protocol data units (BPDUs), also known as configuration messages, as its protocolpackets.STP-enabled network devices exchange BPDUs to establish a spanning tree. BPDUs contain sufficientinformation for the network devices to complete spanning tree calculation.In STP, BPDUs come in two types:z Configuration BPDUs, used for calculating a spanning tree and maintaining the spanning treetopology.z Topology change notification (TCN) BPDUs, used for notifying the concerned devices of networktopology changes, if any.Basic concepts in STP1) Root bridgeA tree network must have a root; hence the concept of root bridge was introduced in STP.
