1-11 MSTP ConfigurationWhen configuring MSTP, go to these sections for information you are interested in:z Overviewz Introduction to STPz Introduction to RSTPz Introduction to MSTPz MSTP Configuration Task Listz Configuring MSTPz Displaying and Maintaining MSTPz MSTP Configuration ExampleOverviewAs a Layer 2 management protocol, the Spanning Tree Protocol (STP) eliminates Layer 2 loops byselectively blocking redundant links in a network, and in the mean time, allows for link redundancy.Like many other protocols, STP evolves as the network grows. The later versions of STP are the RapidSpanning Tree Protocol (RSTP) and the Multiple Spanning Tree Protocol (MSTP). This chapterdescribes the characteristics of STP, RSTP, and MSTP and the relationship among them.Introduction to STPWhy STPSTP was developed based on the 802.1d standard of IEEE to eliminate loops at the data link layer in alocal area network (LAN). Devices running this protocol detect loops in the network by exchanginginformation with one another and eliminate loops by selectively blocking certain ports to prune the loopstructure into a loop-free tree structure. This avoids proliferation and infinite cycling of packets thatwould occur in a loop network and prevents decreased performance of network devices caused byduplicate 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.
