HP V1910 Mstp configuration, STP protocol packets, Basic concepts in STP, Root bridge, Root port

MSTP configuration

As a Layer 2 management protocol, the Spanning Tree Protocol (STP) eliminates Layer 2 loops by selectively blocking redundant links in a network, and also allows for link redundancy.

Recent versions of STP include Rapid Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP). This chapter describes the characteristics of STP, RSTP, MSTP, and the relationship among them.

STP

STP was developed based on the 802.1d standard of IEEE to eliminate loops at the data link layer in a local area network (LAN). Networks often have redundant links as backups in case of failures, but loops are a very serious problem. Devices running STP detect loops in the network by exchanging information with one another, and eliminate loops by selectively blocking certain ports to prune the loop structure into a loop-free tree structure. This avoids proliferation and infinite cycling of packets that would occur in a loop network and prevents decreased device performance caused by receiving duplicate packets.

In the narrow sense, STP refers to the IEEE 802.1d STP. In the broad sense, STP refers to the IEEE 802.1d STP and various enhanced spanning tree protocols derived from that protocol.

STP protocol packets

STP uses bridge protocol data units (BPDUs), also known as configuration messages, as its protocol packets.

STP-enabled network devices exchange BPDUs to establish a spanning tree. BPDUs contain sufficient information for the network devices to complete spanning tree calculation.

STP uses the following types of BPDUs:

∙Configuration BPDUs, used for calculating a spanning tree and maintaining the spanning tree topology.

∙Topology change notification (TCN) BPDUs, which notify network devices of network topology changes.

Basic concepts in STP

Root bridge

A tree network must have a root bridge.

There is only one root bridge in the entire network. The root bridge is not permanent, but can change with changes of the network topology.

Upon initialization of a network, each device generates and periodically sends out configuration BPDUs with itself as the root bridge. After network convergence, only the root bridge generates and periodically sends out configuration BPDUs. The other devices only forward the BPDUs.

Root port

On a non-root bridge, the port nearest to the root bridge is the root port. The root port communicates with the root bridge. Each non-root bridge has only one root port. The root bridge has no root port.

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