Configuring Mstp; Stp; Stp Protocol Packets; Basic Concepts In Stp - HP 1910 User Manual

Configuring MSTP

As a Layer 2 management protocol, the Spanning Tree Protocol (STP) eliminates Layer 2 loops by
selectively 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 Rapid
Spanning Tree Protocol (RSTP) and Multiple Spanning Tree Protocol (MSTP). This chapter describes the
characteristics of STP, RSTP, and MSTP.

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). Devices running this protocol 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 performance of network devices caused by duplicate
packets received.
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.
In STP, BPDUs have the following types:
Configuration BPDUs—Used for calculating a spanning tree and maintaining the spanning tree
•
topology.
Topology change notification (TCN) BPDUs—Used for notifying the concerned devices of network
•
topology changes, if any.

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 fixed, but can change along with changes of the network topology.
Upon initialization of a network, each device generates and sends out BPDUs periodically with itself as
the root bridge. After network convergence, only the root bridge generates and sends out configuration
BPDUs at a certain interval, and the other devices just forward the BPDUs.
Root port
On a non-root bridge, the port nearest to the root bridge is the root port. The root port is responsible for
communication with the root bridge. Each non-root bridge has one and only one root port. The root
bridge has no root port.
143