Mstp Implementation On Switches; Root Bridge Configuration - H3C S7500 Series Operation Manual

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Operation Manual – MSTP

H3C S7500 Series Ethernet Switches

A spanning tree is figured out as follows:

Determining the root bridge

The root bridge is selected by configuration BPDU comparing. The switch with the

smallest root ID is selected as the root bridge.

Determining the root port

For each switch in a network, the port through which the configuration BPDU with the

highest priority is received is chosen as the root port of the switch.

Determining the designated port

First, the switch generates a designated port configuration BPDU for each of its ports

using the root port configuration BPDU and the root port path cost, with the root ID

being replaced with that of the root port configuration BPDU, root path cost being

replaced with the sum of the path cost of the root port configuration BPDU and the path

cost of the root port, the ID of the designated bridge being replaced with that of the

switch, and the ID of the designated port being replaced with that of the port.

The switch then compares the resulting configuration BPDU with the original

configuration BPDU received from the corresponding port on another switch. If the

latter takes precedence over the former, the switch blocks the local port and remains

the port's configuration BPDU unchanged, so that the port can only receive

configuration messages and cannot forward packets. Otherwise, the switch sets the

local port to the designated port, replaces the original configuration BPDU of the port

with the resulting one and releases it regularly.

1.1.4 MSTP Implementation on Switches

MSTP is compatible with both STP and RSTP. That is, switches with MSTP employed

can recognize the protocol packets of STP and RSTP and use them to generate

spanning trees. In addition to the basic MSTP functions, H3C series switches also

provide the following other functions for the convenience of users to manage their

Root bridge retaining

Root bridge backup

Complete the following tasks to configure Root Bridge:

Chapter 1 MSTP Configuration

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