186CHAPTER 8: STP OPERATION

 

a transitional state mechanism is then adopted to ensure the new configuration

 

BPDU has been propagated throughout the network before the root port and

 

designated port begin to send data again. That is, the root port and designated

 

port should undergo a transitional state for a period of Forward Delay before they

 

enter the forwarding state.

 

 

MSTP Overview

The Switch 7750 implements the Multiple Spanning Tree Protocol (MSTP), which is

 

an enhancement to STP, and is compatible with both STP and RSTP. An MSTP

 

switch can recognize both STP and RSTP packets and can calculate the spanning

 

tree with them. Beside the basic MSTP functions, the Switch 7750 provides

 

additional MSTP features which include root bridge hold, secondary root bridge,

 

root protection, and BPDU protection.

 

STP cannot stabilize a network rapidly. Even on the point-to-point link or the edge

 

port, it takes an interval as long as twice the forward delay before the network

 

converges.

 

MSTP makes the network converge rapidly, and distributes the traffic of different

 

VLANs along their respective paths. This provides a better load-balance

 

mechanism for the redundant links.

 

MSTP associates VLAN with a spanning tree domain, and divides a switching

 

network into several regions, each of which has a spanning tree independent of

 

one another. MSTP prunes the network into a loopfree tree to avoid proliferation,

 

it also provides multiple redundant paths for data forwarding to implement the

 

VLAN data forwarding load-balance.

 

Configuring MSTP is described in the following sections:

 

MSTP Concepts

 

MSTP Principles

MSTP Concepts MSTP Concepts are described in the following sections

MST Region

VLAN Mapping Table

Internal Spanning Tree (IST)

Common Spanning Tree (CST)

Common and Internal Spanning Tree (CIST)

Multiple Spanning Tree Instance (MSTI)

MSTI Region root

Common Root Bridge

Boundary port

Port role

There are 4 MST regions in Figure 53.

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3Com 10014298 manual Mstp Overview