Dell PowerConnect B-RX Configuration Manual page 1110

Bigiron rx series configuration guide v02.7.02

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802.1s Multiple Spanning Tree Protocol

Additionally, loops must be prevented in each of the IST instances. Within the IST Region 1, a port is

blocked at port 1/2 of switch 4 to prevent a loop in that region. Within Region 2, a port is blocked at

port 3/2 of switch 3 to prevent a loop in that region.

The following definitions describe the STP instances that define an MSTP configuration.

MSTP configured network

Common Spanning (CST) – MSTP runs a single instance of spanning tree, called the Common

Spanning Tree (CST), across all the bridges in a network. This instance treats each region as a

single bridge. It all other ways, it operates exactly like Rapid Spanning Tree (RSTP).

Internal Spanning Tree (IST) – Instances of spanning tree that operate within a defined region

are called ISTs (Internal Spanning Tree).

Common and Internal Spanning Trees (CIST) – This is the default MSTP instance 0. It contains

all of the ISTs and all bridges that are not formally configured into a region. This instance

interoperates with bridges running legacy STP and RSTP implementations.

Multiple Spanning Tree Instance (MSTI) – The MSTI is identified by an MST identifier (MSTid)

value between 1 and 4090. This defines an individual instance of an IST. One or more VLANs

can be assigned to an MSTI. A VLAN cannot be assigned to multiple MSTIs.

MSTP Region – These are clusters of bridges that run multiple instances of the MSTP protocol.

Multiple bridges detect that they are in the same region by exchanging their configuration

(instance to VLAN mapping), name, and revision-level. Therefore, if you need to have two

bridges in the same region, the two bridges must have identical configurations, names, and

revision-levels.

BigIron RX Series Configuration Guide

53-1001810-01

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