Brocade BigIron RX Series Configuration Guide - Manual (Page 1216)

1138 BigIron RX Series Configuration Guide
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802.1s Multiple Spanning Tree Protocol
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FIGURE 149 MSTP configured network
The following definitions describe the STP instances that define an MSTP configuration.
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; however, VLAN 4090 is a reserved VLAN.
MSTI 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.
Configuring MSTP
To configure a switch for MSTP, you could configure the name and the revision on each switch that
is being configured for MSTP. This name is unique to each switch. You must then create an MSTP
Instance and assign an ID. VLANs are then assigned to MSTP instances. These instances must be
configured on all switches that interoperate with the same VLAN assignments. Port cost, priority
and global parameters can then be configured for individual ports and instances. In addition,
operational edge ports and point-to-point links can be created and MSTP can be disabled on
individual ports.
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Switch 1
Switch 2
Switch 3
Switch 4
Switch 5
Switch 6
Switch 2
Switch 3
Switch 4
Switch 5
Region 1 Region 2
Port2/1
Port2/2
Port2/3
Port2/3
Port2/1
Port2/1
Port1/2
Port1/1 Port1/3
Port1/4
Port1/2
Port1/1
Port1/2
Port2/2
Port1/1
Port1/4
Port1/5
Port1/3
Port1/2
Port3/1
Port3/3
Port3/2
Port3/1
Port3/2