62 Converged Enhanced Ethernet Administrator’s Guide
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MSTP overview
7
DRAFT: BROCADE CONFIDENTIAL
NOTE
Brocade supports 15 MSTP instances and one MSTP region.
MSTP introduces a hierarchical way of managing switch domains using regions. Switches that
share common MSTP configuration attributes belong to a region. The MSTP configuration
determines the MSTP region where each switch resides. The common MSTP configuration
attributes are as follows:
•Alphanumeric configuration name (32 bytes)
•Configuration revision number (2 bytes)
•4096-element table that maps each of the VLANs to an MSTP instance
Region boundaries are determined based on the above attributes. A multiple spanning tree
instance is an RSTP instance that operates inside an MSTP region and determines the active
topology for the set of VLANs mapping to that instance. Every region has a common internal
spanning tree (CIST) that forms a single spanning tree instance that includes all the switches in the
region. The difference between the CIST instance and the MSTP instance is that the CIST instance
operates across the MSTP region and forms a loop-free topology across regions, while the MSTP
instance operates only within a region. The CIST instance can operate using RSTP if all the switches
across the regions support RSTP. However, if any of the switches operate using 802.1D STP, the
CIST instance reverts to 802.1D. Each region is viewed logically as a single STP/RSTP bridge to
other regions.
Configuring MSTP
To configure MSTP, perform the following steps from global configuration mode.
1. Enable MSTP using the global protocol spanning-tree command. For more details see
“Enabling STP, RSTP, or MSTP” on page64.
switch(config)#protocol spanning-tree mstp
2. Specify the region name using the region region_name command. For more details see
“Specifying a name for an MSTP region” on page70.
switch(conf-mstp)#region brocade1
3. Specify the revision number using the revision command. For more details see “Specifying a
revision number for an MSTP configuration” on page70.
switch(conf-mstp)#revision 1
4. Map a VLAN to an MSTP instance using the instance command. For more details see “Mapping
a VLAN to an MSTP instance” on page69.
switch(conf-mstp)#instance 1 vlan 2, 3
switch(conf-mstp)#instance 2 vlan 4-6
switch(conf-mstp)#instance 1 priority 4096
5. Specify the maximum hops for a BPDU to prevent the messages from looping indefinitely on
the interface using the max-hops hop_count command. For more details see “Specifying the
maximum number of hops for a BPDU (MSTP)” on page70.
switch(conf-mstp)#max-hops 25
6. Enter the copy command to save the running-config file to the startup-config file.
switch(conf-mstp)#do copy running-config startup-config