Owner's Manual

560 | Chapter 18. STP
NETGEAR 8800 User Manual
If you have an active MSTP region, NETGEAR recommends that you disable all active
STPDs in the region before renaming the region on all of the participating switches.
• Configuring the MSTP BPDU format identifier
To configure the number used to identify MSTP BPDUs, use the following command:
configure mstp format <format_identifier>
By default, the value used to identify the MSTP BPDUs is 0. The range is 0 to 255.
If you have an active MSTP region, NETGEAR recommends that you disable all active
STPDs in the region before modifying the value used to identify MSTP BPDUs on all
participating switches.
• Configuring the MSTP revision level
Although the configure mstp revision <revision> command is available on the CLI, this
command is reserved for future use.
Unconfiguring an MSTP Region
Before you unconfigure an MSTP region, NETGEAR recommends that you disable all active
STPDs in the region.
To unconfigure the MSTP region on the switch, use the following command:
unconfigure mstp region
After you issue this command, all of the MSTP settings return to their default values. See
Configuring MSTP Region Identifiers on page 559 for information about the default settings.
Common and Internal Spanning Tree
As previously described, MSTP logically divides a Layer 2 network into regions. The
Common and Internal Spanning Tree (CIST) is a single spanning tree domain that
interconnects MSTP regions. The CIST is responsible for creating a loop-free topology by
exchanging and propagating BPDUs across regions to form a Common Spanning Tree
(CST). In essence, the CIST is similar to having a large spanning tree across the entire
network. The CIST has its own root bridge that is common to all MSTP regions, and each
MSTP region elects a CIST regional root that connects that region to the CIST thereby
forming a CST.
The switch assigns the CIST an instance ID of 0, which allows the CIST to send BPDUs for
itself in addition to all of the MSTIs within an MSTP region. Inside a region, the BPDUs
contain CIST records and piggybacked M-records. The CIST records contain information
about the CIST, and the M-records contain information about the MSTIs. Boundary ports
exchange only CIST record BPDUs.
All MSTP configurations require a CIST domain. You must first configure the CIST domain
before configuring any MSTIs. By default, all MSTI ports in the region are inherited by the
CIST. You cannot delete or disable a CIST if any of the MSTIs are active in the system.