Netgear XCM8810 Chassis User Manual - Page 568

The bridges in the MSTP regions Switches A, B, C, E, F, and G advertise their region

Page 568 highlights

NETGEAR 8800 User Manual • Switch A as the CIST root bridge (this is the CIST root bridge for all regions) • Switch A as the CIST regional root bridge • Switch A as the MSTI regional root bridge • Three boundary ports that connect to MSTP region 2 and other 802.1D or 802.1w bridges MSTP Region 2 consists of the following: • Three bridges named Switch E, Switch F, and Switch G • One MSTI STPD named S1 with an MSTI ID of 1 Note: The MSTI ID does not have any significance outside of its region so you can re-use IDs across regions. • VLAN finance mapped to the MSTI STPD, S1 • Switch E as the CIST regional root bridge • Switch F as the MSTI regional root bridge • One master port that connects to the CIST • Three boundary ports that connect to MSTP region 1 and other 802.1D or 802.1w bridges The following sequence describes how the MSTP topology convergences: 1. Determining the CIST root bridge, MSTP regions, and region boundaries. Each bridge believes that it is the root bridge, so each bridge initially sends root bridge BPDUs throughout the network. As bridges receive BPDUs and compare vectors, the bridge with the lowest Bridge ID is elected the CIST root bridge. In our example, Switch A has the lowest Bridge ID and is the CIST root bridge. The bridges in the MSTP regions (Switches A, B, C, E, F, and G) advertise their region information along with their bridge vectors. Segments 1, 3, and 9 receive BPDUs from other regions and are identified as boundary ports for region 1. Similarly, segments 2, 3, and 9 are identified as boundary ports for region 2. 2. Controlling boundary ports. The CIST regional root is advertised as the Bridge ID in the BPDUs exiting the region. By sending CIST BPDUs across regional boundaries, the CIST views the MSTP regions as virtual 802.1w bridges. The CIST takes control of the boundary ports and only CIST BPDUs enter or exit a region boundary. Each MSTP region has a CIST regional root bridge that communicates to the CIST root bridge. The bridge with the lowest path cost becomes the CIST regional root bridge. The port on the CIST regional root bridge that connects to the CIST root bridge is the CIST root port. For region 1, Switch A has the lowest cost (0 in this example) and becomes the CIST regional root. Since the bridge is both the CIST root bridge and the CIST regional root bridge, there is no CIST root port on the bridge. 568 | Chapter 18. STP

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|
Chapter 18.
STP
NETGEAR 8800 User Manual
Switch A as the CIST root bridge (this is the CIST root bridge for all regions)
Switch A as the CIST regional root bridge
Switch A as the MSTI regional root bridge
Three boundary ports that connect to MSTP region 2 and other 802.1D or 802.1w bridges
MSTP Region 2 consists of the following:
Three bridges named Switch E, Switch F, and Switch G
One MSTI STPD named S1 with an MSTI ID of 1
Note:
The MSTI ID does not have any significance outside of its region so you
can re-use IDs across regions.
VLAN finance mapped to the MSTI STPD, S1
Switch E as the CIST regional root bridge
Switch F as the MSTI regional root bridge
One master port that connects to the CIST
Three boundary ports that connect to MSTP region 1 and other 802.1D or 802.1w bridges
The following sequence describes how the MSTP topology convergences:
1.
Determining the CIST root bridge, MSTP regions, and region boundaries.
Each bridge believes that it is the root bridge, so each bridge initially sends root bridge
BPDUs throughout the network. As bridges receive BPDUs and compare vectors, the
bridge with the lowest Bridge ID is elected the CIST root bridge. In our example, Switch A
has the lowest Bridge ID and is the CIST root bridge.
The bridges in the MSTP regions (Switches A, B, C, E, F, and G) advertise their region
information along with their bridge vectors.
Segments 1, 3, and 9 receive BPDUs from other regions and are identified as boundary
ports for region 1. Similarly, segments 2, 3, and 9 are identified as boundary ports for
region 2.
2.
Controlling boundary ports.
The CIST regional root is advertised as the Bridge ID in the BPDUs exiting the region. By
sending CIST BPDUs across regional boundaries, the CIST views the MSTP regions as
virtual 802.1w bridges. The CIST takes control of the boundary ports and only CIST
BPDUs enter or exit a region boundary.
Each MSTP region has a CIST regional root bridge that communicates to the CIST root
bridge. The bridge with the lowest path cost becomes the CIST regional root bridge. The
port on the CIST regional root bridge that connects to the CIST root bridge is the CIST
root port.
For region 1, Switch A has the lowest cost (0 in this example) and becomes the CIST
regional root. Since the bridge is both the CIST root bridge and the CIST regional root
bridge, there is no CIST root port on the bridge.