HP Cisco Nexus 5000 Cisco Nexus 5000 Series Switch CLI Software Configuration - Page 166

MST Terminology, MST Regions, CIST Regional Roots, and CST Root

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Information About MST Chapter 9 Configuring MST Send feedback to [email protected] Figure 9-2 MST Regions, CIST Regional Roots, and CST Root A CIST Regional Root and CST root D Legacy 802.1D MST Region 1 B CIST Regional Root CIST Regional C Root 184441 MST Region 2 MST Region 3 Only the CST instance sends and receives BPDUs. MSTIs add their spanning tree information into the BPDUs (as M-records) to interact with neighboring switches and compute the final spanning tree topology. Because of this, the spanning tree parameters related to the BPDU transmission (for example, hello time, forward time, max-age, and max-hops) are configured only on the CST instance but affect all MSTIs. You can configure the parameters related to the spanning tree topology (for example, the switch priority, the port VLAN cost, and the port VLAN priority) on both the CST instance and the MSTI. MST switches use Version 3 BPDUs or 802.1D STP BPDUs to communicate with 802.1D-only switches. MST switches use MST BPDUs to communicate with MST switches. MST Terminology MST naming conventions include identification of some internal or regional parameters. These parameters are used only within an MST region, compared to external parameters that are used throughout the whole network. Because the CIST is the only spanning tree instance that spans the whole network, only the CIST parameters require the external qualifiers and not the internal or regional qualifiers. The MST terminology is as follows: • The CIST root is the root bridge for the CIST, which is the unique instance that spans the whole network. • The CIST external root path cost is the cost to the CIST root. This cost is left unchanged within an MST region. An MST region looks like a single switch to the CIST. The CIST external root path cost is the root path cost calculated between these virtual switches and switches that do not belong to any region. Cisco Nexus 5000 Series Switch CLI Software Configuration Guide 9-6 OL-16597-01

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Send feedback to [email protected]
9-6
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01
Chapter 9
Configuring MST
Information About MST
Figure 9-2
MST Regions, CIST Regional Roots, and CST Root
Only the CST instance sends and receives BPDUs. MSTIs add their spanning tree information into the
BPDUs (as M-records) to interact with neighboring switches and compute the final spanning tree
topology. Because of this, the spanning tree parameters related to the BPDU transmission (for example,
hello time, forward time, max-age, and max-hops) are configured only on the CST instance but affect all
MSTIs. You can configure the parameters related to the spanning tree topology (for example, the switch
priority, the port VLAN cost, and the port VLAN priority) on both the CST instance and the MSTI.
MST switches use Version 3 BPDUs or 802.1D STP BPDUs to communicate with 802.1D-only switches.
MST switches use MST BPDUs to communicate with MST switches.
MST Terminology
MST naming conventions include identification of some internal or regional parameters. These
parameters are used only within an MST region, compared to external parameters that are used
throughout the whole network. Because the CIST is the only spanning tree instance that spans the whole
network, only the CIST parameters require the external qualifiers and not the internal or regional
qualifiers. The MST terminology is as follows:
The CIST root is the root bridge for the CIST, which is the unique instance that spans the whole
network.
The CIST external root path cost is the cost to the CIST root. This cost is left unchanged within an
MST region. An MST region looks like a single switch to the CIST. The CIST external root path
cost is the root path cost calculated between these virtual switches and switches that do not belong
to any region.
CIST Regional
Root and CST root
A
MST Region 1
D
Legacy 802.1D
B
MST Region 2
MST Region 3
C
184441
CIST Regional
Root
CIST Regional
Root