Cisco Cisco Nexus 5010 Switch Guida Alla Progettazione
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Note: If you need to modify the spanning-tree cost of links in the topology to obtain a certain forwarding
topology, you can use the command spanning-tree cost < cost >.
topology, you can use the command spanning-tree cost < cost >.
Bridge Assurance
As Figure 4 illustrates, the Bridge Assurance feature is useful in regular spanning-tree topologies that do not use
vPC. If a switch in a looped spanning-tree topology stops sending BPDUs because the control plane is not
functioning correctly, then Bridge Assurance suspends the ports to prevent a loop.
Figure 4. Bridge Assurance Is Useful in Regular Spanning-Tree Topologies
By default, Bridge Assurance is enabled globally, so if a port is configured with port type network, Bridge
Assurance is enabled on that port. If a port is configured with port type normal, then Bridge Assurance is not
enabled on that port.
By default, Bridge Assurance is enabled for network ports, but ports by default are set to port type normal and not
port type network, unless you globally configure spanning-tree port type network default.
Bridge Assurance is not very useful in a vPC topology, in which all links are part of a PortChannel. Also, certain
vPC failure scenarios converge better in the absence of Bridge Assurance.
For example, consider a dual-active scenario like the one depicted in Figure 5. In this case, one of the vPC peers
does not receive any more BPDUs from the access-layer device, which causes one of the vPC member ports to
fail. Thus, running Bridge Assurance on vPCs is not recommended.