nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

Dispute Mechanism
The 802.1D-2004 standard specifies a dispute mechanism that can prevent loops created for
a variety of reasons. Two common cases in which the dispute mechanism helps are
unidirectional links or port-channel misconfiguration. Dispute mechanism is enabled by
default and cannot be disabled.
Bridge Assurance
Bridge Assurance is a new feature that can eliminate issues caused by a malfunctioning
bridge. With Bridge Assurance, all ports send and receive BPDUs on all VLANs regardless
of their states. This creates a bidirectional keepalive using BPDUs, and if a bridge stops
receiving BPDUs, these ports are placed into an inconsistent state. This functionality can
prevent loops that can be introduced as a result of a malfunctioning bridge. Bridge
Assurance is enabled by default on any port configured with a spanning tree port type
network but can be disabled globally with the following command:
Congo(config)# no spanning-tree bridge assurance
To enable Bridge Assurance by setting the spanning tree port type, enter the following
commands:
Click here to view code image
Congo(config)# int port-channel 1
Congo(config-if)# spanning-tree port type network
An interesting side effect of Bridge Assurance is an automatic pruning function. In the
topology from Figure 2-5, if a VLAN is defined on Congo but not on Egypt, Bridge
Assurance puts that VLAN into a blocking state because it is not receiving BPDUs for that
VLAN from Egypt. Example 2-54 demonstrates this functionality.
Example 2-54. Bridge Assurance as a Pruning Mechanism
Click here to view code image
Congo# conf t
Enter configuration commands, one per line. End with
CNTL/Z.
Congo(config)# vlan 500
Congo(config-vlan)# exit
Congo(config)# 2009 Oct 28 14:06:53 Congo %STP-2-
BRIDGE_ASSURANCE_BLOCK: Bridge
Assurance blocking port Ethernet2/1 VLAN0500.
2009 Oct 28 14:06:53 Congo %STP-2-BRIDGE_ASSURANCE_BLOCK:
Bridge Assurance
blocking port port-channel100 VLAN0500.