Troubleshooting Convergence Time Issues; Securing The Network Against Forwarding Loops - Cisco Nexus 9000 Series Troubleshooting Manual

Troubleshooting Convergence Time Issues

Troubleshooting Convergence Time Issues

STP convergence can take longer than expected or result in an unexpected final network topology.
To troubleshoot convergence issues, check the following issues:
• Errors in the documented network topology diagram.
• Misconfiguration of the timers; diameter; Cisco extension features such as bridge assurance, root guard,
• Overloaded switch CPU during convergence that exceeds the recommended logical port (port-vlan)
• Software defects that affect STP.

Securing the Network Against Forwarding Loops

To handle the inability of STP to deal correctly with certain failures, Cisco has developed a number of features
and enhancements to protect the networks against forwarding loops.
Troubleshooting STP helps to isolate and find the cause for a particular failure, while the implementation of
these enhancements is the only way to secure the network against forwarding loops.
Before You Begin
• Enable the Cisco-proprietary Unidirectional Link Detection (UDLD) protocol on all the switch-to-switch
• Set up the bridge assurance feature by configuring all the switch-to-switch links as the spanning tree
• Set up all the end-station ports as a spanning tree edge port type.
• Enable the Link Aggregation Control Protocol (LACP) for port channels to avoid any port-channel
Cisco Nexus 9000 Series NX-OS Troubleshooting Guide, Release 7.x
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and BPDU guard; and so on.
limit.
links. For information, see the Cisco Nexus 9000 Series NX-OS Interfaces Configuration Guide.
network port type.
Note You should enable the bridge assurance feature on both sides of the links. Otherwise,
Cisco NX-OS will put the port in the blocked state because of a bridge assurance
inconsistency.
You must set up the STP edge port to limit the amount of topology change notices and subsequent
flooding that can affect the performance of the network. Use this command only with ports that connect
to end stations. Otherwise, an accidental topology loop can cause a data-packet loop and disrupt the
device and network operation.
misconfiguration issues. For information, see the Cisco Nexus 9000 Series NX-OS Interfaces Configuration
Guide.
Do not disable autonegotiation on the switch-to-switch links. Autonegotiation mechanisms can convey
remote fault information, which is the quickest way to detect failures at the remote side. If failures are
detected at the remote side, the local side brings down the link even if the link is still receiving pulses.
Troubleshooting STP