Cisco Catalyst 9300 Stops Looking for Stack Switch — Troubleshooting and Solutions
Selene Gong
Cisco Catalyst 9300 switches are widely used in enterprise networks for their high performance and stacking capabilities. However, network engineers sometimes face a critical issue where a Cisco Catalyst 9300 stops looking for a stack switch, meaning a stack member is no longer detected. This problem can disrupt network redundancy, reduce performance, or cause outages. Quick identification and troubleshooting are essential to maintain network stability.
What Does “Stops Looking for Stack Switch” Mean?
When a Cisco Catalyst 9300 switch "stops looking for stack switch," it indicates that one or more members within the Cisco StackWise virtual stack are no longer recognized by the active switch managing the stack. This loss of communication means the affected switch might show a "Removed" or "Lic-Mismatch" state, especially if licensing is an issue.
Common symptoms include:
Unable to ping or manage the affected switch by its IP.
Loss of Layer 3 connectivity, despite Layer 2 forwarding appearing functional.
Control plane protocols such as STP, ARP, CDP, and LACP malfunctioning on the affected member.
Log errors like %STACKMGR-4-SWITCH_REMOVED, %HMANRP-6-HMAN_IOS_CHANNEL_INFO: EMP_RELAY: Channel DOWN!, or %REDUNDANCY-3-STANDBY_LOST.
This state reduces stack redundancy and high availability, potentially causing a network split or outage.
Common Causes of Stack Detection Failure
Several factors can cause the stack member to disappear:
Physical Issues: Loose, damaged, or improperly installed stack cables and adapters. Incorrect tightening of stack cable thumbscrews is common.
Software Version Mismatch: All switches in a stack must run compatible Cisco IOS XE versions.
Operational Mode Mismatch: Differences between Install and Bundle modes can block stacking.
Improper Switch Addition: Adding a powered-on switch without proper procedures can cause reloads or stack splits.
Hardware Authentication Failures: Specific to certain models with stack adapter issues.
Software Bugs: Some IOS XE bugs cause stack instability or reloads.
CLI Commands to Check Stack Status
Use these commands for diagnosis:
show switch — summarizes stack members, roles, and states.
show switch detail — detailed hardware and port info.
show switch stack-ports summary — checks stack link health, focusing on "Changes to LinkOK."
show switch stack-ports detail — shows CRC errors and bandwidth per stack port.
show switch stack-ring speed — reveals ring status (Full/Half) and bandwidth.
show logging onboard switch <number> uptime detail — checks reload reasons per member.
show version — displays IOS XE version and last reload reason.
show inventory — confirms installed stack adapters on 9300L/9200L.
Hardware Checks: Stack Cables and Adapters
Inspect stack cables carefully:
Look for damage such as cuts or kinks.
Ensure both cable ends are fully and securely seated.
Hand-tighten thumbscrews (not too tight).
For 9300L/9200L, verify stack adapters are installed and recognized.
Reseat cables one at a time during operation to avoid stack partitioning.
Software Bugs Affecting Stack Discovery
Certain IOS XE bugs cause repeated stack reloads or merges, often due to memory leaks or stack communication errors. Refer to Cisco’s advisory releases and upgrade to recommended software versions for your hardware model.
Best Practices to Prevent Stack Issues
Use the same IOS XE version and license level on all stack members.
Power off new switches before adding to an active stack.
Assign switch priorities to control active/standby roles (switch <number> priority <value>).
Provision new switches offline (switch <number> provision <type>).
Enable auto-upgrade in Install mode (software auto-upgrade enable).
Regularly monitor stack port status.
Backup configurations frequently.
FAQ
Q1: How do I reset a Cisco 9300 stack?
Use reload on the active switch to reload the entire stack, or reload slot <number> for individual members.
Q2: Can faulty stack cables cause this issue?
Yes. Damaged or loose stack cables are a common cause of detection failures and instability.
Q3: How to remove a switch from a Cisco 9300 stack?
Power off the switch, disconnect stack cables, remove any provisioning via no switch <number> provision, renumber the switch if needed, and reload it standalone.
Q4: Does Cisco 9300 support stacking?
Yes. It supports StackWise technologies with up to 8 switches per stack.
