Cisco – Troubleshooting with Show Tech-Support and Tac-Pac on NX-OS

Cisco NX-OS, the network operating system running on Nexus series switches, offers powerful troubleshooting tools to network administrators. Among these are the show tech-support and tac-pac commands. This blog will walk you through their usage and advantages, examples, and best practices.

Understanding Show Tech-Support and Tac-Pac

Show Tech-Support is a basic but essential command in NX-OS. It delivers comprehensive information valuable in diagnosing network issues such as link-down situations, routing problems, and much more.

Tac-Pac is a command that compresses and saves the output of ‘show tech-support detail‘ into a tar.gz format file. This command captures verbose logs, which are not included in the ‘show tech-support‘ command, and provides in-depth information for each function on NX-OS.

You can also execute commands like ‘show tech-support “‘ to acquire specific feature information.

These commands answer the common question at the beginning of any troubleshooting process: “What logs should I get?”

Basic Commands for Troubleshooting

When contacting Cisco’s Technical Assistance Center (TAC), the following commands are extremely useful in understanding problems, referencing past cases, and troubleshooting:

• show version: to verify the version
• show inventory: to check the affected product
• show module: to inspect modules and their status (including box-type)
• show environment: to review environmental information, critical for power supply or fan issues
• show running-config: to check the configuration
• show logging logfile: to examine the logfile
• show accounting log: to verify executed commands (including internal system ones)
• show interface brief: for a summary status of interfaces
• show interface: for a detailed review of interfaces
• show ip interface brief: to check IP addresses
• show mac address-table: for MAC address verification, essential during communication failures
• show ip arp: for ARP inspection, also crucial during communication failures
• show ip route: to examine the routing table, another must for communication failures

While this list provides a comprehensive baseline of information, additional data may be requested depending on the specific case.

Commands Included in Show Tech-Support

If you want to review the specific commands included in ‘show tech-support‘, you can use the `egrep` tool as follows:

switch# show tech-support stp | egrep "`show|`slot"

The output includes all commands related to the Spanning Tree Protocol (STP) that are run when you execute ‘show tech-support stp‘. If ‘show tech-support‘ or ‘show tech-support “‘ cannot be executed, you can acquire the same results by running these listed commands individually.

Here are some examples of the commands included when running ‘show tech-support stp‘:

Sure, let’s delve into the individual details of these commands:

• show spanning-tree internal errors: This command is used to display the internal errors associated with the Spanning Tree Protocol (STP). It can help identify any underlying problems within STP that may not be immediately apparent from its external behavior.
• show spanning-tree internal interactions: This command gives an overview of the interactions between different parts of the STP. It can provide insights into how different components of the protocol are interacting and any issues that may be arising from these interactions.
• show spanning-tree internal msgs: It’s used to display internal messages exchanged within the STP. This command can be useful in troubleshooting communication issues within the STP.
• show spanning-tree internal mem-stats: This command provides statistics about memory usage related to the STP. It can help identify memory leaks or excessive memory usage issues that may be affecting the performance of the STP.
• show spanning-tree internal flc-info: This command provides information about Fast-Learning Cache (FLC) within the STP. It’s useful for assessing the performance of the FLC and for diagnosing any issues with it.
• show spanning-tree internal info global: This command displays global information about the internal operations of the STP, giving an overall picture of its status and performance.
• show spanning-tree internal info sps-pending: This command displays information about any Spanning Tree instances that are pending.
• show spanning-tree internal info sps-q-stats: This command provides detailed statistics about the Spanning-Tree Protocol’s queue, a useful tool when diagnosing issues related to queue management in STP.
• show spanning-tree internal info issu: This command shows information about In-Service Software Upgrades (ISSU) within the STP, which can be useful in diagnosing problems related to upgrades.
• show spanning-tree internal event-history all brief: This command provides a brief history of all internal events related to the STP. It’s a powerful tool for diagnosing historical problems or identifying patterns in issues.
• show spanning-tree internal event-history vpc sps: This command displays the history of Virtual Port Channel (vPC) Spanning-Tree Protocol events, providing insights into issues specifically related to vPC.
• show spanning-tree internal event-history vpc pes: This command shows the history of vPC Protocol Endpoint events, useful for troubleshooting issues related to vPC endpoints.
• show spanning-tree active: This command displays information about all the currently active instances of STP.
• show spanning-tree summary: This command provides a summary of the current state of STP, providing a high-level overview of its status.
• show spanning-tree detail: This command displays detailed information about each instance of the STP, which can be invaluable when diagnosing complex issues.
• show spanning-tree mst configuration: This command provides information about the configuration of Multiple Spanning Tree (MST) instances, helpful in troubleshooting issues related to MST.

Each of these commands provides more detailed information about the STP’s internal workings, helping to diagnose and solve any issues you might be experiencing with the STP on your switch.

Final Thoughts

Using ‘show tech-support‘ and ‘tac-pac‘ effectively can significantly simplify and accelerate the troubleshooting process on Cisco NX-OS. However, it’s essential to note that not all issues may be resolved using the data collected by these commands.

Specific CLI commands not included in these tools may sometimes be necessary. Regardless, using these commands is a good starting point and will cover many common scenarios, allowing for efficient problem diagnosis and resolution.