When there are network-related issues on an ESXi host, it can impact the communication between the host, virtual machines, and other network resources. To troubleshoot network issues on ESXi, there are several logs to check. Additionally, if the ESXi host is connected to a physical switch, it’s essential to examine the switch logs as well. Below are the logs to check for ESXi network issues, along with examples:

Logs to Check on ESXi Host:

1. vmkernel.log: This log records ESXi kernel messages, including networking-related events and errors.
2. messages.log: This log contains system messages, including network-related information.
3. vmkwarning.log: This log records various warnings, including networking warnings.
4. net-dvs.log: This log pertains to the Distributed Virtual Switch (DVS) and contains events related to virtual networking.
5. hostd.log: While primarily used for host management events, this log may contain information related to network configuration changes or errors.

Examples of Network Issues in ESXi Logs:

Example 1: Network Connectivity Issue in vmkernel.log:

2023-07-01T12:34:56.789Z cpu1:12345)vmnicX: Link Up event. MAC Address: xx:xx:xx:xx:xx:xx
2023-07-01T12:34:57.123Z cpu2:12346)vmnicX: Link Down event.

In this example, the log shows a network interface (vmnicX) experiencing a link-up event followed by a link-down event, indicating a potential connectivity problem.

Example 2: Duplicate IP Address Detected in vmkwarning.log:

2023-07-01T12:34:56.789Z cpu1:12345)WARNING: VmknicIpRouteAddVmknicVmk0:Netstack Register Route(Vmknic) failed, Error 17099 (No IP Address: xx.xx.xx.xx) on dvPort 12345:Uplink(vmnicX)/0. Action Required: Verify IP Address on Vmknic vmk0.

This log entry indicates that a duplicate IP address has been detected on the vmk0 interface, which may lead to connectivity issues.

Logs to Check on the Physical Switch:

The logs on the physical switch connected to the ESXi host can provide valuable information about network events and errors.

Examples of Switch Logs:

Example 3: Port Flapping in Switch Logs:

2023-07-01T12:34:56.789Z: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/1, changed state to down
2023-07-01T12:34:57.123Z: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/1, changed state to up

These log entries indicate that the physical switch port GigabitEthernet1/0/1 experienced a link down event followed by a link up event, which may cause network interruptions.

Example 4: Switch Port Errors:

2023-07-01T12:34:56.789Z: %ERR-3-IF_DOWN_LINK_FAILURE: Interface GigabitEthernet1/0/1 is down (Link failure)

This log entry suggests that the switch port GigabitEthernet1/0/1 is down due to a link failure.

Conclusion:

When troubleshooting network-related issues on an ESXi host, it’s crucial to check the ESXi logs, such as vmkernel.log, messages.log, and others. These logs can provide insights into network events, warnings, and errors. Additionally, if the ESXi host is connected to a physical switch, examining the switch logs can be equally important in identifying potential switch-related problems. Analyzing the logs and resolving network issues promptly will help ensure the stability and performance of the ESXi host and its virtual machines.