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Verifying network links

Symptoms

Network failure to ESX/ESXi host
Complete or partial network outage
Pinging the physical switch fails
Connection to ESX/ESXi host is down

Purpose

This article provides ways to verify that the network links between the ESX/ESXi host's physical network adapters and the physical switch are up and available for use.

Resolution

Perform one or more of the following options to verify your network links:

Check the network link status within vSphere/ VMware Infrastructure (VI) Client:

Highlight the ESX/ESXi host and click the Configuration tab.
Click the Networking hyperlink.
The Virtual Network Adapters (vmnics) currently assigned to virtual switches are shown in the diagrams in the client. If one has a red X over it, the link is currently down.

Check the status from the ESX/ESXi host:
1. Run the command:
  
  [root@server root]# esxcfg-nics -l
  
  The output appears similar to:
  
  Name   PCI      Driver Link Speed    Duplex Description
  vmnic0 04:04.00 tg3    Up   1000Mbps Full   Broadcom BCM5780 Gigabit Ethernet
  vmnic1 04:04.01 tg3    Up   1000Mbps Full   Broadcom BCM5780 Gigabit Ethernet
  
  Note: To run this command in ESXi, you must enable Tech Support Mode. For more information, see Unable to connect to an ESX host using Secure Shell (SSH) (1003807) and Using Tech Support Mode in ESXi 4.1 (1017910).
2. The Link column specifies the status of the link between the network adapter and the physical switch and can be either Up or Down.
3. If there are several network adapters and some links are up and some links are down, you may need to verify that the adapters are connected to the intended physical switch ports.
4. This can be done by bringing down each of the ESX/ESXi host's ports on the physical switch sequentially and then running the esxcfg-nics -l command to see which vmnic is affected.
5. Utilize Cisco Discovery Protocol (CDP) to discover switch ports corresponding vmnic connections.
Check NIC link status in VI Client. The following image demonstrates a LINK DOWN status:

Note: If a physical network adapter is missing from the list, verify that it is enabled in the server's BIOS settings. See vendor documentation for more information.

Check the status at the physical server's network adapters:

Observe the LED lights on the physical network adapter. Refer to your network adapter or server's documentation for the meaning of the lights. If no lights are illuminated, this typically indicates a link down state or that the integrated network adapter is disabled in the BIOS settings (if applicable).

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