Displaying the ARP and Neighbor Discovery cache for VMkernel network interfaces

Products

• VMware vSphere ESXi

Issue/Introduction

This article provides methods for listing the Address Resolution Protocol (ARP) and Neighbor Discovery (ND) cache maintained for VMkernel network interfaces on ESX/ESXi. Use of this information is outside the scope of this article, but may be useful when troubleshooting

ARP and ND Protocol are used in IPv4 and IPv6 respectively at the network layer for discovering other devices on the same link. A cache of neighboring devices' IP and MAC addresses is maintained by the ESX/ESXi host's VMkernel networking stack. The cache is used for mapping logical IP addresses to link-layer MAC addresses for outbound traffic on VMkernel network interfaces.

Note: This information is only for ESX/ESXi 4.1 and higher. For previous versions of ESX/ESXi, consider capturing network traffic on the VMkernel interface and reviewing it to see whether ARP traffic is being issued and responded to. For more information, see Capturing a network trace in ESXi 4.x using Tech Support Mode (1031186).

Symptoms:

Environment

VMware ESXi 4.1.x Installable
VMware vSphere ESXi 5.0
VMware vSphere ESXi 5.1
VMware ESX 4.1.x
VMware ESXi 4.1.x Embedded

Resolution

To review the ARP and ND cache for the VMkernel network interfaces on an ESX or ESXi host, use the local or remote esxcli command. This command is available at the local console of the ESX/ESXi host, and usable remotely from the vSphere Command Line Interface (vCLI) or from the vSphere Management Assistant (vMA) appliance. For installation and/or usage instruction, see the relevant documentation.

1. Open a console session to the location where the esxcli command is available.
   
   
   • Open a console to the ESX or ESXi host. For more information, see Unable to connect to an ESX host using Secure Shell (SSH) (1003807) or Using Tech Support Mode in ESXi 4.1 and 5.0 (1017910).
   • Install the vSphere Command-Line Interface command set, and open a console session where it was installed. For more information, see the vSphere Command Line Interface (vCLI) documentation.
   • Deploy the vSphere Management Assistant appliance, and open the console. For more information, see the vSphere Management Assistant (vMA) documentation.
   
   
2. Display the list of known network neighbors in the ARP and ND cache for all VMkernel network interfaces using one of the commands:
   
   
   • On ESXi 4.1:
     
     esxcli [--server hostname --username root --password rootpassword] network neighbor list
     
     
   • On ESXi 5.x:
     
     esxcli [--server hostname --username root --password rootpassword] network ip neighbor list
     
     
   Note: If running locally on the ESX/ESXi host console, no server hostname or authentication is required for the esxcli command.
   
   The output appears similar to:
   
   Neighbor Mac Address vmknic Expiry(sec)
-------- ----------- ------ -----------
10.5.6.7 xx:xx:xx:xx:xx:xw vmk0 1200
10.5.6.8 xx:xx:xx:xx:xx:xx vmk0 1197
10.5.6.9 xx:xx:xx:xx:xx:xy vmk0 277
10.200.1.10 xx:xx:xx:xx:xx:xz vmk1 979

Additional Information

The VMware ESX Service Console maintains a separate MAC address cache. For more information, see Troubleshooting network connection issues using Address Resolution Protocol (ARP) (1008184).

Unable to connect to an ESX host using Secure Shell (SSH)
Troubleshooting network connectivity issues using Address Resolution Protocol (ARP)
Using Tech Support Mode in ESXi 4.1, ESXi 5.x, and ESXi 6.x
Capturing a network trace in ESXi using Tech Support Mode or ESXi Shell
VMkernel ネットワーク インターフェイスの ARP およびネイバー検出のキャッシュの表示
显示 VMkernel 网络接口的 ARP 和邻居发现缓存