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A virtual machine cannot connect to the network. Virtual machine tasks fail because of network disconnection. ARP table does not show proper Media Access Control (MAC) addresses.
This article provides information to help you troubleshoot ESX network connectivity issues using ARP.
The ARP table is a dynamic system table that is built when virtual machines communicate over TCP/IP with other nodes. The ARP table automatically maps the IP address of a virtual machine to the MAC address (the network adapter's unique embedded address). After a period of time, if virtual machine A no longer communicates with virtual machine B, the system ages out the entry in the ARP table. Virtual machines use ARP table entries to address packets to send to other nodes. The ARP cache is a list of recently resolved IP addresses to MAC address mappings. If an entry in the ARP cache is incorrect, the IP datagram may be sent to the wrong computer. You must clear the ARP cache. To clear the ARP cache: To list the ARP table, run the command:arp -a To populate the ARP table on a certain interface, run this command from the service console to display all mappings currently in the ARP cache:arping -I vswifX IP_addressWhere IP_address is the IP address of the virtual machine. To clear all entries, run the command:arp -d IP_addressWhere IP_address is an internet address stored in the ARP cache.Run this command for each entry in the ARP cache until all entries have been deleted. When the ARP cache is empty, you see the message:No ARP Entries Found To populate the ARP table, ping a broadcast IP address to get a reply back from all hosts listening on the same subnet.For example:ping 10.10.10.255 Use the tcpdump command to monitor TCP/IP traffic. For more information, see Verifying gateway IP connection using the tcpdump command (1008017). Note: In ESXi tcpdump is changed to tcpdump-uw For information specific to ESXi 5.5, see Clearing the ARP cache table in ESXi 5.5 (2049667).
For related troubleshooting information, see Troubleshooting virtual machine TCP/IP connection issues (1007842). Notes: This article applies only to ESX. It does not apply to ESXi. The only method of clearing the ARP cache on an ESXi 4.1 - 5.1 host is to reboot. In ESXi 4.1, you can list the ARP table using this command:esxcli network neighbor list In ESXi 5, you can list the ARP table using this command:esxcli network ip neighbor list In ESXi 5.5, the ARP table now can be cleared by typing the command:esxcli network ip neighbor remove For more information on: ARP commands for ESXi, see Displaying the ARP and Neighbor Discovery cache for VMkernel network interfaces (2000130). ESXi 5.5 Network commands, see the VMware vSphere 5.5 Documentation Center . To be alerted when this document is updated, click the Subscribe to Article link in the Actions boxESX 3.0.3 and 3.5.x Patches Appear in Depot Even Though VirtualCenter Manages Only 3.5.x HostsTroubleshooting virtual machine TCP/IP connection issuesVerifying gateway IP connection using the tcpdump commandDisplaying the ARP and Neighbor Discovery cache for VMkernel network interfacesClearing the ARP cache table in ESXi 5.5使用地址解析协议 (ARP) 对网络连接问题进行故障排除アドレス解決プロトコル（ARP）使用時のネットワーク接続の問題のトラブルシューティング