How to Identify a Problem with the ARP Cache

To identify an incorrect entry in the ARP cache, first determine the MAC addresses and IPv4 addresses of hosts or gateways on the LAN with which the computer cannot communicate (as shown in the ipconfig /all example in this section). View the ARP cache on the computer that is experiencing the problem. Compare the output with the correct IPv4 address and MAC address combinations. If an entry is incorrect, clear the ARP cache to resolve the problem.

To determine the MAC address of a computer, open a command prompt and run the following command. Then find the Physical Address line in the output for your network adapter (which appears in bold in the code shown here).

Ethernet adapter Local Area Connection:
 Connection-specific DNS Suffix .  :
 Description . . . . . . . . . . . : NVIDIA nForce Networking Controller
 Physical Address. . . . . . . . . : 00-13-D3-3B-50-8F
 DHCP Enabled. . . . . . . . . . . : Yes

After you use IPConfig to determine the correct MAC address, you can view the ARP cache on the problematic computer to determine whether the cached address is incorrect. To view the ARP cache, open a command prompt and run the following command.

Interface: 172.16.0.24 --- 0xe

 Internet 	Address Physical 	Address Type
 172.16.0.1 	00-e0-4d-dd-18-2a 	dynamic
 172.16.255.255 ff-ff-ff-ff-ff-ff 	static
 224.0.0.2 	01-00-5e-00-00-02 	static
 224.0.0.22 	01-00-5e-00-00-16 	static
 224.0.0.251 	01-00-5e-00-00-fb 	static