View ARP cache: solves connection exceptions

In today's article, we will discuss how to manage ARP cache on Windows Server 2008. In the latest server operating system released by Microsoft, the ARP cache is renamed as a neighboring server cache. Although it is different from the previous server version, the actual operation method has been adjusted, however, the basic functions provided do not change much. Next, let's take a look at what ARP is and why it plays such an important role.

The IP Address Resolution Protocol (ARP) is part of the TCP/IP protocol stack. It maps network IP addresses to the MAC addresses of devices. Simply put, the relationship between it and DNS is like the front and back of a coin. When a system calls a DNS host, the DNS first returns the network IP address of the host name. Next, the system can find the corresponding device MAC address in the local ARP cache through the network IP address. If there is no local ARP ing in the system, the ARP request will be sent. Both layer-3 switches and routers save their own ARP caches and manage them separately.

If the cache of the system's neighboring machine is damaged or an incorrect entry exists, what kind of problems will occur? Taking a running website as an example, the ICMP request response and the "website cannot be displayed" error indicating that the connection is inconsistent are typical cases. Basically, if we have confirmed that the DNS record information is correct and the running system has an inconsistent connection problem, the adjacent machine cache should be a key part.

In ARP cache (neighbor cache), there are two basic types of entries: fixed (static) and dynamic. The content of a dynamic entry is often incomplete, accessible, outdated, delayed, and detectable. Therefore, we recommend that you use dynamic entries as the default setting and use static entries as a supplement. Next, we will explain how to replace the server with the original DNS name and IP address. In this case, we will consider using temporary static ing to add new servers to the router ARP table. The next step is to delete the original ARP cache on the server.

To view the ARP cache on Windows Server 2008, open the command line window and enter the following command:

Netsh interface IPv4 SHOW NEIGHBORS

ARP-

To delete an unfixed ARP cache entry on a Windows 2008 server, run the following command:

Netsh interface IPv4 DELETE NEIGHBORS

Alternatively, you can use the following command:

ARP-d *

Run the following command to add a fixed ARP cache (neighbor cache) entry to the list:

Netsh interface IPv4 add neighbors InterfaceNameOrIndex IPAddress MACAddress STORE = ACTIVE | PERSISTANT

ARP-S IPAddress MACAddress InterfaceAddress

Conclusion:

For the network, the neighboring machine cache (or the original ARP cache) is a crucial but often overlooked part. When an incorrect entry or cache is damaged, the server may encounter an exception or inconsistency when connecting to a specific address. When a network card on the server encounters a problem and the other network card uses different MAC addresses, the probability of this problem is particularly prominent. Therefore, when a network connection failure occurs on the Windows server and the exact cause is not found, I will choose to view the fixed ing in the cache and delete dynamic entries for reconstruction.

For most Cisco routers, you only need to run the show arp command in EXEC mode to view the content in the ARP cache.

For most Cisco switches, run the show mac-address-table command to view the content in the ARP cache.