ARP - CMD

Overview

The ARP command in Windows is used to display or modify entries in the ARP cache. The ARP (Address Resolution Protocol) cache is a table that stores mappings between IP addresses and MAC addresses. This command is primarily used for diagnostic and network troubleshooting purposes, allowing users to view and manipulate the information that controls the translation between IP addresses and MAC addresses on the local network.

Syntax

The basic syntax for the ARP command is as follows:

arp [-a [inet_addr] [-N if_addr]] [-g [inet_addr] [-N if_addr]] [-d inet_addr [if_addr]] [-s inet_addr eth_addr [if_addr]]

Where:

inet_addr specifies an internet address.
eth_addr specifies a physical address.
if_addr is the interface address.

Options/Flags

-a: Displays current ARP entries by interrogating the current protocol data. If inet_addr is specified, the command displays the ARP entries for the specified IP address.
-g: Identical to -a.
-d: Deletes the host specified by inet_addr. The if_addr is optional and specifies the interface address where the deletion is to occur. Use * to delete all hosts.
-s: Adds the host and associates the Internet address inet_addr with the Physical address eth_addr. The physical address is given as 6 hexadecimal bytes separated by hyphens. The entry is permanent unless removed manually.

Examples

Viewing all ARP entries:
```
arp -a
```
This command displays all ARP entries for all interfaces.
Viewing ARP entries for a specific interface:
```
arp -a -N 192.168.1.1
```
Replace 192.168.1.1 with the IP address of the interface you want to check.
Adding a static ARP entry:
```
arp -s 192.168.1.120 00-aa-00-62-c6-09
```
This command adds a static ARP entry associating IP address 192.168.1.120 with the MAC address 00-aa-00-62-c6-09.
Removing an ARP entry:
```
arp -d 192.168.1.120
```
This command deletes the ARP entry for the IP address 192.168.1.120.

Common Issues

Permissions: Users might encounter permission errors if they do not run the command with administrative privileges.
Invalid Entries: Errors while adding incorrect IP or MAC addresses. Ensure the formats are correct and valid in your network environment.

Integration

ARP can be combined with other network diagnostic tools for comprehensive troubleshooting and monitoring:

Combining with ping:
```
ping 192.168.1.120 && arp -a
```
This will check the connectivity to the IP and show the ARP entry, helping diagnose network issues.
Scripting ARP checks:
```
@echo off
for /f "tokens=*" %%a in ('arp -a') do (
    echo %%a
)
```
This batch script iterates through all ARP entries, echoing them to the terminal.

ping: Sends ICMP Echo Requests to network hosts.
ipconfig: Displays all current TCP/IP network configuration values and refreshes DHCP and DNS settings.

For more information, refer to the Microsoft Documentation on ARP.