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arp Command in Linux

arp Command in Linux

By Team Scaler
2 mins read
Last updated: 4 Oct 2023
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Overview

In the Linux universe, one command that is vital for network troubleshooting and configuration is the arp command. The arp command, short for 'Address Resolution Protocol', is a protocol used to find the host's MAC (Media Access Control) address given the IP address. This utility is vital for network administration and understanding the mapping between a machine's IP and MAC addresses.

Syntax of arp Command in Linux

The basic syntax of the arp command in Linux is as follows:

Where:

  • [-vn]: The -v option stands for verbose, and -n stands for numerical. The verbose option provides detailed output, while numerical gives numeric IP addresses avoiding domain name resolution.
  • [-H type] [-i if]: -H allows you to specify the hardware type. -i lets you specify the name of the network interface.
  • -a [hostname] | -d hostname [pub] | -s hostname ether_addr [temp] | -s hostname pub [only] [proxy]: -a displays the arp cache. -d deletes an entry. -s creates a new entry. The optional 'hostname', 'ether_addr', and other flags further refine these operations.

Options in arp Command in Linux

  1. -a: Displays the current ARP table entries.

    For example -

    Output:

    This command lists all entries in the ARP table. The output shows the IP address, MAC address and the interface used.

  2. -d: Deletes an entry from the ARP table.

    For example -

    This command deletes the ARP entry for the IP 192.168.1.1.

  3. -s: Creates a new entry in the ARP table.

    For example -

    This command adds a new entry to the ARP table, linking the IP address 192.168.1.2 with the MAC address 00:11:22:33:44:55.

Example Usages

  • Display ARP table:

    Output:

    Explanation: Using 'arp' without any option displays the ARP table showing IP, MAC address, and the interface name.

  • Adding an ARP table entry:

    Explanation: Creates a new ARP entry for the IP address 192.168.1.3 and the MAC address 00:aa:bb:cc:dd.

Tips

  • ARP entries are temporary and may be deleted after a period of time or upon reboot. To create permanent entries, consider updating the ARP configuration files.

  • Incorrect use of arp command can affect network operations. Always double-check before deleting or adding entries.

Advanced Use Cases of arp Command in Linux

  • Delete all ARP entries:

    Explanation: This command combination deletes all entries from the ARP table. It uses awk to filter and construct delete commands, which are then executed by sh.

  • Display ARP entries for a specific interface:

    Output:

    Explanation: This command displays the ARP entries specifically for the network interface 'eth0'.

Conclusion

  • The arp command in Linux is a powerful tool for managing IP to MAC address mappings.

  • It is important for network administration and troubleshooting.

  • The command provides options for displaying, adding, and deleting ARP entries.

  • Though powerful, incorrect usage of the arp command can lead to network issues. Therefore, it's crucial to use it wisely and cautiously.