ARP: Understanding the Address Resolution Protocol and How It Works.
ARP is an abbreviation for Address Resolution Protocol. It is a communication protocol used for resolving IP addresses to MAC (Media Access Control) addresses within a local network segment. MAC address is a unique accreditation that is allotted to a network interface to communicate on the substrate network.
Here’s how ARP works:
- Address Resolution: When a device wants to communicate with another device within the same network segment, it needs to know the MAC address of the target device. It begins with the ARP cache probing where a table is utilized which stores the IP to the MAC address mappings. If the MAC address is found in the ARP cache, the device can use it for communication directly.
- ARP Request: If the MAC address which is in the ARP cache is not available, then the device transmits a request packet which is broadcast to the network. This ARP request contains the IP address of the target device that the sender wants to communicate with.
- ARP Reply: Able to process the ARP request, the device linked to the IP address in question transmits its Mac Address to the requesting device.
- ARP Cache Update: The requesting device updates its ARP cache with the newly acquired MAC address of the target device. Hence, the next communications within the network should be cached without the need to broadcast data to the MAC address directly from the cache.
Here are some commonly used ARP-related commands with examples:
arp -a:
Displays and modifies the ARP cache. Example
- arp -a
It means that this instruction gives the could be a command that allows to show the ARP cache table. This table displays the IP addresses and MAC addresses of devices in the local network segment.
arp -d:
Deletes an entry from ARP cache(s). Example:
- arp -d 192.168.1.2
With the following command, an entry will be removed from the ARP cache, that adds the IP address 192.168.1.2
arp -s:
Inserts a static ARP table entry. Example:
- arp -s 192.168.1.3 00-11-22-33-44-55
This command assigns to the MAC address 00-11-22-33-44-55 a fixed ARP entry mapping the IP address 192.168.1.3.
arp -n:
Shows the ARP cache table which is not resolved into hostnames. It gives a list of networks connected to the host with their corresponding IP addresses. Example:
- arp -n
Displays information about ARP cache consisting of IP addresses (numeric) and destination MAC addresses with no interest in resolving host names.
These commands are usually found in command line interfaces of operating systems such as Windows, Unix, and Linux, allowing the management of ARP cache entries.
