ARP: address resolution protocol
How to determine interface’s MAC address, knowing its IP address?
Using an ARP table: each IP node (host, router) on LAN has an ARP table with:
- IP/MAC address mappings for some LAN nodes:
<IP address; MAC address; TTL>
- TTL (Time To Live): time after which address mapping will be forgotten (typically 20 min)
How ARP works in the same LAN?
- A wants to send datagram to B
- B’s MAC address not in A’s ARP table.
- A broadcasts ARP query packet, containing B's IP address
- Destination MAC address = FF-FF-FF-FF-FF-FF
- All nodes on LAN receive ARP query
- B receives ARP packet, replies to A with its (B's) MAC address
- Frame sent to A’s MAC address (unicast)
- A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out)
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Project
Contact
This resource was developed as part of an Erasmus+ project, funded with support from the European Commission under grant agreement 2016-1-SE01-KA203-22064.
The project was a collaboration between:
- The University of Borås, Sweden
- The University of the Highlands and Islands, Scotland
- The University of Alcalá, Spain
- Digital Connections, Scotland
This resource has been released under Creative Commons license CC-BY-SA 4.0.
Disclaimer
If you would like more information on this resource please contact:
- Academic content – The University of Alcalá (https://www.uah.es/en/)
- Technical resource development – The University of the Highlands and Islands Educational Development Unit - EDU (edu@uhi.ac.uk)
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