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ARP

Lesson 10 of 32 in Coddy's The OSI Model course.

Machines are configured with IP addresses, but frames are delivered to MAC addresses. ARP (Address Resolution Protocol) is the bridge: a machine shouts "who has 10.0.0.7?" to the whole segment, and the owner answers with its MAC.

Answers are cached in the ARP table so the shouting only happens once per neighbor. Reading that table is a everyday diagnostic move: it shows which devices your machine has actually talked to on the local network.

On a real system you would run arp -a; here you get the table as a file.

Challenge

Easy

The file arp_table.txt holds one ip mac pair per line. Use grep to print the single line for 192.168.1.7.

Expected output:

192.168.1.7 aa:bb:cc:00:00:07

Try it yourself

Terminal

All lessons in The OSI Model

1Why Layers

The Layering Idea Seven Layers Numbers and Names Recap - The Stack

4The Network Layer

IP and TTL Ping and ICMP Routing Tables Recap - Layer Three

7Encapsulation

Wrapping Data Headers Everywhere Reading a Capture Recap - Follow the Wrap

2The Physical Layer

Bits on a Wire How Long Will It Take Duplex and Collisions

5Transport: TCP and UDP

Ports The TCP Handshake TCP vs UDP Sockets in Action Recap - Layer Four

8The Journey of a Packet

A Click Happens Crossing the Networks Arriving and Climbing Recap - End to End

3Data Link and MACs

Frames and MACs Reading a MACARPRecap - Layer Two

6The Upper Layers

Session and Presentation The Application Layer Watching the Layers Recap - Top of the Stack

Practice on your own: Terminal playground