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ARP packet inspection

Computer Networks Lab · free online experiment, runs in your browser with no install or sign-up.

Open this experiment in the network simulator

Objective

Watch H1 resolve H2's MAC address with ARP: one broadcast request, one unicast reply, then the answer is cached.

Procedure

Press Run network and watch the first packets: ARP? broadcast, ARP! reply, then ping / pong.
Click a packet on the canvas (or a row in the capture list) to decode the Ethernet and ARP headers.
Select H1 and scrub the time slider: its ARP cache is empty before the reply and has one entry after.

Theory

Before an IP packet can be sent on Ethernet the sender needs the next hop's MAC address. It broadcasts 'who-has 192.168.1.2?'; the owner replies 'is-at <MAC>'. The sender caches the answer (see the ARP cache in the block's property panel while replaying), so later pings need no ARP.

Network blocks used

2 × Host / PC, Switch