PeerScope

When a client talks to a server, every layer of the client talks to the same layer of the server, its peer: HTTP talks to HTTP, TCP to TCP, IP to IP. Each layer adds a header that only its peer on the other side reads and removes. The dashed lines in the diagram show these virtual conversations; the real data goes down the client, across the network and up the server.

1. Choose the protocol (HTTP, HTTPS, DNS or SSH) and the network.
2. Type the data, for example GET /index.html, a name such as www.example.com or a command such as ls -l.
3. Click Start simulation, then Next (or press →).
4. Click any layer in the diagram to see what the two peers exchange at that layer, and check who can see what on the right.