Comment les ports mènent au bon programme, ce qu'est un socket, et lire l'état des connexions en direct.
Ports et état
En bref
Objectifs
- Expliquer port et socket
- Nommer les ports de services courants
- Lire l'état des connexions avec ss
An IP address gets you to a machine; a port gets you to the right program on it. A web server listens on port 80 or 443; SSH on 22. The combination of IP address and port is a socket.
| Port | Service |
|---|---|
| 22 | SSH |
| 53 | DNS |
| 80 / 443 | HTTP / HTTPS |
TCP keeps state for each connection — ESTABLISHED, TIME_WAIT, and so on. You can see it live:
$ ss -tn state established
Recv-Q Send-Q Local Address:Port Peer Address:Port
0 0 10.0.0.5:51514 93.184.216.34:443
Tip
Knowing which ports should be open is the whole basis of a port scan: an unexpected open port is often the first thread an attacker — or a defender doing an audit — pulls on.
À retenir
- Le port choisit le programme ; IP + port = socket
- 22 SSH, 53 DNS, 80/443 web
- Les ports ouverts inattendus lancent audits et attaques