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Ports

Lesson 16 of 32 in Coddy's The OSI Model course.

Layer 3 delivers to a machine; layer 4 delivers to a program on that machine. The program's address is a port: a 16-bit number, so ports run from 0 to 65535.

The first 1024 ports (0-1023) are well-known: reserved by convention for standard services, like 80 for HTTP and 22 for SSH. Ports above that are free for anyone.

An IP address plus a port, like 10.0.0.5:443, pins down exactly one conversation endpoint on the entire internet.

Challenge

Beginner

Print two numbers, one per line: the highest possible port, and how many well-known ports there are.

Expected output:

65535
1024

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

PortsThe 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 MAC ARP Recap - 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