Classify a TCP/UDP Port Number

The Port Number Space

TCP and UDP each give every host 65536 ports numbered 0 through 65535. IANA divides them into three ranges. For example, port 22 is well-known (SSH), port 5432 is registered (PostgreSQL), and port 49152 falls in the dynamic range the kernel assigns to outgoing connections.

The three ranges are:

• Well-known (0-1023): HTTP on 80, HTTPS on 443, DNS on 53. Binding these requires root on Unix.
• Registered (1024-49151): Redis on 6379, MySQL on 3306. Anyone can bind these.
• Dynamic/ephemeral (49152-65535): Assigned by the OS to client sockets after connect().

Why the Ranges Matter

When you later write raw-socket tools and TCP servers in this track, you will constantly reason about these ranges: why your server needs privileges for port 443, why the kernel's ephemeral range shows up in netstat output, and why firewall rules treat low ports differently.

Why This Exercise

This task requires you to read a single port number and classify it. You will use this same mental model every time you read a packet capture and wonder whether a destination port like 8080 is a registered service or an ephemeral client port. nmap labels scan results by these same IANA ranges, and the Linux ip_local_port_range sysctl controls which dynamic ports the kernel hands out.