Port Numbers, In Order: Why the List Has Gaps, and the Best Stories Behind the Numbers
Every TCP or UDP connection you've ever made rides on a 16-bit number between 0 and 65535. That range isn't handed out randomly — it's split into three tiers by convention, policed in part by an actual root-permission check inside the kernel, and dotted with numbers that were picked for reasons ranging from "it was between two other protocols" to "an inside joke about an Italian TV personality." This post walks the range in order, low to high, and stops at every port that has a story worth telling.
Why 16 bits, and why three tiers
A port number is a 16-bit field in the TCP and UDP headers, which is why the ceiling is 65535 (2^16 − 1) and not some rounder number. IANA (the Internet Assigned Numbers Authority) splits that space into three ranges, formalized in RFC 6335:
Range
