Well-known ports 0–1023 in the IANA registry

By Liam CooperOctober 27, 2026IANA registry as updated October 26, 2026

IANA lists at least one assignment on 686 of the 1,024 System Port numbers, 0 to 1023, and 338 carry none: they are reserved, unassigned or set aside for private use. Only 59 of the assigned numbers cite a specification of their own, and only 20 have a registration date.

“Well-known ports” is the older name for this range; RFC 6335 calls it the System Ports and sets IETF Review or IESG Approval as the procedure for new assignments in it.

How full each hundred is

Density varies a lot, and not in step with the number. Ports 400–499 is almost full, with 100 of 100 numbers assigned, while ports 800–1023 holds 44 assignments across 224 numbers. Below 800, the two thinnest ranges are 700–799 (48.0%) and 200–299 (54.0%). Each range name links to its page, where every number is listed with its names and labels.

Four ranges are full or nearly so: 100–199 (98.0%), 400–499 (100.0%), 500–599 (99.0%) and 600–699 (99.0%). The 338 numbers without an assignment are not all alike. 7 are set aside for private use, 11 are reserved on both transports, and the remaining 320 are listed as unassigned or carry a removal note.

Transports

Nearly every System Port is assigned on both TCP and UDP. Only 8 are TCP-only and 4 UDP-only, against 674 with both. 9 also carry an SCTP entry, among them 22 (ssh), 80 (http) and 443 (https).

The 20 dated System Ports

The registry records a date for only 20 numbers in this range. The earliest recorded date is June 2007; the latest is July 15, 2025, for tacacss on 300.

16 of the 20 dated entries are from 2010 or later, so the dates mostly record the newest additions to an old range rather than its origins. Two of them are the RIFT pair, rift-lies on 914 and rift-ties on 915, registered on the same day.

The very first numbers show the range's mix of entries. Port 0 is reserved on TCP and UDP, a row the registry last changed on December 20, 2024. Port 1 carries tcpmux, “TCP Port Service Multiplexer”. Ports 2 and 3 were de-assigned in 2025 and are reserved again. The nine System Ports with an SCTP entry are 9, 20, 21, 22, 80, 179, 443, 1021 and 1022.

Names and references

The 686 assigned System Ports carry 732 service names between them. 39 numbers hold more than one name; on 16 of those, TCP and UDP belong to different services, as on 512, 513 and 514. 15 names replaced an older spelling that broke the current naming rules, such as sql-net for sql*net on 66 and whoispp for whois++ on 63.

The RFC cited by the most System Ports is RFC 8314, “Cleartext Considered Obsolete: Use of Transport Layer Security (TLS) for Email Submission and Access”, on 3 numbers (465, 993 and 995). RFC 9110, “HTTP Semantics”, is shared by 80 and 443. Within the range, the registry pairs 15 plain names with a TLS form that is also a System Port, from http and https to nntp on 119 and nntps on 563.

Recent changes

Most System Port entries carry no modification date either. Of those that do, 11 were last changed in 2022 and 11 in 2018, the two years with the most changes in the range. The newest assignment in the range, tacacss on 300, was registered on July 15, 2025 and cites RFC 9887.

Private use and history

Seven numbers are reserved in the registry for private use: 24, 35, 57, 59, 75, 77 and 87. Their labels read “any private” followed by a purpose, such as mail system, terminal access or printer server. They carry no service name.

The registry also keeps a short history for the range. These dated records note numbers that were removed or de-assigned:

• 2: de-assigned on February 13, 2025 (was compressnet)
• 3: de-assigned on February 13, 2025 (was compressnet)
• 47: removed on May 18, 2017
• 51: removed on May 24, 2013
• 61: removed on May 18, 2017
• 359: de-assigned on November 16, 2023

The full set of history records, including undated ones, is described on the sources page. For any single number, the lookup lists the whole range with its free runs folded.