How we read the registry
Registry as updated October 26, 2026 · RFC index retrieved October 28, 2026
knownports.online restructures one public file: the IANA Service Name and Transport Protocol Port Number Registry. This page explains how a page on this site is built from it, what each statement means and where its scope ends.
How to read a port page
The large number is the port. Beside it are the service names registered on it, with the label IANA gives each one. The paragraph below states the entry and then the facts that set this number apart from its neighbors, rarest first. The strip shows the number between its three nearest assigned neighbors on each side, one lane per protocol, with the count of free numbers in each gap. The tables list every registry row and the RFCs those rows cite.
What an assignment is
An assignment records that IANA has registered a service name for a port number on a transport protocol. It does not record which software listens on that number, and any program can be configured to use any number. This site does not name the software behind a number; it reports what the registry holds.
Port classes
RFC 6335 divides the numbers into System Ports (0–1023), User Ports (1024–49151) and Dynamic Ports (49152–65535). The registry holds no assignment in the Dynamic range. A number marked reserved on one protocol is held back, usually because the service asked for the other transport only; since 2011 that is the normal case for new single-transport assignments.
Dates
The registry records registration and modification dates only for part of its rows, almost all from 2002 on, and some only to the month. “Earliest recorded date” always means the earliest date the registry records, never the age of an assignment.
Range pages
Each range page covers 100 numbers in the System Ports and 1,000 in the User Ports. Above 12000, neighboring ranges are merged until each holds at least 20 assigned numbers, which gives 39 range pages. A number counts as free when it has no assignment on any protocol; reserved numbers count as free, and numbers inside an assigned range such as x11 6000–6063 count as assigned.
The facts a page can lead with
| Fact | Rule |
|---|---|
| Cites an RFC | An entry names an RFC other than RFC 6335, RFC 9260 or RFC 4340, the registry procedure and the SCTP and DCCP base specifications that many entries cite. |
| Same RFC on other numbers | Shown when at most 12 numbers cite that RFC. |
| SCTP or DCCP entry | The number is also assigned on SCTP (88 numbers) or DCCP (9 numbers). |
| Different TCP and UDP services | Both transports are assigned and share no service name. |
| Several names | Three or more names, or two names on the same transport. |
| Older spelling | A conforming name replaced a name that broke the RFC 6335 syntax; the registry keeps both. |
| History | The number carries a removal or de-assignment record and is assigned again. |
| TLS counterpart | Name pair X and X+s, X-s, X-tls, X-ssl or secure-X, where the second label mentions TLS, SSL or security. |
| Earliest or latest recorded date | Rank 1 to 5 by registration date among the dated assignments of the range page, in ranges with at least 15 dated entries. |
| Gap | At least 10 numbers with no assignment on any protocol on both sides, and rank 1 to 5 in the range. |
| Most RFCs in the range | The number cites more RFCs than every other number in its range page, and at least two. |
| Obsoleted RFC | A cited RFC that the RFC Editor index lists as obsoleted by a later RFC. |
TLS counterparts
Two names count as a plain and TLS pair when the second is the first plus “s”, “-s”, “-tls” or “-ssl”, or the first with “secure-” in front, and the second label mentions TLS, SSL, DTLS, security, https or encryption. Pairs with unrelated names are not matched.
Other names built on a name
This section lists registry names that contain the page's service name as a whole hyphen-separated part, or its form with an added “s”. It is a text match, not a statement that the services are related.
Why most numbers have no page of their own
Of 6,091 numbers with an assignment, most differ from their neighbors only by name and label: no date, no reference, no unusual protocol. A page for each would repeat the same template thousands of times. Such numbers are rows on their range page, with an anchor (for example 5432), and complete results in the lookup. A number gets its own page when the registry records at least three distinctive facts for it, or two plus two lesser ones; a page that would stay very short with fewer than three distinctive facts is kept out of search indexes and its number is listed on the range page instead. Pairs whose pages would be near-identical, such as sip and sips, share one page.
History records and withheld names
The registry notes 36 removals and de-assignments. Free-text notes are not copied; only dates and previous names are kept. Two numbers whose service name or label is a person's name appear as “registered service (name withheld on this site)”.
RFC metadata
For every RFC an entry cites, the title, publication month, current status and later changes (obsoleted by, updated by) come from the RFC Editor index, rfc-index.xml. Author names are not shown.
Sources and refresh
Registry: iana.org/assignments/service-names-port-numbers, dedicated to the public domain under CC0 1.0 by IANA and the IETF. RFC metadata: rfc-editor.org/rfc-index.xml. The registry changes most weeks; the site is rebuilt from fresh copies of both files, and every page shows the registry date it was built from.