TCP, UDP, SCTP and DCCP in the IANA port registry

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

Of the 6,091 port numbers with an assignment, 5,327 are assigned on both TCP and UDP, 561 on TCP only and 174 on UDP only. The single-transport numbers are mostly recent: since 2011, IANA assigns only the transport an application asks for and holds the other number as reserved, which is the case for 552 of the 561 TCP-only numbers.

Two further transports have numbers of their own. 88 numbers carry an SCTP entry and 9 a DCCP entry, nearly always alongside TCP and UDP.

One transport or two, by period

Counting each number by its earliest recorded registration date, the shift is plain. The table covers only dated numbers; most System Ports and many older User Ports have no date.

The rule behind the change is RFC 6335 (2011), which asks IANA to assign a number only on the transports an application uses. Before 2011 most dated assignments covered both TCP and UDP, and the registry kept them that way.

Read across the rows, the share of numbers registered for a single transport jumps from 13.2% before 2011 to 78.1% in 2011 to 2017, and stays at 71.9% from 2018 on. The absolute numbers fall at the same time, so the later rows are small, but in both later periods single-transport numbers are the clear majority.

Registrations per year

The busiest year in the dated record is 2006, with 305 numbers. From 2023 to 2026 the counts were 8, 7, 9 and 10.

The yearly counts fell below 100 from 2011 on and have not reached 30 since 2018. With so few new numbers per year, each later period in the table above rests on a few hundred assignments at most.

UDP-only numbers

The 174 UDP-only numbers mirror the TCP-only ones. On 172 of them TCP is held as reserved; on the rest the TCP number has no row at all. Single-transport numbers are almost all User Ports: 553 of the TCP-only and 170 of the UDP-only numbers sit above 1023, against 8 and 4 in the System Ports.

Where the single-transport numbers cluster

The ranges with the most single-transport numbers are in the low User Ports. Ports 5000–5999 has 94 TCP-only numbers, followed by ports 4000–4999 with 88 and ports 8000–8999 with 57. The range pages show each of them with its reserved UDP number.

SCTP

Many SCTP entries share a name with an older TCP entry. Of the 88 numbers with an SCTP entry, 51 repeat a name that is also registered on TCP, such as ssh on 22, http on 80, https on 443 and diameter on 3868. A few numbers use a separate name per transport: 3863 carries asap-sctp, asap-tcp and asap-udp. 37 names are registered on SCTP alone, among them itu-bicc-stc, asap-sctp, asap-sctp-tls and a25-fap-fgw, and 9 of the 88 SCTP numbers are System Ports. 7 of the 88 show the same last-modified date, February 7, 2022, and cite RFC 9260, the current SCTP specification.

Four transports on one number

Only 4 numbers are assigned on all four transports: 9 discard, 1021 exp1, 1022 exp2 and 4195 aws-wsp. Two of them, 1021 and 1022, are the experiment numbers exp1 and exp2, labelled “RFC3692-style Experiment 1” and “2” and citing RFC 4727, “Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers” (2006).

Aviation numbers on SCTP

The clearest example of SCTP names beside older TCP and UDP ones is the run from 5910 to 5913. On october 10, 2008, these four numbers were registered on TCP and UDP to air traffic and airline messaging services, such as ats-atn, “Air Traffic Services applications using ATN”. In May 2011 each number gained a second name on SCTP alone: cm, cpdlc, fis and ads-c, labelled for context management, controller–pilot data link, flight information and surveillance. The same number now carries two unrelated names, one per transport family.

diameter on 3868 and its TLS form diameters on 5868 take the opposite shape: both are assigned on TCP and SCTP but not on UDP.

DCCP

DCCP is the rarest transport in the registry. Only 9 numbers have a DCCP entry, and 3 of those entries carry a DCCP service code, a number that identifies the service inside the protocol.

Apart from 9 and the two experiment numbers, the DCCP numbers are aws-wsp on 4195, dtn-bundle on 4556, avt-profile-1 and avt-profile-2 on 5004 and 5005, syslog-tls on 6514 and ltp-deepspace on 1113.

Port 1113, ltp-deepspace, is assigned on TCP, UDP and DCCP and carries one of the service codes. The full SCTP and DCCP list is on the SCTP and DCCP pattern page.