knownports / Ports 0–99 / Port 23
Port23
telnet
IANA has registered port 23 to telnet on TCP and UDP. The entry cites RFC 854. Its TLS counterpart, telnets, is registered on port 992.
Registry entries
| Service | Protocols | Registered | Modified | RFCs | Other specs |
|---|---|---|---|---|---|
telnet | TCPUDP | — | — | RFC 854 | — |
Cited RFCs
| RFC | Title | Published | Status | Later changes |
|---|---|---|---|---|
| RFC 854 | Telnet Protocol Specification | May 1983 | Internet Standard | updated by RFC 5198 |
Where it sits in the registry
Port 23 is one of 70 numbers with an assignment in ports 0–99 (70.0% of the range). 64 other numbers in the range are assigned on exactly the same transports, TCP and UDP, the usual pattern for older entries. The registry records no registration date for it, as for 69 other numbers in the range; dates were recorded mainly from 2002 on.
Status on each protocol
| Protocol | On port 23 | Other numbers with the same status | Nearest with the same status |
|---|---|---|---|
| TCP | assigned to telnet | 5,887 | 22 ssh |
| UDP | assigned to telnet | 5,500 | 22 ssh |
| SCTP | no entry | 5,999 | 25 smtp |
| DCCP | no entry | 6,080 | 22 ssh |
5,273 other assigned numbers in the registry have exactly this combination across all four protocols.
The nearest assigned numbers
| Port | Service | Label | Protocols | Registered | Distance |
|---|---|---|---|---|---|
| 20 | ftp-data | File Transfer [Default Data] | TCPUDPSCTP | — | 3 |
| 21 | ftp | File Transfer Protocol [Control] | TCPUDPSCTP | — | 2 |
| 22 | ssh | The Secure Shell (SSH) Protocol | TCPUDPSCTP | — | 1 |
| 25 | smtp | Simple Mail Transfer | TCPUDP | — | 2 |
| 27 | nsw-fe | NSW User System FE | TCPUDP | — | 4 |
| 29 | msg-icp | MSG ICP | TCPUDP | — | 6 |
Other names built on telnet
Other entries that mention telnet
The text telnet appears in the name or label of nine other registry entries, every one shown here. It is a text match, not a statement that the services are related.
- 89
su-mit-tg“SU/MIT Telnet Gateway” - 107
rtelnet“Remote Telnet Service” - 513
login“remote login a la telnet; automatic authentication performed based on priviledged port numbers and distributed data bases which identify "authentication domains"” - 902
ideafarm-door“self documenting Telnet Door” - 903
ideafarm-panic“self documenting Telnet Panic Door” - 992
telnets“telnet protocol over TLS/SSL” - 1618
skytelnet - 3696
telnetcpcd“Telnet Com Port Control” - 6623
ktelnet“Kerberos V5 Telnet”
Listed in Ports that cite an RFC · Plain and TLS port pairs · Remote access ports: ssh, telnet, 3389 and 5900