curl supports about 28 protocols. We say about because it depends on how youcount and what you consider to be distinctly different protocols.
DICT
DICT is a dictionary network protocol, it allows clients to ask dictionaryservers about a meaning or explanation for words. See RFC 2229. Dict serversand clients use TCP port 2628.
FILE
FILE is not actually a network protocol. It is a URL scheme that allows youto tell curl to get a file from the local file system instead of getting itover the network from a remote server. See RFC 1738.
FTP
FTP stands for File Transfer Protocol and is an old (originates in the early1970s) way to transfer files back and forth between a client and a server. SeeRFC 959. It has been extended greatly over the years. FTP servers and clientsuse TCP port 21 plus one more port, though the second one is usuallydynamically established during communication.
See the external page FTP vsHTTP for how it differs fromHTTP.
FTPS
FTPS stands for Secure File Transfer Protocol. It follows the tradition ofappending an 'S' to the protocol name to signify that the protocol is donelike normal FTP but with an added SSL/TLS security layer. See RFC 4217.
This protocol is problematic to use through firewalls and other networkequipment.
GOPHER
Designed for "distributing, searching, and retrieving documents over theInternet", Gopher is somewhat of the grandfather to HTTP as HTTP has mostlytaken over completely for the same use cases. See RFC 1436. Gopher servers andclients use TCP port 70.
GOPHERS
Gopher over TLS. A recent extension to the old protocol.
HTTP
The Hypertext Transfer Protocol, HTTP, is the most widely used protocol fortransferring data on the web and over the Internet. See RFC 9110 for generalHTTP Semantics, RFC 9112 for HTTP/1.1, RFC 9113 forHTTP/2 and RFC 9114 for HTTP/3. HTTP servers andclients use TCP port 80.
HTTPS
Secure HTTP is HTTP done over an SSL/TLS connection. See RFC 2818. HTTPSservers and clients use TCP port 443, unless they speakHTTP/3 which then uses QUIC (RFC 8999) and isdone over UDP.
IMAP
The Internet Message Access Protocol, IMAP, is a protocol for accessing,controlling and "reading" email. See RFC 3501. IMAP servers and clients useTCP port 143. Whilst connections to the server start out as cleartext, SSL/TLScommunication may be supported by the client explicitly requesting to upgradethe connection using the STARTTLS command. See RFC 2595.
IMAPS
Secure IMAP is IMAP done over an SSL/TLS connection. Such connectionsimplicitly start out using SSL/TLS and as such servers and clients use TCPport 993 to communicate with each other. See RFC 8314.
LDAP
The Lightweight Directory Access Protocol, LDAP, is a protocol for accessingand maintaining distributed directory information. Basically a databaselookup. See RFC 4511. LDAP servers and clients use TCP port 389.
LDAPS
Secure LDAP is LDAP done over an SSL/TLS connection.
MQTT
Message Queuing Telemetry Transport, MQTT, is a protocol commonly used in IoTsystems for interchanging data mostly involving smaller devices. It is aso-called "publish-subscribe" protocol.
POP3
The Post Office Protocol version 3 (POP3) is a protocol for retrieving emailfrom a server. See RFC 1939. POP3 servers and clients use TCP port 110. Whilstconnections to the server start out as cleartext, SSL/TLS communication may besupported by the client explicitly requesting to upgrade the connection usingthe STLS command. See RFC 2595.
POP3S
Secure POP3 is POP3 done over an SSL/TLS connection. Such connectionsimplicitly start out using SSL/TLS and as such servers and clients use TCPport 995 to communicate with each other. See RFC 8314.
RTMP
The Real-Time Messaging Protocol (RTMP) is a protocol for streaming audio,video and data. RTMP servers and clients use TCP port 1935.
RTSP
The Real Time Streaming Protocol (RTSP) is a network control protocol tocontrol streaming media servers. See RFC 2326. RTSP servers and clients useTCP and UDP port 554.
SCP
The Secure Copy (SCP) protocol is designed to copy files to and from a remoteSSH server. SCP servers and clients use TCP port 22.
SFTP
The SSH File Transfer Protocol (SFTP) that provides file access, filetransfer, and file management over a reliable data stream. SFTP servers andclients use TCP port 22.
SMB
The Server Message Block (SMB) protocol is also known as CIFS. It is anapplication-layer network protocol mainly used for providing shared access tofiles, printers, and serial ports and miscellaneous communications betweennodes on a network. SMB servers and clients use TCP port 445.
SMBS
SMB done over TLS.
SMTP
The Simple Mail Transfer Protocol (SMTP) is a protocol for emailtransmission. See RFC 5321. SMTP servers and clients use TCP port 25. Whilstconnections to the server start out as cleartext, SSL/TLS communication may besupported by the client explicitly requesting to upgrade the connection usingthe STARTTLS command. See RFC 3207.
SMTPS
Secure SMTP, is SMTP done over an SSL/TLS connection. Such connectionsimplicitly start out using SSL/TLS and as such servers and clients use TCPport 465 to communicate with each other. See RFC 8314.
TELNET
TELNET is an application layer protocol used over networks to provide abidirectional interactive text-oriented communication facility using a virtualterminal connection. See RFC 854. TELNET servers and clients use TCP port 23.
TFTP
The Trivial File Transfer Protocol (TFTP) is a protocol for doing simple filetransfers over UDP to get a file from or put a file onto a remote host. TFTPservers and clients use UDP port 69.
WS
WebSocket is a bidirectional TCP-like protocol, setup over an HTTP(S)request. WS is the scheme for the clear text version done over plain HTTP.Experimental support for this was added to curl 7.86.0.
WSS
WebSocket is a bidirectional TCP-like protocol, setup over an HTTP(S)request. WSS is the scheme for the secure version done over HTTPS.Experimental support for this was added to curl 7.86.0.
