## Internet Domain: TCP, UDP, SSL, and TLS

PHP 4, PHP 5. ssl:// & tls:// since PHP 4.3.0 sslv2:// & sslv3:// since PHP 5.0.2

> Note: If no transport is specified, tcp:// will be assumed.

- 127.0.0.1
- fe80::1
- www.example.com
- tcp://127.0.0.1
- tcp://fe80::1
- tcp://www.example.com
- udp://www.example.com
- ssl://www.example.com
- sslv2://www.example.com
- sslv3://www.example.com
- tls://www.example.com

Internet Domain sockets expect a port number in addition to a target address. In the case of fsockopen() this is specified in a second parameter and therefore does not impact the formatting of transport URL. With stream_socket_client() and related functions as with traditional URLs however, the port number is specified as a suffix of the transport URL delimited by a colon.

- tcp://127.0.0.1:80
- tcp://[fe80::1]:80
- tcp://www.example.com:80

> Note: IPv6 numeric addresses with port numbers
> In the second example above, while the IPv4 and hostname examples are left untouched apart from the addition of their colon and portnumber, the IPv6 address is wrapped in square brackets: [fe80::1]. This is to distinguish between the colons used in an IPv6 address and the colon used to delimit the portnumber.

The ssl:// and tls:// transports (available only when openssl support is compiled into PHP) are extensions of the tcp:// transport which include SSL encryption. Since PHP 4.3.0 OpenSSL support must be statically compiled into PHP, since PHP 5.0.0 it may be compiled as a module or statically.

ssl:// will attempt to negotiate an SSL V2, or SSL V3 connection depending on the capabilities and preferences of the remote host. sslv2:// and sslv3:// will select the SSL V2 or SSL V3 protocol explicitly.