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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)                 9  Uniform Resource Locators (URLs)

URL General Syntax 1 2 3 4 5 URL Relative Syntax and Base URLs

Telnet URL Syntax (telnet)

This scheme is used to open a Telnet connection to a server. This is the syntax:

telnet://<user>:<password>@<host>:<port>

In practice, the user name and password are often omitted, which causes the Telnet server to prompt for this information. Alternately, the “<user>” can be supplied and the password left out (to prevent it being seen) and the server will prompt for just the password. The port number defaults to the standard port for Telnet, 23, and is also often omitted.

This type of URL is interesting in that it identifies a resource that is not an object but rather a service.

This is a special URL type used for referring to files on a particular host computer. The standard syntax is:

file://<host>:<url-path>

This type of URL is also somewhat interesting, in that it describes the location of an object but not an access method. It is not sufficiently general to allow access to a file anywhere on an internetwork, but is often used for referencing files on computers on a local area network where names have been assigned to different devices.

A special syntax is also defined to refer specifically to files on the local computer:

file:///<url-path>

Here, the entire “//<host>:” element has been replaced by a set of three slashes, meaning specifically, “look on the local host”.

Additional syntax rules are often used by browsers to support the quirks of Microsoft operating systems, especially for the “file” scheme. First, the backslashes used by Microsoft Windows are expressed as forward slashes as required by TCP/IP. Second, since colons are used in drive letters specifications in Microsoft operating systems, these are replaced by the “vertical pipe” character, “|”, which “sorta looks like a colon” (play along, please. J)

So, to refer to the file “C:\WINDOWS\SYSTEM32\DRIVERS\ETC\HOSTS”, the following URL could be used:

file:///C|/WINDOWS/SYSTEM32/DRIVERS/ETC/HOSTS

Note however that some browsers actually do allow the colon in the drive specification.

URL General Syntax 1 2 3 4 5 URL Relative Syntax and Base URLs