Internet organisation and infrastructure


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A Uniform Resource Identifier (URI) is a string of characters that unambiguously identifies a particular resource. The URI itself only provides identification; access to the resource is neither guaranteed nor implied by the presence of a URI. Instead, any operation associated with a URI reference is defined by the protocol element, data format attribute, or natural language text in which it appears.

URI syntax was finalised in RFC 3986 (2005). The URI generic syntax consists of a hierarchical sequence of five components:

URI = scheme:[//authority]path[?query][#fragment]

where the authority component divides into three subcomponents:

authority = [userinfo@]host[:port]


A Uniform Resource Name (URN) is a URI that identifies a resource by name in a particular namespace. A URN may be used to talk about a resource without implying its location or how to access it For example, in the International Standard Book Number (ISBN) system, ISBN 0-486-27557-4 identifies a specific edition of Shakespeare's play Romeo and Juliet. The URN for that edition would be urn:isbn:0-486-27557-4. However, it gives no information as to where to find a copy of that book.

A Uniform Resource Locator (URL) is a URI that specifies the means of acting upon or obtaining the representation of a resource, i.e. specifying both its primary access mechanism and network location. For example, the URL refers to a resource identified as /wiki/Main_Page, whose representation, in the form of HTML and related code, is obtainable via the Hypertext Transfer Protocol (http:) from a network host whose domain name is

A URN may be compared to a person's name, while a URL may be compared to their street address.

Further info:

Relation to XML namespaces

In XML, a namespace is an abstract domain to which a collection of element and attribute names can be assigned. The namespace name is a character string which must adhere to the generic URI syntax. However, the name is generally not considered to be a URI, because the URI specification bases the decision not only on lexical components, but also on their intended use.

An XML namespace name does not necessarily imply any of the semantics of URI schemes. For example, a namespace name beginning with http: may have no connotation to the use of the HTTP.

Main protocols


The Content-Security-Policy HTTP response header helps reduce XSS risks on modern browsers by declaring which dynamic resources are allowed to load. See

HTTP in a nutshell

The request message consists of: Request methods: The response message consists of the following: An HTTP cookie (web cookie, browser cookie) is data that a server sends to a browser. The browser may store it and send it back with the next request to the same server. It's used to tell if two requests came from the same browser — keeping a user logged-in, for example. It remembers stateful information for the stateless HTTP protocol.

When receiving an HTTP request, a server can send a Set-Cookie header with the response. The cookie is usually stored by the browser, and then the cookie is sent with requests made to the same server inside a Cookie HTTP header. With every new request to the server, the browser will send back all previously stored cookies to the server using the Cookie header.

To help mitigate cross-site scripting (XSS) attacks, HttpOnly cookies are inaccessible to JavaScript's Document.cookie API. They are only sent to the server. For example, cookies that persist server-side sessions don't need to be available to JavaScript, and the HttpOnly flag should be set.



IP and IPv6

Internet in Europe

Internet security

Internet2, IPv6, ... mobile IP ...

Internet analysis

ISP's and peering


Peering between ISPs: Internet eXchanges (typically layer 2)