An intranet is a local area network (LAN) used internally in an organisation to facilitate communication and access to information that is sometimes access-restricted. Sometimes the term refers only to the most visible service, the internal web site. The same concepts and technologies of the Internet such as clients and servers running on the Internet protocol suite are used to build an intranet. HTTP and other internet protocols are commonly used as well, especially FTP and email. There is often an attempt to use internet technologies to provide new interfaces with corporate 'legacy' data and information systems.
There does not necessarily have to be any access from the organisations's internal network to the internet itself. Where there is, there will be a firewall with a gateway through which all access takes place. Traffic going through the gateway can be monitored by the organisation's security department. This means that organisations that allow their staff internet access can normally determine which internet web sites are being viewed, block access to specific sites they don't want them to see (such as pornographic sex sites), and even trace offenders who persistently attempt to view them. They can also block certain types of web content (such as objects) which they consider a particular security risk.
Where external email access is provided, known sources of spam and specific types of email attachment can be blocked by the organisation. It should also be noted that emails sent and received this way can be required to be produced by the organisation in the event of legal action against it by a third party.