An Intranet is nothing but a Private Local Network (LAN) where we use the Internet Protocols and their available services. This network is then connected to Internet through router or firewall. The following figure sows what it is said.
The network in left local ambit is an Intranet. It can be then connected to all other networks form the Internet worldwide network. The technologies used in the Intranet for the layers 1 and 2 of the OSI model are all the ones studied in this packet (Ethernet, Fast Ethernet, IEEE 802.3, Token Ring, ..). Above layer 2 we use the Internet Protocol Suite, as shown in figure:
The IP protocol is a network protocol. The TCP and UDP protocols are the transport protocols. Above them there are the protocols supporting the typical services of an Intranet. The most important among then are:Service Protocol Description Terminal Emulation Telnet Emulates a terminal for the connection to a host through the LAN Files Transfer FTP Allows the files transfer from a server to a client Electronic Mail SMTP Allows to exchange messages among network users World Wide Web HTTP Allows to unload hypertextual pages from a network server Domain Name Server DNS Allows the management of the host names and translation into IP addresses