Interior gateway protocol

An Interior Gateway Protocol (usually IGP) is, in the TCP/IP protocol suite's routing architecture, a routing protocol used to do path selection in a disconnected internet, or in a local portion of the Internet. (These local portions are termed 'autonomous systems' (ASs); basically, they are parts of the Internet which are under separate control from other parts.)

There are three main IGPs in use:

• RIP
• OSPF
• IS-IS