# Boarder gateway protocol (BGP)

This is a class of protocols that are used for interdomain routing . That is sharing subnets between AS . Two routers connected over BGP are called BGP peers. They open a semi-permanent TCP connection where they exchange routes. There are two varieties of this class.

• iBGP: For internal to the AS communication between boarder routers.
• eBGP: For two routers who are in different AS . The difference between iBGP and IGP is that iBGP is communicating about what external subnets are available from that router wheres IGP is communicating about what internal subnets there are.