Chapter 2 Advanced Routing for FortiOS 5.0 : Border Gateway Protocol (BGP) : BGP background and concepts
  
BGP background and concepts
The border gateway protocol contains two distinct subsets — internal BGP (iBGP) and external BGP (eBGP). iBGP is intended for use within your own networks. eBGP is used to connect many different networks together, and is the main routing protocol for the Internet backbone. FortiGate units support iBGP, and eBGP only for communities.
The following topics are included in this section:
Background
Parts and terminology of BGP
How BGP works