A Quick Introduction to BGP

BGP, or Border Gateway Protocol, was created in the late 1980s by the Internet Engineering Task Force as a replacement for Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP). Its purpose is to connect different autonomous systems on the Internet. The first version, BGP-1, was defined in 1989 in a document called RFC 1105. The current version, BGP-4, was defined in 1995 in another document called RFC 1771.

BGP and IPv4 & IPv6

BGP, or Border Gateway Protocol, is responsible for distributing routing information for both IPv4 and IPv6 addresses. It is an exterior gateway protocol, which means that it is used to exchange routing information between different Autonomous Systems (ASes) and not within a single AS. BGP has two versions: iBGP (Internal BGP) for routers within the same AS and eBGP (External BGP) for routers in different ASes. eBGP is generally used between network Providers so that they can share or advertise routes between each other.

When to use BGP

BGP, or Border Gateway Protocol, is commonly used by service providers and large businesses to link their networks to the Internet or to establish multiple networks in a Virtual Private Network (VPN). It is also employed in data centers for connecting multiple locations or for ensuring redundancy. When selecting a routing protocol, it is important to evaluate the size and complexity of the network and the specific needs of the environment.

iBGP and eBGP

iBGP (Internal BGP) is utilized when all the routers are in the same Autonomous System. iBGB routers are not obligated to have a direct connection to each other, but they can use any internal IGP to establish communication. iBGP routers typically do not propagate routes learned from other iBGP routers to other iBGP routers, which helps prevent routing loops within an Autonomous System.

On the other hand, eBGP (External BGP) is used when routers are in different Autonomous Systems. eBGP routers must have a direct connection to exchange routing information. eBGP routers usually disseminate routes learned from other eBGP routers to all other eBGP routers.

More Reading 

For a more detailed write up on BGP and other Protocols like IS-IS and OSPF check out the following links on Web Review Star - A Review and Tech Site

An Introduction to BGP, including IPv4 and IPv6, iBGP and eBGP 

An Introduction to IS-IS Routing - Intermediate System to Intermediate System

Understanding the Benefits and Limitations of OSPFv3 Routing Protocol for Enterprise Networks

Understanding CIDR Notation - Address Allocation and Routing for IPv4 and IPv6 

And Lastly a guide to IPv6

The Complete Guide to Understanding IPv6 (Maybe not a "Complete guide" but a good start)