Do you need BGP routing?

BGP or 'Border Gateway Protocol' is the routing protocol used to exchange routing information across the Internet. BGP is an exterior routing protocol and as such is concerned with routing between networks rather than within them (this is the domain of the interior routing protocols such as RIP, OSPF, IS-IS).

If you have only a single connection to the Internet there is not a lot to be gained from using BGP because you already know where to send all traffic not destined to one of your networks, that is to your provider. Everyone should be conscious of keeping the Internet's routing table as small as possible. This can be best addressed by aggregating addresses using CIDR blocks (Classless InterDomain Routing= protocol which allows the assignment of Class C IP addresses in multiple contingious blocks). If you are only single-homed your telecom carrier may choose to aggregate your networks with the networks of other single-homed customers and thus announce a single CIDR block under their ASN (Abstract Syntax Notation= defines the syntax and format of communication between managed devices and management applications) in order to reduce the table size.

If you are going to "Multi-home" which means having multiple connections to the Internet, you should use BGP for control. When you decided to multi-home it was for a reason, maybe extra capacity, redundancy, or tariffing, so in order to actually perform any of these functions you need to control how your networks are announced to your providers. If you don't exchange routes with them but rely on them announcing your routes you could find your traffic flowing down an expensive low capacity link with the other cheaper, higher capacity links mostly idle! Using BGP also means configuring it on your router and announcing routing information with it. Static routing is typically not removed for networks until they are seen reliably announced via BGP.

BGP is the only protocol that is designed to deal with a network of the Internet's size, and the only protocol that can deal well with having multiple connections to unrelated routing domains. It has proven to be an inter-Autonomous System which is scalable, stable and provides the mechanisms needed to support complex routing policies. When people talk about "BGP" today, they implicitly mean BGP4. There is no need to specify the -4 version number because no one uses earlier versions, and very few vendors even still support them.