Information Technology Reference
In-Depth Information
Foundation Topics
BGP Review
This section covers BGP theory and design concepts.
The current version of BGP, version 4 (BGP4), is defined in RFC 1771 (March 1995). BGP is
an interdomain routing protocol. The primary function of BGP is to provide and exchange
network reachability information between domains or autonomous systems. BGP uses TCP
port 179 as its transport protocol between BGP peers or neighbors. BGP4 was created to
provide classless interdomain routing (CIDR), a feature that was not present in the earlier
versions.
CIDR is described in RFC 1519. CIDR provides the capability of forwarding packets that are
based on IP prefixes with no distinction of IP address class. CIDR was created as a solution to
the scaling problem of IP addressing in the Internet that was imminent in the early 1990s. At
that time, there was an increased growth of the Internet routing tables and a reduction of Class
B address space. CIDR provides a way for service provider's to assign address blocks smaller
NOTE
than a Class B network but larger than a Class C network.
BGP Neighbors
BGP is usually configured between two directly connected routers that belong to different
autonomous systems. Each AS is under different technical administration: Usually, one is the
enterprise company and the other is the service provider, or between different service providers,
as shown in Figure 9-1.
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