The Border Gateway Protocol: Border Gateway Protocol

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Before networks became extensive, there was no such thing as interior and exterior gateway protocols. A network simply just ran on a generic routing protocol. This eventually ran into problems so Routing Information Protocol (RIP) was developed and ran as the single routing protocol for many years [1]. As the internet grew, however, this single routing protocol could no longer handle all the traffic. Because of this, over time numerous other routing protocols were developed to meet the needs of routing. One of the numerous gateway protocols that were developed was Border Gateway Protocol (BGP), which is classified as an exterior gateway protocol (EGP).
BGP was developed in January 1989 at the 12th Internet Engineering Task Force Meeting in Austin, Texas, by two men, Yakov Rekhter and Kirk Lougheed [1]. Interestingly enough, the initial design of BGP was detailed on a napkin, which shortly after was transfer to paper and quickly implemented. From this initial design on a napkin came the basics of the gateway protocol, BGP, which will be discussed in the remaining of this paper.
OVERVIEW:
BASICS:
BGP is the biggest existing routing protocol as it has to find all the possible routes and carry information around the world. Because it is so big, however, it is also the slowest routing protocol. Mainly, BGP is used to connect local networks with external networks to get access to the internet or other organizations [2]. Additionally, BGP communication systems are to exchange reachability information on a network with other BGP systems [3]. This information includes a list of autonomous systems (AS), in which a table can be constructed showing possible routing loops. Autonomous systems are discussed in detail later.
To exchange the n...

... middle of paper ...

...icated list of metrics, which is part of the reason why BGP is so complex. From these metrics, BGP has to select a single path that it feels is the best to get from a host to a network. This selection algorithm analyzes the each paths metrics to determine which route to install in the forwarding routing table [2]. Standard policy configurations of BGP can also influence BGP’s forwarding path [2]. The information that is trying to be accessed across the internet is then sent using forwarding table that was made by BGP. This also requires the best path to be sent to external BGP neighbors. Typically, BGP speakers only advertise routes to peers that it uses itself [3].
BGP assigns the first path that is valid as the current best path, and then compares it with the next path in the list until it finds the best path in the list of valid paths. The following figure shows

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