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Network Configuration—Routing and BridgingRunning BGP—OpenBGPDBorder Gateway Protocol version 4(BGP4) is one of the most important protocolsin the today's Internet that glues networks together. Internet is a complex set ofinterconnected networks, each called an Autonomous System. An AutonomousSystem (AS) is a network that is controlled by an administrative entity, such as anISP. Each AS has at least one unique AS number that is assigned by the RegionalInternet Registry (RIR) as well as a few network prefixes.BGP Protocol (RFC 4271) is used to exchange routing information between ASs. Ituses permanents TCP connections (typically on port 179) to send routing updates tothe directly connected peers. Each BGP router makes routing decisions based on itsown view of the network, and installs appropriate routes in the routing table.OpenBGPD is a secure and open-source implementation for BGP4 protocol whichcomes from OpenBSD project. It is available in ports system under /usr/ports/net/openbgpd.Before running OpenBGPD, you should have the following information:• AS number• Network prefixesOnce you have installed the software, you should create a configuration file tospecify your environment, such as your AS number, peers, which routes should beadvertised to each peer, and which routes should be permitted to be imported (thatis route filters).A sample network representing the bgpd.conf example is shown in thefollowing figure:[ 166 ]