BGP is an Exterior Gateway Routing Protocol and BGP is used for exchanging the routing information between the auto system numbers. Let’s look into some of the BGP’s basic features.
BGP Keypoints..!
- BGP is a Path Vector Protocol.
- BGP is an open standard protocol.
- BGP is an exterior gateway routing protocol and it is designed for inter-AS domain routing to scale a Large network like the internet
- it supports classless interdomain Routing.
- Updates are incremental and trigger BGP to send updates to manually defined neighbors as unicast.
- BGP is an application layer protocol that uses TCP for reliability and BGP uses TCP port 179.
- Many options are available in BGP for path manipulation because in BGP, It is easy to implement the routing policy compares to IGP and the most important thing in BGP is that the BGP attributes are attached to the prefix, not to the link like IGP .so the traffic engineering is very easy.
- Administrative distance is 20 for external updates ( EBGP) and 200 for internal updates (i BGP).
- Popular routing Protocol in ISP network.
- BGP has lots of extensibility, which means there are lots of AFI and SAFI like VPNv4 and VPNv6.Multicast routing that supports BGP.
- The most important thing is that In BGP it’s easy to control the outbound traffic path of your ASN but the inbound traffic path does not work 100% in your way because we don’t know how others are routing towards our AS.
- BGP uses Unicast communication.
Why BGP is an Application ??
Technically BGP is not a routing protocol, BGP is an application, and BGP relies on IGP.
Before you establish the BGP peering you must be able to reach the peer IP and also make sure you have the TCP port 179 reachability between the peers. That’s the reason in most of the cases BGP need IGP to run first for establishing the BGP transport. So before you run the BGP, make sure your transport is UP and peers have TCP and IP reachability.
Note:-BGP peers do not need to be directly connected but there must be a route to that peer IP through IGP.So if there is no route to the peer’s IP then the TCP session cant be initiated.
BGP is used for exchanging the routing information between the AS number. But it does not have complete visibility of the path. it means BGP will give you the next-hop IP of a route but it depends on your IGP who will recurse the route towards the next hop.