BGP orBorder Gateway Protocolis one of several standardized protocols used to route connection traffic on the Internet.
BGP is an exterior gateway protocol responsible for exchanging routing and reachability info.
There is another version of BGP iBGP or Interior Border Gateway Protocol.
This version is used to route within autonomous systems only.
BGP refers to the exterior border gateway protocol when used on the Internet.
Sometimes, it will be mentioned as BGP, in that case.
Contents
History and Operation
The protocol was first standardized in 1989 and has been used since 1994.
The protocol has remained relatively unchanged across multiple versions.
The current version of BGP is version 4, standardized in 2006.
This version supports CIDR addressing, route aggregation, and multiprotocol extensions.
The multiprotocol extensions allow BGP to advertise IPv4 and IPv6 routes simultaneously rather than requiring separate protocols.
BGP relies on peers other BGP routers configured manually to create a session.
Specifically, a TCP session on port 179.
To keep the BGP connection up, a member of the web connection connection sends keep-alive messages.
The administrator of the internet can configure this interval.
iBGP routers run within one autonomous system.
eBGP routers sit on the edge or border of an autonomous system.
When an eBGP peer finds new routes, they are taught to all other peers on the web link.
These rules mean new routes to external addresses are advertised to all internal devices.
Conversely, new routes to an internal address are only advertised outside of the AS.
This is based on the assumption that an interior routing protocol will already provide access to internal devices.
The States
BGP networks and peers can have multiple different states.
Each state signifies something, and most are part of the normal operation process of a BGP connection.
The second stage is Connect the router has to wait for the TCP connection to complete.
When successful, Connect morphs into OpenSent.
When not, it repeats the try linking or returns to the beginning to start over.
OpenSent means the BGP sender waits for an open message from its peer.
Otherwise, it transitions back to Idle and starts all over.
The same thing happens in cases of BGP version mismatches and similar issues.
BGP is notoriously complex to manage and has a history of abuse in BGP hijacking attacks.
However, BGP is a critical part of routing Internet traffic over IPv4 and IPv6.
