(UPDATED)

The Border Gateway Protocol (BGP) is the routing protocol of the Internet. For anyone wishing to enter into a peering relationship with another network, BGP will almost always be required.

The only exception is a single link from the local network to an upstream provider, usually where most newcomer network operators start in life. As soon as the local network obtains a connection to another network they become what is know as multihomed, and the only way to make a multihoming connection function is by the use of BGP, the routing protocol designed for interconnections between different autonomous networks.

A collection of routers and other network infrastructure solely owned and operated by a single entity, and having a unique routing policy.

Any one entity can operate more than one autonomous system - because an autonomous system represents a single routing policy. For example, a network operator may have distinct autonomous systems for their access network, their data housing infrastructure, their mobile network, and their transit network; each of these will have distinct routing policies.

(There have been a few cases where multiple entities use just one autonomous system, but this scenario is not recommended by the authors due to the management complexity.)

The decisions that any one autonomous network represented by an autonomous system will make with regard to routes they announce to a neighbour, and routes they receive from a neighbour.

When an autonomous network has at least two (or more connections) to another autonomous network (or networks).

Even two separate links to the same provider is considered to be an example of multihoming.

The section of the Toolbox dedicated to listing useful BGP Resources which will be useful for further study.

This content is sourced from many contributors, including:

• BGP presentation repository - Philip Smith
• BGP Videos - Network Startup Resource Center
• BGP for Network Engineers - DE-CIX
• BGP Toolkit - Hurricane Electric looking glass (and more)
• RouteViews - Global BGP looking glass
• R&E Network BGP status - Network Startup Resource Center

Back to Home page