Chapter 19. BGP

Table of Contents

19.1. What is BGP?
19.2. BGP Setup
19.2.1. Overview
19.2.2. Standards
19.2.3. Simple example setup
19.2.4. Peer type
19.2.5. Route filtering
19.2.5.1. Matching attributes
19.2.5.2. Action attributes
19.2.6. Well known community tags
19.2.7. Announcing black hole routes
19.2.8. Grey holes
19.2.9. Announcing dead end routes
19.2.10. Bad optional path attributes
19.2.11. <network> element
19.2.12. <route>, <subnet> and other elements
19.2.13. Route feasibility testing
19.2.14. Status
19.2.15. Diagnostics
19.2.16. Router startup and shutdown
19.2.17. TTL security

19.1. What is BGP?

BGP (Border Gateway Protocol) is the protocol used between ISPs to advise peers of routes that are available. Each ISP tells its peers the routes it can see, being the routes it knows itself and those that it has been advised by other peers.

In an ideal world everyone would tell everyone else the routes they can see; there would be almost no configuration needed; all packets would find the best route accross the Internet automatically. To some extent this is what happens between major transit providers in the Internet backbone.

In practice things are not that simple and you will have some specific relationships with peers when using BGP. For most people there will be transit providers with which you peer. The FB2900 cannot take a full table (map of the whole Internet) from a transit provider so you would typically have a default route to them. You can advise the transit provider of your own routes for your own network so that they can route to you, and they tell their peers that they can route to you via that provider. This only works if you have IP address space of your own that you can announce to the world - unless you are an ISP then this is not commonly the case.

Even though IPv4 address space has already run out, it is possible to obtain IPv6 PI address space and an AS number to announce your own IPv6 addresses to multiple providers for extra resilience.

You can use BGP purely as an internal routing protocol to ensure parts of your network know how to route to other parts of your network, and can dynamically reroute via other links when necessary.

In most cases, unless you are an ISP of some sort, you are not likely to need BGP.