BGP / RFC 1771

This routing Protokol is an exterior routing protocol. It’s not neede on local area networks. It’s neede converge the internet. It’s completly different from the internel routing protocols like OSPF, EIGRP, RIP or IS-IS.

Here is a basic overview:

  • It’s used to route between AS (autonomous systems)
  • It’s an enhanced vector routing protocol
  • uses tcp for transissions, three way handshake, port 179
  • support cidr
  • triggered updates
  • granular metrics
  • garanteed to be loopfree

Defintion of Autonomous System (AS):

A set of routers under a single technical administration using an interior gateway routing protocol and common metrics to route packets.

The AS is using an exterior gateway routing protocol to route packets to other ASs.

BGP Basic EBG Peer Connection

Terminology:

  • A connection – is something like a adjacency between bgp peers using port tcp 179. The connection is not dependend on the routers between. They don’t have to be on the same subnet. There can be multiple routers in between.
  • Update – is used to exchange routing information, including in every route a destination network and an as path list.
  • AS Path list – it contains a list of AS’s that have to be passed to reach a certain destination, it’s including path attributes
  • Routing information Bases are stored in RiBs, updates are stored in RiB’s, Adj-RiB-In, Loc-RiB, Adj-RiB-Out
  • decision process – how a best route is choosen, bgp will weight the result of all of it’s attributes
  • policies – support of routing through policies, to controll the flow of routes


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