Allied Telesis VERSION 5.4.3-2.6 manual BGP and BGP4+ Terminology, Term Description

BGP and BGP4+ Introduction

BGP and BGP4+ Terminology

See the below table for descriptions of BGP and BGP4+ terms used through this chapter:

Term	Description
AS number (ASN)	A number that identifies an Autonomous System. Previously, an
	ASN was a 16-bit number between 1 and 64,511 (public) and
	64,512 and 65,535 (private) assigned to an AS for the purpose of
	BGP operation. Since RFC 6793, an ASN is now 32-bit with a
	range of decimal values between 1 and 4,294,967,295 .
AS_Path	A BGP path attribute that lists ASNs through which the route has
	been advertised.
AS_Sequence	A type of AS_Path segment consisting of an ordered list of ASNs
	through which the route has been advertised.
auto summary	A routing protocol feature in which a router that connects to
	more than one classful network advertises summarized routes
	for each entire classful network when sending updates out
	interfaces connected to other classful networks.
Autonomous System	A set of routers inside a single administrative authority, grouped
(AS)	together for the purpose of controlling routing policies for the
	routes advertised by that group to the Internet.

BGP best path algorithm

The process that BGP uses to examine competing BGP paths (routes) in its BGP table, for a single prefix, choosing one route as the best route. The best path algorithm results in a choice of a single route for each prefix as that router’s best BGP path. BGP compares the current best path against the next path in the list.

BGP peer	A BGP neighbor. A BGP neighbor is a router running BGP that
	formed a BGP neighbor relationship to exchange BGP Updates.
BGP peer group	A configuration construct in which multiple neighbors’
	parameters can be configured as a group to reduce the length
	of the configuration. BGP performs routing policy logic against
	one set of Updates for the peer group, improving convergence
	time and reducing the CPU load.
BGP synchronization	A feature in which BGP routes cannot be considered to be a best
	route to reach a prefix unless that same prefix exists in the
	router’s IP routing table as learned via some IGP. When
	synchronization is enabled, BGP does not advertise a route
	learned via an iBGP peer to external peers, until the route is
	learned locally, or via an IGP and is present in the routing table.
	When synchronization is disabled, BGP can use and advertise
	routes from an iBGP peer to external peers, which are not
	present in the routing table.
BGP table	A table inside a router that holds the path attributes known by
	BGP on that router.

Border Gateway Protocol (BGP)

An exterior routing protocol designed to exchange prefix information between different autonomous systems. The information includes characteristics called path attributes, which allow for great flexibility regarding routing choices.

	Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches
1.42	AlliedWare PlusTM Operating System - Software Version 5.4.3-2.6	C613-50032-01 REV D