Introduction - Huawei Quidway NetEngine80E Configuration Manual

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing

8.1 Introduction

BGP is a dynamic routing protocol used between ASs.
8.1.1 BGP Overview
The Border Gateway Protocol (BGP) advertises and maintains a large number of routes between
autonomous systems (ASs).
Background
When Internal Gateway Protocol (IGP) was first deployed, it was able to meet network
deployment requirements because networks were not as large as they now are. However,
increasing numbers of routes on large modern networks impose tough challenges on the
performance of devices. To solve this problem, ASs were introduced. One IGP runs within an
AS, and one Exterior Gateway Protocol (EGP) runs between ASs.
EGP, however, has the following shortcomings: It forwards routes without selecting optimal
routes and therefore cannot avoid loops. Therefore, EGP was replaced with BGP.
BGP overcomes these shortcomings and can advertise and maintain a large number of routes
more efficiently. BGP is deployed between ASs that may be under different technical
administrations. Therefore, BGP must have powerful routing control capabilities and can be
easily extended so that network security can be ensured.
BGP-1 (defined in RFC 1105), BGP-2 (defined in RFC 1163), and BGP-3 (defined in RFC 1267)
are three earlier-released versions of BGP. The current BGP version is BGP-4 defined in RFC
4271. As an exterior routing protocol on the Internet, BGP is widely used among Internet Service
Providers (ISPs).
BGP Characteristics
Characteristics of BGP are as follows:
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Issue 02 (2014-09-30)
NOTE
This document refers to BGP-4, unless stated otherwise.
Different from IGPs such as the Open Shortest Path First (OSPF) and Routing Information
Protocol (RIP), BGP is an EGP, which controls route advertisement and selects the optimal
route between ASs rather than discover or calculate routes.
BGP uses the Transport Control Protocol (TCP) with port number 179 as the transport layer
protocol. The reliability of BGP is therefore enhanced.
BGP supports Classless Inter-Domain Routing (CIDR).
BGP transmits only the updated routes, saving the bandwidth used for route distribution.
Therefore, BGP is applicable to the Internet where a large number of routes are transmitted.
BGP eliminates routing loops by adding AS_Path information to BGP routes.
BGP provides multiple routing policies for flexible route selection and filtering.
BGP can be easily extended and can adapt to the development of networks.
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8 BGP Configuration

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