Border Gateway Protocol – BGP4

5/10/06


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Table of Contents

Border Gateway Protocol – BGP4

Border Gateway Protocol (BGP4)

BGP Part 0

Consider a typical small ISP

Small ISP with one upstream provider

What happens with other ISPs in the same country

Keeping Local Traffic Local

Keeping Local Traffic Local

Consider a larger ISP with multiple upstreams

A Large ISP with more than one upstream provider

Terminology: “Policy”

“Policy” (continued)

“Policy” Implementation

Terminology: “Peering” and “Transit”

Terminology: “Aggregation”

“Aggregation” (continued)

“Aggregation” (continued)

Summary: Why do I need BGP?

BGP Part 1

Routing versus Forwarding

Routing Table/RIB

Forwarding Table/FIB

Routing Tables Feed the Forwarding Table

IP Routing

IP Routing

IP routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

IP route lookup: Longest match routing

Static vs. Dynamic routing

Dynamic Routing

BGP Part 2

Interior vs. Exterior Routing Protocols

IGP

EGP

Why Do We Need an EGP?

Scalability and policy issues

Scalability: Not using static routes

Scalability: Not using IGP (OSPF)

Using BGP instead

Border Gateway Protocol

BGP Part 3

BGP Building Blocks

Autonomous System (AS)

Autonomous System (AS)

Autonomous System (AS)

Autonomous System numbers

Using AS numbers

Routing flow and packet flow

Egress Traffic

Ingress Traffic

Types of Routes

Hierarchy of Routing Protocols

DeMarcation Zone (DMZ)

Basics of a BGP route

BGP Part 4

Basic BGP commands

Inserting prefixes into BGP

“network” command

“redistribute static”

“redistribute static”

Aggregates and Null0

BGP Case Study 1 and Exercise 1

Case Study 1: Small ISP with one upstream provider

Case Study 1: Small ISP with one upstream provider

Case Study 1: Routing Protocols

Case Study 1: BGP is not needed

Exercise 1: Upstream provider with small customers

Exercise 1: Upstream provider & small customers

Exercise 1: BGP configuration

Exercise 1: Transit through upstream provider

Exercise 1: What you should see

Exercise 1: Did BGP “network” statement work?

BGP Part 5

BGP Protocol Basics

BGP Protocol Basics

Terminology

Terminology

BGP Basics …

Interior BGP vs. Exterior BGP

BGP Peers

BGP Peers – External (eBGP)

BGP Peers – Internal (iBGP)

Configuring eBGP peers

Configuring iBGP peers

Configuring iBGP peers: Full mesh

Configuring iBGP peers: Loopback interface

Configuring iBGP peers

Configuring iBGP peers

Configuring iBGP peers

BGP Part 6

BGP Updates — NLRI

BGP Updates — Attributes

AS-Path Attribute

Next Hop Attribute

Next Hop Attribute

Next Hop Attribute

Next Hop Attribute (more)

Community Attribute

BGP Updates – Withdrawn Routes

BGP Updates – Withdrawn Routes

BGP Routing Information Base

BGP Routing Information Base

BGP Routing Information Base

BGP Routing Information Base

BGP Routing Information Base

BGP Routing Information Base

An Example…

BGP Case Study 2 and Exercise 2

Case Study 2: Another ISP in the same country

Case Study 2: Another ISP in the same country

Case Study 2: Bringing down costs

Case Study 2: Keeping Local Traffic Local

Exercise 2: Connect to another local ISP

Exercise 2: BGP configuration

Exercise 2: What you should see

Exercise 2: What you should see

Exercise 2: Do you see transit routes through your peers?

BGP Part 7

Terminology: “Policy”

Routing Policy

Filter list rules: Regular Expressions

Regular expressions (cisco specific)

Filter list – using as-path access list

Policy Control – Prefix Lists

Prefix Lists – Examples

Prefix Lists – More Examples

Policy Control Using Prefix Lists

Policy Control – Route Maps

Route-map match & set clauses

Route Map: Example One

Route Map: Example Two

BGP Exercise 3

Exercise 3: Filtering peer routes using AS-path

Exercise 3: Filtering peer routes using AS-path

Exercise 3: What you should see

Exercise 3: Did it work?

BGP Exercise 4

Exercise 4: Filtering peer routes using prefix-lists

Exercise 4: Filtering peer routes using prefix-list

Exercise 4: What you should see

Exercise 4: Did it work?

BGP Part 8

BGP Path Attributes: Why ?

BGP Path Attributes...

AS-PATH

AS-Path

Next-Hop

Next Hop...

Local Preference

Local Preference

Multi-Exit Discriminator

Multi-Exit Discriminator (MED)

Origin

Communities

Communities

Weight

Administrative Distance

Synchronization

Synchronization

BGP route selection (bestpath)

BGP route selection (bestpath)

BGP route selection (bestpath)

BGP Route Selection...

BGP Exercise 5

Exercise 5: Configure iBGP

Exercise 5: Configure iBGP

Exercise 5: Configure iBGP

Exercise 5: What you should see

BGP Part 9

PPT Slide

Stub AS

PPT Slide

Multi-homed AS

Service Provider Network

Common Service Provider Network

Load-sharing – single path

Load-sharing – multiple paths from the same AS

Redundancy – Multi-homing

Default from all providers

Default from all providers

Customer prefixes plus default from all providers

Customer routes from all providers

Full routes from all providers

Full routes from all providers

Best Practices IGP in Backbone

Best Practices... Connecting to a customer

Best Practices... Connecting to other ISPs

Best Practices... The Internet Exchange

Summary

Author: Alan Barrett (2004)

Home Page: http://www.ws.afnog.org

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