Table of Contents for
Packet Tracer Network Simulator

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Packet Tracer Network Simulator by Jesin A Published by Packt Publishing, 2014
  1. Cover
  2. Table of Contents
  3. Packet Tracer Network Simulator
  4. Packet Tracer Network Simulator
  5. Credits
  6. About the Author
  7. About the Reviewers
  8. www.PacktPub.com
  9. Preface
  10. Who this book is for
  11. Conventions
  12. Reader feedback
  13. Customer support
  14. 1. Getting Started with Packet Tracer
  15. Installing Packet Tracer
  16. Interface overview
  17. Creating a simple topology
  18. Summary
  19. 2. Network Devices
  20. Customizing devices with modules
  21. Emulating WAN
  22. Accessing the CLI
  23. Summary
  24. 3. Generic IP End Devices
  25. Servers
  26. Other end devices
  27. Configuring end devices
  28. Summary
  29. 4. Creating a Network Topology
  30. Testing connectivity with PDUs
  31. Using the simulation mode
  32. Clustering a topology
  33. Summary
  34. 5. Navigating and Modifying the Physical Workspace
  35. Moving devices physically
  36. Managing cables and distances
  37. Customizing icons and backgrounds
  38. Summary
  39. 6. Configuring Routing with the CLI
  40. Dynamic routing protocols
  41. The Routing table
  42. Load sharing
  43. Summary
  44. 7. Border Gateway Protocol (BGP)
  45. BGP versus dynamic routing protocols
  46. Configuring BGP in Packet Tracer
  47. Summary
  48. 8. IPv6 on Packet Tracer
  49. IPv6 static and dynamic routing
  50. Using both IPv4 and IPv6
  51. Summary
  52. 9. Setting Up a Wireless Network
  53. Wireless networks and physical workspaces
  54. Summary
  55. 10. Configuring VLANs and Trunks
  56. InterVLAN routing with routers and layer 3 switches
  57. Switch-to-switch trunk links
  58. Analyzing broadcasts in the simulation mode
  59. Summary
  60. 11. Creating Packet Tracer Assessments
  61. The initial network
  62. The answer network
  63. Testing the activity
  64. Summary
  65. Index

Chapter 7. Border Gateway Protocol (BGP)

The Internet is a huge network and is made up of many smaller networks. To learn about routes in other networks, each network has to run a routing protocol. While protocols such as EIGRP (Enhanced Interior Gateway Routing Protocol), OSPF (Open Shortest Path First), and RIP (Routing Information Protocol) work well for many networks, they do not scale to support the needs of a gigantic network like the Internet, nor do they provide the level of administrative separation required. So, BGP (Border Gateway Protocol) is used by ISP (Internet Service Provider) and large enterprises to advertise IP routes to one another.

In this chapter, we'll learn about BGP and its features when compared to other routing protocols. We will also learn the commands used in BGP and configure it in Cisco Packet Tracer.

What is BGP?

BGP is a very robust routing protocol that is used to exchange routing information between multiple Autonomous Systems (AS). This brings up the question of what an AS is. An AS is a collection of IP prefixes (read IP networks) that are maintained by a network operator. This network operator could be an enterprise or an ISP.

Each AS has a number assigned to it called ASN (Autonomous System Number). Public AS numbers are assigned by the IANA (Internet Assigned Numbers Authority) to the RIRs (Regional Internet Registries). These RIRs, in turn, assign them to individual enterprises or ISPs.

Configuration of BGP largely depends on how an organization is connected to an ISP. There are four possible ways in which this can be done:

  • Single homed (one link to one ISP): This is the simplest design (shown in the following screenshot) and has one link from the enterprise connecting to the ISP. This design has no redundancy or failover:
    What is BGP?
  • Dual homed (two or more links to one ISP): This design has a single ISP but has two or more links connecting to it. This provides some amount of reliability in the event of link issues. The following screenshot has examples of dual homed design:
    What is BGP?
  • Single multihomed (one link to two or more ISPs): This case (shown in the following screenshot) has multiple ISPs with one link connecting to each of them:
    What is BGP?
  • Dual mutihomed (two or more links per ISP to two or more ISPs): This design (shown in the following screenshot) provides the highest level of reliability and availability. In this case, there are two or more ISPs with two or more links connecting each of them:
    What is BGP?

BGP may not always be used in all the previously-discussed designs. For some designs such as single homed, it is better to just have a static default route in the enterprise router towards the ISP, and another on the ISP side for just the network prefix of the enterprise. However, implementing BGP on multihomed networks ensures that the most efficient route is used as these networks have two or more links to ISP(s).

There are two types of BGP:

  • eBGP (External BGP)
  • iBGP (Internal BGP)

External BGP

This type of BGP is used to exchange routes between two types of AS. The administrative distance of eBGP is 20. By default, the update packets in eBGP have the TTL set to 1, so that only directly connected BGP routers receive it. However, this behavior can be changed by using commands. Also, an eBGP peer will advertise all the valid routes it has learned from its eBGP and iBGP peers. When an eBGP neighbor advertises a route, it sets the next-hop field of the route to its own address.

Internal BGP

This type of BGP is used to exchange routes within an AS. The administrative distance of iBGP is 200. Updates in iBGP do not have TTL value limitations. An iBGP peer does not advertise a route to another iBGP peer if the route was learned via iBGP. This is done to prevent routing loops within an AS. The next-hop field of the route updates remains unchanged when one iBGP peer advertises to another iBGP peer. This behavior can be modified with the use of commands.

Note

Cisco Packet Tracer Version 5.3.3 does not support iBGP.