[...]... sequencing, and retransmission of data BGP Versions 1, 2, and 3 should be considered completely obsolete Whenever BGP is used, it means BGP- 4 When BGP neighbors establish a TCP session, they start exchanging BGP information in the form of “messages.” Each message starts with a header, followed by the contents of the message, as shown in Table 2-2 Table 2-2 BGP message header format Marker Length... Chapter 5, Getting Started with BGP, explains in detail how to configure external BGP (eBGP) to a single ISP and how to determine whether your address block shows up on routers in other networks The chapter provides examples of how to use a second router to connect to a second ISP and how to configure internal BGP sessions The chapter also describes a setup in which two BGP routers run the Cisco Hot... the Title of the Book, eMatter Edition Copyright © 2007 O’Reilly & Associates, Inc All rights reserved xi Chapter 10, BGP in Larger Networks, examines the challenges of designing a large, stable network It discusses BGP peer groups, use of loopback addresses for internal BGP (iBGP), iBGP scaling using route reflectors and confederations, and preservation of CPU cycles by dampening route flaps It also... and ran over TCP BGP Version 1 (RFC 1105) still had the notion of up, down, or horizontal relationships, as in EGP This limitation was abandoned in BGP- 2 (1163), along with major changes to the message formats BGP- 3 (RFC 1267) introduced, among other things, the BGP identifier field in the open message and defined how to use this field to decide which connection is terminated when two BGP neighbors each... Cisco BGP- capable platforms x | Preface This is the Title of the Book, eMatter Edition Copyright © 2007 O’Reilly & Associates, Inc All rights reserved Chapter 2, IP Addressing and the BGP Protocol, is about IP addressing and the inner workings of the BGP protocol, including the multiprotocol extensions and the BGP route selection algorithm The chapter ends with a discussion of previous versions of BGP. .. yourself There are some important disadvantages to using BGP A pessimist might say that you gain a lot of complexity to lose a lot of stability Implementing BGP shouldn’t be taken lightly Even if you do everything right, there will be times when you are unreachable because of BGP problems, when your network would have been reachable if you hadn’t used BGP There is a lot you can do to keep the number of... Associates, Inc All rights reserved Chapter 2 CHAPTER 2 IP Addressing and the BGP Protocol This chapter provides an overview of the IP address architecture and some interdomain routing history, followed by an explanation of the BGP protocol, information on how BGP relates to routing in general, and a discussion of Multiprotocol BGP IP Addresses IP addresses are made up of two parts: the network part and... book is to help you achieve common BGPrelated goals, such as reliability and balancing traffic over multiple connections, and provide an introduction into the world of interdomain routing The book is by no means a reference on the BGP protocol or BGP configuration on a Cisco router Consult the Cisco documentation at http://www.cisco.com for additional details on Cisco’s BGP implementation and IOS in general... that networks don’t care about the inner details of other networks Thus, instead of listing every router along the way, BGP groups network together within ASes so they may be viewed as a single entity, whether an AS contains only a single BGP- speaking router or hundreds of BGP- and non -BGP- speaking routers Figure 1-4 shows the differences between the two views: the EGP sees ASes as a whole; the IGP sees... the chapter are protecting BGP against problems caused by other networks, intentionally or unintentionally This includes extensive information on using BGP to deflect (Distributed) Denial of Service attacks Chapter 8, Day-to-Day Operation of the Network, talks about the requirements interdomain routing imposes on the Network Operations Center and how to manage day-to-day BGP operation This includes . Started with BGP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Enabling BGP 75 Monitoring BGP 78 Clearing BGP Sessions. Border Gateway Protocol (BGP) . The majority of this book deals with BGP in a practical, hands-on manner. My involvement with BGP started in 1995, when