Chapter 8. Configuring Border Gateway Protocol


Terms you'll need to understand:

  • Border Gateway Protocol version 4 (BGP-4)

  • Exterior Gateway Protocol (EGP)

  • BGP speakers

  • BGP peers or neighbors

  • Open message

  • Notification message

  • Update message

  • Keepalive message

  • Autonomous system number (ASN)

  • Path vector protocol

  • Interior Border Gateway Protocol (IBGP)

  • Transit AS

  • Multihomed AS

  • Attributes

  • Synchronization

  • Black hole

  • Peer group

  • Community

Techniques you'll need to master:

  • Understanding the process for connecting to other autonomous systems

  • Knowing the basics behind BGP routing policy functions

  • Understanding how BGP synchronization works

  • Understanding BGP peering functions with peer groups and communities

  • Configuring and verifying BGP

As you have learned so far, routing involves the transport of packets and the determination of optimal routing paths through an internetwork. A key protocol that addresses the mission of path determination in modern internetworks is the Border Gateway Protocol (BGP). Presently, four versions can run on a Cisco router. This chapter focuses on the default standard BGP as defined in RFC 1771 ”BGP version 4, or simply, BGP-4. BGP achieves interdomain routing in TCP/IP networks.

Routing protocols are often categorized according to whether they are exterior gateway protocols or interior gateway protocols. Interior gateway protocols (IGPs) are needed to share information within (intradomain) an autonomous system. Interior routing protocols are implemented to learn the internal network topology and IP subnet information to maintain loop-free networks. Some common examples of IGPs are RIP, IGP, OSPF, and EIGRP. Exterior gateway protocols (EGPs), on the other hand, are utilized to exchange information between (interdomain) multiple autonomous systems and to maintain loop-free paths. BGP is a prime example of an exterior gateway protocol.

BGP-4 offers a lot of improvements and enhancements over other routing protocols. This is the primary reason that it is used over the Internet to connect ISPs and enterprise internetworks. As you have learned, OSPF and EIGRP are interior routing protocols, whereas BGP is considered an exterior routing protocol. OSPF is a link-state protocol that uses cost for a metric, whereas EIGRP and BGP are in a category of advanced distance vector protocols with several enhancements. EIGRP uses a composite metric of bandwidth and delay. BGP uses network reachability information called path vectors (or attributes ) for its metric. These attributes include an inventory of the full path that a route takes to reach a destination. Another comparison is that OSPF requires a hierarchical design for proper address summarization, whereas EIGRP and BGP do not need a hierarchy. OSPF uses cost, which on Cisco routers is based on bandwidth, as its metric. EIGRP uses a composite metric, similar to the IGRP metric.

The acronym EGP has a dual meaning in that it also stands for an obsolete protocol that was developed in the beginning phases of the Internet to isolate networks from each other. The BGP routing protocol is a chief successor to this Exterior Gateway Protocol (EGP). BGP was intended to replace the now obsolete Exterior Gateway Protocol (EGP), as the standard exterior gateway “routing protocol used in the global Internet. BGP solves serious problems with EGP and scales to Internet growth more efficiently . In this book, the acronym EGP refers to a generic exterior gateway protocol such as BGP.




Cisco BSCI Exam Cram 2 (Exam Cram 642-801)
CCNP BSCI Exam Cram 2 (Exam Cram 642-801)
ISBN: 0789730170
EAN: 2147483647
Year: 2003
Pages: 170

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