Building Scalable Cisco Networks by Catherine Paquet, Diane Teare |, Paperback | Barnes & Noble
Building Scalable Cisco Networks

Building Scalable Cisco Networks

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by Catherine Paquet, Diane Teare
     
 

Prepare for CCNP or CCDP certification with the official BSCN Coursebook

  • Understand the principles of classful and classless routing and the difference between link-state and distance vector protocol behavior
  • Select and configure the appropriate services for simplifying IP address management at branch offices by proper address allocation and

Overview

Prepare for CCNP or CCDP certification with the official BSCN Coursebook

  • Understand the principles of classful and classless routing and the difference between link-state and distance vector protocol behavior
  • Select and configure the appropriate services for simplifying IP address management at branch offices by proper address allocation and summarization
  • Implement the appropriate technologies for a scalable, routed network that uses link-state protocols and redistribution
  • Configure edge routers to properly interconnect to a BGP network through either a single or multihomed interconnection
  • Control and optimize routing update information by implementing filters, metrics, and policy-based routing and changing administrative distance
  • Examine case studies that show you how to build a scalable internetwork including multiple routing protocols

Based on the new BSCN instructor-led course developed by Cisco Systems, Building Scalable Cisco Networks teaches you how to design, configure, maintain, and scale routed networks that are growing in size and complexity. This book focuses on using Cisco routers connected in LANs and WANs typically found at medium to large network sites. Upon completion of this book, you will be able to select and implement the appropriate Cisco IOS(r) Software services required to build scalable, routed networks.

As the replacement for the Advanced Cisco Router Configuration (ACRC) course, BSCN is one of four new courses recommended by Cisco for Cisco Certified Network Professional (CCNP) and Cisco Certified Design Professional (CCDP) preparation.

In Building Scalable Cisco Networks you willstudy a broad range of technical details on topics related to routing, including routing principles, IP addressing issues such as variable-length subnet masks (VLSMs), route summarization, and protocol redistribution. The routing protocols Open Shortest Path First (OSPF), Enhanced Interior Gateway Routing Protocol (EIGRP), and Border Gateway Protocol (BGP) are investigated in detail. Configuration examples and sample verification output demonstrate troubleshooting techniques, and a case study is used throughout the book to review key concepts and to discuss critical issues surrounding network operation. Chapter-ending configuration exercises and review questions illustrate and help solidify the concepts presented in the book.

Product Details

ISBN-13:
9781578702282
Publisher:
Cisco Press
Publication date:
10/27/2000
Series:
CCNP/Ccdp Certification and Training Series
Pages:
810
Product dimensions:
7.69(w) x 9.45(h) x 1.94(d)

Read an Excerpt


1. Routing Principles

This chapter covers the principles of routing. Classful and classless routing are reviewed, as are the differences between distance vector and link-state routing protocol behavior. Convergence issues surrounding the most commonly used interior routing protocols for the Internet Protocol (IP) are also presented.

After reading this chapter, you will be able to list the key information routers need to route data, describe classful and classless routing protocols, compare distance vector and linkstate protocol operation, and describe the use of the fields in a routing table. Finally, given a preconfigured network, you should be able to discover the topology, analyze the routing table, and test connectivity using accepted troubleshooting techniques.

Routing Fundamentals

This section reviews routing in general, the requirements for routing, and how routing decisions are made, including the use of administrative distance and metrics.

Routing Defined

Routing is a relay process in which items are forwarded from one location to another. In computer networks, user-generated traffic-such as electronic mail or graphic and text documents-is forwarded from a logical source to a logical destination. Each device in the network has a logical address so that it can be reached individually; in some cases, devices can also be reached as part of a larger group of devices.

For a muter to act as an effective relay device, it must have knowledge of the logical topology of the network and be capable of communicating with its neighboring devices. A router can be configured to recognize several different logical addressing schemes and to regularly exchange topology information with other devices in the network.

The mechanism of learning and maintaining awareness of the network topology is considered to be the routing function. The actual movement of transient traffic through the muter, from an inbound interface to an outbound interface, is a separate function and is considered to be the switching function. A routing device must perform both the routing and the switching functions to be an effective relay device.

NOTE: Appendix E, "Open System Interconnection (OSI) Reference Model," contains a review of the Open System Interconnection (OSI) reference model. Under this reference model, a router is an OSI Layer 3 device that has an understanding of the logical topology of the network. The routing and switching functions described here refer to the forwarding of a Layer 3 protocol data unit (PDU), also referred to as a packet (or datagram). A packet contains a logical source and a logical destination address that the routing device interprets during the packet forwarding process.

Routing Requirements

A router must know three items in order to route:

  • The router must determine whether it has the protocol suite active.
  • The router must know the destination network.
  • The router must know which outbound interface is the best path to the destination.

    For a routing device to make a routing decision, it must first understand the logical destination address. For this to happen, the protocol suite that uses that logical addressing scheme must be enabled and currently active on the router. Some examples of common protocol suites are Transmission Control Protocol/Internet Protocol (TCP/IP), Internetwork Packet Exchange (IPX), and Digital Equipment Corporation's DECnet.

    After the router can understand the addressing scheme, the second decision is to determine whether the destination logical network is a valid destination within the current routing table. If the destination logical network does not exist in the routing table, routing devices might be programmed to discard the packet and to generate an error message (for example, an IP Internet Control Message Protocol [ICMP] message) to notify the sender of the event. Some network managers have successfully reduced the size of their network's routing tables by including only a few destination networks and then specifying a default route entry. If specified, a default route will be followed if the destination logical network is not included as part of the device's routing table.

    The final decision that the routing device must make if the destination network is in the routing table is to determine through which outbound interface the packet will be forwarded. The routing table will contain only the best path (or paths) to any given destination logical network. The best path to a destination network will be associated with a particular outbound interface by the routing protocol process. Routing protocols use a metric to determine the best path to a destination. A smaller metric indicates a preferred path; if two or more paths have an equal lowest metric, then all those paths will be equally shared. Sharing packet traffic across multiple paths is referred to as load balancing to the destination. When the outbound interface is known, the router must also have an encapsulation method (in other words, a Layer 2 frame type) to use when forwarding the packet to the next-hop logical device in the relay path.

    Routing Information

    The information required to perform the routing operation is included in the router's routing table and is generated by one or more routing protocol processes. The routing table is composed of multiple entries, each of which indicates the following:

  • The mechanism by which the route was learned. Learning methods can be either dynamic or manual.
  • The logical destination, either a major network or a subnetwork (also called a subnet) of a major network. In isolated cases, host addresses may be contained in the routing table.
  • The administrative distance, which is a measure of the trustworthiness of the learning mechanism. Administrative distance is discussed further in the next section, "Administrative Distance."
  • The metric, which is a measure of the aggregate path "cost," as defined by the routing protocol. Routing metrics are discussed further in the section "Routing Metric," later in this chapter.
  • The address of the next-hop relay device (router) in the path to the destination.
  • How current the information about the route is. This field indicates the amount of time the information has been in the routing table since the last update. Depending on the routing protocol in use, route entry information may be refreshed periodically to ensure that it is current.
  • The interface associated with reaching the destination network. This is the port through which the packet will leave the router and be forwarded to the next-hop relay device.

    Administrative Distance

    The routing process is responsible for selecting the best path to any destination network. Because more than one learning mechanism can exist on a router at any given time, a method to choose between routes is needed when the same route is learned from multiple sources. For IP within a Cisco router, the concept of an administrative distance is used as a selection method for IP routing protocols.

    Administrative distance is used as a measure of the trustworthiness of the source of the IP routing information. It is important only when a router learns about a destination route from more than one source.

    Lower values of administrative distance are preferred over higher values. In general, default administrative distances have been assigned with a preference for manual entries over dynamically learned entries, and routing protocols with more sophisticated metrics over routing protocols with simple metrics. A comparison chart of the default administrative distances is presented in Table 1-2...

  • Meet the Author


    Catherine Paquet is a Senior Network Architect with Global Knowledge Network (Canada), Inc., Cisco's largest worldwide training partner. There, she provides consulting and training services to customers in North America and Europe. She was also a member of the team at Cisco Systems that developed the Building Scalable Cisco Networks (BSCN) instructor-led course.

    Catherine has in-depth knowledge of routing technologies and access services, mainly in the area of Frame Relay, ISDN, and asynchronous connections. Catherine's internetworking career started as a LAN manager; she was promoted to MAN manager and eventually became the nationwide WAN manager for a federal department. She currently is the course director/master instructor for the Building Cisco Remote Access Networks (BCRAN) and Managing Cisco Network Security (MCNS) courses at Global Knowledge Network (Canada) Inc. She has a master's degree in business administration, with a major in management information systems. Catherine edited Building Cisco Remote Access Networks and co-authored Building Scalable Cisco Networks, both from Cisco Press.

    Diane Teare is a Senior Network Architect with Global Knowledge Network (Canada), Inc., Cisco's largest worldwide training partner. There, she provides consulting and training services to customers in North America and Europe. She was also a member of the team at Cisco Systems that developed the Building Scalable Cisco Networks (BSCN) instructor-led course.

    Diane has more than 15 years of experience in design, implementation, and troubleshooting of network hardware and software. She also has been involved in teaching, course design, and projectmanagement. Diane is the course director/master instructor for the BSCN and Designing Cisco Networks (DCN) courses at Global Knowledge Network (Canada) Inc. She is a CCSI, CCDA, and CCNP, and has authored and edited networking books and articles. Diane has a bachelor's degree in applied science in electrical engineering and a master's degree in applied science in management science. She edited Designing Cisco Networks and co-authored Building Scalable Cisco Networks, both from Cisco Press.

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