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572 Appendix D: Comparisons of Dynamic Routing Protocols

RIP Version 2

RIP Version 2 (RIP-2), as currently defined in RFC 2453, defines several enhancements to the original RIP protocol, which is called RIP Version 1. (Chapter 5 covers RIP Version 1 details.) Like RIP-1, RIP-2 uses distance vector logic; uses hop count for the metric; sends full, periodic updates; and still converges relatively slowly.

RIP-2 does add support for VLSM, as compared with RIP-1, making it a classless routing protocol, with RIP-2 including the subnet mask for each subnet in the routing updates. Table D-2 outlines the improvements made to RIP with the creation of RIP-2.

Table D-2 Improvements Made to RIP by RIP V2

Feature

Description

 

 

Transmits subnet mask with

This feature allows VLSM by passing the mask along with

route

each route so that the subnet is defined exactly. It allows

 

VLSM, making RIP-2 a classless routing protocol.

 

 

Provides authentication

Both clear text (RFC-defined) and MD5 encryption (Cisco-

 

added feature) can be used to authenticate the source of a

 

routing update.

 

 

Includes a next-hop router IP

A router can advertise a route but direct any listeners to a

address in its routing update

different router on that same subnet.

 

 

Uses external route tags

RIP can pass information about routes learned from an

 

external source and redistributed into RIP. Another router

 

then can pass these external tags to that same routing

 

protocol in a difference part of the network, effectively

 

helping that other routing protocol pass information.

 

 

Uses multicast routing updates

Instead of broadcasting updates to 255.255.255.255 like

 

RIP-1, the destination IP address is 224.0.0.9, an IP multicast

 

address. 224.0.0.9 is reserved specifically for use by RIP-2.

 

This reduces the amount of processing required on non–RIP-

 

speaking hosts on a common subnet.

 

 

The most important feature comparing the two is that RIP-2 supports VLSM. Today, when choosing a routing protocol, RIP-1 would not be the best choice—in fact, the RIP- 1 RFC has been designated for historic status. Both protocols work well, but RIP-2 is more functional. If you want a routing protocol that uses a public standard and you want to avoid the complexity of link-state protocols, RIP-2 is your best choice today.

Routing Protocol Overview 573

The Integrated IS-IS Link State Routing Protocol

Once upon a time, the world of networking consisted of proprietary networking protocols from the various computer vendors. For companies that bought computers from only that one vendor, there was no problem. However, when you used multiple vendor’s computers, networking became more problematic.

One solution to the problem was the development of a standardized networking protocol, such as TCP/IP. Skipping a few dozen years of history, you get to today’s networking environment, where a computer vendor couldn’t sell a computer without it also supporting TCP/IP. Problem solved!

Well, before TCP/IP became the networking protocol standard solving all these problems, the International Organization for Standardization (ISO) worked hard on a set of protocols that together fit into an architecture called Open System Interconnection (OSI). OSI defined its own protocols for Layers 3 through 7, relying on other standards for Layers 1 and 2, much like TCP/IP does today. OSI did not become commercially viable, whereas TCP/IP did—the victory going to the nimbler, more flexible TCP/IP.

So, why bother telling you all this now? Well, OSI defines a network layer protocol called the Connectionless Network Protocol (CLNP). It also defines a routing protocol—a routing protocol used to advertise CLNP routes, called Intermediate System-to- Intermediate System (IS-IS). IS-IS advertises CLNP routes between “intermediate systems,” which is what OSI calls routers.

Later in life, IS-IS was updated to include the capability to advertise IP routes as well as CLNP routes. To distinguish it from the older IS-IS, this new updated IS-IS is called Integrated IS-IS. The word integrated identifies the fact that the routing protocol can exchange routing information for multiple Layer 3 routed protocols.

IS-IS and OSPF are Link State protocols. Link-state protocols prevent loops from occurring easily because each router essentially has a complete map of the network. If you take a trip in your car and you have a map, you are a lot less likely to get lost than someone else who is just reading the signs by the side of the road. Likewise, the detailed topological information helps link-state protocols easily avoid loops. As you will in chapter 5, the main reasons that distance vector protocols converge slowly are related to the loop-avoidance features. With link-state protocols, those same loop-avoidance features are not needed, allowing for fast convergence—often in less than 10 seconds.

574 Appendix D: Comparisons of Dynamic Routing Protocols

Integrated IS-IS has an advantage over OSPF because it supports both CLNP and IP route advertisement, but most installations could not care less about CLNP, so that advantage is minor. Table D-3 outlines the key comparison points with all Interior routing protocols for both Integrated IS-IS and OSPF.

Table D-3 IP Link-State Protocols Compared

Feature

OSPF

Integrated IS-IS

 

 

 

Period for individual reflooding of

30 minutes

15 minutes

routing information

 

 

 

 

 

Metric

Cost

Metric

 

 

 

Supports VLSM

Yes

Yes

 

 

 

Convergence

Fast

Fast

 

 

 

Summary of Interior Routing Protocols

Before finishing your study for the INTRO or CCNA exam, you will learn a lot more about RIP-1, IGRP, EIGRP, and OSPF. This appendix has introduced you to some of the key terms and points of comparison for these routing protocols, as well covering a few details about other routing protocols. Table D-4 summarizes the most important points of comparison between the interior routing protocols, and Table D-5 lists some of the key terminology.

Table D-4 Interior IP Routing Protocols Compared: Summary

 

 

 

Supports VLSM and

Default Period

Routing

 

Convergence

Is a Classless

for Full Routing

Protocol

Metric

Speed

Routing Protocol

Updates

 

 

 

 

 

RIP-1

Hop count

Slow

No

30 seconds

 

 

 

 

 

RIP-2

Hop count

Slow

Yes

30 seconds

 

 

 

 

 

IGRP

Calculated based

Slow

No

90 seconds

 

on constraining

 

 

 

 

bandwidth and

 

 

 

 

cumulative delay

 

 

 

 

 

 

 

 

EIGRP

Same as IGRP,

Very fast

Yes

N/A

 

except multiplied

 

 

 

 

by 256

 

 

 

 

 

 

 

 

OSPF

Cost, as derived

Fast

Yes

N/A

 

from bandwidth

 

 

 

 

by default

 

 

 

 

 

 

 

 

Integrate

Metric

Fast

Yes

N/A

d IS-IS

 

 

 

 

 

 

 

 

 

 

 

Routing Protocol Overview 575

Table D-5 Routing Protocol Terminology

 

 

 

 

Term

Definition

 

 

 

 

Routing protocol

A protocol whose purpose is to learn the available routes, place

 

 

the best routes into the routing table, and remove routes when

 

 

they are no longer valid.

 

 

 

 

Exterior routing protocol

A routing protocol designed for use between two different

 

 

organizations. These typically are used between ISPs or between

 

 

a company and an ISP. For example, a company would run

 

 

BGP, an exterior routing protocol, between one of its routers

 

 

and a router inside an ISP.

 

 

 

 

Interior routing protocol

A routing protocol designed for use within a single

 

 

organization. For example, an entire company might choose the

 

 

IGRP routing protocol, which is an interior routing protocol.

 

 

 

 

Distance vector

The logic behind the behavior of some interior routing

 

 

protocols, such as RIP and IGRP.

 

 

 

 

Link state

The logic behind the behavior of some interior routing

 

 

protocols, such as OSPF.

 

 

 

 

Balanced hybrid

The logic behind the behavior of EIGRP, which is more like

 

 

distance vector than link state but is different from these other

 

 

two types of routing protocols.

 

 

 

 

Dijkstra Shortest Path First

Magic math used by link-state protocols, such as OSPF, when

 

(SPF) algorithm

the routing table is calculated.

 

 

 

 

Diffusing Update Algorithm

The process by which EIGRP routers collectively calculate the

 

(DUAL)

routes to place into the routing tables.

 

 

 

 

Convergence

The time required for routers to react to changes in the

 

 

network, removing bad routes and adding new, better routes so

 

 

that the current best routes are in all the routers’ routing tables.

 

 

 

 

Metric

The numeric value that describes how good a particular route

 

 

is. The lower the value is, the better the route is.

 

 

 

A P P E N D I X E

Configuring Cisco

1900 Switches

In years past, Cisco used the Catalyst 1900 switch line as the recommended switches in their courses relating to CCNA. The 1900 series is no longer a reasonable choice when purchasing a new switch from Cisco – in fact, you cannot even buy a new one any more. So, Cisco has added coverage of both 1900’s and 2950 series switches to their courses, so the Cisco Learning Partner teaching the course can effectively use an older lab, or update their labs and use the more modern 2950 switches. In the end, Cisco simply wants you to learn the types of things you configure on a switch – so using an older model can still be useful for learning.

We strive to ensure that all possible exam topics are included somewhere in these books, even the ones that may be less likely to be on the exams. So, while you’ll find lots of coverage of 2950’s in the main chapters, the 1900 coverage is relegated to this appendix. Simply put, the topics in this appendix could be covered on one of the exams, but the investment of study time in these topics may not be worth the return. For those of you who want to be super-prepared, this appendix lists some pertinent details about 1900 series switches.

Basic 1900 Switch Configuration

On the Catalyst 1900 switch, three different configuration methods exist:

Menu-driven interface from the console port

Web-based Visual Switch Manager (VSM)

IOS command-line interface (CLI)

578 Appendix E: Configuring Cisco 1900 Switches

As mentioned earlier, this chapter focuses on using the CLI to configure the switch. Table E-1 lists the switch commands referred to in this section.

Table E-1 Commands for Catalyst 1900 Switch Configuration

Command

Description

 

 

ip address address subnet-mask

Sets the IP address for in-band management

 

of the switch

 

 

ip default-gateway

Sets the default gateway so that the

 

management interface can be reached from a

 

remote network

 

 

show ip

Displays IP address configuration

 

 

show interfaces

Displays interface information

 

 

mac-address-table permanent mac-address

Sets a permanent MAC address

type module/port

 

 

 

mac-address-table restricted static mac-address

Sets a restricted static MAC address

type module/port src-if-list

 

 

 

port secure [max-mac-count count]

Sets port security

 

 

show mac-address-table {security}

Displays the MAC address table; the security

 

option displays information about the

 

restricted or static settings

 

 

address-violation {suspend | disable | ignore}

Sets the action to be taken by the switch if

 

there is a security address violation

 

 

show version

Displays version information

 

 

copy tftp://host/src_ file {opcode [type module]

Copies a configuration file from the TFTP

| nvram}

server into NVRAM

 

 

copy nvram tftp://host/dst_ file

Saves a configuration file to the TFTP server

 

 

delete nvram [type module]

Removes all configuration parameters and

 

returns the switch to factory default settings

 

 

Default 1900 Configuration

The default values vary depending on the features of the switch. The following list provides some of the default settings for the Catalyst 1900 switch. (Not all the defaults are shown in this example.)

IP address: 0.0.0.0

CDP: Enabled