Dial-on-Demand Routing

Dial-on-demand routing (DDR) is useful in applications that don't require a permanent connection between two sites. This is often the case for small offices or home users who can't justify the expense of a permanent connection. Instead, communication is through some sort of dial-up terminal server using standard telephone service (either analog or ISDN). The router places a call when it has traffic to send and establishes an IP connection using PPP. When the connection is idle, the router should hang up automatically.[*]

[*] Newer services, such as xDSL and cable modems, could potentially reduce the need for dial-on-demand routing. Both of these services establish permanent connections at low cost. However, dial-up services will be with us for the foreseeable future, especially as a backup when DSL or cable service is down.

DDR is also useful for backup links; a router can establish a dial-up connection if a permanent, leased-line connection fails. It's also useful if you need to make connections to many sites through a limited number of modems or asynchronous ports.

Cisco's IOS support for dial-on-demand routing falls into two categories:


Legacy DDR

In legacy DDR, all the DDR commands are tied to a specific interface. This includes commands to set up dialer scripts, timeouts, dialer groups ("interesting" traffic), and other DDR information. Legacy DDR is supported from the earliest of IOS versions.


Dialer profiles

Dialer profiles allow you to create a single profile that contains all the DDR information necessary. The profile can then be applied across many dialer interfaces.

I'll cover both types in this chapter. But first, let's examine the basic DDR commands.

Getting Started

IOS Images and Configuration Files

Basic Router Configuration

Line Commands

Interface Commands

Networking Technologies

Access Lists

IP Routing Topics

Interior Routing Protocols

Border Gateway Protocol

Quality of Service

Dial-on-Demand Routing

Specialized Networking Topics

Switches and VLANs

Router Security

Troubleshooting and Logging

Quick Reference

Appendix A Network Basics


Cisco IOS in a Nutshell
Cisco IOS in a Nutshell (In a Nutshell (OReilly))
ISBN: 0596008694
EAN: 2147483647
Year: 2006
Pages: 1031
Authors: James Boney

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