Sample Legacy DDR Configurations

One common application for DDR is a dial-up connection to the Internet. Here’s a configuration that dials an ISP any time there is traffic that needs to go to the Internet:

! Define the chat scripts
chat-script modem1 "" "atz\r" OK "atdt \T" TIMEOUT 30 CONNECT \c
chat-script login1 TIMEOUT 20 login: "bob\r"  password: "mypassword\r"
! Set up the dialer interface
interface async1
   ! We are going to let the router negotiate its IP address through PPP
   ip address negotiated
   encapsulation ppp
        ! Enable dialing on this interface
   dialer in-band
        ! Set the idle timeout
   dialer idle-timeout 600
   ! Map our provider's IP address
   dialer map modem-script modem1 system-script login1 14105551212
   dialer-group 2
! Assign the dialer group to an access list
dialer-list 2 list 101
access-list 101 permit ip any any
! Set a default route
ip route async1

In some respects, this is a simpler configuration than the previous one. We use a negotiated IP address (i.e., an address assigned to us by the ISP) rather than specifying the address explicitly. We specify PPP encapsulation, but don’t do any special authentication; authentication is handled by a simple login sequence, which we implement in the chat scripts. This is typical of many ISP connections.

This configuration uses a few newer features of IOS. First, we have separated the chat script into two parts, a modem script and a system script, both of which are specified in our dialer map. This ...

Get CISCO IOS in a Nutshell now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.