The purpose of this short tutorial is to show you how to configure a dial on demand backup link on a Cisco router. For the purposes of the article the hardware used was a Cisco 1720 (12.3(26)) and a WIC T1-DSU and a WIC-1AM
Initial setup
I am starting from the point where I already have a working T1 connection. So the first thing to do is to configure the actual dial-up connection.
So firstly setup the async interface, in my case it was async2
interface Async2 ip address negotiated encapsulation slip dialer in-band dialer pool-member 1 async dynamic routing async mode interactive
Next configure up a dialler interface
interface Dialer0 ip address negotiated ip nat outside encapsulation ppp dialer pool 1 dialer idle-timeout 300 dialer string 12093361010 dialer-group 11 no cdp enable
Configure your LAN interface for NAT
interface FastEthernet0 ip nat inside
Now configure your chat script
chat-script sillyman "" "atdt 12093361010" TIMEOUT 60 "CONNECT"
And your NAT overload statement, access-list, and dialler-list
dialer-list 11 protocol ip permit access-list 101 permit ip 192.168.1.0 0.0.0.255 any ip nat inside source list 101 interface Dialer0 overload
Configure up the line interfaces
line 2 modem InOut modem autoconfigure discovery stopbits 1 speed 115200 flowcontrol hardware
Now tell your serial interface about your dial-up backup interface
int serial0 backup delay 10 10 backup interface Dialer0