Dial-on-Demand routing refers to a collection of Cisco features that allows two or more Cisco routers to establish a dynamic connection over simple dialup facilities on an as-needed basis and is used for low-volume, periodic network connections over an ISDN network or Public Switched Telephone Network.
There are five basic steps of DDR operation:
- The route to the destination is determined
- Interesting packets dictate a DDR call
- The dialer information is looked up
- Traffic is transmitted
- The call is terminated
There are three stages for configuring legacy DDR:
- Define the static route
- Specify interesting traffic
- Configure the dialer information
When using static routes, all participating routers must have static routes defined so that they can reach the remote networks. This requirement is necessary because static routes replace routing updates
Interesting traffic, which triggers a DDR call, is designated by an administrator and can be defined on the basis of a variety of criteria, such as protocol type or addresses for source or destination hosts.
The dialer information configuration process consists of four steps:
- Select the physical interface for the dial-up line
- Configure its network address
- Configure the encapsulation type
- Link the interesting traffic definition to the interface
To configure legacy DDR, define the static routes with the, ip route command, specify interesting traffic with the dialer list command, and configure dialer information with the dialer group command