5.5 Static and Default Routing
5.5.6 Configuring a router for initiating an ISDN call
Some basic configuration is necessary on a router in order for DDR to function correctly. Figure shows the topology of router-to-router DDR. The configuration shows how you can combine commands to set up ISDN and DDR. DDR is configured to connect Cisco-a to Cisco-b by using legacy DDR, which uses dialer map statements. Table describes the commands used in the configuration.

Note: Click on the topology to view router configurations.

In Figure , the network between the serial interfaces of the two routers uses eight bits of subnetting. Static route statements define the IP route to the Cisco-b LAN interfaces over 192.168.1.0. Interesting traffic is defined as any IP traffic that initiates a DDR call to Cisco-b.

The number dialed is for the remote ISDN device. The service provider offering the ISDN service provides this number. Traffic is routed to the LAN shown on the right in Figure . Before a connection can be made, static routes of how to reach those networks must be in place. When Cisco documentation mentions legacy DDR, it refers to configurations that use dialer-map statements.

Lab Activity 
  The Denver office needs to control what interesting traffic will bring up the ISDN connection to the Phoenix office. You will setup an extended ACL and apply it to the dialer group.