5.4 Configuring Dial on Demand Routing (DDR)
5.4.4 Step 3 - Defining destination parameters

Once you define what constitutes interesting traffic, you must provide the interface responsible for initiating the call with all the parameters necessary to reach the destination. The dialer map command identifies destination router information, such as the phone number to dial:

Router(config-if)#dialer map protocol next-hop-address [name hostname] [broadcast] dial-string

The dialer map command has many other optional parameters available to it. However, these commands will suffice for most connections.

What are we mapping?  
Cisco commands often contain the word “map,” which is used to map statically Layer 2 addresses to Layer 3 addresses. For example, the command
frame-relay map is used to define a Layer 3 next-hop-address to its Layer 2 address-in this case, a DLCI number. With a dialer-map statement, you bundle a Layer 3 address (IP in this chapter) to a dial-up Layer 2 address (which, in this case, is a phone number).