6.4 Scaling Dial-on-Demand Routing
6.4.9 Configuring the remote site routers
With the exception of the host name and the IP address of the Ethernet interface of each remote site router, the configuration of each remote site router is the same.

Chat Script Configuration for Dialing the Central Site
The configuration of each remote router includes the
chat-script global configuration commands shown in Figure . The chat-script command defines a chat script named CENTRALDIAL that is used to place calls to the central site. The CENTRALDIAL chat script specifies the telephone number (555-1111) of the central site and the expect-send sequences that guide the modem through the dial-up process. A key feature of the chat script is that when the remote router receives the string > (the prompt indicating that the remote site router has successfully logged in to a central-site access router), the remote router sends the EXEC command ppp 172.16.2.1. This informs the central-site access router of the remote router's IP address.

Configuring the Asynchronous Interface
The configuration of each remote router includes the commands shown in Figure that configure the asynchronous interface. The
speed line configuration command sets the baud rate to 38400 bits per second for both sending and receiving. The modem-type command specifies the initialization string sent to the modem when the interface is reset or when a clear interface async command is issued. The initialization string is defined by the modem-def command for usr-sport-v32. The dialer rotary-group interface configuration command assigns asynchronous interface 1 to dialer rotary group 1.

Using the Site Command
The configuration of each remote router includes the
site configuration commands shown in Figure . The site global configuration command defines a remote location that the router can dial in to or that can dial in to this router, or both, and names it CENTRAL. The name is used to authenticate the central site when it dials in.

The dial-on site configuration command uses the demand keyword to specify that the central site is to be dialed and a connection established only when packets are queued for the central site. The encapsulation site configuration command specifies that when the router establishes a connection with the central site, it is to use PPP encapsulation.

The ip address interface configuration command associates IP address 172.16.1.1 with the CENTRAL site. Note that IP address 172.16.1.1 is the address of the dialer 20 interface on each of the central-site access routers. The routing rip interface configuration command and the broadcast keyword specify that when the router is connected to the central site, IP routing updates are to be broadcast, but any incoming IP routing updates are to be ignored.

The dial-group command specifies that dial group 1 is to be used when connecting to the central site. Earlier in the configuration, the dialer rotary-group command assigned asynchronous interface 1 to group 1.

The session-timeout site configuration command specifies that if a period of five minutes elapses during which there is no input or output traffic, the router is to close the connection. The system-script site configuration command specifies that the CENTRALDIAL chat script is to be used to dial the central site. The password site configuration command specifies that when a central-site access router logs in, its password must be the string "secret."

Static Routing Configuration
The configuration of each remote router includes the
ip route global configuration commands shown Figure . The ip route commands establish static IP routes for networks located at the central site, all reachable through a next-hop address of 172.16.1.1, which is the IP address shared by all of the access routers at the central site. All ip route commands specify an administrative distance of 1, which is the default.