6.4 Scaling Dial-on-Demand Routing
6.4.3 The hardware solution
A Cisco AS5100 is installed at the central site to provide 48 asynchronous interfaces. The Cisco AS5100 consists of three access server cards based on the Cisco 2511 access server, making the Cisco AS5100 equivalent to three Cisco 2511 access servers. Each access server card provides 16 asynchronous lines. Each asynchronous line is equipped with a built-in U.S. Robotics Courier modem.

Note: For the purposes of this case study, the three Cisco AS5100 access server cards are referred to as the central-site access routers.

Each remote site is equipped with a Cisco 1020 router. The Cisco 1020 provides a single asynchronous interface and an Ethernet interface for connecting to the remote site LAN. The Cisco 1020 runs a limited set of protocols, including TCP/IP and RIP. U.S. Robotics Sportster modems provide connectivity at the remote sites. Using the same brand of modem throughout the access network simplifies chat scripts and modem definition, and makes the network more manageable.

A Cisco 4500 controls routing between the new access portion of the network and the backbone. In particular, the Cisco 4500 ensures that when hosts on the other side of the backbone need to connect to a remote site, the connection is made through the optimum central-site access router. The Figure shows the topology of the access portion of the network.