1.4 Selecting Cisco Remote Access Solutions
1.4.3
Determining the appropriate interfaces - modular interfaces
If you select a fixed-configuration router, you receive the router with the interfaces on the box. However, you cannot add or change interfaces on a fixed-configuration router. Modular routers and access servers are usually built with one or more slots that allow you to customize the box.

You can determine the types of interfaces on the router by selecting various feature cards, network modules, or WAN interfaces, such as those shown in the Figure. Although modular routers require more equipment than fixed-configuration routers, they are more scalable and will allow your network to grow.