There are many types of infrastructure routers available. In fact, Cisco routers are designed to address the needs of:
- Branch - Teleworkers, small business, and medium-size branch sites. Includes Cisco 800, 1900, 2900, and 3900 Integrated Series Routers (ISR) G2 (2nd generation).
- WAN - Large businesses, organizations, and enterprises. Includes the Cisco Catalyst 6500 Series Switches and the Cisco Aggregation Service Router (ASR) 1000.
- Service Provider - Large service providers. Includes Cisco ASR 1000, Cisco ASR 9000, Cisco XR 12000, Cisco CRS-3 Carrier Routing System, and 7600 Series routers.
The focus of CCNA certification is on the branch family of routers. The figure displays the Cisco 1900, 2900, and 3900 ISR G2 family of routers.
Regardless of their function, size or complexity, all router models are essentially computers. Just like computers, tablets, and smart devices, routers also require:
- Operating systems (OS)
- Central processing units (CPU)
- Random-access memory (RAM)
- Read-only memory (ROM)
A router also has special memory that includes Flash and nonvolatile random-access memory (NVRAM).