A scalable network requires a hierarchical network design. The focus of the preceding chapters was on the access and distribution layers. As shown in Figure 1, Layer 2 switches, link aggregation, LAN redundancy, and wireless LANs are all technologies that provide or enhance user access to network resources.
Scalable networks also require optimal reachability between sites. Remote network reachability is provided by routers and Layer 3 switches which operate in the distribution and core layers as shown in Figure 2. Routers and Layer 3 switches learn about remote networks in one of two ways:
- Manually - Remote networks are manually entered into the route table using static routes.
- Dynamically - Remote routes are automatically learned using a dynamic routing protocol such as Enhanced Interior Gateway Routing Protocol (EIGRP) or Open Shortest Path First (OSPF).