Another important part of network design is reliability. Even small businesses often rely on their network heavily for business operation. A failure of the network can be very costly. In order to maintain a high degree of reliability, redundancy is required in the network design. Redundancy helps to eliminate single points of failure. There are many ways to accomplish redundancy in a network. Redundancy can be accomplished by installing duplicate equipment, but it can also be accomplished by supplying duplicate network links for critical areas, as shown in the figure.
The smaller the network, the less the chance that redundancy of equipment will be affordable. Therefore, a common way to introduce redundancy is through the use of redundant switch connections between multiple switches on the network and between switches and routers.
Also, servers often have multiple NIC ports that enable redundant connections to one or more switches. In a small network, servers typically are deployed as web servers, file servers, or email servers.
Small networks typically provide a single exit point toward the Internet via one or more default gateways. With one router in the topology, the only redundancy in terms of Layer 3 paths is enabled by utilizing more than one inside Ethernet interface on the router. However, if the router fails, the entire network loses connectivity to the Internet. For this reason, it may be advisable for a small business to pay for a least-cost option account with a second service provider for backup.