Multi-homed networks are increasingly popular because they provide networks with better reliability and performance to the end-user. This is accomplished by having multiple connections to the Internet via multiple ISPs to deliver reliable and high-throughput service. Better reliability results from the fact that the network is protected in case one of the Internet links or access routers fails. If a connection with one ISP is lost or degraded, companies can automatically redirect traffic to links that are functioning. When more bandwidth is required, companies just add additional links. There are up to five ways to multi-home, but the two most common are:

• Using multiple links with a single IP address: This requires the use of multiple routers and a protocol called the Border Gateway Protocol (BGP). With this type of multi-homing, the end-site announces this address space to its upstream links. When one of the links fails, the BGP protocol notices this on both sides and traffic is no longer sent over the failing link. For reasons due to the complexity of this technique, it can take as long as 30 minutes to redirect traffic to a functioning link. Usually this method is used to multi-home a single site, and not for single hosts.
• Using multiple links, multiple IP addresses: This method uses a specialized WAN Optimization Controller (WOC) with link load balancing capabilities that is located between the firewall and the link routers. No special configuration is required in the ISP's routers. Using a WOC with link load balancing capabilities allows businesses to use all the links at the same time to increase the total available bandwidth (bandwidth aggregation), and detects link saturation and failures in real-time to redirect traffic. Incoming link load balancing is usually performed with real-time DNS (Domain Name System) resolution.

FAQ terms to describe WAN optimization