Having multiple connections to the Internet via multiple providers to provide a reliable and high throughput service. Multi-homed networks are increasingly popular because they provide networks with better reliability and performance to the end-user. 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 still functioning. When more bandwidth is required, companies just add more 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 protocol notices this on both sides and traffic is no longer sent over the failing link. For reasons due to the complexity of the 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 Link Load Balancer appliance (such as PowerLink) between the firewall and the link routers. No special configuration is required in the ISP's routers. Using a load balancer device 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. Algorithms allow traffic management. Incoming load balancing is usually performed with real-time DNS (Domain Name System) resolution.
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