Internet Redundancy 101
Sure your data is backed up... but how's your Internet connection?
Internet redundancy comes in many types and flavors, most common methods are BGP (Border Gateway Protocol) and link balancing.
Border Gateway Protocol
BPG is a complex routing protocol which is used by the Internet to push dynamic routing updates between core routers and different ISPs. When used with a small organization BPG is typically used to provide failover between two Internet connections. BGP is very useful for providing failover, however it does not do a good job load balancing traffic.
BPG has several resource requirements, including a fast and powerful edge router, an AS number which is granted by ARIN, and cooperation between two or more ISPs which are deliverying the two or more Internet connections.
The advantages of BGP is that it can handle very large networks and the failover management is very simple, once it is setup all of the routing is handled dynamically. The disadvantages of BGP is that it can not be used for load balancing in most circumstances, it is also very difficult to setup and in most instances is not something an IT manager will want to attempt. Just getting an AS number can take months and the entire process will be very expensive.
Link Balancing
Link balancing leverages a network appliance at the edge of a companies network to connect two or more ISP connections and is able to utilize both links at the same time using various routing techniques. Link balancing is also able to perform failover by using a form of dynamic DNS.
Unlike BGP link balancing does not require extensive resources and is typically less expensive to implement. Additionally link balancing does not require ISP cooperation or AS numbers, etc.
The advantages of link balancing include faster link failover, full utilization of each WAN link, lower cost, and overall much simpilar installation. The disadvantages include inbound failover requires DNS name not IP address, and more complexity and management for very large networks, i.e. with many servers and/or networking subnets.
Summary
In general link balancing is a better solution for small to mid-sized companies and/or enterprises which do not have many network subnets or large numbers (hundreds) of servers requiring inbound connectivity. For ISPs or organizations with many sub-networks or users behind many levels of networks, each of which are routed together using existing network protocols, then BGP is a better solution.