You do multihoming for the same reason that you have multiple servers, RAID disk storage, automated daily data backups, backup batteries and even backup power generation. It's for protection. The more you have to lose, the more important it is that you protect your enterprise from any single failure that will stop your operation dead in its tracks.
How important is the Internet to your company? What happens if you lose your Internet connection? If the answer is just a minor inconvenience and you can easily wait for service restoration, then you might be perfectly happy with DSL or Cable Modem service. They're your least costly access. If that's not good enough, then get a fractional or full T1 line with a service level guarantee. Order ISP and web services from the highest reliability providers you can. Still not good enough? You need multihoming.
The important concept with multihoming is diversity. You want separate T1, T3 or OC3 dedicated lines running to different ISPs located in different geographical areas. Those ISPs should have at least partially different backbones to the Internet. Don't buy two telco lines on the same pole or in the same trench. Any accident or back hoe dig can cut both your lines and you'll be no better off than before.
The technical magic of multihoming uses BGP or Border Gateway Protocol within the routers to advertise routes with different IP addresses from different ISPs to and from your location. If one ISP goes down, the routing will redirect traffic through the other. Some companies go further to add RO or Route Optimization in addition to BGP. RO lets you balance loads, select a preferred provider for particular traffic like VoIP, and get the most bandwidth from your two or more Internet connections.
If you would like to explore the possibilities of ISP multihoming for your network, we have experts available to assist you. Please enter a request at T1 Rex.
