Multi-homed networks require strong management

Filling your network pipes with multiple Internet service providers -- a strategy known as multi-homing -- may provide speed, backup and continual access to critical applications. Be prepared, however, to make an ongoing commitment to managing the process.

That's the advice of Clarence Briggs, founder of Web hosting company Advanced Internet Technologies (AIT) of Fayetteville, N.C. "With multi-homing, you have to manage your bandwidth, your load balancing and your distribution almost on a daily basis, because networks are dynamic," say Briggs. "Does a multi-homed network really provide redundancy? The answer is 'yes' if you manage it and 'no' if you don't."

AIT rents space on its computer equipment to more than 160,000 Internet domains around the world. Its multi-homed network includes four telecommunications providers -- AT&T, UUnet, Sprint, and Cwix -- to relay Internet traffic. "If any one of our providers goes down, we are able to balance the load and keep our customers up," says Briggs.

It's difficult to say definitively if Briggs's company represents a new trend in enterprise networking. Reliable data on the adoption rate of multi-homing is hard to come by, although there are signs the trend is growing -- at least among larger enterprises. Aside from using more than one ISP, a multi-homing strategy usually includes linking your network to an equivalent number of telecommunications companies. "We haven't collected any data on this, but anecdotally I would say most of the Global 3,500 companies probably are using multiple providers on their networks," says Jeanne Schaaf, senior analyst with Forrester Research Inc. in Cambridge, Mass. "They have to make sure their networks are reliable, available, and always up."

Also, the Internet Engineering Task Force has formed a working group to study the use of multi-homed networks. Their aim is to find ways to handle the growing burden placed on the Internet's routing table, says Randy Bush, who serves on the working group. That burden is traced to industry forecasts that suggest soaring Internet use will outstrip the handling capacity of existing routers.

Bush likens multi-homing to having more than one entrance into a building. "Ask your providers to show you the physical path your information is taking," says Bush, who also is a network architecture specialist with AT&T Labs Research in Seattle, Wash. "Multi-homing is about having technical diversity, physical diversity and telecom diversity."

Briggs agrees, noting that simply adding more ISP connections to your network server won't do the trick. For best results, he recommends having each ISP link to your local telecom through a dedicated, separate connection. Single-connectivity topography -- in which each ISP routes its traffic through the same local trunk line as competing ISPs -- is like throwing money away. AIT periodically requests updated topographic maps from its provider to ensure its connections are redundant. "If you're using three different ISPs, you need three different lines for each one -- not the same conduit for all three providers. That's not network redundancy," says Briggs.

The architecture of multi-homed networks relies on Border Gateway Protocol 4, designed to ensure proper Internet routing. Todd Hanson, an analyst with Stamford, Conn.-based Gartner, says companies wanting to multi-home need to enough RAM to accommodate a full-blown routing table.

"It is generally desirable to use (multiple) connections at the same time so they can be load balanced in some way," says Hanson. "Also, some form of scalable routing should be present so if one connection goes down the others maintain access to the Internet."

Provisioning network traffic across multiple Internet connections -- one for inbound traffic and another for outbound traffic, for example -- enables companies to upgrade their networks without triggering outages, adds Pepe Garcia, IP routing-protocol product manager with Cisco Systems' IOS Technologies Division in San Jose, Calif.

"Let's say you're using two links and both hit 50% capacity. You could shut down one and upgrade the other," without having to power down your enterprise, says Garcia.

Managing a multi-homed network could require an investment in your networking department, says Bush. This might mean adding staff or bringing existing personnel up to speed. Bush suggests weighing potential gains against cost factors to determine if multi-homing makes sense.

"Multi-homing (adoption) is directly related to the size of your IT staff. If you're a company that can't afford serious (investment in) networking staff, then you'll probably take whatever bandwidth you can afford and do the best you can with it," says Bush.

Briggs estimates maintaining a multi-homed network costs $40,000 to $60,000 a month, depending on different providers' rates and amount of bandwidth consumed. The type of transmission lined used is another potential cost factor.

Garcia says companies in a wide array of industries -- manufacturers, financial services, retailers and others -- have adopted multi-homing. The decision varies from business to business, with the size of your enterprise likely to play a role in the decision. "I would say a good barometer (for considering multi-homing) might be an enterprise with 25 to 50 people," Garcia says.

Schaaf says multi-homing could produce other benefits as market competition equalizes subscription prices and forces ISPs to meet heightened customer expectations. "Almost any astute buyer will have more than vendor, if only to keep the other vendors honest on price, service and quality," she says.

About the author: Garry Kranz is a freelance business and technology writer based in Richmond, Va. Contact him at gkranz@ureach.com