Multihomed corporate nets on the rise
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Back in 1995, EarthLink was a small, Southern California ISP with dreams of building a nationwide network and audience.To grow rapidly, EarthLink chose a novel approach of using multiple carriers, including UUNET, PSINet and Sprint, to create a large and reliable network for running Internet applications.
Today, EarthLink executives credit this approach - dubbed multihoming - as key to its success in attracting a customer base of more than 3.4 million.
Specifically, multihoming refers to the use of multiple ISPs to provide Internet access. The typical setup uses two ISPs: one for incoming Internet traffic and the other for outbound Internet traffic. Network engineers use high-end routers running the Border Gateway Protocol (BGP) to load balance the traffic between the ISPs. Most ISPs require a minimum of a T-3 line for multihoming.
"Multihoming allowed us to expand very quickly, and it allowed us to insulate our customer base from shortfalls in capacity to a greater degree than our competitors," says Jon Irwin, executive vice president of operations at EarthLink.
A growing number of dot-coms and large firms are copying the ISP industry and creating multihomed nets of their own. Among the users of multihoming are securities firm Smith Barney, online brokerage firm eTrade, e-commerce companies eBay and Amazon.com and high-tech giants IBM and Hewlett-Packard.
These companies are multihoming to improve the reliability of their Internet access, particularly between their data centers and carriers' point-of-presence (POP) sites where traffic enters the backbone of the Internet. What drives these companies to take on the technical and management challenges of multihoming is fear of catastrophic failures caused by fires, earthquakes or backhoes.
"We definitely see more customers wanting to be connected - multihomed - to different ISPs due to the fact that more mission-critical applications are going on the Internet . . . and companies can't afford downtime," says Alan Bavosa, group product manager of access services for Concentric, a San Jose company that provides Internet business solutions. "As companies fill up their pipes with one ISP, it's a good, sound business strategy to diversify and to move some pipes to another ISP so they don't have all their eggs in one basket."
The rise in multihomed networks is shown in data gathered by the American Registry for Internet Numbers (ARIN). Each multihomed net requires an Autonomous System Number (ASN) assigned by ARIN. ASNs are unique numbers used to identify systems that can exchange exterior routing information with neighboring ASN-qualified systems.
ARIN President Kim Hubbard says the growth in ASN assignments is directly tied to the rise in multihomed networks. The amount of ASNs assigned each month by ARIN has grown sharply since January 1999 (see graphic). This year is on track to be a record breaker. Altogether, ARIN has assigned more than 12,000 ASNs.
But multihoming is not a trend that ISPs like to discuss. They prefer to tout the reliability of their own networks and their high-availability offerings. ISPs also are quick to reference customers that are giving them exclusive deals rather than multihomed arrangements where they carry half or less of a company's traffic.
But companies with multihomed networks view those networks as the only way to guarantee 100% uptime. Multihoming also helps companies reduce their Internet access costs by pitting ISPs against each other to bid on additional capacity.
24/7 Mail uses a multihomed net to run an e-mail marketing service that sends more than 25 million messages per day. The Denver division of 24/7 Media uses two ISPs, Verio and Rocky Mountain Internet, to carry the outbound e-mail traffic via dual DS-3 lines at 45M bit/sec each. 24/7 Mail has two Cisco 7206 VXR routers that run BGP V4. Two network engineers manage the Cisco routers and monitor route balancing.
"We've been multihomed for about two years because there is no ISP or local-loop provider that can provide the highest level of availability," says Lonnie Maynard, chief technologist at 24/7 Mail. "We've had no downtime since we put this strategy in place."
Maynard expects by next year his network will carry 100 million messages per day and require bandwidth of 175M bit/ sec. "My strategy is only to connect to tier-one ISPs that prove they have sufficient bandwidth and peering relationships," Maynard says.
Healtheon/WebMD takes multihoming a step further by using five ISPs - UUNET, Sprint, Qwest, @work and AT&T - to carry traffic to and from its Santa Clara data center. The medical Web site moves traffic between the carriers to avoid outages and optimize network performance.
"We can sometimes manipulate routing to avoid congested public peering points to improve performance," says Steve Curd, chief information officer at Healtheon/ WebMD. He says points where major Internet carriers connect to each other "experience congestion very often, adding to the network latency and degrading network performance."
Although it ensures reliability, multihoming has its drawbacks. It requires high-end routers and network engineers who know BGP and understand the Internet's routing system. Companies also can run into problems with IPv4 Internet address space, particularly if it was delegated from an ISP rather than ARIN.
Companies also face management challenges in getting multiple ISPs to work together to solve problems. That's why ISPs push alternatives to multihoming, such as collocation, mirrored data sites, hot and cold back-up sites and multiple access lines to POPs.
Pete Charbonneau, network and systems administrator at Williams College in rural Massachusetts, tried multihoming but switched back to one ISP after multihoming became too expensive. In 1999, Williams College employed two T-1 lines - one from GTE and one from Cable & Wireless - to provide Internet access to its 3,500 users.
"We did it for redundancy purposes and to increase our bandwidth," Charbonneau says. "But it was costing us $4,000 a month for one of our T-1s and $2,800 a month for the other T-1. That's a very costly proposition to [multihome] out in the sticks where no one wants to serve us."
So this year Charbonneau purchased three T-1 lines from Cable & Wireless, using inverse multiplexers to handle failover if any of the lines go down. "It's easier to get redundancy from one carrier," he says.
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