Internet service providers (ISPs) say the routers that form the backbone of the global network are being stretched to capacity by the enormous routing tables and complex calculations required to send information to the right places. And at current growth rates, demand for online access will begin to overwhelm the backbone of the Internet as early as next quarter, according to sources.
Routers at peering centres, where large ISPs exchange information, have to keep track of approximately 35,000 possible routes, which are updated constantly. "Routing tables on the backbone routers are relatively near capacity," says Robert Berger, founder of InterNex Information Services, an Internet services company in Santa Clara, California. "This is the most dangerous issue on the Internet today."
These central devices, most of them Series 7000 or 7500 routers made by Cisco Systems, make the Internet what it is today. To keep track of the best way to send information across the complex network, the routers must constantly update routing tables, which contain information on the layout of the network. Cisco's Internetwork Operating System software uses complex algorithms to calculate these routes.
Many recent Internet traffic problems have been the result of "routing flaps", which occur when routers repeatedly crash, recover and then send rapidly changing path information to other routers. "Sometimes even a Cisco 7000 can't deal with current loads effectively," says a systems administrator at another regional ISP. "Routing flaps can drive the CPU mad on one of those."
Some ISPs, overwhelmed by the volume of traffic, are using reflective routing to reduce their own loads. When traffic destined for another ISP's network arrives at the router, reflective routing does not send the traffic on to the destination ISP but bounces it back where it came from, further complicating the work of the Internet's routers.
Efforts by Cisco and ISPs have helped to slow the growth of routing tables and solve capacity problems in the short term. Cisco's 7500 router, introduced late last year, improved on the performance of the 7000 with a more powerful RISC processor. Large ISPs that have installed the 7500 say that with 64Mb of RAM, it can handle today's Internet routing tables.
But those tables keep growing, despite the work of the Internet Engineering Task Force to slow their expansion. Classless interdomain routing, an IETF initiative to place all Internet addresses in logical blocks, has slowed the exponential growth of routing tables, says Gordon Cook, editor and publisher of The Cook Report on the Internet, in Ewing, New Jersey.
However, this simpler addressing means some inconvenience for users. When an organisation moves to a new ISP, it must now give up its IP addresses for new ones that fit into the new ISP's block. Despite these temporary fixes, finding routes across this rapidly expanding network is becoming increasingly tough. And barring any major advances in router algorithms from Cisco, sources within the company say they expect an increasing number of Internet brownouts next quarter, particularly with the beginning of the school year.
"It's getting more difficult," says Morgan Littlewood, director of the ISP marketing group at Cisco. "We're getting more experience in the real world."