Internet gridlock escalates, ISPs predict autumn Web brownouts
By Stephen Lawson
Posted at 10:02 AM PT, Jul 15, 1996
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
And at current growth rates, demand for online access will begin to overwhelm
the backbone of the Internet as early as this fall, according to sources.
Routers at peering centers, where large ISPs exchange information, have to
keep track of approximately 35,000 possible routes, which are updated
"Routing tables on the backbone routers are relatively near capacity," said
Robert Berger, founder of InterNex Information Services Inc., an Internet
services company in Santa Clara, Calif. "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 Inc., 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,"
said 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, said Gordon Cook, editor and publisher of The Cook Report on Internet,
in Ewing, N.J.
However, this simpler addressing means some inconvenience for users. When an
organization 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
this fall, particularly with the beginning of the school year.
"It's getting more difficult," said Morgan Littlewood, director of the ISP
marketing group at Cisco. "We're getting more experience in the real world."