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Many minds, one goal: Curb bad traffic

By , Network World
July 11, 2005 12:06 AM ET

Network World - CAMBRIDGE, Mass. - Some of the best Internet minds in the world met for the first time last week to brainstorm new ways to defend against 'Net-clogging threats.

The Usenix invitation-only workshop - called Steps to Reducing Unwanted Traffic on the Internet (SRUTI ) - brought together more than 50 technical staff from equipment vendors and ISPs, as well as academics from all over the world, to develop practical methods to cut down on spam, viruses, worms and denial-of-service attacks. (Sruti, by the way, is a Sanskrit word meaning "that which is heard".)

Participants exposed fresh ideas to expert criticism, sometimes resulting in helpful suggestions and sometimes pointing out significant problems.

One promising proposal would help wipe out the bulk of distributed DoS attacks near their sources, but not those attacks in which the aggressor machines use spoofed IP addresses. Even though the proposal wouldn't block all attacks, it was still considered feasible because it would mitigate the bulk of distributed DoS exploits that rely on networks of unspoofed zombie machines - botnets - to fire off the attacks.

On the flip side, another presentation advanced a relatively simple method of encrypting e-mail that would also authenticate the sender and receiver. But this was pretty much shot down when one attendee pointed out that encrypting e-mail would render useless spam filters that search content and subject lines for key words. "You have just proposed an excellent tool for spammers," he said. The author didn't have an answer for that.

Practicality seemed the watchword for the day. The author of the presentation on blocking distributed DoS attacks said there have been proposals that would be extremely effective if there were separate IP address spaces for servers and clients. "This has real possibilities if only we were redesigning the Internet from scratch," says Mark Handley, a researcher from University College London in the U.K., who presented the proposal.

Instead, his proposal would introduce devices near Internet servers and at the edge routers of ISPs to mark and monitor traffic to the servers. When a distributed DoS attack was detected, these devices would block at the edge routers traffic from addresses identified as the source of the attack. These devices could effectively reduce distributed DoS traffic within a single ISP's network, Handley says. This enforcement could be extended to other ISPs and block attacks even closer to the source if the ISPs involved could develop enough trust to share knowledge about their networks, he says.

Dealing with spam

While distributed DoS drew much attention, SRUTI presenters also focused on spam, which accounts for the vast majority of e-mail crossing the Internet.

One researcher described a way to analyze the senders and recipients of e-mails in conjunction with a traditional spam filter to boost the overall effectiveness of spam protection. The algorithm reduces the amount of good e-mail that is identified as spam by about 20%, according to Jussara Almeida, a researcher at Universidade Federal de Minas Gerais in Brazil. "This is important since the cost of false positives is usually believed higher than the cost of false negatives," she said.

The study by her team divided senders and recipients into groups based on who routinely receives legitimate e-mail from whom. The memberships of these groups - essentially contact lists - are more stable than criteria used for other screening methods such as looking for keywords, Almeida said. Spammers can change the words selected for spam to duck keyword filters, but establishing themselves as members of trusted groups is more difficult, she said.

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