Hashemian Blog
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Wednesday, July 28, 2004
DDoS – Deliberate Denial of Service
A week ago one of our salespeople approached me with a simple question. Some of the people in his client company were unable to browse to our company’s Web site. He was rather embarrassed at the prospect that our company’s Web site (and by extension, our company) could be viewed as shaky and unreliable.
While I am biased, I believe our Web site is highly reliable and it operates as flawlessly as they come. Sure, there are the occasional hiccups, but in most cases reported issues have been at the users’ end and not ours.
So after carefully examining the Web server and running some internal and external tests, I declared our systems healthy and asked the salesperson to relay the findings back to the company. We all agreed that our Web site appeared completely accessible. Even employees from other departments at the same company had no problems reaching our site. The problem was spotty and I speculated that the company’s IT department should be able to resolve it rather quickly.
But a few days later I received an interesting email from their IT manager. They had inspected their systems and had found no issues on their end. They were prepared to dig deeper into the problem, but they made a simple request first. “I would like to ensure that you are not blocking [our IP address] in an ACL list on your ingress router.”, the email requested.
“Impossible”, I thought. But just to humor him I logged on to the firewall and looked up the deny list. And there it was, their IP address almost at the top of the list with my own note from over a year ago declaring it a rogue address due to packet flooding. Turns out that their network had caught a virus at that time and was flooding us causing a denial of service, and that had landed them in our deny list.
This incident is now resolved, but I wonder how many deny lists like ours are there with old, dated, or even wrong information. It's a deliberate type of denial of service or reverse denial of service that can hamper progress on the Internet just as much as the real thing can.
At least it keeps us employed.
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// posted by rh
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