Recently I had problems with a web server denying connections (HTTP error 406) from a certain IP address.
At first I thought it was because of some wacky firewall or tcpwrapper rule.
I couldn't be more wrong - It was mod_security verifying the remote IP against Spamhaus RBL...
While it may seem like a good idea at first, turns out it is not:
1. Because it slows down the request (as Apache has to lookup IPs against the RBL all the time).
2. Some IPs are in a RBL for the wrong reason.
As it turns out that particular IP belongs to BT,
and BT in their infinite wisdom decided to list in Spamhaus a good part of their IP space... Cool, huh?
More info here (and a screenshot for posterity here).
You got to love the corporations!
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