<story><title>I may be the only evil (bit) user on the internet (2015)</title><url>https://blog.benjojo.co.uk/post/evil-bit-RFC3514-real-world-usage</url></story><parent_chain></parent_chain><comment><author>js2</author><text>Maybe 20 years ago now, I wrote a simple email-to-sms script that I ran from procmail. To send the email out as SMS, it connected to a Verizon web site. This was before Verizon provided their own email-to-sms gateway.&lt;p&gt;I wrote and tested the script under OS X and it worked fine. I then moved it to my Linux server on the same network and it couldn&amp;#x27;t connect to Verizon&amp;#x27;s web site.&lt;p&gt;After using tcpdump to figure out what the difference was, I noticed that Linux was setting the ECN bit. Verizon had a firewall in front of their site that was apparently dropping packets with the ECN bit set. ECN was only a couple years old at that point. I think I figured out that it was due to an out-of-date Cisco PIX firewall on the Verizon end, but I&amp;#x27;m not sure how I would have figured that out.&lt;p&gt;The solution was to disable ECN on the Linux box.&lt;p&gt;&lt;a href=&quot;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Explicit_Congestion_Notification&quot; rel=&quot;nofollow noreferrer&quot;&gt;https:&amp;#x2F;&amp;#x2F;en.wikipedia.org&amp;#x2F;wiki&amp;#x2F;Explicit_Congestion_Notificati...&lt;/a&gt;</text></comment>
<story><title>I may be the only evil (bit) user on the internet (2015)</title><url>https://blog.benjojo.co.uk/post/evil-bit-RFC3514-real-world-usage</url></story><parent_chain></parent_chain><comment><author>lucb1e</author><text>This is the sort of thing that comes back to bite you. Websites that you think are down and ignore for now, annoyed but ok happens, only to later notice it was your own doing.&lt;p&gt;I played this on myself by setting X-Forwarded-For: &amp;#x27;&amp;quot; which would trigger an sql error if someone assumes an IP address is safe to insert without escaping or parameterization. Very few sites broke, but the first one that did I remember sold TLS certificates.</text></comment>