I first heard of the Bogon list a few months ago when a network administrator for a company had contacted me in regards to customers not being able to reach my site. He said they had allotted new IP addresses to these customers that were recently released from the "Bogon List". I had no idea what the Bogon list was. (Google it for more information).
Well I have since learned that it is a reserved list of IP ranges that have not been allocated yet for public use. In the past they were commonly abused by DDOS attackers and because of this, many routers and ISP's will block them by default... In fact, they go a step further and ignore/drop all requests originating from these ranges to save on processing time... Since no one should be using them.
So why should we care about them? Well, as I recently discovered, it is common practice when a firewall is setup on a server to have this list included in the configuration as IP ranges that should be ignored.
Unknown to me when I bought my server last year and requested a firewall be installed, the Bogon list (at that time, one year ago) was configured as well within the firewall (APF on Linux).
As the months went by I did not notice any problems. But in the last few months I started finding some weird issues in other discussion forums. Folks were posting threads asking if my site was gone... saying they had not been able to access it in weeks. At first I thought it was isolated, but then I found more users posting around the web saying they could not get to our site. Luckily I stumbled across these posts, because the users themselves could not tell me about the problem, since they could no longer access my site.
Long story short, these users were using recently allocated IP addresses released from the Bogon list. My server was blocking them since I had not kept my firewall rules up to date. I had no idea this was something I even needed to worry about. It finally took a call from a Time Warner network guy to help me realize the problem was my server. My own ISP support team even told me it was not my server, they said they don't configure anything with Bogon directly on servers...
So at last I found the configuration file called "reserved-networks" (go figure!). In it contained the very old Bogon list. I was unknowingly blocking about 10 new IP ranges!
After removing the blocks, my traffic went up about 15% immediately. I started seeing comments on the site from users who were saying they had been trying to get to the site for months and now finally can access it again.
Moral of the story: Bogon can be your friend and your enemy... If you manage your own server with a firewall, make sure you know what is being blocked by default. If you block Bogon IP ranges, stay on top of the changes to that list. Every month or so new IP ranges get released and you might be blocking potential new customers.