Lower net.max_halfopen to 4 (Can be found in Preferences > Advanced)

[gunsmokez]

Hi

Well, I was having a problem with utorrent and browsing the internet so i did search and went through Ultimas guide. Well, i clicked a bunch of stuff from his guide and my internet is running again with my utorrent on. Now, the thing that helped was "Lower net.max_halfopen to 4 (Can be found in Preferences > Advanced)" .

Can someone tell me what i just did and why it worked. What is that max_halfopen?

Btw, thnx for the guide

[Falcon4]

It's a workaround for WinXP SP2's new "maximum half-open connections" limit. Going back to the all powerful phone system analogy to the internet, it's like the maximum number of "phones" your computer could be dialing at the same time and waiting for an answer. A half-open connection is one that's just ringing, and waiting for the computer to pick up. In the past, there was no limit, but since worms can spread by "dialing" random addresses and checking for replies (e.g. blaster), MS decided to cap the limit.

If you check your Event Viewer - Control Panel -> Administrative Tools -> Event Viewer - you might be seeing a large number of events described as "the security limit imposed on the maximum number of concurrent tcp/ip connection attempts has been reached". At this point, no more connections can be made and guess what? Your internet stops working too, since it revolves around making and breaking connections.

max_halfopen just sets the number of connections a Peer-to-Peer program will try making. Instead of using that, though, you should patch the tcpip.sys file that's responsible for limiting these connections - a good number is 100. http://www.lvllord.de/ is the site. Grab the patch and run it. Then set your max_halfopen to the number you chose, minus 10 to allow for happy web browsing ;-)

[Switeck]

Even if you patch windows half open limit to 100, there may be other networking software and hardware that cannot handle that rate.

Even assuming you have top-notch industrial-grade networking software and hardware, you will probably see a net LOSS in download+upload speed if µTorrent is set beyond 50 half open connections...on anything short of a T-3 line. (A T-3 line has 45 megabits/sec down and up bandwidth!)

So long as connections respond quickly, you can reach 100+ total connections in less than 5 minutes with net.max_halfopen set to 4. Also, if µTorrent is NOT firewalled (green light at bottom), you should be getting incoming connections from other peers+seeds connecting to (phone calling) you. These do not count against your half open limits. On very busy torrents with 10,000+ peers+seeds, this can actually be very bad...as your connection may be "hit" by 1,000+ connection attempts a minute. This would resemble a DDoS attack from your ISP's point-of-view.