The XP SP2 Half Open Connections Limit Myth

I still see this bandied about as a possible factor in slow P2P speeds. It is easily misunderstood, but the half open connections limit imposed by XP SP2 and Vista does not matter for P2P speeds. It limits the rate at which connections can be made, not the total number of simultaneous connections.

Now, 10 half open connections seem a little low, but most ordinary users do not need more than this. Even heavy P2P users such as myself.

I usually run eMule and Bittorrent at the same time and I do not usually partake in very popular torrents (my usual haunts: Pleasuredome and DIME; what would I do without you guys?) but I usually have no problem maxing out the bandwidth available to my 3 Mbps connection. Sure, the clients spin up a little slower than before but how does it matter? I wasted maybe two or three minutes? The other negative side effect would be the occasional 4226 error in the Event Log, but I don’t care about that.

I am not denouncing LvlLord’s patch as evil as I really do not care if everybody installs it, but it won’t increase your P2P speeds. It won’t make your computer run better. It won’t solve the global poverty problem and it definitely won’t make you more popular with the gents/ladies.


  1. I’ll second that. I reduced the number of half open connections in my bittorrent client to 6. Reasoning: to avoid winxp’s delays imagined to be associated with managing half open connections at the limit… and letting the bittorrent client manage it. My upload speed is easy at 90KB for direct uploads, but my ISP damages that for torrent activity. For torrents I set max upload to 5KB!! Guess what.. the client attaches and maintains connection to more seeds this way and download speeds are in the 50 to 300KB/sec zone depending on swarm size. I see no change in how fast connections are made.. and they seem to be more reliable. Maybe someone technical can comment.

  2. erv: It is recommended that you limit your upload speed to 80% of your maximum possible upload speed, so that could be what gave you the improvement.

  3. How do you explain the fact that without the patch, even at low bittorrent speeds, my browser surfing slows to nil, but with the patch, I have full browsing speed and full downloading speed? Coincidence? Come on.

  4. bsj2312: Of course I can’t explain it when I don’t have the specifics of your system configuration.

    Not changing the limit is working out well for me and numerous others so I’m thinking it could be something else, your upload limit perhaps? But hey, if you think the patch works out well for you, more power to you.

    That said, after my original post I discovered that Vista Home Basic’s limit is 2, which *is* way too low. Another reason why Home Basic is a joke of an OS.

  5. You guys seem to overlook the fact that while a program like a p2p app is constantly making and therefore saturating the half-open attempts limit, other programs are slowed (technically, delayed, which appears to the user as being slow because it takes a long time to get anywhere) such as a web browser, which itself is trying to make multiple simultaneous connections out (and many users tweak that value up to make web pages download faster)!

  6. NW: Of course if you don’t apply the patch, it follows that you should limit the half open connections settings for your P2P applications to below your hard OS limit. Most new P2P applications installations default to below 10.
    And don’t forget, this is a limit on half open connection attempts, not a limit on connection attempts. There is a difference.
    As I stated though, if you think it works better, more power to you.

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