(Any) Torrent cilent causing HTTP timeouts in Firefox/Safari

Discussion in 'macOS' started by otron, Apr 28, 2010.

  1. otron macrumors newbie

    Apr 28, 2010

    I'm a new to the mac world, having recently got a new 15" MBP with the Core i5 Processor.

    I've found some very strange behaviour that I'm trying to get to the bottom of, if anyone can help?

    When I have a torrent client running (utorrent or transmission), I get frequent HTTP timeouts in firefox and Safari. This happens regardless of whether the torrent client is actually transferring data.

    When I click on a link, in firefox I can see "connecting to www.google.com" for a long time - sometimes the link loads, sometimes it just times out. This happens 80%+ of the time.

    I should say that a PC on the same (WiFi) network is able to load these same pages at the same time, so the issue isn't down to connectivity.

    Has anyone seen this before?

    I phone apple support and unsurprisingly they weren't willing (so far) to go beyond checking the basics:
    - Creating a connection profile
    - Deleting my networking config
    - Rebooting on the Snow Leopard disk and checking filesystem permissions
    - Trying from a different account on the same machine.

    The guy on the phone told me he could go no further - I don't accept that an O/S should allow this to happen, no matter how errant an application might be, but I said I'd try to resolve this myself before I called back and argued the case.

    My next steps are to see if I can see anything in Netstat or wireshark.

    So ... If anyone has any experience or suggestions, I'd love to hear them.

  2. 92jlee macrumors 6502

    Sep 11, 2009
    Cardiff, Wales, UK

    This happens to me when I am downloading, but stops when I pause.

    I don't see why it would do that when there isn't network traffic, have you tried both LAN and WIFI?

    On another note, you seem to know your stuff, How can I change the QOS to allow HTTP browsing when I'm also torrenting?
  3. otron thread starter macrumors newbie

    Apr 28, 2010
    Hi 92JLee, All,

    Firstly, I'm afraid I have no idea about configuring QOS, but from what I understand it wouldn't solve the problem as QOS needs to be supported within the network on every router on the path... in other words, it doesn't work on the internet. The closest you can get to it is to use uTorrent which (on the PC version anyway) uses a new protocol called uTP, which is designed to allow non-torrent traffic to be unaffected during heavy torrenting.

    In any case, this is not the problem here. I've investigated my problem and it seems to be the same as yours - it only happens when a transfer is underway so I was mistaken in my original post.

    I've run a wireshark trace and can see that when a torrent is being transferred, the initial TCP SYN for my HTTP request is not getting a SYN ACK. I can see the TCP stack reattempting this SYN once per second to no avail. At the same time there are SYN's related to Torrent traffic working just fine.
    This all happens at very low torrent data volumes (several KB's) and with any combination of torrent client (Transmission or uTorrent) and browser (Firefox & Safari).

    It looks to be an issue with the Snow Leopard TCP/IP Stack to me.
  4. otron thread starter macrumors newbie

    Apr 28, 2010
    Replying to my own post with resolution information, for anyone who might have the same issue in the future.

    I isolated the problem to my broadband router. Once I disabled the 'Syn Flood protection' this problem disappeared. The router was obviously seeing multiple outgoing connection attempts and mistook them for malicious (why outgoing connection attempts should be filtered in this way is questionable anyway).

    What threw me is the fact that this only happens for Mac torrent clients, and not PC ones. Ah well ... I'm not bothered trying to see what the difference in behaviour is.
  5. CypherCS macrumors newbie

    May 11, 2011
    Hey Otron,

    Just registered to tell you that I have this same exact issue on a WinXP PC.

    So rest easy :)

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