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  • SeqAnswers connectivity problems

    For a few weeks now we've been experiencing consistent connectivity problems to SeqAnswers from our institute. I've been chasing this up with our networking people who say that they can't see any reason for the problem at our end so I'd like to try to track this from the SeqAnswers side as well. All page loads are currently taking around 30 seconds, but generate no errors and the site works normally (if very slowly).

    As far as we can tell it's only SeqAnswers which is affected - we've not seen similar behaviour on other sites, and the problem seems to be related to our site, in that if I go to the site from my home connection then it's back to normal levels of responsiveness. Unfortunately the problem is bad enough that several people here have basically stopped using the site from work, which is a shame as they were making heavy use of it before.

    I've tried to collect some useful diagnostic information to try to localise where the problem is happening, and have stuck some data up on our website.

    We've tried running a traceroute to seqanswers but it looks like a server somewhere close to your site swallows the UDP packets so we can't get a full trace - but it looks quick enough up to that point.

    I've also done a wireshark packet capture of a simple GET request for your index page. Looking at the results (which you'll need to view in wireshark) it looks like it takes 29 seconds to get an ACK response to our initial GET request which really does make it look like it's the seqanswers end which is taking the extra time - though I'm guessing our setup might be related.

    If I were to take a wild guess I'd note that this slowdown happened at about the time we make some big DNS changes on our site. Is it possible that seqanswers is doing a reverse lookup on our IPs when we access the site, and that this is timing out each time we make a request?

    I'm happy to spend some time debugging this as I'd like to get our users back on the site - any help we can get from the seqanswers end would be much appreciated.

    Thanks

    Simon.

  • #2
    Another side effect, a lot of the time now, when I write a new post I get an error after about 30 seconds saying:

    This forum requires that you wait 30 seconds between posts. Please try again in 15 seconds.

    So it looks like something is trying to process my request twice?

    Comment


    • #3
      Simon: I wonder if the hosting provider for SeqAnswers.com is using some list of domains that are flagged/blacklisted for spam/network attacks. Your institute's domain may have got on that list for some reason, affecting connectivity.

      We have seen this locally when an email provider like Yahoo periodically blacklists the entire university domain because of a perceived spam threat. It takes some time to convince Yahoo that it is not the case. This generally affects email delivery to yahoo.com addresses but I wonder if same could apply to connectivity.

      Comment


      • #4
        I guess we could be being greylisted (the site does work eventually so we're not being blocked) by whoever is hosting the server, but normally those sorts of blocks are temporary and expire after a while, and this has been going on for weeks. In any case we'd need the cooperation from someone on the seqanswers side to find this out for us.

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        • #5
          I had been seeing problems where the site would take ages to connect, making it frustrating to use. I'm glad to say it seems to work far better now and I am back online with everyone at SEQanswers.
          I've even posted a couple of responses today.

          Comment


          • #6
            Hey guys, sorry about the issues. Simon/James as far as I've heard you're the only reports of slowness...but I'll look at your tracert and see if my host has anything to offer as far as a solution.

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            • #7
              Can you ping ds1715.dreamservers.com and see if it's just as slow?

              Comment


              • #8
                I can't ping ds1715.dreamservers.com from here, but if I try to ssh to it it takes about 30 seconds to get a login prompt, so I guess whatever issue we're seeing affects that too.

                Comment


                • #9
                  We've now managed to get onto a machine which doesn't block our ping packets, and the ping times to ds1715.dreamservers.com is about 1.5ms so the basic connectivity is fine, and there's something about the interaction with the web server itself which is slow.

                  Comment


                  • #10
                    Thanks Simon. Can you email or PM me the IP address you're having problems accessing the site from?

                    Comment


                    • #11
                      Oh and your packet capture doesn't appear to be a packet capture to me...looks like a text capture of some HTML of the front page.

                      Comment


                      • #12
                        The capture file is a tcpdump capture file which you'd view in wireshark. The only bits which are human readable are the text parts which are sent by your sever which is why it looks like that in a text editor. I'll see if I can export a completely text version for you if you'd prefer that.

                        The problem seems to be affecting the whole of our IP range which is 149.155.144-151.* If you want to investigate a single IP then you can try 149.155.147.36 which is the linux development box where I did the packet capture and on which I've just reloaded the home page.

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                        • #13
                          I've put up a full text version of the capture here. You should be able to view this just in a browser.

                          Comment


                          • #14
                            Thanks again Simon. Support tickets have been filed, I'll let you know.

                            Comment


                            • #15
                              I'm in between James and Simon, closer to James actually but it was working fine today and for the past few weeks I don't remember any problems.

                              Must be Babraham rd.....

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