We are encountering a strange issue with two servers running IIS 8.5 behind a load balancer where periodically both servers stop responding to any requests on port 80 for a short period of time (sometimes less than a minute). Any secure sites running on port 443 continue to work fine.

We have managed to reproduce this when we remote onto the servers and connecting to the local address of a site. Which rules out the load balancers being an issue.

Windows firewall is disabled on both servers although we do have Sophos Endpoint Security and Control installed.

Does any one have any suggestions?

Thanks Neil

  • If possible, disable Sophos and see if that resolves the problem. It could be that it's being a bit overzealous and temporarily blocking the ports. – Mr. Smythe Aug 26 '15 at 18:02
  • Thanks for the suggestion, we have finally managed to track this down to syn flood attacks. We ended up using Microsoft Message Analyzer to review the raw TCP traffic. – Neil Sep 8 '15 at 20:40

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