Symptoms Website randomly goes down a few times a week Server stopped responding Network and CPU logs show a small spike, but not enough to lock up a server Stopping and starting the server resolves the problem Details This pattern repeated several weeks until the customer grew tired of rebooting the server. The evidence did not seem to lead to a system issue or network or security security problem such as a denial of service.

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The phrase, “I can’t access my shared drive” was intermittent, but becoming common for a remote location connected via an MPLS circuit. Without hesitation the finger was pointed at the network and my phone rang. People connect to shared drives everyday, but it is one of those things they take for granted. Behind the scenes there are many layers of technology, protocols, and devices working together to make those connections happen.

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One of the most common problems any IT admin faces is a software update. While software updates are generally considered a good thing, because they patch security flaws, fix bugs, try to improve performance, and more, they are also a common source of problems. Every admin knows to be ready for calls after a scheduled maintenance window. This issue was no different.   A ticket came in stating users could not access a web app through the backend system after an upgrade to Java 1.

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Problem I have come to expect vague error messages that seemingly blame the network. This one is no different. Server Error in ‘/’ Application. The network path was not found Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.ComponentModel.Win32Exception: The network path was not found

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Have you ever had a nightmare where you are being chased and you can’t just seem to run away fast enough? No? Well, maybe you’ve tried running through snow up to your knees or swimming while wearing jeans. All of those examples point to situations that feel like something isn’t quite right. Cases where there could be better performance if only something was changed or improved. Sometimes this same thing happens to network devices.

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Several hundred users lost network connectivity. They went down randomly, one by one, and over a short period of time. Some users had intermittent connectivity. All of the network devices were online and functional. Users were roaming the halls and getting bored. This called for a packet capture, but with clients offline it had to be done on a network switch. In this instance, the capture was performed at the distribution switch on the layer 3 VLAN.

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While the general rule of thumb is to capture at the client, or at least start there, sometimes it’s necessary to take captures at both ends of a connection. The client perspective will allow you to view the problem as it is seen from the client. The server perspective might show the same thing. Or, in some cases like this one, it will provide the reason for the problem. The problem was that a webpage wouldn’t load.

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Author's picture

Chris Sereno

For 11 years networking was my profession with a specialized focus on proactive and reactive performance analysis. More recently I have embraced the AWS platform. This blog reflects my experience both past and present.

AWS Architect at Caterpillar, Inc.

US