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How to troubleshoot slow VPN connections

Suffering slow VPN connection? Try checking VPN concentrators and caching.

We are a small company with two remote offices: A head office in Calgary and remote offices in Vancouver and Houston....

We need them to connect to our server and use our database. We have installed VPNs, but a connection that takes 2.5 seconds in the main office takes 35 to 40 minutes in the remote offices. Is there another way of connecting our remote offices to our server and database?

Have you ever walked into the branch office only to see the employees huddled around the coffee pitcher? Or perhaps notice that suddenly everyone is leaning back in their chairs, flying paper airplanes across the cubes? Or the ultimate coup de grace of filling the vacationing coworkers cube with Styrofoam peanuts? If you have, it's probably not because they don't want to get work done and get home, but because they've launched the application and need to distract themselves for 30 minutes while it's loading due to a slow VPN connection.

When connecting remote users to hosted databases and servers in a central office, there are numerous technologies that can help you overcome these response time challenges. It is helpful to truly understand what the response time bottlenecks are before employing one of these options so that you are making an informed decision to alleviate your problem. The last thing you want to do is increase your bandwidth if your VPN concentrator is fragmenting packets due to a smaller MTU, for example.

Checking the VPN concentrators and router configuration

First you should investigate exactly how the network is configured and architected. Keeping the K.I.S.S (keep it simple silly) approach in mind, let's start with basic understanding of VPN connectivity. I would start first with the VPN concentrators to ensure that they are not dropping, fragmenting, or discarding packets. Depending on the data volumes transferred, VPN concentrators, routers, and interfaces may be under-sized to transfer data. In this investigation you might also find out that there are mis-configured routers or identify traffic that could be routed outside of the VPN.

In environments like this, I often recommend splitting your routing through the VPN. If you can, try routing internet transactions (web browsing, etc) through a separate route than going through the VPN connection. The VPN connection ideally would only be for accessing your internally networked applications.

Caching proxying for troubleshooting a slow VPN connection

While there are several ways to improve performance between central and remote sites, one popular method is to cache or proxy traffic. In larger environments technologies such as WAN optimization and caching tools make a lot of sense. However in this small office environment, one of the easiest things to deploy would be a Citrix Presentation server. Essentially the Citrix Presentation server would be deployed at the home office and users on the remote sites would connect to it and launch their connections to the servers and databases through it. With less overhead, this type of server will proxy your connection causing the server and database connections to be launched locally and reduce the amount of traffic sent across the VPN to the remote users

Essentially, by investing a little more time in understanding the architecture and deploying some optimization capabilities, you'll start to see improvements in the response times for the remote users accessing your servers in the main office. And then users will leave the peanut-filled cubicle pranks for after hours (in theory).

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This was last published in July 2010

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