performance analysis

Where do TCP resets come from?

I recently came across an excellent article on the topic of TCP resets. TCP is a connection-oriented protocol as opposed to the connectionless nature of UDP. So, if there are TCP resets on your network, this is not a bad thing and is just inherent in the protocol. Without TCP resets, a host could have a lot of partial connections established which are in the wait state awaiting further transmissions. This can exhaust the number of available sockets and cause the host to become unresponsive. This is what happened several years back with the TCP SYN flood and LAND denial of service attacks. Another reset type includes the ACK/RST. This is where a client attempts to connect to a service that is not available on that destination host.

If you manage a network and have taken packet captures to work on a problem and have seen RST packets or if you need to do this at some point in your career, you need to understand the purpose and source of the RST packets. Take a few minutes, read this excellent article that is the best explanation that I have seen on this topic. You will become better informed and better able to understand the nature of the network beast.

Where do resets come from? (No, the stork does not bring them.)

Thanks for reading and let’s continue to be good network citizens.

Performance monitoring dashboard - fping and URL ping

In part one of this series, I discussed ping and pathping. These tools are good for some interactive realtime testing. However, what do you do when you want to run these types of tools over an extended period and then do statistical analysis? In cases like this I use the fping tool. I recently completed an analysis task requiring comparison of network ping times against web server response times. The tool I used for measuring webserver response (time to first byte) is called URL ping. Users were reporting slow webserver (Sharepoint) performance. Everyone was saying it is a network issue. Since there are so many “moving” parts between the users and the webserver farm, I wanted to prove to them that the network was not the issue but that something inherent in the way the webserver responds to the requests is the real issue.

Continued »

Did you see this? - Free Wireless LAN planning, deployment and management tools

Xirrus is a WLAN equipment manufacturer. They have some very cool products and if you have not checked them out and are looking for installing, adding or replacing any WLAN network gear, then I suggest you take a look at their offerings before making a decision.

Xirrus has a page on their website where they offer some cool free tools for planning, deploying and managing wireless networks. The tools will work on any 802.11 wireless network as well as on wired networks. Some of the tools available include:

Xirrus Wi-Fi Inspector
The Xirrus Wi-Fi Inspector is a powerful tool for managing and troubleshooting the Wi-Fi on a Windows XP or Vista laptop. Built in tests enable you to characterize the integrity and performance of your Wi-Fi connection.

Xirrus Wi-Fi Monitor Gadgets/Widgets
The Xirrus Wi-Fi Monitor allows you to monitor your Wi-Fi environment and connection in real time from your desktop in an easy-to-use mini-application. Nine different color skins allow you customize the Wi-Fi Monitor to your desktop

Iperf
Iperf is an easy to use and very popular tool that every IT professional should have that measures maximum throughput. Iperf provides you the data to tune TCP and UDP characteristics. Iperf reports throughput, delay jitter, and datagram loss in easy to understand tables and graphs. You can run Iperf from and command line or a GUI interface.

Qcheck
Qcheck is a must have and handy tool for any IT professional. It does much more than the traditional “ping” command

Other tools are available on this excellent website. I recommend that you take a few minutes, review the offerings and add to your toolbox those tools of value to you.

Thanks for reading and let’s continue to be good network citizens.