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Providing QoS with Diffserv in ISA 2004

One of the new features in ISA 2004 SP2 is Diffserv. Diffserv is a method of packet prioritization that applies to all web traffic passing through an ISA 2004 SP2 Server. Using the Diffserv Web filter, the ISA server can scan the Uniform Resource Locator (URL) or domain name and apply packet priority using DiffServ bits.

The Diffserv web filter has been given a high priority, and is near the top in the list of Web filters. The Diffserv web filter must be made aware of the size of the request/response being sent and has to inspect the data when it is being sent/recieved by the ISA server. It is crucial that you do not change the priority of the Diffserv web filter. Before we get started configuring this, you should be aware of the following: – Diffserv prioritization only applys to HTTP and HTTPS traffic – ISA may strip Diffserv bits for traffic using other protocols – First packet priority is not assigned to responses coming from the cache – By default, the size of the first chunk is not taken into account for first packet priority To begin, open the ISA Management MMC and expand the Configuration node and then click on General. Click on Specify Diffserv Preferences.

On the General tab, ensure the box next to “Allow the setting of Diffserv bits according to URLs and domain names” is checked.

On the Priorities tab, click Add to create a priority. Enter the name for the priority and the Diffserv Codepoint. The Codepoint is a 6-digit binary value which specifies the priority level. There is more information about the different Diffserv Codepoints at the end of this article. For this example we will use 100110 which is one of the high priority Codepoints.

Add another priority called Low and give it a value of 001010.

Next select the URLs tab and click Add. Enter the URL (wildcards are supported) and choose one of the priorities you created in the previous steps.

Here I have added two URLs, one with high priority and one with low.

URL Diffserv settings only apply to HTTP traffic. If you wish to set priorities to HTTPS traffic you must use the Domains setting.

Finally, under the Networks tab, you can choose which Network Sets to apply the Diffserv filter to.

Once you are done configuring the Diffserv preferences, apply the configuration to the ISA server and you are good to go!

For more information see: 

QoS and Diffserv Codepoints

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