Bandwidth Monitoring and IIS

posted on 16 December 2007 | posted in Performance

Bandwidth Monitoring and IIS Any web server should be configured to cope with large scale traffic. The amount of traffic your server receives depends on the popularity of the websites being hosted, the content they show, and how they have been developed.

We wrote earlier about caching for database-driven websites to help reduce CPU overhead. Now we want to talk about bandwidth monitoring - helping you identify websites that may be needlessly using up a lot of bandwidth.

Firstly, we make the assumption that the web host is also the web developer for the sites being hosted. This is becoming more common now, and we make this assumption, because this article talks about tweaking website content to optimize bandwidth usage.

Setting up bandwidth monitoring

Firstly make sure logging is switched on in IIS. You can do this by going into IIS, then right-clicking in "Web Sites" and selecting Properties. You will now see a checkbox with "Enable logging" next to it. Make sure it is checked.

Next you will need software to read the website log files and extrapolate bandwidth information from them. We use Live Bandwidth and find it to be adequate for bandwidth monitoring which breaks bandwidth down by website, and by time (individual days, or from date A to date B). We don't want to plug one particular solution, so you can see for yourself other solutions via a Google search : bandwidth monitor solutions found via Google Search.

Any decent bandwidth monitor solution will breakdown bandwidth usage by website, and also by time.

Once you have this kind of information in front of you, you can start to see which websites are using up the most bandwidth. One particular sign to look out for:-

  • a website uses up a lot of bandwidth in relation to the number of visitors it receives

This may be because it is hosting large files such as PDF files for users to download. If this is the case, you'd expect high bandwidth usage per user. However, it could be that the site has unoptimized images on its pages. It's not uncommon to find websites with thumbnail images that are over 1MB in size! It doesn't look obvious because of the physical size of the image on the page, but its actual size is a lot bigger (it's just that the image has been forced down to a physically small size). WYSIWYG editors are notorious for causing such problems. The website admin thinks the editor is great because they can upload a large image, then reduce it in physical size while editing the page. The problem is, it's not actually reducing the file size, just the physical size of the image. Such images waste bandwidth needlessly. There are other areas that waste bandwidth:-

  • Hosting of videos - not really necessary these days with the likes of offering free storage
  • Automatic playing of Flash files that contain large mp3 files/video (hosted on the server)
  • Unoptimized images


Bandwidth monitoring is about understanding how your server's bandwidth is being used by your websites, and identifying bandwidth wastage and reducing bandwidth by tidying up any websites that needlessly use up a lot of bandwidth.

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