Broken pages nowadays account for half of my nightmare support scenarios, you know those ones where you have half loaded, broken or endlessly loading pages. This is usually accompanied with a comment about how its fine on the users 3G/DSL/whatever network.  In the past this was usually more likely to be a MTU related issue, but with the proliferation of CDN hosting nowadays, your more likely suspect is now a broken path to a CDN.

The situation in South Africa lends itself to this as some of the larger ISP’s have private CDN deployments alongside open peered deployments. Often a user is trying to get content from a CDN they should not have access to, or a CDN that is not optimal. Sometimes this is because of bad CDN configuration but more often than not its because your users are not using the correct DNS servers for resolution.

CDN relies heavily on DNS for being able to determine the origin AS and location of a request, and then replies based on this information accordingly.  Google and OpenDNS are often culprits here as well intentioned users love to use these (I blame google for making it so easy with 8.8.8.8). While extensions to DNS have helped with being able to identify the source of the request the issues are not completely gone and will continue to rear their head for some time still. I have also seen scenarios where domain controllers are set up to use one network provider (DNS settings included) while LAN users use a different provider/gateway (aka you), meaning the domain controller gives DNS responses to your clients from a server on a different network altogether

The tools I usually for troubleshooting these kinds of issues are

• dig/nslookup to check resolution discrepancies between you and the client network.
• The browsers developer view. Just head on over to the sources tab and see what resources the page is actually loading, gone are the days of simple sites, all sites now include content from all over the show for advertising, tracking and to load balance.
• http://www.cdnplanet.com/tools/cdnfinder/ . It lets you point it to a web site and it reports what external resources the site uses and what CDN’s those resources are on.

If this doesn’t resolve your issues then possibly your issue is with your upstream providers. They either have a broken transparent application cache/accelerator (good luck finding someone there that knows something about them) or you are running on a seriously messed up bonded link. I have dealt with both of these before and maybe I will share more on this another day.