Right, so this is a lesson of “It’s obvious when you think about it”.

The new company that I work for have had a policy of adding the IP addresses of their gateways to the Sitecore.Analytics.ExcludeRobots.config file. The idea behind this is that we don’t want to pollute customer’s analytics data with traffic from ourselves, particularly if we are running health monitoring service that occasionally polls their website. That all seems sensible enough.

Here’s the problem – our tester was trying to test some of the pages we’d built on a live site. There was a problem with that – more in a later post – but the upshot was that it appeared that on two identical devices (iPhones) one would work, and the other would receive the yellow screen of death. A straw poll of iPhones in the office showed 3 working, and 3 failures. Curious…

After much head-scratching it hit me – the difference between the devices was the network they connected over. If using 3G, 4G or the Guest wireless, all was good. If using the Office wireless, the devices didn’t work – due to an exception caused by the page not using analytics data (but like I say, more on that later), as it had been excluded by IP Address in Sitecore.Analytics.ExcludeRobots.config

Conclusion – if wanting to exclude traffic from analytics like health monitoring, try and do it with User Agent, not IP address – and do test Sirecore systems with disabled analytics to make sure nothing blows up.