Why cache busting?
Cache busting is a must if you are trafficking a third party ad code and want the third party ad server be able to track impressions accurately. You need not worry about this for a DFP hosted creative as DFP takes care of it by its inbuilt mechanism.
How’s cache busting done for DFP hosted creatives?
Cache busting in third party ads?
DFP gives a provision of Cache-buster Macro(%%CACHEBUSTER%%) which can be used in your third party ad code. The macro expands to a random number, thus achieving cache busting. Every 3rd party ad code have its own placeholder for inserting Cache-buster macro and some syntax mention it as random number placeholder. You can refer our article Third Party Macro Placement.
DART Tag Cache busting
PS: All DFP macros are case sensitive.
What if I don’t feel like using Cache-buster ?
Nothing much. Feel free. But your third party ad server will report relatively very less impressions messing up the campaign. As only the first impression request is sent to the third party server while requesting the creative and for the consequent ones the browser serves from its cache for which impressions are not counted by your third party server.
Some third party code has inbuilt random number generator which takes care of cachebusting while making a request to their server (for eg., PointRoll). You can identify whether a third party tag requires a cachebuster macro or not by inspecting the ad call by simply previewing it. If the request contains a variable that’s changing in every ad request made to third party server, a separate cachebuster isn’t required. Typically they are in the form rand=12312312, r=12245, cbust=233322 etc., and varies with third party servers.