Prevent smaller ad creative from showing in larger ad slot

Question

I'm having a 300x250 size creative show in a 300x600 ad slot.

The header call defines only one size, 300x600 like so:

googletag.defineSlot('/1030735/website_300x600', [300, 600], 'website_300x600').addService(googletag.pubads());

And the ad unit itself in dfp is setup with only one size, 300x600.

However, I get some network ads come in through the ad unit that are 300x250, and it's happening more often than the correct 300x600 size.

How can I force it to show only a 300x600 size ad on the unit?
I thought that having only one ad unit size is the way to do it?

Answer 1

This is happening probably because the third-party adNetwork who serves to you the banners that you have places in your creative of 300x600 is returning sometimes 300x600 banners and sometimes 300x250. Since you have configured your creative as a 300x600 creative, DFP it's not smart enough to detect it.

If this is the scenario, you have to options:

• To contact to your third party adServer to limit the campaigns to the size you need: 300x600.
• To add to the line item and the implied creatives the size of 300x250, this way DFP should be able to detect when it's one size or the other.