AllThingsD reports that Yahoo is trying to unload its ad network. The rumor is that Yahoo’s Right Media exchange – a marketplace of networks for ad buyers and sellers Yahoo acquired in 2007 – is on the block, along with Yahoo’s own ad-buying and targeting infrastructure. When new CEO Scott Thompson stepped in, I wrote that Yahoo should forget about being a technology platform, a social media company or an ad network, and concentrate on being content and services portal that sells premium advertising to big brands. Much as I liked the idea of Yahoo teaming up with other name-brand publishers (AOL, Microsoft and others) to create a premium ad exchange, it could outsource the infrastructure of such a thing. And AllThingsD says Microsoft is a potential buyer, along with Google. If Google’s interested, that could work out for Yahoo, although it might re-introduce the complications of switching search technology providers.