domain name system - How wordpress.com do scalability

Out of curiosity, I wanted to know, how Wordpress.com scale their architecture, specifically:

1. how they handle sub-domains.

   
   
   

   I believe they have millions of subdomains.CMIIW. How do they scale their DNS to handle it?




2. They also support custom domains.

   
   
   

   How do they handle the translation and also, how do they scale the requests?

note, I choose the wordpress tag, because I'm not allowed yet to create wordpress.com tag.