I haven't found the answer to this question anywhere and I'm a bit confused.. I want to know if the root DNS servers are queried iteratively or recursively? As far as my understanding of the subject goes, they can be queried recursively,as they are the 'last option' to resove a name, so they must answer with the IP address/error message. Am I correct? Please make this clear for me. Thanks.
Recursive servers (i.e. the ones serving end-user clients) perform iterative queries to authoritative servers.
In response to those iterative queries, each authoritative server in the chain down from the root will either return the answer if it's authoritative for that domain, or a referral to the next servers down the chain that might have the answer.
The root name servers do not offer fully recursive service, only referrals to the name servers run by each TLD.