DNS resolution errors

Hi everyone, This is weird, or not. I don't know much about DNS so any help is greatly appreciated. My primary DNS server is returning non-authoritative answers for nslookups on external addresses. On internal addresses, I get SERVFAIL, and then it goes to my backup DNS: andrew-caldwells-macbook-pro:~ andrew$ nslookup mail.mnn.org ;; Got SERVFAIL reply from 192.168.1.32, trying next server Server: 192.168.1.27 Address: 192.168.1.27#53 mail.mnn.org canonical name = od-replica.mnn.org. Name: od-replica.mnn.org Address: 192.168.1.27 What's the deal? It's worthwhile noting that this is a recent development in the past day. TIA, Andrew