I had an obscure DNS problem, and EasyDNS pointed me in the right direction.

When looking up ns3.reppep.com, I was getting 66.92.104.200, which is wrong (that address is actually ns1.reppep.com) from some DNS servers, but not others. I confirmed that the record was correct in the reppep.com zone (hosted by EasyDNS), and forced a serial number update, but some servers kept returning the wrong address.

It turns out that years ago, when VeriSlime managed the DNS registration for reppep.com, they picked up the wrong address (it might have been correct when they picked up the IP, but hasn't been for years). When I transferred the domain registration (which is separate from the DNS service -- basically authoritative nameservers) to Dreamhost, the stale glue data remained. The solution is to have Dreamhost update the glue record for ns3.reppep.com.

You can see the glue with the whois command, e.g., "whois ns3.reppep.com. It should agree with "host ns3.reppep.com", but doesn't yet (still waiting on Dreamhost to get it together).