Internal PTR queries going to the internet
Posted on 2013-06-10
Hello all. I was recently informed by my ISP that they were receiving reverse DNS lookup requests for addresses on my LAN. We run Microsoft Active Directory and AD integrated DNS services using Windows Server 2008 R2. All machines on the network use two internal DNS servers which are also domain controllers.
The firewall has been configured to not allow anything on the network to go to the internet on DNS ports (TCP/UDP 53). Packet captures at the firewall have confirmed that the reverse DNS queries are being forwarded from the two Active Directory DNS servers. (DC's)
The strange thing is that they are forwarding reverse DNS lookups for domains in which they have authoritative zones for... For example the subnet is:
AD has an integrated PTR zone 1.168.192.in-addr.arpa.
Internal PTR testing using nslookup works just fine, but the log that the ISP has sent me still shows the same internal IPs in which these tested records pass as being forwarded to the public DNS server. Anyone else run into this? How would I go about making sure that these queries are not forwarded to the internet, but answered by the local PTR zone?