It is part of the Frontier Anycast DNS System(74.40.74.40). That is the server your dns queries actually are received by & which response to your dns queries. The particular server which recieves & responds to your queries will be different depending on where you are in the Frontier network.
Here are some samples of the test with other anycast systems
208.67.222.222/208.67.220.220
159.247.233.2/159.247.233.18