The choice between TCP and UDP isn't whether you want your system to be reliable. It's whether you want to handle reliability in the application vs in the prot

The choice between TCP and UDP isn't whether you want your system to be reliable. It's whether you want to handle reliability in the application vs in the protocol. TCP does reliability for you. UDP lets you implement whatever form of reliability you want in the application. For DNS, you can do a much better job implementing DNS-specific forms of reliability. For example, if you have multiple nameservers, just move on to the next one instead of trying to retransmit packets to the first one that fails.