[djs55]

The DNS resolving code in Docker for Mac is in the VPNkit project which is open-source: https://github.com/docker/vpnkit. A DNS timeout is a fairly general symptom and it's hard to diagnose fully without a packet capture, but there's one issue that I'm aware of: if the primary server is down then the UDP DNS queries and responses will use the host's second server. However if a response is large and requires TCP then unfortunately we will still forward it to the primary server, which obviously won't work :( I've filed this issue about it: https://github.com/docker/vpnkit/issues/96. We hope to improve DNS, VPN and general proxy support for 1.13 -- please do file issues for any other bugs you find!