At some point I must have gotten cute with the OpenVPN’s client settings on macOS. I somehow entered OpenVPN’s “Advanced Settings” and enabled a feature called “DNS Fallback”. This seemed like a decent idea at the time, what I didn’t know is that would start to slow down my client-side OpenVPN connections a period of time after the VPN connection was established to the OpenVPN server. After this period of time, it would start to slowly (if ever) resolve domain names for external websites (the client side DNS resolution had latency on the order of seconds or more when it decided to use Google DNS.) Disabling the DNS Fallback feature brought speedy OpenVPN connections back to my client machine.

When these drop-offs or slow downs in resolving domain names occurred, the macOS OpenVPN client was producing these log messages: “UDP send exception: send: no buffer space available”. I will watch the log again to see if disabling the above “DNS Fallback” feature stops these UDP messages.