MacOS IPv6 “happy eyeballs” diagnostic CLI performance tool

“Happy Eyeballs” is the IPv6 feature (RFC8305) where the OS tests response time on IPv4 and IPv6 per destination and tries to optimize performance by choosing the “fastest” protocol for hostnames which have both A-records and AAAA-records. Some recent implementations also give a preference to IPv6 (I’ve heard of preferences from 25msec to 300msec). I…

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