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Cuong Manh Le
b6d5abfae8
After a network change, the OS resolver keeps the previous network's nameservers until a read finds the new ones. In Standard mode that usually waits for the recovery to remove ctrld's DNS settings: while 127.0.0.1 is configured, the system reports nothing else, and on macOS an RDNSS-only IPv6 network has no other source. macOS resolves ipv4only.arpa through ctrld right after the change to discover the NAT64 prefix; a fast SERVFAIL from the stale set ends that discovery, macOS never starts its CLAT, and an IPv4-only upstream never recovers. On every accepted network change, on all platforms and in both Standard and intercept mode, mark the OS resolver stale and read the nameservers once before the re-bootstrap, without the scutil retry loop. While the set is stale, a failed ipv4only.arpa AAAA lookup gets no reply, so the host retries it. A read that finds nameservers clears the mark, and the mark expires after 30s. Network-change recovery also re-reads the nameservers right after the reset and then at 1s, 2s, 5s and every 30s while it waits, for networks that publish their resolvers late.