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James Tucker af5a845a87 net/dns/resolver: fix dns-sd NXDOMAIN responses from quad-100 ... mdnsResponder at least as of macOS Sequoia does not find NXDOMAIN responses to these dns-sd PTR queries acceptable unless they include the question section in the response. This was found debugging #13511, once we turned on additional diagnostic reporting from mdnsResponder we witnessed: ``` Received unacceptable 12-byte response from 100.100.100.100 over UDP via utun6/27 -- id: 0x7F41 (32577), flags: 0x8183 (R/Query, RD, RA, NXDomain), counts: 0/0/0/0, ``` If the response includes a question section, the resposnes are acceptable, e.g.: ``` Received acceptable 59-byte response from 8.8.8.8 over UDP via en0/17 -- id: 0x2E55 (11861), flags: 0x8183 (R/Query, RD, RA, NXDomain), counts: 1/0/0/0, ``` This may be contributing to an issue under diagnosis in #13511 wherein some combination of conditions results in mdnsResponder no longer answering DNS queries correctly to applications on the system for extended periods of time (multiple minutes), while dig against quad-100 provides correct responses for those same domains. If additional debug logging is enabled in mdnsResponder we see it reporting: ``` Penalizing server 100.100.100.100 for 60 seconds ``` It is also possible that the reason that macOS & iOS never "stopped spamming" these queries is that they have never been replied to with acceptable responses. It is not clear if this special case handling of dns-sd PTR queries was ever beneficial, and given this evidence may have always been harmful. If we subsequently observe that the queries settle down now that they have acceptable responses, we should remove these special cases - making upstream queries very occasionally isn't a lot of battery, so we should be better off having to maintain less special cases and avoid bugs of this class. Updates #2442 Updates #3025 Updates #3363 Updates #3594 Updates #13511 Signed-off-by: James Tucker <james@tailscale.com>		2 months ago
..
debug.go	all: use Go 1.22 range-over-int	7 months ago
doh_test.go	net/dns/resolver: remove maxDoHInFlight	2 years ago
forwarder.go	net/dns/resolver: fix dns-sd NXDOMAIN responses from quad-100	2 months ago
forwarder_test.go	net/dns/resolver: fix dns-sd NXDOMAIN responses from quad-100	2 months ago
macios_ext.go	all: avoid repeated default interface lookups	2 years ago
tsdns.go	net/dns, health: raise health warning for failing forwarded DNS queries (#12888)	4 months ago
tsdns_server_test.go	all: update copyright and license headers	2 years ago
tsdns_test.go	net/dns, health: raise health warning for failing forwarded DNS queries (#12888)	4 months ago