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app: a DNS reply is not a DNS answer

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The probe counted any well-formed packet from the server as "the server
answers", checking only the transaction id and a minimum length. REFUSED
and SERVFAIL are well-formed packets. So a server actively refusing this
client would have been reported as healthy, and the finding — whose whole
output is "the network is fine, your device is not" — would have pointed
confidently at the wrong component.

It now requires rcode 0 and at least one record, and reports a refusal as
what it is: a working server saying no, which points back at the network.
The rcode is named rather than numbered, because "REFUSED" is a fact an
operator can act on and "rcode 5" is a lookup.

Caught by decoding what fmr's router actually replied — ab cd 81 80 00 01
00 02, NOERROR with two answers — after realising the earlier check only
counted bytes. The reply was genuinely good, so the finding on the tablet
stands; the check was wrong regardless.

The advice is broader too. That tablet's fault survived a reboot, which
makes "toggle wifi and it clears" wrong as a flat claim: it now says what
to look at when a restart does not fix it — something on the device
filtering DNS, or a per-client rule on the router.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
mrambossek
2026-08-02 10:10:36 +02:00
co-authored by Claude Opus 5
parent 2ed4d1f478
commit cfa58e8d60
2 changed files with 57 additions and 10 deletions
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echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt
+9 -5
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@@ -681,11 +681,15 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
confidence = Confidence.HIGH,
title = "This device cannot resolve names, but the DNS server is fine ($where)",
description = "A DNS query sent straight from this device was " +
"answered by ${str("servers") ?: "the configured server"}, yet " +
"asking Android to resolve the same name fails. The network is " +
"working; this device's resolver is not. Turning wifi off and on " +
"again, or rejoining the network, usually clears it. If it " +
"returns after a restart, look at the network instead.",
"answered by ${str("servers") ?: "the configured server"} with " +
"a valid result, yet asking Android to resolve the same name " +
"fails. Whatever is wrong sits between this device's resolver " +
"and a server that demonstrably works. " +
"Turning wifi off and on, or rejoining the network, clears the " +
"common case. If it survives a restart it is not a stuck " +
"resolver: look for something on this device that filters DNS " +
"— an ad blocker, a private-DNS or VPN app — or a per-device " +
"rule on the router aimed at this client.",
evidenceRefs = listOf(EvidenceRef(t.id)),
)
)