fix(iroh-dns): drop link-local and unspecified system nameservers#4210
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fix(iroh-dns): drop link-local and unspecified system nameservers#4210Frando wants to merge 1 commit into
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Documentation for this PR has been generated and is available at: https://n0-computer.github.io/iroh/pr/4210/docs/iroh/ Last updated: 2026-04-29T10:40:07Z |
## Description Android tethered through an iPhone publishes link-local nameservers in `LinkProperties.getDnsServers()`. Without a scope ID those are not routable from a connected UDP socket and every query times out before falling back. Generalize the existing `WINDOWS_BAD_SITE_LOCAL_DNS_SERVERS` filter into `is_usable_nameserver`, which also drops link-local IPv4 (`169.254.0.0/16`), link-local IPv6 (`fe80::/10`), and the unspecified addresses. The filter applies on every platform. ## Breaking Changes None. ## Notes & open questions This is a reachability filter, not a trust boundary. Authenticated DNS still requires DNS-over-HTTPS or DNSSEC on top. ## Change checklist - [x] Self-review. - [x] Tests if relevant. - [x] All breaking changes documented.
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Ugh, good catch but I don't think filtering out the link-local DNS servers is generally a good idea. Can we not use them correctly? |
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I don't know. We just have the report of an Android phone being tether to an Iphone failing to resolve DNS. We'd need to try to replicate this I guess. |
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Description
We have reports of Android handing out link-local nameservers in
LinkProperties.getDnsServers()when the device is tethered through an iPhone. Without a scope ID those addresses are not reachable from a connected UDP socket, so every DNS query times out before the public-DNS fallback kicks in.The system-config reader already filters Windows IPv6 site-local anycast (the deprecated
fec0:0:0:ffff::/96range that Windows still configures alongside the loopback adapter). This PR generalizes that into a singleis_usable_nameserverhelper and adds three more drops:fe80::/10)169.254.0.0/16)0.0.0.0,::)The filter applies on every platform; nothing here is Android-specific. The iPhone-tether case was just the one we noticed.
Breaking Changes
None.
Notes & open questions
Change checklist