Support ipv6 link-local servers and %iface syntax #646
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This was referenced Dec 5, 2023
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Tested on Ubuntu 22.04 after disabling systemd-resolved with another ubuntu host using radvd to advertise its link local address as a DNS server. Works as intended, and specifically does not work if you omit the %iface. |
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and iOS. The issue only happens when using system default link-local IPv6 DNS. Specifying link-local IPv6 DNS address manually works. Disabling libresolv and using the manual parsing fixes the issue after the change made in c-ares#646 On macOS and iOS c-ares uses libresolv and assumes that its API res_getservers() fills sin6_scope_id in case of a link-local IPv6 DNS addresses in /etc/resolv.conf. Unfortunately this is not the case. See res_getservers() here: https://opensource.apple.com/source/libresolv/libresolv-60/res_init.c.auto.html
shpala
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The issue only happens when using system default link-local IPv6 DNS. Specifying link-local IPv6 DNS address manually works. Disabling libresolv and using the manual parsing fixes the issue after the change made in c-ares#646 On macOS c-ares uses libresolv and assumes that its API res_getservers() fills sin6_scope_id in case of a link-local IPv6 DNS addresses in /etc/resolv.conf. Unfortunately this is not the case. See res_getservers() here: https://opensource.apple.com/source/libresolv/libresolv-60/res_init.c.auto.html
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Some environments may send router advertisements on a link setting their link-local (fe80::/10) address as a valid DNS server to the remote system. This will cause a DNS entry to be created like
fe80::1%iface, since all link-local network interfaces are technically part of the same /10 subnet, it must be told what interface to send packets through explicitly if there are multiple physical interfaces.This PR adds support for the %iface modifier when setting DNS servers via
/etc/resolv.confas well as viaares_set_servers_csv().For MacOS and iOS it is assumed that libresolve will set the
sin6_scope_idand should be supported, but my test systems don't seem to read the Router Advertisement for RDNSS link-local. Specifying the link-local dns server on MacOS via adig has been tested and confirmed working.For Windows, this is similar to MacOS in that the system doesn't seem to honor the RDNSS RA, but specifying manually has been tested to work.
At this point, Android support does not exist.
Fixes Bug #462
Supersedes PR #463
Fix By: Brad House (@bradh352) and Serhii Purik (@sergvpurik)