Public bug reported:
On a fresh Ubuntu Server 26.04 install, /etc/nsswitch.conf was
configured by default with mdns4_minimal for mDNS host resolution, while
the rest of the stack, including avahi-daemon, appears to be configured
for dual-stack IPv4/IPv6 operation by default.
This creates a misleading debugging situation: IPv6 mDNS is working at
the Avahi and network levels, but normal application name resolution
through NSS ignores IPv6 mDNS answers.
In my case, avahi-resolve could resolve the .local hostname to a valid
IPv6 address, and packet capture showed IPv6 mDNS AAAA advertisements on
ff02::fb UDP/5353. However, applications using the standard resolver
path, such as ssh -6 hostname.local, failed with temporary name
resolution errors.
The root cause was that NSS was using mdns4_minimal, which only
participates in IPv4 mDNS resolution. Changing the hosts: line in
/etc/nsswitch.conf to use mdns_minimal instead, and adding mdns as a
final mDNS fallback, allowed IPv6 .local resolution to work correctly
through normal applications.
Expected behavior: if Ubuntu Server and Avahi are dual-stack by default,
the default NSS mDNS configuration should also support IPv6 mDNS
resolution, or this limitation should be clearly documented.
$ lsb_release -rd
Description: Ubuntu 26.04 LTS
Release: 26.04
libc-bin version: 2.43-2ubuntu2
** Affects: glibc (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2159573
Title:
mdns resolution is ipv4 only by default
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