[Bug 2003778] Re: systemd-resolved uses malformed link-local IPv6 forwarder

[geppi]

I'm on Ubuntu 22.04 LTS. I always need to provide the interface
specification when using link-local IPv6-addresses, e.g. a simple 'ping
fe80::2a0:57ff:fe24' doesn't work but 'ping fe80::2a0:57ff:fe24%2' does
the trick. I couldn't figure out why this is required on my desktop
Ubuntu system. In contrary on a Debian bullseye server the IPv6-addresss
without the interface specifier is sufficient. Any idea?

However, since it is required on my Ubuntu system the systemd-resolved
stub doesn't work and I have to employ the workaround mentioned in my
initial post. The '/run/systemd/resolve/resolv.conf' file contains the
proper link-local IPv6-address of my name server including the interface
specifier.

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Title:
  systemd-resolved uses malformed link-local IPv6 forwarder

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  In a network with a local nameserver that has IPv4-address 10.1.0.1
  and link-local IPv6-address fe80::2a0:57ff:fe24:b041%2 'resolvectl'
  returns:

  Global
         Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  resolv.conf mode: uplink

  Link 2 (ens33)
      Current Scopes: DNS
           Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
  Current DNS Server: fe80::2a0:57ff:fe24:b041
         DNS Servers: 10.1.0.1 fe80::2a0:57ff:fe24:b041%21905
          DNS Domain: < edited >

  Name resolution fails because the indicated 'Current DNS Server'
  IPv6-address is an incomplete link-local address. Also the link-local
  IPv6-address indicated in the second position of the 'DNS Servers'
  line is malformed. Issuing consecutive 'resolvectl' calls have the
  last 4 digits in this line changing, i.e. they all show
  'fe80::2a0:57ff:fe24:b041%2', which would be the correct link-local
  IPv6-address including the interface specification, but then 4 digits
  that are not constant.

  Workaround:

  Take systemd-resoved out of stub-mode with:

  (cd /etc && sudo rm -f resolv.conf && sudo ln -s
  /run/systemd/resolve/resolv.conf resolv.conf)

  The auto generate file '/run/systemd/resolve/resolv.conf' has the
  proper specification of the name servers link-local IPv6-address:

  nameserver 10.1.0.1
  nameserver fe80::2a0:57ff:fe24:b041%2
  search < edited >

  The broken stub mode is configured with:

  (cd /etc && rm -f resolv.conf && ln -s /run/systemd/resolve/stub-
  resolv.conf resolv.conf)

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