[Bug 1853669] Re: systemd resolves own hostname to link local ipv6 address

[Andreas L]

It was no "assumption", but an "observation".

$ nslookup $(hostname)     # a blank name without any domain
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
Name:	xxx                      # my "$(hostname)"
Address: 192.168.0.1
Name:	xxx
Address: fe80::4687:fcff:fe9e:4ac7

$ sudo fuser -n udp 53
53/udp:              22620
$ ps uww 22620
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
systemd+ 22620  0.0  0.0  52368  2220 ?        Ss   Nov29   1:50 /lib/systemd/systemd-resolved
$ dpkg -S /lib/systemd/systemd-resolved
systemd: /lib/systemd/systemd-resolved
$ dpkg -l systemd | cat  # (no UUOC, but prevent dpkg from fitting output to terminal)
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version          Architecture Description
+++-==============-================-============-=================================
ii  systemd        237-3ubuntu10.33 amd64        system and service manager
$ 

At which points does your output differ?

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https://bugs.launchpad.net/bugs/1853669

Title:
  systemd resolves own hostname to link local ipv6 address

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  I've got an ethernet-device that only has a configured ipv4 address,
  and some auto-generated link-local (aka "scope link") ipv6 address.

  Any tool doing a DNS query (and /lib/systemd/systemd-resolved is the
  DNS-server listening on 127.0.0.53) for this host's hostname gets back
  two addresses: the correct ipv4 address, and a broken ipv6 address.

  Unlike on ipv4,  it is possible for the same ipv6-address to be
  assigned to multiple devices, and therefore the address is only valid
  in the context of the eth-device.

  Now, if "ifconfig" shows "inet6 fe80::4687:fcff:fe9e:4ac7  prefixlen 64  scopeid 0x20<link>"
  then "fe80::4687:fcff:fe9e:4ac7" is NOT a connectable address, and syscall connect() typically fails with EINVAL.

  To make it a valid address, it needs to be suffixed with a "%" and the device name, like:
  fe80::4687:fcff:fe9e:4ac7%enp4s0

  Either the resolver can return the link name attached to the address
  separated with a "%" char, or it needs to ignore link-local inet6
  addresses.

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