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

[Andreas L]

Ok, just to check, I changed /etc/resolv.conf to remove second
nameserver, added "domain .hm" and "search hm", added "fpc.hm"
to the respective entry in 10.2.2.3's /etc/hosts.

Result is, that localhost's systemd-resolved now no longer
knows about upstream dns 10.2.2.3 -- where else am I supposed
to configure that?

So, I re-added "nameserver 10.2.2.3" to /etc/resolv.conf, and
it really seems like it would once again take the second
nameserver-entry as that for upstream-dns.

Apparently, with "domain" and "search" in place, systemd-resolved
no longer makes any attempt to obtain information from routing
table, thus appears to work.

Nevertheless, apparently systemd-resolved DOES have a feature
where it queries local information about network devices to
get a list of ip-addresses whenever there is no domain/search
defined and a bare name queried. What is the reason behind
that feature, if the suggested solution to this ticket is just:
"don't use bare hostnames"?


** Changed in: systemd (Ubuntu)
       Status: Invalid => Confirmed

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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:
  Confirmed

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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