[Bug 1821491] Re: DNS lookup fails for local hosts

[Dan Streetman]

> Sorry thought I was using dig at your request...

yes, sorry - dig is useful *but* it does only what you ask it
specifically to do (i.e. lookup the specific hostname you ask it for,
without appending any search domains to it).  this is different from
everything else on your system, which uses getaddrinfo(), which will
append search domains listed in /etc/resolv.conf.

> ping often works when nslookup fails

i can't say *exactly* why this is, but I suspect it's because you had
two nameservers listed in /etc/resolv.conf; your router (which *will*
resolve the hostname without any domain suffix) and your local systemd-
resolved resolver (which *will not* resolve the hostname without a
domain suffix, since it won't pass the "single label" hostname to your
router nameserver).

i believe (don't remember the specifics of the glibc internals tho) that
getaddrinfo() will do round-robin queries of each nameserver you list in
/etc/resolv.conf, so it may be random chance that one thing looks up
your host right, and the next request doesn't.

> so clearly the domain is set

that will let you do "single label" lookups *from your router only*.
setting the router's search domain(s) will have *no effect at all* on
lookups from any other system.

just make sure:

-your router's dhcp configuration includes your local subnet domain (i.e. provides it to your dhcp clients)
-your router's dnsmasq (or whatever public nameserver program) has your local subnet hosts *including local subnet domain* defined

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https://bugs.launchpad.net/bugs/1821491

Title:
  DNS lookup fails for local hosts

Status in systemd package in Ubuntu:
  Invalid

Bug description:
  Mint 19 (Ubuntu Bionic) 
  Laptop so Using NetworkManager, and connecting wirelessly to LAN
  Upgraded from Mint 18.3 so using resolvconf...

  Versions:
  network-manager: 1.10.6-2ubuntu1.1
  resolvconf: 1.79ubuntu10.18.04.3 or 1.79ubuntu10.18.04.2
  systemd: 237-3ubuntu10.15

  dns is specified in NetworkMananager as 192.168.2.1
  the dns is a router, and has static ips assigned to certain hosts on my lan...

  $cat resolv.conf
  nameserver 127.0.0.53
  search phs
  options edns0

  $ nslookup phspi05
  Server:		127.0.0.53
  Address:	127.0.0.53#53

  ** server can't find phspi05: SERVFAIL

  If I explicity specify the dns:

  $ nslookup phspi05 192.168.2.1
  Server:		192.168.2.1
  Address:	192.168.2.1#53

  Non-authoritative answer:
  Name:	phspi05
  Address: 192.168.2.35

  I get the correct ip address...

  Same with dig...

  I would expect that the nameserver set in network-manager would be
  used....

  From tail of $ systemd-resolve --status

  Link 2 (wlp2s0)
        Current Scopes: DNS
         LLMNR setting: yes
  MulticastDNS setting: no
        DNSSEC setting: no
      DNSSEC supported: no
           DNS Servers: 192.168.2.1
            DNS Domain: phs

  So the dns address had been picked up from NetworkManager, but
  apparently is not being used...

  Thought it might be related to this bug:
  https://bugs.launchpad.net/ubuntu/bionic/+source/resolvconf/+bug/1817903

  So installed the proposed fix, but no change. I also tried removing
  package resolvconf, again no change...

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