[Bug 1714803] Re: Search list in resolv.conf breaks resolving for that domain

Wed Oct 11 14:25:23 UTC 2017

Tried that, and it started using the DHCP-provided search path (yay!).

Setting the search path in NetworkManager (which is responsible for the
interface in question) works, ie. honors the search path and doesn't
break resolving for those domains, with both single and multiple search
paths:

[ipv4]
dns-search=disy.inf.uni-konstanz.de;inf.uni-konstanz.de;uni-konstanz.de
method=auto

[ipv6]
addr-gen-mode=stable-privacy
dns-search=disy.inf.uni-konstanz.de;inf.uni-konstanz.de;uni-konstanz.de
method=auto

Having to do this for each connection and for both IPv4 and IPv6 sucks,
but it's better than not having a search path.

Trying to set the search path to Domains=ubuntu.com globally in resolved.conf still breaks ubuntu.com, of course. Out of curiosity, I then put this in resolved.conf:

Domains=uni-konstanz.de inf.uni-konstanz.de disy.inf.uni-konstanz.de
ubuntu.com

This works for the domains listed in the interface, honoring the search
path and correctly resolving both short (git) and long (git.uni-
konstanz.de) domains. But it breaks resolution completely for ubuntu.com
and subdomains.

So: Does systemd-resolved need to have a network interface "associated"
with each search domain?? This is very much not how DNS works but it's a
boundary case that might be easy to get wrong.

(This is all on the 17.10 VM, and with resolved.conf empty apart from
[Resolve] and the Domains= line, where mentioned.)

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https://bugs.launchpad.net/bugs/1714803

Title:
  Search list in resolv.conf breaks resolving for that domain

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  Ubuntu 17.04
  systemd 232-21ubuntu5

  Adding a domain to the search list in /etc/resolv.conf breaks
  resolving for that domain. Not only does the search list not get used
  as expected, but host names in the domain cannot be resolved by
  systemd-resolved at all.

  I just ran into this after upgrading from ubuntu 16.04 to 17.04 which
  enabled systemd-resolved. I have for a long time used resolveconf to
  add a 'search my-domain'-line to my /etc/resolv.conf.

  Example of expected behaviour. With Googles DNS server (8.8.8.8) and ubuntu.com in the search list in /etc/resolv.conf. Both dig and systemd-resolve can resolve www.ubuntu.com and www:

      $ cat /etc/resolv.conf 
      nameserver 8.8.8.8
      search ubuntu.com
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55037
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 512
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A

      ;; ANSWER SECTION:
      www.ubuntu.com.		501	IN	A	91.189.89.115

      $ dig +search +nostat +nocmd www
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25772
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 512
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A

      ;; ANSWER SECTION:
      www.ubuntu.com.		382	IN	A	91.189.89.103

      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: 91.189.89.115

      -- Information acquired via protocol DNS in 2.7ms.
      -- Data is authenticated: no
      $ systemd-resolve www
      www: 91.189.90.59
           (www.ubuntu.com)

      -- Information acquired via protocol DNS in 3.8ms.
      -- Data is authenticated: no

  Ubuntu 17.04 default config, with the systemd-resolved name server in
  /etc/resolv.conf and no search list. www.ubuntu.com can still be
  resolved correctly:

      $ cat /etc/resolv.conf
      nameserver 127.0.0.53
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 64646
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A

      ;; ANSWER SECTION:
      www.ubuntu.com.		482	IN	A	91.189.89.110
      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: 91.189.90.58

      -- Information acquired via protocol DNS in 18.2ms.
      -- Data is authenticated: no

  Broken behaviour, using the systemd-resolved name server and specify
  ubuntu.com in search list. Resolving fails for www.ubuntu.com and www,
  both using dig (DNS) and using sytemd-resolve:

      $ cat /etc/resolv.conf
      nameserver 127.0.0.53
      search ubuntu.com
      $ dig +nostat +nocmd www.ubuntu.com
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 33334
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A

      $ dig +search +nostat +nocmd www
      ;; Got answer:
      ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 50588
      ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

      ;; OPT PSEUDOSECTION:
      ; EDNS: version: 0, flags:; udp: 65494
      ;; QUESTION SECTION:
      ;www.ubuntu.com.			IN	A

      $ systemd-resolve www.ubuntu.com
      www.ubuntu.com: resolve call failed: No appropriate name servers or networks for name found
      $ systemd-resolve www
      www: resolve call failed: All attempts to contact name servers or networks failed

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