extra left-behind domains break domain name rsolution

[Roland Dreier]

This seems related to LP: #1717995 but that is marked fixed.

I used my laptop at work, where I have a docking station with USB ethernet included (interface enx0050b6cf4d4a). The dhcp on the wired ethernet includes my work domain, purestorage.com. I undocked, suspended, and came home, where I have no USB ethernet (just wifi wlp4s0), and dhcp on wifi doesn't mention purestorage.com. However, I still have leftover state that stops purestorage.com names from resolving:

$ systemd-resolve webvpn.purestorage.com
webvpn.purestorage.com: resolve call failed: No appropriate name servers or networks for name found

$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.

nameserver 127.0.0.53
search lan purestorage.com dev.purestorage.com

$ systemd-resolve --status
Global
          DNS Domain: lan
                      purestorage.com
                      dev.purestorage.com
          DNSSEC NTA: 10.in-addr.arpa
                      16.172.in-addr.arpa
                      168.192.in-addr.arpa
                      17.172.in-addr.arpa
                      18.172.in-addr.arpa
                      19.172.in-addr.arpa
                      20.172.in-addr.arpa
                      21.172.in-addr.arpa
                      22.172.in-addr.arpa
                      23.172.in-addr.arpa
                      24.172.in-addr.arpa
                      25.172.in-addr.arpa
                      26.172.in-addr.arpa
                      27.172.in-addr.arpa
                      28.172.in-addr.arpa
                      29.172.in-addr.arpa
                      30.172.in-addr.arpa
                      31.172.in-addr.arpa
                      corp
                      d.f.ip6.arpa
                      home
                      internal
                      intranet
                      lan
                      local
                      private
                      test

Link 3 (wlp4s0)
      Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: 10.1.0.1
                      fda0:5173:b519::1
          DNS Domain: lan

Link 2 (enp0s31f6)
      Current Scopes: none
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no

It seems there are still issues around network interfaces being removed but leaving behind their DNS config.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: systemd 234-2ubuntu12
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Oct 25 17:48:47 2017
InstallationDate: Installed on 2016-09-01 (419 days ago)
InstallationMedia: Ubuntu 16.10 "Yakkety Yak" - Alpha amd64 (20160901)
Lsusb:
 Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
 Bus 001 Device 004: ID 138a:0090 Validity Sensors, Inc.
 Bus 001 Device 003: ID 13d3:5248 IMC Networks
 Bus 001 Device 005: ID 056a:5087 Wacom Co., Ltd
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: LENOVO 20FRS2FK00
ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.13.0-16-generic root=UUID=30d5ada5-835d-4cf7-96cf-3329c0316107 ro quiet splash vt.handoff=7
SourcePackage: systemd
UpgradeStatus: Upgraded to artful on 2017-07-26 (91 days ago)
dmi.bios.date: 07/13/2017
dmi.bios.vendor: LENOVO
dmi.bios.version: N1FET53W (1.27 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20FRS2FK00
dmi.board.vendor: LENOVO
dmi.board.version: SDK0J40697 WIN
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 31
dmi.chassis.vendor: LENOVO
dmi.chassis.version: None
dmi.modalias: dmi:bvnLENOVO:bvrN1FET53W(1.27):bd07/13/2017:svnLENOVO:pn20FRS2FK00:pvrThinkPadX1Yoga1st:rvnLENOVO:rn20FRS2FK00:rvrSDK0J40697WIN:cvnLENOVO:ct31:cvrNone:
dmi.product.family: ThinkPad X1 Yoga 1st
dmi.product.name: 20FRS2FK00
dmi.product.version: ThinkPad X1 Yoga 1st
dmi.sys.vendor: LENOVO

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Steve Langasek (vorlon)]

Thank you for reporting this bug and helping to improve Ubuntu.

Why do you believe that the problem here is one of 'leftover state'? The systemd-resolve --status output shows a simple config, with a domain search list and two DNS servers (one ipv4 address, one ipv6 address). If some of this state is "leftover", it's not clear what state that is.

Are 10.1.0.1 and fda0:5173:b519::1 the correct DNS servers for your home wifi? Do these DNS lookups work correctly when you issue them directly against the configured nameservers? (nslookup webvpn.purestorage.com 10.1.0.1; nslookup webvpn.purestorage.com fda0:5173:b519::1) What happens if you try to do the lookup with 'nslookup webvpn.purestorage.com' instead of with systemd-resolve? (systemd-resolve uses a different protocol to talk to systemd-resolved, and may give different results - which normally indicates a bug.)

Can you provide a network trace of the DNS traffic when these lookups fail?

[Launchpad Janitor (janitor)]

[Expired for systemd (Ubuntu) because there has been no activity for 60 days.]