[systemd-devel] Where does resolved takes its data from?

[Wojtek Swiatek]

OK , I think I found the reason.

I get the IP via DHCP, which also brings in the DNS servers (the two
secondaries). This somehow gets used by resolved, as it puts the resolvers
in /run/systemd/resolve/resolv.conf.

Since /etc/hosts is linked to /run/systemd/resolve/stub-resolv.conf which
just points to 127.0.0.53, I believe that resolved internallmy sees teh
secondaries (provided by DHCP), shows this by putting them into
/run/systemd/resolve/resolv.conf and 127.0.0.53 uses that information (also
visible via resolvctl status).

This makes sense, leaving /etc/systemd/resolved.conf for static
configurations (no DHCP), and probably as a way to overwrite DHCP provided
data.

Sorry for the noise.




Le mer. 5 sept. 2018 à 08:11, Wojtek Swiatek <w at swtk.info> a écrit :

> Hello everyone,
>
> I decided to clean up my DNS resolving mess and fully go the
> systemd-resolved way = on every machine:
> - have /etc/resolv.conf linked to /run/systemd/resolve/stub-resolv.conf
> - have the resolver stub running on 127.0.0.53
> - provide internal upstream and fallback servers in
> /etc/systemd/resolved.conf
> - hope for the best
>
> "every machine" above are actually nspawn containers with their own IP
> addresses (provided and resolved by the host, via dnsmasq)
> I removed any other resolvers (if they were present), everything is under
> networkd control.
>
> My first step was to have a broken machine (DNS wise), with a fully
> commented out /etc/systemd/resolved.conf (as it is by default), expecting
> not to be able to resolve anything and go from there.
>
> To my surprise google.com resolved fine. OK, this must be an invisible
> default pointing to 8.8.8.8 or something like that (as the fallbacks are
> still commented out).
>
> But I also tried to resolve an internal name, known only by the host and
> secondary internal servers (which would be the upstream servers mentioned
> above, when actually configured in /etc/systemd/resolved.conf).
>
> I have no idea how resolved managed to get information from other DNS
> servers (whihc could be either the host, which runs dnsmasq on 0.0.0.0:53,
> or the secondaries which run bind on their_IP:53)).
> Where could that resolution come from?
>
> The situation on the machines, showing that resolved is the only one
> resolver:
>
> root at dev ~# lsof -i -P -n
> COMMAND    PID            USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
> systemd-n   51 systemd-network   18u  IPv6   56615      0t0  UDP
> [fe80::685a:94ff:fecc:37ce]:546
> systemd-n   51 systemd-network   20u  IPv4   59162      0t0  UDP
> 10.200.0.50:68
> rsyslogd    56          syslog    8u  IPv4   66478      0t0  UDP *:57004
> salt-mini   68            root   21u  IPv4  829402      0t0  TCP
> 10.200.0.50:46988->52.210.137.123:4505 (ESTABLISHED)
> systemd-r 2519 systemd-resolve   12u  IPv4 1272287      0t0  UDP
> 127.0.0.53:53
> systemd-r 2519 systemd-resolve   13u  IPv4 1272288      0t0  TCP
> 127.0.0.53:53 (LISTEN)
>
>
> root at dev ~# ps -ef
> UID        PID  PPID  C STIME TTY          TIME CMD
> root         1     0  0 Sep04 ?        00:00:00 /lib/systemd/systemd
> root        18     1  0 Sep04 ?        00:00:00
> /lib/systemd/systemd-journald
> systemd+    51     1  0 Sep04 ?        00:00:00
> /lib/systemd/systemd-networkd
> root        52     1  0 Sep04 ?        00:00:00 /usr/bin/python3
> /usr/bin/networkd-dispatcher
> root        53     1  0 Sep04 ?        00:00:00 /lib/systemd/systemd-logind
> root        54     1  0 Sep04 ?        00:00:00 /usr/sbin/cron -f
> message+    55     1  0 Sep04 ?        00:00:00 /usr/bin/dbus-daemon
> --system --address=systemd: --nofork --nopidfile --systemd-activation
> --syslog-only
> syslog      56     1  0 Sep04 ?        00:00:00 /usr/sbin/rsyslogd -n
> root        62     1  0 Sep04 ?        00:00:00 /usr/bin/python
> /usr/bin/salt-minion
> root        63     1  0 Sep04 console  00:00:00 /sbin/agetty -o -p -- \u
> --noclear --keep-baud console 115200,38400,9600 vt220
> root        68    62  0 Sep04 ?        00:00:34 /usr/bin/python
> /usr/bin/salt-minion
> root        71    68  0 Sep04 ?        00:00:00 /usr/bin/python
> /usr/bin/salt-minion
> root       873     1  0 Sep04 pts/0    00:00:00 /usr/bin/fish
> root       875     1  0 Sep04 ?        00:00:00 /lib/systemd/systemd --user
> root       876   875  0 Sep04 ?        00:00:00 (sd-pam)
> systemd+  2519     1  0 07:42 ?        00:00:00
> /lib/systemd/systemd-resolved
> root      3352   873  0 08:06 pts/0    00:00:00 ps -ef
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/systemd-devel/attachments/20180905/33f77179/attachment-0001.html>