Public bug reported: I have a setup where a host (say A) in the network runs knot-resolver as a caching nameserver.
Among the other hosts, some of them run ubuntu 20.04 and use systemd- resolved. The dhcp setup make all these host use A as their nameserver. The issue with systemd- The issue is that if I do: host -t SOA foo.local the hosts running systemd-resolved answer foo.local has SOA record foo.local. nobody.invalid. 1 3600 1200 604800 10800 making up the SOA record from nowhere (sort of). In fact, if I do the same query pointing directly at A host -t SOA foo.local <ip address of A> I correctly get no SOA record. ---- The incorrect response of resolved breaks mDNS resolution. In fact, if nsswitch.conf is set at hosts: files mdns4_minimal [NOTFOUND=return] dns any call requiring name resolution first goes through the hosts files, then mdns is attempted. However, the nss mdnd implementation first checks if the DNS server responds to SOA queries for the top level local name and if this is the case, it gives up. As a consequence, trying to access hosts on the .local domain always fail. The reason why systemd-resolved makes up a SOA record for hosts such as foo.local is that knot resolver replies to queries about it without an answer, but including an authority section ;; AUTHORITY SECTION: foo.local. 10800 IN SOA foo.local. nobody.invalid. 1 3600 1200 604800 10800 ;; ADDITIONAL SECTION: explanation.invalid. 10800 IN TXT "Blocking is mandated by standards, see references on https://www.iana.org/assignments/special-use-domain-names/special-use-domain-names.xhtml"; and systemd-resolved turns that AUTHORITY section into a SOA record. It is not totally clear to me if the fault is on knot-resolver, systemd-resolved or both, but I tend to think it is the second one. Unfortunately, trying to inquire upstream about systemd-resolved appears to be forbidden for anybody not running the last two releases of systemd. Furthermore, I understand that the nature of systemd makes it extra hard or impossible to test a more recent version of systemd- resolved than the one shipped in ubuntu focal. Interestingly, the issue seems to bite those running omnia turris router too (see https://forum.turris.cz/t/avahi-local-domain-warning-on- ubuntu/13437). Maybe they use knot-resolver as their caching nameserver. ** Affects: systemd (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1950520 Title: systemd-resolved delivers SOA information when it should not To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1950520/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
