[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
** Attachment added: "Wireshark capture of successful resolution, showing IPv6 stuff happening" https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+attachment/4997138/+files/Screenshot%20from%202017-10-26%2018-36-23.png ** Summary changed: - DNS resolver silently switches to an unknown DNS server + DNS resolver mixes IPv6 and IPv4 caches -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver mixes IPv6 and IPv4 caches To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
This is still happening with 17.10 final. I have been digging a bit and found something that makes me think that this is a caching / IPv6 issue. Attached is the screenshot of a Wireshark capture of the DNS packets on all interfaces on the affected machine (the IP address of the machine is 192.168.0.154). When querying a hostname that should be resolved to a local network address (in this case odoo.caligrafix.cl), the resolver makes two requests to our local DNS server 192.168.0.2 (and not to any external DNS server, as I first thought): 1. The request for odoo.caligrafix.cl 2. A request for o3.caligrafix.cl. The second request is made before receiving the response to the first request. This second request can be explained by the fact that outside of our network, the name odoo.caligrafix.cl resolves to a CNAME o3.caligrafix.cl, and for some reason the resolver uses this cached information instead of waiting for the result of the first request. The response to the first request, which correctly indicates the expected local network address, seems to be discarded, and the result of subsequent requests that resolves to our public address trough a chain of CNAMES, is used instead. The funny thing is that after flushing the resolver's cache, the resolver also makes two requests to our local DNS server, but both with the name odoo.caligrafix.cl, and gets the correct answer. But then it makes a request for the (IPv6) record, and gets the chain the CNAME records that lead to our public IP. So it seems that somehow the IPv6 and IPv4 caches get mixed up afterwards. Although I guess I could (and will attempt to) mitigate the issue by configuring the record differently on our DNS server, I think the current behavior of the resolver is incorrect, as it uses cached info for an IPv6 record when querying an IPv4 record. ** Attachment added: "Wireshark capture of failed resolution" https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+attachment/4997137/+files/Screenshot%20from%202017-10-26%2018-22-20.png -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver mixes IPv6 and IPv4 caches To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
It looks like this has been fixed, it is not occurring anymore. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
Sorry, sorry, it does still happen. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
Output of systemd-resolve --status when the problem does not occur ** Attachment added: "sr-ok.txt" https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+attachment/4954625/+files/sr-ok.txt -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
I attached the output of systemd-resolve --status in both cases. There is no difference. In both cases it says the DNS server is 192.168.0.2 (our local resolver), although it seems it is using another, external DNS server after a while. Indeed the cache seems to be flushed when changing networking (e.g. turning ethernet off and back on through Gnome). Thus resolving works correctly for a while after changing networking. But after a few dozen seconds, it starts failing (ie. returning our public IP, as if it was using an external DNS server) again. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
Output of systemd-resolve --status when the problem occurs ** Attachment added: "sr-bad.txt" https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+attachment/4954624/+files/sr-bad.txt -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
The caches should be flushed each time machine changes networking =/ does your system e.g. bounce between "public dns wifi network" and a "internal dns ethernet network"? A full output of $ systemd-resolve --status -> would be helpful to see. Especially "when everything works correctly" and "when things are broken" to see if there are any differences in the resolved state. If that information is private, you may change the settings on this bug report to Private, such that it is only shared with Ubuntu developers and is not public. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
[Bug 1716976] Re: DNS resolver silently switches to an unknown DNS server
Maybe interesting: systemd-resolve --status eth2 always reports the correct, internal DNS server, even though names are incorrectly resolved to their public IPs (I tried resolving with both dig and systemd- resolve). gpothier@tadzim3:~$ systemd-resolve --status eth2 Link 3 (eth2) Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6 LLMNR setting: yes MulticastDNS setting: no DNSSEC setting: no DNSSEC supported: no DNS Servers: 192.168.0.2 DNS Domain: ozone.caligrafix.cl Also, sudo systemd-resolve --flush-caches temporarily solves the problem, in the same way restarting the service does. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1716976 Title: DNS resolver silently switches to an unknown DNS server To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1716976/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
