** Description changed: [Impact] dnsmasq 2.79 and below omits EDNS0 OPT records when returning an empty answer for a domain it is authoritative for. systemd-resolved seems to get confused by this in certain circumstances; when using the stub resolver and requesting an address for which there are no AAAA records, there can sometimes be a five second hang in resolution. [Fix] This is fixed by upstream commit http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=1682d15a744880b0398af75eadf68fe66128af78 Not sure if it is worth cherry picking? I imagine the most likely trigger will be dnsmasq on routers which are not likely to be running Ubuntu, but maybe just in case. I also think there are some logic issues in systemd-resolved, upstream bug filed: https://github.com/systemd/systemd/issues/9785 [Test Case] - Simple-ish test case: + Simple-ish test case for bionic: --- IFACE=dummy0 SUBNET=10.0.0 ip link add $IFACE type dummy ifconfig $IFACE ${SUBNET}.1/24 - dnsmasq -h -R -d -C /dev/null -2 $IFACE -z -i $IFACE -I lo --host-record=test.test,${SUBNET}.1 & + dnsmasq -h -R -d -C /dev/null -2 $IFACE -z -i $IFACE -I lo --host-record=test.test,${SUBNET}.1 --server=/test/ & dig -t a test.test @10.0.0.1 | grep EDNS # should return "; EDNS ..." dig -t aaaa test.test @10.0.0.1 | grep EDNS # again, should return "; EDNS ..." but doesn't --- To reproduce the systemd-resolved side of the problem --- # as above, but # now configure systemd-resolved to look at only 10.0.0.1, then systemd-resolve --reset-server-features # should exhibit five second delay then connect, assuming sshd is running :) ssh test.test --- + + + More detailed test case for focal and later: + + install dnsmasq on a bionic system and start it, listening to an + interface that is externally reachable, e.g. for a normal libvirt vm + with interface name 'ens3': + + IFACE=ens3 + dnsmasq -h -R -d -C /dev/null -2 $IFACE -z -i $IFACE -I lo --host-record=test.test,1.2.3.4 --server=/test/ + + note that the '1.2.3.4' address doesn't matter, any addr is ok. + + then setup a test system that can reach the dnsmasq system, and + configure networkd to use the dnsmasq server, e.g. using config like: + + [Match] + Name=ens3 + + [Network] + DHCP=yes + DNS=DNSMASQ_IP_ADDRESS + Domains=test + + [DHCPv4] + UseDNS=no + UseDomains=no + + replace 'DNSMASQ_IP_ADDRESS' with the addr of the bionic system where + dnsmasq is running, and replace 'ens3' with whatever the test system + interface name is. Then restart systemd-networkd, and test: + + systemd-resolve --reset-server-features + systemd-resolve --flush-caches + host test.test + + The lookup using 'host' should complete immediately;. [Discussion] ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: dnsmasq-base 2.79-1 ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18 Uname: Linux 4.15.0-23-generic x86_64 ApportVersion: 2.20.9-0ubuntu7.2 Architecture: amd64 Date: Sat Aug 4 11:33:56 2018 InstallationDate: Installed on 2018-05-31 (64 days ago) InstallationMedia: Xubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426) ProcEnviron: TERM=xterm PATH=(custom, no user) LANG=en_GB.UTF-8 SHELL=/bin/bash SourcePackage: dnsmasq UpgradeStatus: No upgrade log present (probably fresh install)
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1785383 Title: missing EDNS0 record confuses systemd-resolved To manage notifications about this bug go to: https://bugs.launchpad.net/systemd/+bug/1785383/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
