We've been investigating a similar issue in Ubuntu 20.04 (and now 22.04) on Azure where Running PPS re-use fails to perform DHCP for 5 minutes when dhclient is invoked by cloud-init. dhclient is run by cloud-init, but sees no DHCPOFFER. It varies due to unknown reasons but it has affected a ~0.3-2% of deployments in this scenario over time.
We instrumented our images to capture network traffic and see what is happening and sure enough DHCP offers are coming through to the guest by dhclient doesn't see them. We instrumented dhclient and the "got_one()" callback is never invoked in these failures. 18.04 does not have this issue. This behavior can be reproduced multiple ways: - Reproduce similar test environment to above scenario using cloud-init (switch hyperv nic to a different vnet while waiting the link status to reset, then perform dhcp). This test case will reproduce in ~1,500 runs, though it varies and requires more complex setup. - Repeatedly run dhclient in a loop until it fails (see test-sequential.sh). It may take a while, but even this simple test will reproduce this behavior in ~50k runs for me in an LXD VM. - Simply launch instances of dhclient in parallel (see test-parallel.sh). There is an excellent chance at least one of those dhclients will fail this way. I noticed the uprev of bind9 libs in focal: focal (net): 1:9.11.16+dfsg-3~build1 focal-updates (net): 1:9.11.16+dfsg-3~ubuntu1 impish (net): 1:9.11.19+dfsg-2.1ubuntu1 jammy (net): 1:9.11.19+dfsg-2.1ubuntu3 kinetic (net): 1:9.11.19+dfsg-2.1ubuntu3 I couldn't find any related issue on the isc-dhcp tracker, etc. I did build dhclient from the Debian master branch (https://salsa.debian.org/debian/isc-dhcp/-/commits/master/debian) which uses the in-tree bind libs and that seems to have addressed the issue for all scenarios. Not that it helps much to bisect this just yet. ** Attachment added: "parallel test" https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139/+attachment/5593045/+files/test-parallel.sh -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu. https://bugs.launchpad.net/bugs/1926139 Title: dhclient doesn't receive dhcp offer from kernel Status in isc-dhcp package in Ubuntu: New Bug description: Platform: Qemu/libvirt on AMD64 Ubuntu version: 20.04 isc-dhcp-client version: 4.4.1-2.1ubuntu5 Problem: When dhclient is used during boot every few reboots the DHCP OFFER packets aren't pushed from the kernel to dhclient. The DISCOVER packets can be seen in strace and tcpdump. The OFFER packets can be seen in tcpdump, but no read event is triggered. Ubuntu 18.04 doesn't have the problem, neither does Debian 10. Building these dhclient versions on Ubuntu 20.04 alleviates the problem a little, but it still occurs. So this issue might also be kernel related. Attached diff shows a strace of all threads and a pcap showing the tcpdump output. Edit: - Sometimes the dhclient command does receive the OFFER packet and connection is restored. - In my testing running dhclient manually from the terminal when the OFFERs aren't received will result in a new dhclient session which does receive the OFFER packet and connection is restored. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
