- Package:
- isc-dhcp-client
- Source:
- isc-dhcp
- Description:
- DHCP client for automatically obtaining an IP address
- Submitter:
- Martijn van Duren
- Date:
- 2026-08-05 17:34:38 UTC
- Severity:
- normal
Starting with Debian 11 once in a blue moon dhclient doesn't receive the dhcp packets from the kernel. During this capture it took over 100 full system reboots to trigger. Attached are the pcap and strace showing this behaviour. root@debian11-ifup:~# lsof -p 348 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME dhclient 348 root cwd DIR 8,1 4096 2 / dhclient 348 root rtd DIR 8,1 4096 2 / dhclient 348 root txt REG 8,1 516816 17655 /usr/sbin/dhclient dhclient 348 root mem REG 8,1 51696 1978 /usr/lib/x86_64-linux-gnu/libnss_files-2.31.so dhclient 348 root mem REG 8,1 3076960 3072 /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1 dhclient 348 root mem REG 8,1 149520 1982 /usr/lib/x86_64-linux-gnu/libpthread-2.31.so dhclient 348 root mem REG 8,1 18688 1970 /usr/lib/x86_64-linux-gnu/libdl-2.31.so dhclient 348 root mem REG 8,1 1839792 1969 /usr/lib/x86_64-linux-gnu/libc-2.31.so dhclient 348 root mem REG 8,1 483800 17639 /usr/lib/x86_64-linux-gnu/libisc-export.so.1105.0.2 dhclient 348 root mem REG 8,1 2298032 17645 /usr/lib/x86_64-linux-gnu/libdns-export.so.1110.0.2 dhclient 348 root mem REG 8,1 177928 1964 /usr/lib/x86_64-linux-gnu/ld-2.31.so dhclient 348 root 0u CHR 1,3 0t0 4 /dev/null dhclient 348 root 1u CHR 1,3 0t0 4 /dev/null dhclient 348 root 2u CHR 1,3 0t0 4 /dev/null dhclient 348 root 3u unix 0x00000000ba5a44e9 0t0 11329 type=DGRAM dhclient 348 root 4r FIFO 0,12 0t0 11335 pipe dhclient 348 root 6w FIFO 0,12 0t0 11335 pipe dhclient 348 root 7w REG 8,1 651 29482 /var/lib/dhcp/dhclient.ens3.leases dhclient 348 root 8u pack 11357 0t0 ALL type=SOCK_RAW dhclient 348 root 9u IPv4 11359 0t0 UDP *:bootpc root@debian11-ifup:~# uname -a Linux debian11-ifup 5.10.0-8-amd64 #1 SMP Debian 5.10.46-5 (2021-09-23) x86_64 GNU/Linux Instance running under qemu-system-x86_64 -enable-kvm. Restarting dhclient/running dhclient by hand allows the kernel to return the packet and restore network connectivity.
We believe we've also observed this bug at Google on Debian 11. We confirmed that packets are received by the kernel, but dhclient doesn't catch them. The root cause appears to be a race condition, and we provided some details in https://gitlab.isc.org/isc-projects/dhcp/-/issues/264 to ISC, but we understand dhclient is being deprecated. The bug was also reported to Ubuntu at https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1926139 and there's a detailed discussion of the bug, reproduction cases, and proposed fixes, the last of which was accepted into Ubuntu Jammy. We built a test package with Ubuntu's fix applied to Debian 11 and confirmed over the weekend (more than 100k runs) that it resolves the issue. Because of some risk that the fix could cause issues elsewhere, the patch included an option to revert the change at runtime. I haven't found evidence of anyone needing to use that option. Oddly we also find that Debian 12 does not have this issue, even though the later version of dhclient does not include any fix for this. There must be some other reason why the race condition is not hit there.
Dear submitter, as the package isc-dhcp has just been removed from the Debian archive unstable we hereby close the associated bug reports. We are sorry that we couldn't deal with your issue properly. For details on the removal, please see https://bugs.debian.org/1143544 The version of this package that was in Debian prior to this removal can still be found using https://snapshot.debian.org/. Please note that the changes have been done on the master archive and will not propagate to any mirrors until the next dinstall run at the earliest. This message was generated automatically; if you believe that there is a problem with it please contact the archive administrators by mailing ftpmaster@ftp-master.debian.org. Debian distribution maintenance software pp. Thorsten Alteholz (the ftpmaster behind the curtain)