Host-name DHCP Option Ignored on Cumulus Linux

Issue

If a Cumulus Linux switch running 5.9.1 or later with NVUE enabled receives a DHCP lease containing the host-name option, it ignores the received hostname and does not apply it.

Environment

• Cumulus Linux 5.9.1 and later.
• Active DHCP lease containing the host-name option cached in /var/lib/dhcp/dhclient.eth0.leases, and, or a DHCP server offering a lease containing the host-name option.
• You use NVUE to manage the switch or the nvued and nvue-startup services are enabled.

Cause and Resolution

Cumulus Linux 5.9.1 and later ignores the DHCP host-name option because NVUE manages the hostname in the /etc/nvue.d/startup.yaml file and prevents DHCP from overwriting it. If you do not manage your switch with NVUE, you can enable the DHCP hostname as follows:

1. Disable and stop the nvued and nvue-startup services:

cumulus@switch:~$ sudo systemctl stop nvued.service
cumulus@switch:~$ sudo systemctl stop nvue-startup.service
cumulus@switch:~$ sudo systemctl disable nvued.service
cumulus@switch:~$ sudo systemctl disable nvue-startup.service

2. Edit the /etc/dhcp/dhclient-exit-hooks.d/dhcp-sethostname file and change the SETHOSTNAME variable to yes:

cumulus@switch:~$ sudo nano /etc/dhcp/dhclient-exit-hooks.d/dhcp-sethostname 
...
SETHOSTNAME="yes"
if [ $SETHOSTNAME = "yes" ] && [ ! -z $new_host_name ]
then
    hostname $new_host_name
    sed --in-place -e "/127\.0\.1\.1/s/^.*$/127.0.1.1  $new_host_name/" /etc/hosts
fi

3. Reboot the switch with the sudo reboot command or renew the DHCP lease on the interface by bringing it down and up again:

cumulus@switch:~$ sudo ifdown eth0; sudo ifup eth0