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DASKAjA
Asked: 2021-07-14 00:02:43 +0800 CST

Dynamic DNS updates via DHCP on CentOS

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I'm running mostly Ubuntu VMs in an vSphere cluster where a VLAN is managed by a Windows DHCP and DNS. From the Ubuntu VMs I can update the DNS records in the Windows DNS to point the dynamic IP to its hostname (set in /etc/hostname) with dhcp-identifier: mac addition in /etc/netplan/00-installer-config.yaml:

cat /etc/netplan/00-installer-config.yaml
# This is the network config written by 'subiquity'
network:
  ethernets:
    ens160:
      dhcp4: true
      dhcp-identifier: mac
  version: 2

After these modification a call to dhclient -r also updates the DNS record to point to the newly dhcp-assigned IP address.

But now I want to achieve the same DNS update functionality in a CentOS 7 VM. First I setted /etc/hostname to myhost.example.tld and rebooted the machine. After that I tried to change serveral variables in /etc/sysconfig/network-scripts/ifcfg-ens192:

  • Setting MACADDR to either preserve or permanent
  • Setting DHCP_HOSTNAME to myhost but not DHCP_FQDN
  • Setting DHCP_FQDN to myhost.example.tld but not DHCP_HOSTNAME

Every change to ifcfg-ens192 were followed by the invocation of dhclient -r ens192; dhclient ens192 and a reboot.

domain-name-system networking dhcp

1 Answers

  1. I just found the solution. One needs to create /etc/dhcp/dhclient.conf and add send fqdn.fqdn = gethostname(); to it. After that, a dhclient -r; dhclient sends the hostname in the DHCP* message.

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