DNS Nameserver Order Consistency¶
In Neutron subnets, DNS nameservers are given priority when created or updated. This means if you create a subnet with multiple DNS servers, the order will be retained and guests will receive the DNS servers in the order you created them in when the subnet was created. The same thing applies for update operations on subnets to add, remove, or update DNS servers.
Get Subnet Details Info¶
$ openstack subnet list
+--------------------------------------+---------+--------------------------------------+-------------+
| ID | Name | Network | Subnet |
+--------------------------------------+---------+--------------------------------------+-------------+
| 1a2d261b-b233-3ab9-902e-88576a82afa6 | private | a404518c-800d-2353-9193-57dbb42ac5ee | 10.0.0.0/24 |
+--------------------------------------+---------+--------------------------------------+-------------+
$ openstack subnet show 1a2d261b-b233-3ab9-902e-88576a82afa6
+----------------------+--------------------------------------+
| Field | Value |
+----------------------+--------------------------------------+
| allocation_pools | 10.0.0.2-10.0.0.254 |
| cidr | 10.0.0.0/24 |
| created_at | 2024-02-13T21:42:34Z |
| description | |
| dns_nameservers | 8.8.4.4, 8.8.8.8 |
| dns_publish_fixed_ip | None |
| enable_dhcp | True |
| gateway_ip | 10.0.0.1 |
| host_routes | |
| id | 1a2d26fb-b733-4ab3-992e-88554a87afa6 |
| ip_version | 4 |
| ipv6_address_mode | None |
| ipv6_ra_mode | None |
| name | private |
| network_id | a404518c-800d-2353-9193-57dbb42ac5ee |
| project_id | 3868290ab10f417390acbb754160dbb2 |
| revision_number | 0 |
| segment_id | None |
| service_types | |
| subnetpool_id | |
| tags | |
| updated_at | 2024-02-13T21:42:34Z |
+----------------------+--------------------------------------+
Update Subnet DNS Nameservers¶
Note
--no-dns-nameserver must be passed to clear the current list,
otherwise a conflict will be raised if there are duplicates.
$ openstack subnet set --no-dns-nameserver --dns-nameserver 8.8.8.8 \
--dns-nameserver 8.8.4.4 1a2d261b-b233-3ab9-902e-88576a82afa6
$ openstack subnet show 1a2d261b-b233-3ab9-902e-88576a82afa6
+----------------------+--------------------------------------+
| Field | Value |
+----------------------+--------------------------------------+
| allocation_pools | 10.0.0.2-10.0.0.254 |
| cidr | 10.0.0.0/24 |
| created_at | 2024-02-13T21:42:34Z |
| description | |
| dns_nameservers | 8.8.8.8, 8.8.4.4 |
| dns_publish_fixed_ip | None |
| enable_dhcp | True |
| gateway_ip | 10.0.0.1 |
| host_routes | |
| id | 1a2d26fb-b733-4ab3-992e-88554a87afa6 |
| ip_version | 4 |
| ipv6_address_mode | None |
| ipv6_ra_mode | None |
| name | private |
| network_id | a404518c-800d-2353-9193-57dbb42ac5ee |
| project_id | 3868290ab10f417390acbb754160dbb2 |
| revision_number | 1 |
| segment_id | None |
| service_types | |
| subnetpool_id | |
| tags | |
| updated_at | 2024-02-13T21:42:34Z |
+----------------------+--------------------------------------+
As shown in above output, the order of the DNS nameservers has been updated. New virtual machines deployed to this subnet will receive the DNS nameservers in this new priority order. Existing virtual machines that have already been deployed will not be immediately affected by changing the DNS nameserver order on the neutron subnet. Virtual machines that are configured to get their IP address via DHCP will detect the DNS nameserver order change when their DHCP lease expires or when the virtual machine is restarted. Existing virtual machines configured with a static IP address will never detect the updated DNS nameserver order.
