How to configure network zones#

Note

Network zones are available for the OVN network and the Bridge network.

Network zones can be used to serve DNS records for LXD networks.

You can use network zones to automatically maintain valid forward and reverse records for all your instances. This can be useful if you are operating a LXD cluster with multiple instances across many networks.

Having DNS records for each instance makes it easier to access network services running on an instance. It is also important when hosting, for example, an outbound SMTP service. Without correct forward and reverse DNS entries for the instance, sent mail might be flagged as potential spam.

Each network can be associated to different zones:

  • Forward DNS records - multiple comma-separated zones (no more than one per project)

  • IPv4 reverse DNS records - single zone

  • IPv6 reverse DNS records - single zone

LXD will then automatically manage forward and reverse records for all instances, network gateways and downstream network ports and serve those zones for zone transfer to the operator’s production DNS servers.

Project views#

Projects have a features.networks.zones feature, which is disabled by default. This controls which project new networks zones are created in. When this feature is enabled new zones are created in the project, otherwise they are created in the default project.

This allows projects that share a network in the default project (i.e those with features.networks=false) to have their own project level DNS zones that give a project oriented “view” of the addresses on that shared network (which only includes addresses from instances in their project).

Generated records#

Forward records#

If you configure a zone with forward DNS records for lxd.example.net for your network, it generates records that resolve the following DNS names:

  • For all instances in the network: <instance_name>.lxd.example.net

  • For the network gateway: <network_name>.gw.lxd.example.net

  • For downstream network ports (for network zones set on an uplink network with a downstream OVN network): <project_name>-<downstream_network_name>.uplink.lxd.example.net

  • Manual records added to the zone.

You can check the records that are generated with your zone setup with the dig command. For example, running dig @<DNS_server_IP> -p 1053 axfr lxd.example.net might give the following output:

lxd.example.net.                        3600 IN SOA  lxd.example.net. ns1.lxd.example.net. 1669736788 120 60 86400 30
lxd.example.net.                        300  IN NS   ns1.lxd.example.net.
lxdtest.gw.lxd.example.net.             300  IN A    192.0.2.1
lxdtest.gw.lxd.example.net.             300  IN AAAA fd42:4131:a53c:7211::1
default-ovntest.uplink.lxd.example.net. 300  IN A    192.0.2.20
default-ovntest.uplink.lxd.example.net. 300  IN AAAA fd42:4131:a53c:7211:216:3eff:fe4e:b794
c1.lxd.example.net.                     300  IN AAAA fd42:4131:a53c:7211:216:3eff:fe19:6ede
c1.lxd.example.net.                     300  IN A    192.0.2.125
manualtest.lxd.example.net.             300  IN A    8.8.8.8
lxd.example.net.                        3600 IN SOA  lxd.example.net. ns1.lxd.example.net. 1669736788 120 60 86400 30

Reverse records#

If you configure a zone for IPv4 reverse DNS records for 2.0.192.in-addr.arpa for a network using 192.0.2.0/24, it generates reverse PTR DNS records for addresses from all projects that are referencing that network via one of their forward zones.

For example, running dig @<DNS_server_IP> -p 1053 axfr 2.0.192.in-addr.arpa might give the following output:

2.0.192.in-addr.arpa.                  3600 IN SOA  2.0.192.in-addr.arpa. ns1.2.0.192.in-addr.arpa. 1669736828 120 60 86400 30
2.0.192.in-addr.arpa.                  300  IN NS   ns1.2.0.192.in-addr.arpa.
1.2.0.192.in-addr.arpa.                300  IN PTR  lxdtest.gw.lxd.example.net.
20.2.0.192.in-addr.arpa.               300  IN PTR  default-ovntest.uplink.lxd.example.net.
125.2.0.192.in-addr.arpa.              300  IN PTR  c1.lxd.example.net.
2.0.192.in-addr.arpa.                  3600 IN SOA  2.0.192.in-addr.arpa. ns1.2.0.192.in-addr.arpa. 1669736828 120 60 86400 30

Enable the built-in DNS server#

To make use of network zones, you must enable the built-in DNS server.

To do so, set the core.dns_address configuration option (see Core configuration) to a local address on the LXD server. This is the address on which the DNS server will listen. Note that in a LXD cluster, the address may be different on each cluster member.

Note

The built-in DNS server supports only zone transfers through AXFR. It cannot be directly queried for DNS records. Therefore, the built-in DNS server must be used in combination with an external DNS server (bind9, nsd, …), which will transfer the entire zone from LXD, refresh it upon expiry and provide authoritative answers to DNS requests.

Authentication for zone transfers is configured on a per-zone basis, with peers defined in the zone configuration and a combination of IP address matching and TSIG-key based authentication.

Create and configure a network zone#

Use the following command to create a network zone:

lxc network zone create <network_zone> [configuration_options...]

The following examples show how to configure a zone for forward DNS records, one for IPv4 reverse DNS records and one for IPv6 reverse DNS records, respectively:

lxc network zone create lxd.example.net
lxc network zone create 2.0.192.in-addr.arpa
lxc network zone create 1.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa

Note

Zones must be globally unique, even across projects. If you get a creation error, it might be due to the zone already existing in another project.

You can either specify the configuration options when you create the network or configure them afterwards with the following command:

lxc network zone set <network_zone> <key>=<value>

Use the following command to edit a network zone in YAML format:

lxc network zone edit <network_zone>

Configuration options#

The following configuration options are available for network zones:

Key

Type

Required

Default

Description

peers.NAME.address

string

no

-

IP address of a DNS server

peers.NAME.key

string

no

-

TSIG key for the server

dns.nameservers

string set

no

-

Comma-separated list of DNS server FQDNs (for NS records)

network.nat

bool

no

true

Whether to generate records for NAT-ed subnets

user.*

*

no

-

User-provided free-form key/value pairs

Add a network zone to a network#

To add a zone to a network, set the corresponding configuration option in the network configuration:

  • For forward DNS records: dns.zone.forward

  • For IPv4 reverse DNS records: dns.zone.reverse.ipv4

  • For IPv6 reverse DNS records: dns.zone.reverse.ipv6

For example:

lxc network set <network_name> dns.zone.forward="lxd.example.net"

Zones belong to projects and are tied to the networks features of projects. You can restrict projects to specific domains and sub-domains through the restricted.networks.zones project configuration key.

Add custom records#

A network zone automatically generates forward and reverse records for all instances, network gateways and downstream network ports. If required, you can manually add custom records to a zone.

To do so, use the lxc network zone record command.

Create a record#

Use the following command to create a record:

lxc network zone record create <network_zone> <record_name>

This command creates an empty record without entries and adds it to a network zone.

Record properties#

Records have the following properties:

Property

Type

Required

Description

name

string

yes

Unique name of the record

description

string

no

Description of the record

entries

entry list

no

A list of DNS entries

config

string set

no

Configuration options as key/value pairs (only user.* custom keys supported)

Add or remove entries#

To add an entry to the record, use the following command:

lxc network zone record entry add <network_zone> <record_name> <type> <value> [--ttl <TTL>]

This command adds a DNS entry with the specified type and value to the record.

For example, to create a dual-stack web server, add a record with two entries similar to the following:

lxc network zone record entry add <network_zone> <record_name> A 1.2.3.4
lxc network zone record entry add <network_zone> <record_name> AAAA 1234::1234

You can use the --ttl flag to set a custom time-to-live (in seconds) for the entry. Otherwise, the default of 300 seconds is used.

You cannot edit an entry (except if you edit the full record with lxc network zone record edit), but you can delete entries with the following command:

lxc network zone record entry remove <network_zone> <record_name> <type> <value>