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How to configure network zones

How to configure network zones

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

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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.

This assumes that core.dns_address was set to <DNS_server_IP>:<DNS_server_PORT>. (Setting that configuration option causes the backend to immediately start serving on that address.)

In order for the dig request to be allowed for a given zone, you must set the peers.NAME.address configuration option for that zone. NAME can be anything random. The value must match the IP address where your dig is calling from. You must leave peers.NAME.key for that same random NAME unset.

For example: lxc network zone set lxd.example.net peers.whatever.address=192.0.2.1.

Note
It is not enough for the address to be of the same machine that dig is calling from; it needs to match as a string with what the DNS server in lxd thinks is the exact remote address. dig binds to 0.0.0.0, therefore the address you need is most likely the same that you provided to core.dns_address.

For example, running dig @<DNS_server_IP> -p <DNS_server_PORT> axfr lxd.example.net might give the following output:

~$ dig @192.0.2.200 -p 1053 axfr lxd.example.net

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 <DNS_server_PORT> axfr 2.0.192.in-addr.arpa might give the following output:

~$ dig @192.0.2.200 -p 1053 axfr 2.0.192.in-addr.arpa

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 to a local address on the LXD server. To avoid conflicts with an existing DNS we suggest not using the port 53. 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:

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

Key: dns.nameservers
Type: string set
Required: no

network.nat
Whether to generate records for NAT-ed subnets

Key: network.nat
Type: bool
Default: true
Required: no

peers.NAME.address
IP address of a DNS server

Key: peers.NAME.address
Type: string
Required: no

peers.NAME.key
TSIG key for the server

Key: peers.NAME.key
Type: string
Required: no

user.*
User-provided free-form key/value pairs

Key: user.*
Type: string
Required: no

Note
When generating the TSIG key using tsig-keygen, the key name must follow the format <zone_name>_<peer_name>.. For example, if your zone name is lxd.example.net and the peer name is bind9, then the key name must be lxd.example.net_bind9.. If this format is not followed, zone transfer might fail.

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:

config
User-provided free-form key/value pairs

Key: config
Type: string set
Required: no

The only supported keys are user.* custom keys.

description
Description of the record

Key: description
Type: string
Required: no

entries
List of DNS entries

Key: entries
Type: entry list
Required: no

name
Unique name of the record

Key: name
Type: string
Required: yes

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>
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