ubuntu@jumphost:~$ maas admin subnets read  
Success.
Machine-readable output follows:
[
    {
        "name": "oam",
        "description": "",
        "vlan": {
            "vid": 0,
            "mtu": 1500,
            "dhcp_on": true,
            "external_dhcp": null,
            "relay_vlan": null,
            "name": "untagged",
            "secondary_rack": null,
            "id": 5001,
            "space": "oam-space",
            "primary_rack": "4ds8d6",
            "fabric": "fabric-0",
            "fabric_id": 0,
            "resource_uri": "/MAAS/api/2.0/vlans/5001/"
        },
        "cidr": "172.30.205.128/25",
        "rdns_mode": 2,
        "gateway_ip": "172.30.205.129",
        "dns_servers": [],
        "allow_dns": true,
        "allow_proxy": true,
        "active_discovery": false,
        "managed": true,
        "id": 1,
        "space": "oam-space",
        "resource_uri": "/MAAS/api/2.0/subnets/1/"
    },
    {
        "name": "external",
        "description": "",
        "vlan": {
            "vid": 0,
            "mtu": 1500,
            "dhcp_on": false,
            "external_dhcp": null,
            "relay_vlan": null,
            "name": "untagged",
            "secondary_rack": null,
            "id": 5003,
            "space": "external-space",
            "primary_rack": null,
            "fabric": "fabric2",
            "fabric_id": 2,
            "resource_uri": "/MAAS/api/2.0/vlans/5003/"
        },
        "cidr": "172.30.204.128/26",
        "rdns_mode": 2,
        "gateway_ip": null,
        "dns_servers": [],
        "allow_dns": true,
        "allow_proxy": true,
        "active_discovery": false,
        "managed": true,
        "id": 3,
        "space": "external-space",
        "resource_uri": "/MAAS/api/2.0/subnets/3/"
    },
    {
        "name": "overlay",
        "description": "",
        "vlan": {
            "vid": 300,
            "mtu": 9000,
            "dhcp_on": false,
            "external_dhcp": null,
            "relay_vlan": null,
            "name": "overlay",
            "secondary_rack": null,
            "id": 5005,
            "space": "sdn-transport",
            "primary_rack": null,
            "fabric": "fabric3",
            "fabric_id": 3,
            "resource_uri": "/MAAS/api/2.0/vlans/5005/"
        },
        "cidr": "192.168.254.0/24",
        "rdns_mode": 2,
        "gateway_ip": null,
        "dns_servers": [],
        "allow_dns": true,
        "allow_proxy": true,
        "active_discovery": false,
        "managed": true,
        "id": 4,
        "space": "sdn-transport",
        "resource_uri": "/MAAS/api/2.0/subnets/4/"
    },
    {
        "name": "appformix",
        "description": "",
        "vlan": {
            "vid": 0,
            "mtu": 1500,
            "dhcp_on": false,
            "external_dhcp": null,
            "relay_vlan": null,
            "name": "untagged",
            "secondary_rack": null,
            "id": 5002,
            "space": "appformix-space",
            "primary_rack": null,
            "fabric": "fabric-1",
            "fabric_id": 1,
            "resource_uri": "/MAAS/api/2.0/vlans/5002/"
        },
        "cidr": "172.30.204.192/27",
        "rdns_mode": 2,
        "gateway_ip": "172.30.204.193",
        "dns_servers": [],
        "allow_dns": true,
        "allow_proxy": true,
        "active_discovery": false,
        "managed": true,
        "id": 2,
        "space": "appformix-space",
        "resource_uri": "/MAAS/api/2.0/subnets/2/"
    }
]