Comment 0 for bug 1669504

Given a network configuration that includes ipv4 and ipv6 configuration for an interface, as in:

   "networks": [
      {
         "id": "public-ipv6",
         "ip_address": "2604:A880:0400:00D0:0000:0000:1714:F001/64",
         "link": "interface-public",
         "netmask": "",
         "neutron_network_id": "937c94de-7029-586e-6e36-ea9af2d815de",
         "type": "ipv6",
         "routes": [
            {
               "gateway": "2604:A880:0400:00D0:0000:0000:0000:0001",
               "netmask": "::",
               "network": "::"
            }
         ]
      },
      {
         "id": "public-ipv4",
         "ip_address": "198.199.75.198",
         "link": "interface-public",
         "netmask": "255.255.255.0",
         "neutron_network_id": "7d9cd798-2dc0-502f-41ca-e04b552ddffd",
         "type": "ipv4",
         "routes": [
            {
               "gateway": "198.199.75.1",
               "netmask": "0.0.0.0",
               "network": "0.0.0.0"
            }
         ]
      }
    ]

cloud-init will fail because both subnets provide a default route, resulting in the error:

    Duplicate declaration of default route found for interface eth0