Virtual network does not have both 'default_gateway' and 'dns_server_address' in some cases like below;
When VM uses Global IP address without both default gateway and dhcp, customer aims to use all of Global IP address for VM. Because each Global IP address is not wealth. Hence, customer wants to set both 'default_gateway' and 'dns_server_address' as '0.0.0.0'. 

However, if both attributes are set '0.0.0.0', there is no Interface of pkt0 for sending APR packet from vRouter. As a result, nova live-migration will not work well.
To avoid this issue, I'd like to propose two solutions below.
1) At least one Pkt0 interface will be allocated to each virtual-network even if both 'default_gateway' and 'dns_server_address' are set "0.0.0.0". If vrouter sends ARP request to VM, use "0.0.0.0" for Sender IP address in ARP packet.
 see DAD mode http://linux.die.net/man/8/arping 

2) Allow dummy IP address to 'dns_server_address' such as '169.254.169.1' when Customer does not want to consume any IP address for Contrail internal use.
   As per my test, nova live-migration with AAP worked well when I configured '169.254.169.1' to 'default_gateway'. I think dummy address will work in 'dns_server_address' after fixing this bug.
This is the JSON which I tested.
{
    "virtual-network": {
        "display_name": "test1", 
        "flood_unknown_unicast": false, 
        "fq_name": [
            "default-domain", 
            "admin", 
            "test1"
        ], 
        "href": "http://172.27.113.202:8082/virtual-network/02cf8444-8fdd-4451-91b5-967b7e6faf35", 
        "id_perms": {
            "created": "2016-03-03T00:55:47.726224", 
            "creator": null, 
            "description": null, 
            "enable": true, 
            "last_modified": "2016-03-03T00:55:47.841816", 
            "permissions": {
                "group": "admin", 
                "group_access": 7, 
                "other_access": 7, 
                "owner": "admin", 
                "owner_access": 7
            }, 
            "user_visible": true, 
            "uuid": {
                "uuid_lslong": 10499463563430571829, 
                "uuid_mslong": 202525938261247057
            }
        }, 
        "is_shared": false, 
        "name": "test1", 
        "network_ipam_refs": [
            {
                "attr": {
                    "ipam_subnets": [
                        {
                            "addr_from_start": true, 
                            "allocation_pools": [], 
                            "default_gateway": "169.254.169.1", 
                            "dhcp_option_list": {
                                "dhcp_option": [
                                    {
                                        "dhcp_option_name": "6", 
                                        "dhcp_option_value": "0.0.0.0"
                                    }
                                ]
                            }, 
                            "dns_server_address": "0.0.0.0", 
                            "enable_dhcp": false, 
                            "host_routes": {
                                "route": []
                            }, 
                            "subnet": {
                                "ip_prefix": "10.0.0.0", 
                                "ip_prefix_len": 24
                            }, 
                            "subnet_uuid": "88a0d5fa-60ee-4eef-8d25-514ce1f2625e"
                        }
                    ]
                }, 
                "href": "http://172.27.113.202:8082/network-ipam/1e12f68b-f45e-4b25-96b8-f97d212365a0", 
                "to": [
                    "default-domain", 
                    "default-project", 
                    "default-network-ipam"
                ], 
                "uuid": "1e12f68b-f45e-4b25-96b8-f97d212365a0"
            }
        ], 
        "parent_href": "http://172.27.113.202:8082/project/1ab63ac7-e359-4ff9-b6a4-fc15e303e1a0", 
        "parent_type": "project", 
        "parent_uuid": "1ab63ac7-e359-4ff9-b6a4-fc15e303e1a0", 
        "route_target_list": {}, 
        "router_external": false, 
        "routing_instances": [
            {
                "href": "http://172.27.113.202:8082/routing-instance/89e60b33-19a4-47fd-9341-6566a936e222", 
                "to": [
                    "default-domain", 
                    "admin", 
                    "test1", 
                    "test1"
                ], 
                "uuid": "89e60b33-19a4-47fd-9341-6566a936e222"
            }
        ], 
        "uuid": "02cf8444-8fdd-4451-91b5-967b7e6faf35", 
        "virtual_network_network_id": 8, 
        "virtual_network_properties": {
            "allow_transit": false, 
            "forwarding_mode": null
        }
    }
}