Not sure where the AttributeError on dns_name is coming from.

But looks like that this '"dns_name": null,' coming from "Routers returned to l3 agent"

http://logs.openstack.org/62/324262/3/gate/gate-grenade-dsvm-neutron-multinode/9af98c8/logs/new/screen-q-svc.txt.gz#_2016-07-25_10_18_57_090

2016-07-25 10:18:57.090 31579 DEBUG neutron.api.rpc.handlers.l3_rpc [req-8614958e-93af-4166-9642-7dbdecee2900 - -] Routers returned to l3 agent:
 [
     {
          "status": "ACTIVE",
          "_interfaces": [
               {
                    "status": "ACTIVE",
                    "subnets": [
                         {
                              "dns_nameservers": [],
                              "ipv6_ra_mode": "slaac",
                              "gateway_ip": "fda4:bff1:9226::1",
                              "cidr": "fda4:bff1:9226::/64",
                              "id": "fd6b43b3-e384-4458-b5d3-94cb8ddeeffc",
                              "subnetpool_id": null
                         }
                    ],
                    "binding:host_id": "ubuntu-trusty-2-node-rax-ord-2845415",
                    "description": "",
                    "allowed_address_pairs": [],
                    "extra_dhcp_opts": [],
                    "updated_at": "2016-07-25T09:58:10",
                    "device_owner": "network:router_interface",
                    "port_security_enabled": false,
                    "binding:profile": {},
                    "mtu": 1400,
                    "fixed_ips": [
                         {
                              "subnet_id": "fd6b43b3-e384-4458-b5d3-94cb8ddeeffc",
                              "prefixlen": 64,
                              "ip_address": "fda4:bff1:9226::1"
                         }
                    ],
                    "id": "09d20977-0258-462a-9dde-f38d3cabdba1",
                    "security_groups": [],
                    "device_id": "d8c9b97c-1fd0-4644-a224-8250b144f40a",
                    "name": "",
                    "admin_state_up": true,
                    "network_id": "f1ad1be3-f572-4f14-b562-bf960cc1d2e1",
                    "dns_name": null,
                    "binding:vif_details": {
                         "port_filter": true,
                         "ovs_hybrid_plug": true
                    },
                    "address_scopes": {
                         "4": null,
                         "6": null
                    },
                    "binding:vnic_type": "normal",
                    "binding:vif_type": "ovs",
                    "tenant_id": "b583b372fa3e4828b7d7807529e0c61d",
                    "mac_address": "fa:16:3e:80:b3:c1",
                    "extra_subnets": [
                         {
                              "dns_nameservers": [],
                              "ipv6_ra_mode": null,
                              "gateway_ip": "10.1.0.1",
                              "cidr": "10.1.0.0/20",
                              "id": "b2c49785-5d6a-4ed3-9eef-ba80fcf353da",
                              "subnetpool_id": null
                         }
                    ],
                    "created_at": "2016-07-25T09:58:09"
               },
               {
                    "status": "ACTIVE",
                    "subnets": [
                         {
                              "dns_nameservers": [],
                              "ipv6_ra_mode": null,
                              "gateway_ip": "10.1.0.1",
                              "cidr": "10.1.0.0/20",
                              "id": "b2c49785-5d6a-4ed3-9eef-ba80fcf353da",
                              "subnetpool_id": null
                         }
                    ],
                    "binding:host_id": "ubuntu-trusty-2-node-rax-ord-2845415",
                    "description": "",
                    "allowed_address_pairs": [],
                    "extra_dhcp_opts": [],
                    "updated_at": "2016-07-25T09:58:04",
                    "device_owner": "network:router_interface",
                    "port_security_enabled": false,
                    "binding:profile": {},
                    "mtu": 1400,
                    "fixed_ips": [
                         {
                              "subnet_id": "b2c49785-5d6a-4ed3-9eef-ba80fcf353da",
                              "prefixlen": 20,
                              "ip_address": "10.1.0.1"
                         }
                    ],
                    "id": "7c9429d6-6469-467a-8792-8f6a37dc1ddf",
                    "security_groups": [],
                    "device_id": "d8c9b97c-1fd0-4644-a224-8250b144f40a",
                    "name": "",
                    "admin_state_up": true,
                    "network_id": "f1ad1be3-f572-4f14-b562-bf960cc1d2e1",
                    "dns_name": null,
                    "binding:vif_details": {
                         "port_filter": true,
                         "ovs_hybrid_plug": true
                    },
                    "address_scopes": {
                         "4": null,
                         "6": null
                    },
                    "binding:vnic_type": "normal",
                    "binding:vif_type": "ovs",
                    "tenant_id": "b583b372fa3e4828b7d7807529e0c61d",
                    "mac_address": "fa:16:3e:d7:b8:22",
                    "extra_subnets": [
                         {
                              "dns_nameservers": [],
                              "ipv6_ra_mode": "slaac",
                              "gateway_ip": "fda4:bff1:9226::1",
                              "cidr": "fda4:bff1:9226::/64",
                              "id": "fd6b43b3-e384-4458-b5d3-94cb8ddeeffc",
                              "subnetpool_id": null
                         }
                    ],
                    "created_at": "2016-07-25T09:58:01"
               }
          ],