Using Ansible to executed COPP Test, Ansible hangs up。

RUN TEST ：

ansible-playbook -i lab --limit dut-nephos-01 test_sonic.yml -e "testcase_name=copp testbed_type=ptf32 testbed_name=ptf1-m ptf_host=10.255.0.188"

TASK [test : PTF Test - COPP test - ARPTest]
Wednesday 27 December 2017 18:56:49 +0000 (0:00:00.211) 0:00:13.645
ok: [dut-nephos-01] => {
"msg": "ptf --test-dir ptftests copp_tests.ARPTest --qlen=100000 --platform nn -t "verbose=False;pkt_tx_count=0" --device-socket 0-3@tcp://127.0.0.1:10900 --device-socket 1-3@tcp://10.251.0.188:10900 --disable-vxlan --disable-geneve --disable-erspan --disable-mpls --disable-nvgre 2>&1"
}

TASK [test : command]
Wednesday 27 December 2017 18:56:49 +0000 (0:00:00.251) 0:00:13.896

Then Ansible-playbooks hangs up

I connect PTF docker，cat the info of the ptf.log as follows

18:56:49.755 root : INFO : Wed Dec 27 18:56:49 2017
18:56:49.783 scapy.loading: WARNING : Failed to execute tcpdump. Check it is installed and in the PATH
18:56:49.813 scapy.runtime: WARNING : No route found for IPv6 destination :: (no default route?)
18:56:49.927 root : INFO : Importing platform: nn
18:56:49.928 root : DEBUG : Configuration: {'xunit_dir': 'xunit', 'disable_ipv6': False, 'minsize': 0, 'list_test_names': False, 'test_file': None, 'test_spec': '', 'allow_user': False, 'test_order_seed': 2746, 'default_negative_timeout': 0.1, 'platform': 'nn', 'log_dir': None, 'xunit': False, 'disable_erspan': True, 'device_sockets': [(0, set([3]), 'tcp://127.0.0.1:10900'), (1, set([3]), 'tcp://10.251.0.188:10900')], 'disable_geneve': True, 'socket_recv_size': 4096, 'profile': False, 'default_timeout': 2.0, 'platform_args': None, 'relax': False, 'random_seed': None, 'interfaces': [], 'test_case_timeout': None, 'port_map': {(0, 3): 'tcp://127.0.0.1:10900', (1, 3): 'tcp://10.251.0.188:10900'}, 'disable_vxlan': True, 'disable_nvgre': True, 'qlen': 100000, 'test_order': 'default', 'profile_file': 'profile.out', 'fail_skipped': False, 'test_params': 'verbose=False;pkt_tx_count=0', 'test_dir': 'ptftests', 'list': False, 'platform_dir': '/usr/lib/python2.7/dist-packages/ptf/platforms', 'disable_mpls': True, 'debug': 'verbose', 'log_file': 'ptf.log', 'failfast': False}
18:56:49.928 root : INFO : port map: {(0, 3): 'tcp://127.0.0.1:10900', (1, 3): 'tcp://10.251.0.188:10900'}
18:56:49.928 root : INFO : Autogen random seed: 31938508

I try to ping sonic switch in ptf docker ,it is reachable

ping 10.0.0.0

64 bytes from 10.0.0.0: icmp_seq=1 ttl=64 time=3.36 ms

ping 10.0.0.2

64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=2.46 ms

If someone encountered a similar problem ,please give me a solution, thanks