gw arp didn't resolve

neutron router lab's gw arp didn't resolve, as a result, group 200001 drops all packets.

stack@NVP-Zan-cp1-c1-m1-mgmt:~/logs$ sudo ovs-ofctl -Oopenflow13 dump-groups br-int
OFPST_GROUP_DESC reply (OF1.3) (xid=0x2):
group_id=210004,type=all,bucket=actions=group:210003,bucket=actions=set_field:0x138a->tun_id,output:8,bucket=actions=set_field:0x138a->tun_id,output:6,bucket=actions=set_field:0x138a->tun_id,output:7,bucket=actions=set_field:0x138a->tun_id,output:5
group_id=200001,type=all,bucket=actions=drop
group_id=210002,type=all,bucket=actions=group:210001,bucket=actions=set_field:0x1389->tun_id,output:8,bucket=actions=set_field:0x1389->tun_id,output:6,bucket=actions=set_field:0x1389->tun_id,output:7,bucket=actions=set_field:0x1389->tun_id,output:5
group_id=210001,type=all,bucket=actions=set_field:0x10->tun_id,resubmit(,55)
group_id=209999,type=all
group_id=210003,type=all,bucket=actions=set_field:0x11->tun_id,resubmit(,55)
group_id=150000,type=all,bucket=actions=set_field:fa:16:3e:b2:c9:ec->eth_dst,load:0x1100->NXM_NX_REG6[],resubmit(,220)
group_id=210000,type=all,bucket=actions=group:209999,bucket=actions=load:0x700->NXM_NX_REG6[],resubmit(,220)