Open Stack

Hi,

I'm trying to create instance in OpenStack Victoria. But, I am
facing an issues about dhcp of neutron.I have OpenStack 
Victoria running in one baremetl server with uniontech os
(a downstream of centos 8). 

I have a Flat network created in the range of 10.12.21.190-
10.12.21.195. I selected to have a DHCP. The instance ran,
and neutron-dhcp-agent.service had allocated an IP to it. 
# openstack server list
+--------------------------------------+-------+--------+-----------------------+----------------+--------+
| ID                                   | Name  | Status | Networks              | Image          | Flavor |
+--------------------------------------+-------+--------+-----------------------+----------------+--------+
| 4ccae37e-fbfe-4acb-a109-e1bc9175c2e0 | inst1 | ACTIVE | provider=10.12.21.192 | centos8-server | h2     |
+--------------------------------------+-------+--------+-----------------------+----------------+--------+
But the instance can't get a response from DHCP.  No any
error in log. And if I setup the ip manually in the instance
I can get access to the gateway, dhcp port and external 
network.

I can catpure the DHCP request in any network device in
the server, include dhcp port. But no response.  Dnsmasq
process was running and had allocated an IP for instance. 


For details information: 
https://paste.opendev.org/show/811477/

I would very very appreciate any kind of guidance or help.

Thanks,
Han Guangyu