DHCP service start failed

[shihanzhang]

In neutron.conf, I set 'force_gateway_on_subnet = False', then create a subnet with gateway ip out of
 subnet' CIDR, I found a error happen in dhcp.log, the log is bellow:

 [-] Unable to enable dhcp for af572283-3f32-4a12-9419-1154e9c386f9.
 Traceback (most recent call last):
   File "/usr/lib64/python2.6/site-packages/neutron/agent/dhcp_agent.py", line 128, in call_driver
     getattr(driver, action)(**action_kwargs)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/dhcp.py", line 167, in enable
     reuse_existing=True)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/dhcp.py", line 727, in setup
     self._set_default_route(network)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/dhcp.py", line 615, in _set_default_route
     device.route.add_gateway(subnet.gateway_ip)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/ip_lib.py", line 368, in add_gateway
     self._as_root(*args)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/ip_lib.py", line 217, in _as_root
     kwargs.get('use_root_namespace', False))
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/ip_lib.py", line 70, in _as_root
     namespace)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/ip_lib.py", line 81, in _execute
     root_helper=root_helper)
   File "/usr/lib64/python2.6/site-packages/neutron/agent/linux/utils.py", line 75, in execute
     raise RuntimeError(m)
 RuntimeError:
 Command: ['sudo', '/usr/bin/neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ip', 'netns', 'exec', 'qdhcp-af572283-3f32-4a12-9419-1154e9c386f9', 'ip', 'route', 'replace', 'default', 'via', '80.80.1.1', 'dev', 'tapcb420785-8d']
 Exit code: 2
 Stdout: ''
 Stderr: 'RTNETLINK answers: No such process\n'
 TRACE neutron.agent.dhcp_agent

[Sridhar Gaddam (sridhargaddam)]

Hi shihanzhang,

Looking at the error code, I feel that its expected as there is no route to reach the default gateway in the dhcp namespace.

I'm trying to understand the use-case, like what you plan to do by configuring a subnet with default gateway set to a value which is not part of the subnet CIDR. Please provide some details about your use-case.

--Sridhar.

[shihanzhang (shihanzhang)]

I don't have use-case for this problem, I also want to know why neutron provide this setting 'force_gateway_on_subnet', what is the real scenario?

[Salvatore Orlando (salvatore-orlando)]

In some IPv6 scenarios, the gateway might be outside of the subnet cidr.