Comment 4 for bug 1979528

Hi Bence, thanks for the update. The problem of the "--gateway none" is removing the actual GW from the agent subnet as well, which makes all DNS requests coming from VMs to dnsmasq to fail. This trick works temporarily until the agent is "refreshed" (new config) or a new port is added, etc.

I found the source for the "0.0.0.0/0" route: https://bugs.launchpad.net/neutron/+bug/1317935
I'm not a network expert, but here is a quote from https://datatracker.ietf.org/doc/html/rfc3442

Local Subnet Routes

   In some cases more than one IP subnet may be configured on a link.
   In such cases, a host whose IP address is in one IP subnet in the
   link could communicate directly with a host whose IP address is in a
   different IP subnet on the same link. In cases where a client is
   being assigned an IP address on an IP subnet on such a link, for each
   IP subnet in the link other than the IP subnet on which the client
   has been assigned the DHCP server MAY be configured to specify a
   router IP address of 0.0.0.0.

   For example, consider the case where there are three IP subnets
   configured on a link: 10.0.0/24, 192.168.0/24, 10.0.21/24. If the
   client is assigned an IP address of 10.0.21.17, then the server could
   include a route with a destination of 10.0.0/24 and a router address
   of 0.0.0.0, and also a route with a destination of 192.168.0/24 and a
   router address of 0.0.0.0.

   A DHCP client whose underlying TCP/IP stack does not provide this
   capability MUST ignore routes in the Classless Static Routes option
   whose router IP address is 0.0.0.0. Please note that the behavior
   described here only applies to the Classless Static Routes option,
   not to the Static Routes option nor the Router option.

For me 0.0.0.0/0 is not the same as 0.0.0.0 (or 0.0.0.0/32). Please correct me if I'm wrong.