Comment 5 for bug 1668145

If I understand correctly, what you need is a way to disable advertisement of local static routes from DHCP agent, right?
I haven't understood how neutron "segments" feature does not work for you.

> a) Segments cannot be safely backported. This could?

In General, any new feature cannot be backported according to the OpenStack backport policy.

Do you mean you backport something by yourself?

> b) Segments do not currently work with DHCP-relay. This approach would.

I think this depends on what DHCP implementation is provided for a subnet.
DHCP relay just forwards DHCP requests with unicast communication.
What is a problem if local subnet routes is advertised? Are you thinking your own DHCP server?
I might be missing something.

> Source: https://tools.ietf.org/html/rfc3442
...
> The rfc says, quote:
> "the DHCP server MAY be configured to specify a router IP address of 0.0.0.0."

"0.0.0.0" in this case just means a corresponding subnet is reachable directly.
Do you mean this can be disabled perhaps?