Comment 6 for bug 1979528

Hi Bence,

Apologies for a late response. Has a lot of stuff to do...

> We can set the dns servers also from dhcp options

This is true, but then you're loosing the dnsmasq caching possibility. If I set upstream DNS servers, they may be bombarded by DNS clients in the private networks.

> What exactly do you mean by this?

It's hard to explain, because I haven't digged into this deeper. My actual "trick" is this one:

openstack subnet set subnet-data --gateway 10.180.0.1 # sets the default GW on the agent and DHCP option
oopenstack subnet set subnet-data --gateway none # unsets it, but it is still kept on the agent for some time

The default GW on the agent disappears after some time and DNS requests become unusable again.

> To be honest, I don't see how this quote is relevant here.

Initial change (https://bugs.launchpad.net/neutron/+bug/1317935) introduced the "0.0.0.0/0,10.180.0.1" route option, which basically means the default gateway. RFC3442 doesn't tell that there must be the "0.0.0.0/0" CIDR, it mentions only the "0.0.0.0" address.

Long story short: DHCP agents don't have default gateway when the "--gateway none" is set and they become useless.