Can/should ACA configure gateway when only subnet state is provided?

[zzxgzgz]

Current observation from @cj-chung is that, when a VM is created, it sends a DHCP request, and got the gateway address from the DHCP reply, and the VM will try to ping the gateway. However, because there's no arp entry or flow added for the gateway, the gateway cannot be pinged.

As we can see in https://github.com/futurewei-cloud/alcor/blob/master/schema/proto3/subnet.proto#L41, gateway IP and MAC are provided in a subnet state.

Can/should ACA configure gateway(Add flow/ add arp entry) if the goalstate doesn't have a router state, but has a subnet state, which contains the gateway info?

[er1cthe0ne]

I am guessing without configuring the gateway, below scenario would be broken, can you confirm?

1. create a VM without router connected
2. connect the router later

If the above is confirmed broken, then I think the answer is yes.

[cj-chung]

This is the scenario#5 I am working on. It should work after merge my dpm code.
I think the question here is that when VM booting up without attach its subnet to router, the VM actually will get its default gw from DHCP server, but the VM cannot ping the default gateway since there is no router for its subnet yet. Should we let the VM able to ping its default gw even there is no router exist?

[er1cthe0ne]

Two few things to think about:

1. if VM cannot ping the default gateway when it boots, does the default gateway setting stick so that L3 traffic will work later when router is added?
2. it will be good to mirror neutron's behavior, I believe a real gateway port exists and pingable when subnet is created. Please confirm.