No Internet Connectivity in VLAN created with external DHCP server
I've created a few interface VLANs for groups of related devices and it's been relatively straightforward.
Internet connectivity has never been a problem.
Today, I setup a VLAN to test a configuration with DHCP not hosted on the router.
The reason behind this all is that I want local DNS and I'd like DHCP & DNS to be hosted on the same box to avoid having to correlate bits of information across multiples machines.
So I setup a NUC with Ubuntu, created a virtual NIC for the VLAN, and configured dnsmasq to handle DHCP/DNS for that VLAN/subnet only.
On the controller side, I created a TEST VLAN as usual (VLAN ID included in the fixed part of the range).
I disabled the DHCP server and specified a 10.x.x.2 address for the legal DHCP server (that's the address of the virtual NIC on the NUC).
I used the typical 10.x.x.1 for the gateway in the subnet.
Then I changed the profile of the switch port used by my test machine and released/renewed DHCP.
All went fine. I got an IP in the proper range, the Default Gateway is properly set to 10.x.x.1. The subnet mask is fine, as is the DNS domain.
BUT I can't ping that .1 address (gateway/router). I can ping the .2 address (DHCP/DNS server) though.
Somehow, the physical router does not seem to act as a gateway in this specific configuration (or maybe at another IP that I don't know how to discover).
In all my other VLANs, I can ping 10.y.y.1 from devices in that VLAN, as expected.
I attribute the lack of internet connectivity to the absence of a gateway at this 10.x.x.1 address. If the gateway picked another one (I didn't see a DHCP request for any other device), I don't know how to find it.
What am I missing?