SDN: "Backend isolated network" DHCP failing without gateway

[Shlee]

Hey team, I'm on the latest packages on a enterprise sub.

I want to build a SDN Zone that is private/internally routed only... a nice dumb switch with no internet access.


I've added a simple Zone, with a VNET... and added a subnet called BE with a DHCP range


This results in an eth interface with no IPv4 from the DHCP


Now.. adding a gateway to the subnet


This fixes the DHCP lease for IPv4...

but also breaks my routing!


I assume this might be worth a bug report in the bugzilla, but I've never used that before (I'll look into it if this issue is not user error)

 

[spirit]

your subnet is wrong (192.168.100.1/24).

it should be 192.168.100.0/24


(I think we need to add some verification in the code to avoid this kind of error ^_^ )

 

[Shlee]

I will confirm.. thank you for catching that

edit: I've fixed the subnet.. but the original issue remains (no IPv4 via DHCP)

 

[spirit]

you need an ip on the vnet (currently this is the gatewayip), to be able to receive ip from dhcp. (dhcp server need a source ip address,and currently we reuse same ip than gateway, and a default gw route is also send)


so, your problem is that you have 2 default gw on webwp... ? (do you have 2 interfaces ? if yes, both on vnets with dhcp ?)

 

[Shlee]

In short yeah, the gateway isn't actually the problem... it's the fact the route for the VNET seems to be 0.0.0.0/0 instead of the subnet.
I'd expect a second ETH interface to route to the subnet.

example:
Based on my default routes... once I add the secondary internal VNET interface. "BE"

I'd want to see `192.168.100.0/24 dev BE` etc etc

 

[spirit]

In short yeah, the gateway isn't actually the problem... it's the fact the route for the VNET seems to be 0.0.0.0/0 instead of the subnet.
I'd expect a second ETH interface to route to the subnet.

example:
Based on my default routes... once I add the secondary internal VNET interface. "BE"
View attachment 59924
I'd want to see `192.168.100.0/24 dev BE` etc etc

ok thanks. So It's really that you don't want to receive the default gw on this second interface.
I think it's on the coming roadmap (also managing static routes)

just to be sure, can you try to edit

/etc/dnsmasq.d/<zone>/10-<vnet>.conf (with vnet of the secondary iface)

and remove the first line
"dhcp-option=....option:router,..."

then "systemctl restart dnsmasq@zone"

 

[arthurrosa]

I'm trying to do the same thing! I tried what @spirit recommended and removed the first line from the dnsmasq configuration, then requested a new lease. My VM was still handed a default route on that interface. It's easy enough to tell my systems to ignore the default route in their config but it would be great to not have to do that on every machine I connect to this backend transit network.