gateway reappears after reconfiguring dhcp

[webteam-app]

Bug originally filed by arif-ali at https://bugs.launchpad.net/bugs/1903586

MAAS version: 2.8.2
Package: snap and deb

If we have MAAS running with any subnet where we are providing dhcp, MAAS will automatically add a gateway IP address if the subnet is reconfigured and the Reconfigure DHCP button is pressed.

Steps to re-produce:

1. Click Subnets
2. Add a new subnet, name "test" -> CIDR "10.0.6.0/24" -> "Add subnet"
3. Click on the vlan associated with the new subnet
4. Click on "Reconfigure DHCP"
5. Choose the subnet and Start IP Address: 10.0.6.101, End IP Address: 10.0.6.199, blank out the Gateway IP. Click "Reconfigure DHCP"
6. On the new page, click 10.0.6.0/25 under the "Subnets on this VLAN". We will see that the Gateway IP has not been set
7. Go back click on "Reconfigure DHCP" and on the new page click "Reconfigure DHCP"
8. On the new page, click 10.0.6.0/25 under the "Subnets on this VLAN". We will see that the Gateway IP has now been set to 10.0.6.1

If we set the Start IP address to 10.0.6.1, then the Gateway IP is also set, but now to 10.0.6.254 instead of 10.0.6.1, as that is now being used.

We are also able to see the same updates in /var/lib/maas/dhcpd.conf where the parameter "option routers 10.0.6.1;" will exist.

We should not expect the gateway to be set, if the gateway is blank in the UI.

[vtapia]

I believe the issue comes from line 345 in legacy/src/app/controllers/vlan_details.js:

340 if (angular.isString(suggested_gateway)) {
341 if (forRelay) {
342 dhcp.gatewayIP = "";
343 dhcp.gatewayPlaceholder = suggested_gateway + " (optional)";
344 } else {
345 dhcp.gatewayIP = suggested_gateway;
346 dhcp.gatewayPlaceholder = suggested_gateway;
347 }

Is there a reason why the gateway has to be generated/populated based on subnet.statistics?

[Caleb-Ellis]

Hi @vtapia! Thanks for looking into this.

I've got no idea why the gateway is being set based on subnet.statistics - we haven't yet reached the Subnets tab in our efforts to modernise the codebase so can't answer any "why" questions just yet. My guess it it's just for convenience so a user doesnt have to enter the IP manually, but at some point a bug has been introduced where in certain cases dhcp.gatewayIP is not surfaced in the UI and is therefore both sent unknowingly and completely unchangeable.

I think your fix in vtapia@a7808e1 is sound. If you create a pull request on this repo I'll be happy to approve it.

[vtapia]

Done, thanks @Caleb-Ellis !