[24.7] New Install in KVM (virt-manager) DNS issue

[AnyThing]

What I have in my mind/want to achieve:
- One NAT-ed interface
- One Isolated interface (created through virt-manager->edit->connection details->virtual networks->Add network->mode: Isolated, no DHCP, ip range 192.168.15.0/24)

Connect opnsense vm with the above two interface, WAN: NAT, LAN: Isol (192.168.15.0/24, enable dhcp inside opnsense)

I added the DNS 1.1.1.1 (WAN_GW-wan) and 8.8.8.8 (none) in http://192.168.15.1/system_general.php
Unbound DNS is running

Start an Ubuntu VM (connected to ONLY Isolated interface)

"browse internet normally (without doing anything)"

Issue:
T1: ping 8.8.8.8
T2: ping google.com

T1,T2 both works if I log in and try from opensense server itself (using option 7-ping host and 8-shell)

T1 works but T2 doesn't from ubuntu VM, with error msg: "Ping: google.com: Temporary failure in name resolution".

I am able to access the opnsense web-gui from ubuntu VM. Tried from http://192.168.15.1/ui/diagnostics/dns_diagnostics, hostname: google.com, dns-server: <Blank>, got response "AAAA   google.com. 300 IN AAAA 2404:6800:4007:81d::200e". T1, T2 worked from http://192.168.15.1/ui/diagnostics/ping as well.

Not sure, what I am missing. Any help on how to proceed further?

Thank you very much.

[AnyThing]

Okay.
Added DNS 8.8.8.8 and 1.1.1.1 to http://192.168.13.1/services_dhcp.php?if=lan (services->dhcpv4->[LAN]).
It worked. But not sure what is the DNS settings used for in the general->settings page, and why not LAN or unbound DNS not defaulted to that.

A separate issue, If I restart my ubuntu VM. I need to redo setup option 2 (in opnsense vm), Set interface IP address (LAN part) everytime, even to make T1 work or to access the web gui in the ubuntu VM. Not sure, why and how to overcome.