incusd/network/ovn: Fallback to OVN router address as DNS server

When no uplink is attached to an OVN network, use the OVN router's own
address as the advertised DNS address through DHCP.

Signed-off-by: Gwendolyn <[email protected]>

Author: gwenya

internal/server/network/driver_ovn.go

@@ -2660,6 +2660,8 @@ func (n *ovn) setup(update bool) error {
 
 		if uplinkNet != nil {
 			opts.RecursiveDNSServer = uplinkNet.dnsIPv4
+		} else {
+			opts.RecursiveDNSServer = []net.IP{routerIntPortIPv4}
 		}
 
 		err = n.ovnnb.UpdateLogicalSwitchDHCPv4Options(context.TODO(), n.getIntSwitchName(), dhcpv4UUID, dhcpV4Subnet, opts)
@@ -2677,6 +2679,8 @@ func (n *ovn) setup(update bool) error {
 
 		if uplinkNet != nil {
 			opts.RecursiveDNSServer = uplinkNet.dnsIPv6
+		} else {
+			opts.RecursiveDNSServer = []net.IP{routerIntPortIPv6}
 		}
 
 		err = n.ovnnb.UpdateLogicalSwitchDHCPv6Options(context.TODO(), n.getIntSwitchName(), dhcpv6UUID, dhcpV6Subnet, opts)
@@ -2698,6 +2702,8 @@ func (n *ovn) setup(update bool) error {
 		var recursiveDNSServer net.IP
 		if uplinkNet != nil && len(uplinkNet.dnsIPv6) > 0 {
 			recursiveDNSServer = uplinkNet.dnsIPv6[0] // OVN only supports 1 RA DNS server.
+		} else {
+			recursiveDNSServer = routerIntPortIPv6
 		}
 
 		err = n.ovnnb.UpdateLogicalRouterPort(context.TODO(), n.getRouterIntPortName(), &networkOVN.OVNIPv6RAOpts{