check that the lease includes an IP address of the requested family b…

…efore configuring the flannel interface

pkg/backend/vxlan/vxlan.go

@@ -220,11 +220,17 @@ func (be *VXLANBackend) RegisterNetwork(ctx context.Context, wg *sync.WaitGroup,
 	// This IP is just used as a source address for host to workload traffic (so
 	// the return path for the traffic has an address on the flannel network to use as the destination)
 	if config.EnableIPv4 {
+		if lease.Subnet.Empty() {
+			return nil, fmt.Errorf("failed to configure interface %s: IPv4 is enabled but the lease has no IPv4", dev.link.Attrs().Name)
+		}
 		if err := dev.Configure(ip.IP4Net{IP: lease.Subnet.IP, PrefixLen: 32}, config.Network); err != nil {
 			return nil, fmt.Errorf("failed to configure interface %s: %w", dev.link.Attrs().Name, err)
 		}
 	}
 	if config.EnableIPv6 {
+		if lease.IPv6Subnet.Empty() {
+			return nil, fmt.Errorf("failed to configure interface %s: IPv6 is enabled but the lease has no IPv6", v6Dev.link.Attrs().Name)
+		}
 		if err := v6Dev.ConfigureIPv6(ip.IP6Net{IP: lease.IPv6Subnet.IP, PrefixLen: 128}, config.IPv6Network); err != nil {
 			return nil, fmt.Errorf("failed to configure interface %s: %w", v6Dev.link.Attrs().Name, err)
 		}

pkg/backend/wireguard/wireguard.go

@@ -171,13 +171,21 @@ func (be *WireguardBackend) RegisterNetwork(ctx context.Context, wg *sync.WaitGr
 	}
 
 	if config.EnableIPv4 {
+		if lease.Subnet.Empty() {
+			return nil, fmt.Errorf("failed to configure wg interface: IPv4 is enabled but the lease has no IPv4")
+		}
+
 		err = dev.Configure(lease.Subnet.IP, config.Network)
 		if err != nil {
 			return nil, err
 		}
 	}
 
 	if config.EnableIPv6 {
+		if lease.IPv6Subnet.Empty() {
+			return nil, fmt.Errorf("failed to configure wg interface: IPv6 is enabled but the lease has no IPv6")
+		}
+
 		if cfg.Mode == Separate {
 			err = v6Dev.ConfigureV6(lease.IPv6Subnet.IP, config.IPv6Network)
 		} else {