[management, client] Add IPv6 overlay support (#5631)

client/firewall/manager/routerpair.go

@@ -1,6 +1,8 @@
 package manager
 
 import (
+	"net/netip"
+
 	"github.com/netbirdio/netbird/route"
 )
 
@@ -10,6 +12,10 @@ type RouterPair struct {
 	Destination Network
 	Masquerade  bool
 	Inverse     bool
+	// Dynamic indicates the route is domain-based. NAT rules for dynamic
+	// routes are duplicated to the v6 table so that resolved AAAA records
+	// are masqueraded correctly.
+	Dynamic bool
 }
 
 func GetInversePair(pair RouterPair) RouterPair {
@@ -20,5 +26,17 @@ func GetInversePair(pair RouterPair) RouterPair {
 		Destination: pair.Source,
 		Masquerade:  pair.Masquerade,
 		Inverse:     true,
+		Dynamic:     pair.Dynamic,
 	}
 }
+
+// ToV6NatPair creates a v6 counterpart of a v4 NAT pair with `::/0` source
+// and, for prefix destinations, `::/0` destination.
+func ToV6NatPair(pair RouterPair) RouterPair {
+	v6 := pair
+	v6.Source = Network{Prefix: netip.PrefixFrom(netip.IPv6Unspecified(), 0)}
+	if v6.Destination.IsPrefix() {
+		v6.Destination = Network{Prefix: netip.PrefixFrom(netip.IPv6Unspecified(), 0)}
+	}
+	return v6
+}