identify: filter nat64 well-known prefix ipv6 addresses (#2392)

p2p/protocol/identify/obsaddr.go

@@ -375,6 +375,11 @@ func shouldRecordObservation(host addrsProvider, network listenAddrsProvider, co
 		return false
 	}
 
+	// Provided by NAT64 peers, these addresses are specific to the peer and not publicly routable
+	if manet.IsNAT64IPv4ConvertedIPv6Addr(observed) {
+		return false
+	}
+
 	// we should only use ObservedAddr when our connection's LocalAddr is one
 	// of our ListenAddrs. If we Dial out using an ephemeral addr, knowing that
 	// address's external mapping is not very useful because the port will not be

p2p/protocol/identify/obsaddr_glass_test.go

@@ -4,6 +4,7 @@ package identify
 // can access internal types.
 
 import (
+	"fmt"
 	"testing"
 
 	ma "github.com/multiformats/go-multiaddr"
@@ -103,3 +104,50 @@ func TestShouldRecordObservationWithWebTransport(t *testing.T) {
 
 	require.True(t, shouldRecordObservation(h, h, c, observedAddr))
 }
+
+func TestShouldRecordObservationWithNAT64Addr(t *testing.T) {
+	listenAddr1 := ma.StringCast("/ip4/0.0.0.0/tcp/1234")
+	ifaceAddr1 := ma.StringCast("/ip4/10.0.0.2/tcp/4321")
+	listenAddr2 := ma.StringCast("/ip6/::/tcp/1234")
+	ifaceAddr2 := ma.StringCast("/ip6/1::1/tcp/4321")
+
+	h := &mockHost{
+		listenAddrs:      []ma.Multiaddr{listenAddr1, listenAddr2},
+		ifaceListenAddrs: []ma.Multiaddr{ifaceAddr1, ifaceAddr2},
+		addrs:            []ma.Multiaddr{listenAddr1, listenAddr2},
+	}
+	c := &mockConn{
+		local:  listenAddr1,
+		remote: ma.StringCast("/ip4/1.2.3.6/tcp/4321"),
+	}
+
+	cases := []struct {
+		addr          ma.Multiaddr
+		want          bool
+		failureReason string
+	}{
+		{
+			addr:          ma.StringCast("/ip4/1.2.3.4/tcp/1234"),
+			want:          true,
+			failureReason: "IPv4 should be observed",
+		},
+		{
+			addr:          ma.StringCast("/ip6/1::4/tcp/1234"),
+			want:          true,
+			failureReason: "public IPv6 address should be observed",
+		},
+		{
+			addr:          ma.StringCast("/ip6/64:ff9b::192.0.1.2/tcp/1234"),
+			want:          false,
+			failureReason: "NAT64 IPv6 address shouldn't be observed",
+		},
+	}
+	for i, tc := range cases {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+
+			if shouldRecordObservation(h, h, c, tc.addr) != tc.want {
+				t.Fatalf("%s %s", tc.addr, tc.failureReason)
+			}
+		})
+	}
+}