identify: filter nat64 well-known prefix ipv6 addresses

p2p/protocol/identify/obsaddr.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"sort"
+	"strings"
 	"sync"
 	"time"
 
@@ -378,6 +379,11 @@ 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 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
@@ -435,6 +441,20 @@ func shouldRecordObservation(host addrsProvider, network listenAddrsProvider, co
 	return true
 }
 
+// isNAT64IPv4ConvertedIPv6Addr returns whether addr is an IPv6 address that begins with
+// the well known prefix "64:ff9b" used for NAT64 Translation
+// see RFC 6052
+func isNAT64IPv4ConvertedIPv6Addr(addr ma.Multiaddr) bool {
+	ip, err := addr.ValueForProtocol(ma.P_IP6)
+	if err != nil {
+		return false
+	}
+	if strings.HasPrefix(ip, "64:ff9b::") {
+		return true
+	}
+	return false
+}
+
 func (oas *ObservedAddrManager) maybeRecordObservation(conn network.Conn, observed ma.Multiaddr) {
 	shouldRecord := shouldRecordObservation(oas.host, oas.host.Network(), conn, observed)
 	if shouldRecord {

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 +104,39 @@ func TestShouldRecordObservationWithWebTransport(t *testing.T) {
 
 	require.True(t, shouldRecordObservation(h, h, c, observedAddr))
 }
+
+func TestIsWellKnownPrefixIPv4ConvertedIPv6Address(t *testing.T) {
+	cases := []struct {
+		addr          ma.Multiaddr
+		want          bool
+		failureReason string
+	}{
+		{
+			addr:          ma.StringCast("/ip4/1.2.3.4/tcp/1234"),
+			want:          false,
+			failureReason: "ip4 addresses should return false",
+		},
+		{
+			addr:          ma.StringCast("/ip6/1::4/tcp/1234"),
+			want:          false,
+			failureReason: "ip6 addresses doesn't have wellknown prefix",
+		},
+		{
+			addr:          ma.StringCast("/ip6/::1/tcp/1234"),
+			want:          false,
+			failureReason: "localhost addresses should return false",
+		},
+		{
+			addr:          ma.StringCast("/ip6/64:ff9b::192.0.1.2/tcp/1234"),
+			want:          true,
+			failureReason: "ip6 address begins with well-known prefix",
+		},
+	}
+	for i, tc := range cases {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			if isNAT64IPv4ConvertedIPv6Addr(tc.addr) != tc.want {
+				t.Fatalf("%s %s", tc.addr, tc.failureReason)
+			}
+		})
+	}
+}