3 files changed, 28 insertions, 13 deletions
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 46d3a6646..3e6196aee 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -451,7 +451,7 @@ func (n *NIC) primaryIPv6Endpoint(remoteAddr tcpip.Address) *referencedNetworkEn
 	cs := make([]ipv6AddrCandidate, 0, len(primaryAddrs))
 	for _, r := range primaryAddrs {
 		// If r is not valid for outgoing connections, it is not a valid endpoint.
-		if !r.isValidForOutgoing() {
+		if !r.isValidForOutgoingRLocked() {
 			continue
 		}
 
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index ebb6c5e3b..13354d884 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -551,11 +551,13 @@ type TransportEndpointInfo struct {
 	RegisterNICID tcpip.NICID
 }
 
-// AddrNetProto unwraps the specified address if it is a V4-mapped V6 address
-// and returns the network protocol number to be used to communicate with the
-// specified address. It returns an error if the passed address is incompatible
-// with the receiver.
-func (e *TransportEndpointInfo) AddrNetProto(addr tcpip.FullAddress, v6only bool) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
+// AddrNetProtoLocked unwraps the specified address if it is a V4-mapped V6
+// address and returns the network protocol number to be used to communicate
+// with the specified address. It returns an error if the passed address is
+// incompatible with the receiver.
+//
+// Preconditon: the parent endpoint mu must be held while calling this method.
+func (e *TransportEndpointInfo) AddrNetProtoLocked(addr tcpip.FullAddress, v6only bool) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
 	netProto := e.NetProto
 	switch len(addr.Addr) {
 	case header.IPv4AddressSize:
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index edf6bec52..e15db40fb 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -2790,13 +2790,14 @@ func TestNewPEBOnPromotionToPermanent(t *testing.T) {
 
 func TestIPv6SourceAddressSelectionScopeAndSameAddress(t *testing.T) {
 	const (
-		linkLocalAddr1   = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
-		linkLocalAddr2   = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
-		uniqueLocalAddr1 = tcpip.Address("\xfc\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
-		uniqueLocalAddr2 = tcpip.Address("\xfd\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
-		globalAddr1      = tcpip.Address("\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
-		globalAddr2      = tcpip.Address("\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
-		nicID            = 1
+		linkLocalAddr1         = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+		linkLocalAddr2         = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
+		linkLocalMulticastAddr = tcpip.Address("\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+		uniqueLocalAddr1       = tcpip.Address("\xfc\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+		uniqueLocalAddr2       = tcpip.Address("\xfd\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
+		globalAddr1            = tcpip.Address("\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+		globalAddr2            = tcpip.Address("\xa0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02")
+		nicID                  = 1
 	)
 
 	// Rule 3 is not tested here, and is instead tested by NDP's AutoGenAddr test.
@@ -2870,6 +2871,18 @@ func TestIPv6SourceAddressSelectionScopeAndSameAddress(t *testing.T) {
 			expectedLocalAddr: linkLocalAddr1,
 		},
 		{
+			name:              "Link Local most preferred for link local multicast (last address)",
+			nicAddrs:          []tcpip.Address{globalAddr1, uniqueLocalAddr1, linkLocalAddr1},
+			connectAddr:       linkLocalMulticastAddr,
+			expectedLocalAddr: linkLocalAddr1,
+		},
+		{
+			name:              "Link Local most preferred for link local multicast (first address)",
+			nicAddrs:          []tcpip.Address{linkLocalAddr1, uniqueLocalAddr1, globalAddr1},
+			connectAddr:       linkLocalMulticastAddr,
+			expectedLocalAddr: linkLocalAddr1,
+		},
+		{
 			name:              "Unique Local most preferred (last address)",
 			nicAddrs:          []tcpip.Address{uniqueLocalAddr1, globalAddr1, linkLocalAddr1},
 			connectAddr:       uniqueLocalAddr2,