4 files changed, 125 insertions, 1 deletions
diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
index 07d09abed..de3c7e2c3 100644
--- a/pkg/tcpip/header/BUILD
+++ b/pkg/tcpip/header/BUILD
@@ -45,7 +45,10 @@ go_test(
 go_test(
     name = "header_test",
     size = "small",
-    srcs = ["ndp_test.go"],
+    srcs = [
+        "eth_test.go",
+        "ndp_test.go",
+    ],
     embed = [":header"],
     deps = ["//pkg/tcpip"],
 )
diff --git a/pkg/tcpip/header/eth.go b/pkg/tcpip/header/eth.go
index 1bb3bb5e6..f5d2c127f 100644
--- a/pkg/tcpip/header/eth.go
+++ b/pkg/tcpip/header/eth.go
@@ -48,6 +48,28 @@ const (
 
 	// EthernetAddressSize is the size, in bytes, of an ethernet address.
 	EthernetAddressSize = 6
+
+	// unspecifiedEthernetAddress is the unspecified ethernet address
+	// (all bits set to 0).
+	unspecifiedEthernetAddress = tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00")
+
+	// unicastMulticastFlagMask is the mask of the least significant bit in
+	// the first octet (in network byte order) of an ethernet address that
+	// determines whether the ethernet address is a unicast or multicast. If
+	// the masked bit is a 1, then the address is a multicast, unicast
+	// otherwise.
+	//
+	// See the IEEE Std 802-2001 document for more details. Specifically,
+	// section 9.2.1 of http://ieee802.org/secmail/pdfocSP2xXA6d.pdf:
+	// "A 48-bit universal address consists of two parts. The first 24 bits
+	// correspond to the OUI as assigned by the IEEE, expect that the
+	// assignee may set the LSB of the first octet to 1 for group addresses
+	// or set it to 0 for individual addresses."
+	unicastMulticastFlagMask = 1
+
+	// unicastMulticastFlagByteIdx is the byte that holds the
+	// unicast/multicast flag. See unicastMulticastFlagMask.
+	unicastMulticastFlagByteIdx = 0
 )
 
 const (
@@ -90,3 +112,25 @@ func (b Ethernet) Encode(e *EthernetFields) {
 	copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr)
 	copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr)
 }
+
+// IsValidUnicastEthernetAddress returns true if addr is a valid unicast
+// ethernet address.
+func IsValidUnicastEthernetAddress(addr tcpip.LinkAddress) bool {
+	// Must be of the right length.
+	if len(addr) != EthernetAddressSize {
+		return false
+	}
+
+	// Must not be unspecified.
+	if addr == unspecifiedEthernetAddress {
+		return false
+	}
+
+	// Must not be a multicast.
+	if addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0 {
+		return false
+	}
+
+	// addr is a valid unicast ethernet address.
+	return true
+}
diff --git a/pkg/tcpip/header/eth_test.go b/pkg/tcpip/header/eth_test.go
new file mode 100644
index 000000000..6634c90f5
--- /dev/null
+++ b/pkg/tcpip/header/eth_test.go
@@ -0,0 +1,68 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+	"testing"
+
+	"gvisor.dev/gvisor/pkg/tcpip"
+)
+
+func TestIsValidUnicastEthernetAddress(t *testing.T) {
+	tests := []struct {
+		name     string
+		addr     tcpip.LinkAddress
+		expected bool
+	}{
+		{
+			"Nil",
+			tcpip.LinkAddress([]byte(nil)),
+			false,
+		},
+		{
+			"Empty",
+			tcpip.LinkAddress(""),
+			false,
+		},
+		{
+			"InvalidLength",
+			tcpip.LinkAddress("\x01\x02\x03"),
+			false,
+		},
+		{
+			"Unspecified",
+			unspecifiedEthernetAddress,
+			false,
+		},
+		{
+			"Multicast",
+			tcpip.LinkAddress("\x01\x02\x03\x04\x05\x06"),
+			false,
+		},
+		{
+			"Valid",
+			tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06"),
+			true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if got := IsValidUnicastEthernetAddress(test.addr); got != test.expected {
+				t.Fatalf("got IsValidUnicastEthernetAddress = %t, want = %t", got, test.expected)
+			}
+		})
+	}
+}
diff --git a/pkg/tcpip/header/ipv6.go b/pkg/tcpip/header/ipv6.go
index b125bbea5..f1e60911b 100644
--- a/pkg/tcpip/header/ipv6.go
+++ b/pkg/tcpip/header/ipv6.go
@@ -101,6 +101,15 @@ var IPv6EmptySubnet = func() tcpip.Subnet {
 	return subnet
 }()
 
+// IPv6LinkLocalPrefix is the prefix for IPv6 link-local addresses, as defined
+// by RFC 4291 section 2.5.6.
+//
+// The prefix is fe80::/64
+var IPv6LinkLocalPrefix = tcpip.AddressWithPrefix{
+	Address:   "\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
+	PrefixLen: 64,
+}
+
 // PayloadLength returns the value of the "payload length" field of the ipv6
 // header.
 func (b IPv6) PayloadLength() uint16 {