Add MTU options related to RA and config & daemon test

Signed-off-by: enigamict <[email protected]>

README.md

@@ -16,7 +16,7 @@ declarative configuration interface on top of it.
 
 - Basic RA mechanism defined in RFC4861
 - Router MAC address discovery with Source Link Layer Address option
-- TBD: MTU discovery with MTU option
+- MTU discovery with MTU option
 - Stateless Address Auto Configuration (SLAAC) with Prefix Information option
 - TBD: DNS auto configuration with RDNSS option
 

config.go

@@ -68,6 +68,11 @@ type InterfaceConfig struct {
 	// this router.
 	RetransmitTimeMilliseconds int `yaml:"retransmitTimeMilliseconds" json:"retransmitTimeMilliseconds" validate:"gte=0,lte=4294967295"`
 
+	// The maximum transmission unit (MTU) that should be used for outgoing
+	// This value specifies the largest packet size, in bytes,
+	// If set to zero or not specified, MTU opton will not be advertised
+	MTU int `yaml:"mtu" json:"mtu" validate:"gte=0,lte=4294967295"`
+
 	// Prefix-specific configuration parameters. The prefix fields must be
 	// non-overlapping with each other. The slice itself and elements must
 	// not be nil.

config_test.go

@@ -281,6 +281,36 @@ func TestConfigValidation(t *testing.T) {
 			errorField:  "RetransmitTimeMilliseconds",
 			errorTag:    "lte",
 		},
+		{
+			name: "MTU > 0",
+			config: &Config{
+				Interfaces: []*InterfaceConfig{
+					{
+						Name:                   "net0",
+						RAIntervalMilliseconds: 1000,
+						MTU:                    -1,
+					},
+				},
+			},
+			expectError: true,
+			errorField:  "MTU",
+			errorTag:    "gte",
+		},
+		{
+			name: "MTU > 4294967295",
+			config: &Config{
+				Interfaces: []*InterfaceConfig{
+					{
+						Name:                   "net0",
+						RAIntervalMilliseconds: 1000,
+						MTU:                    4294967296,
+					},
+				},
+			},
+			expectError: true,
+			errorField:  "MTU",
+			errorTag:    "lte",
+		},
 		{
 			name: "Nil PrefixConfig",
 			config: &Config{

daemon_test.go

@@ -39,8 +39,8 @@ outer:
 		}
 	}
 
-	// Ensure the interval is correct. We let 5ms of error margin.
-	mergin := float64(5 * time.Millisecond)
+	// Ensure the interval is correct. We let 60ms of error margin.
+	mergin := float64(60 * time.Millisecond)
 	diff0 := ras[1].tstamp.Sub(ras[0].tstamp)
 	diff1 := ras[2].tstamp.Sub(ras[1].tstamp)
 
@@ -59,6 +59,7 @@ func TestDaemonHappyPath(t *testing.T) {
 				RouterLifetimeSeconds:      10,
 				ReachableTimeMilliseconds:  10000,
 				RetransmitTimeMilliseconds: 10000,
+				MTU:                        1500,
 			},
 			{
 				Name:                   "net1",
@@ -112,6 +113,17 @@ func TestDaemonHappyPath(t *testing.T) {
 		require.Equal(t, time.Second*10, ra.msg.RouterLifetime)
 		require.Equal(t, time.Millisecond*10000, ra.msg.ReachableTime)
 		require.Equal(t, time.Millisecond*10000, ra.msg.RetransmitTimer)
+
+		// Find MTU option
+		var mtuOption *ndp.MTU
+		for _, option := range ra.msg.Options {
+			if opt, ok := option.(*ndp.MTU); ok {
+				mtuOption = opt
+				break
+			}
+		}
+		require.NotNil(t, mtuOption, "MTU option is not advertised")
+		require.Equal(t, uint32(1500), mtuOption.MTU, "Invalid MTU")
 	})
 
 	t.Run("Ensure the status is running and the result is ordered by name", func(t *testing.T) {

ra_sender.go

@@ -51,6 +51,22 @@ func newRASender(initialConfig *InterfaceConfig, ctor rAdvSocketCtor, logger *sl
 	}
 }
 
+func (s *raSender) setOptions(config *InterfaceConfig) []ndp.Option {
+	options := []ndp.Option{
+		&ndp.LinkLayerAddress{
+			Direction: ndp.Source,
+			Addr:      s.sock.hardwareAddr(),
+		},
+	}
+
+	if config.MTU > 0 {
+		options = append(options, &ndp.MTU{
+			MTU: uint32(config.MTU),
+		})
+	}
+	return options
+}
+
 func (s *raSender) reportRunning() {
 	s.statusLock.Lock()
 	defer s.statusLock.Unlock()
@@ -157,12 +173,7 @@ reload:
 			RouterLifetime:       time.Duration(config.RouterLifetimeSeconds) * time.Second,
 			ReachableTime:        time.Duration(config.ReachableTimeMilliseconds) * time.Millisecond,
 			RetransmitTimer:      time.Duration(config.RetransmitTimeMilliseconds) * time.Millisecond,
-			Options: []ndp.Option{
-				&ndp.LinkLayerAddress{
-					Direction: ndp.Source,
-					Addr:      s.sock.hardwareAddr(),
-				},
-			},
+			Options:              s.setOptions(config),
 		}
 
 		for _, prefix := range config.Prefixes {