Internal macvlan networks don't need a gateway address.

Signed-off-by: Rob Murray <rob.murray@docker.com>

integration/network/macvlan/macvlan_test.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"strings"
 	"testing"
+	"time"
 
 	containertypes "github.com/docker/docker/api/types/container"
 	"github.com/docker/docker/api/types/network"
@@ -627,3 +628,35 @@ func TestMACVlanDNS(t *testing.T) {
 		})
 	}
 }
+
+// TestPointToPoint checks that no gateway is reserved for a macvlan network
+// with no parent interface (an "internal" network).
+func TestPointToPoint(t *testing.T) {
+	ctx := testutil.StartSpan(baseContext, t)
+	apiClient := testEnv.APIClient()
+
+	const netName = "p2pmacvlan"
+	net.CreateNoError(ctx, t, apiClient, netName,
+		net.WithMacvlan(""),
+		net.WithIPAM("192.168.135.0/31", ""),
+	)
+	defer net.RemoveNoError(ctx, t, apiClient, netName)
+
+	const ctrName = "ctr1"
+	id := container.Run(ctx, t, apiClient,
+		container.WithNetworkMode(netName),
+		container.WithName(ctrName),
+	)
+	defer apiClient.ContainerRemove(ctx, id, containertypes.RemoveOptions{Force: true})
+
+	attachCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+	res := container.RunAttach(attachCtx, t, apiClient,
+		container.WithCmd([]string{"ping", "-c1", "-W3", ctrName}...),
+		container.WithNetworkMode(netName),
+	)
+	defer apiClient.ContainerRemove(ctx, res.ContainerID, containertypes.RemoveOptions{Force: true})
+	assert.Check(t, is.Equal(res.ExitCode, 0))
+	assert.Check(t, is.Equal(res.Stderr.Len(), 0))
+	assert.Check(t, is.Contains(res.Stdout.String(), "1 packets transmitted, 1 packets received"))
+}

libnetwork/drivers/macvlan/macvlan_network.go

@@ -40,7 +40,6 @@ func (d *driver) CreateNetwork(nid string, option map[string]interface{}, nInfo
 	// if parent interface not specified, create a dummy type link to use named dummy+net_id
 	if config.Parent == "" {
 		config.Parent = getDummyName(config.ID)
-		config.Internal = true
 	}
 	foundExisting, err := d.createNetwork(config)
 	if err != nil {
@@ -62,6 +61,15 @@ func (d *driver) CreateNetwork(nid string, option map[string]interface{}, nInfo
 	return nil
 }
 
+func (d *driver) GetSkipGwAlloc(opts options.Generic) (ipv4, ipv6 bool, _ error) {
+	cfg, err := parseNetworkOptions("dummy", opts)
+	if err != nil {
+		return false, false, err
+	}
+	// "--internal" networks don't need a gateway address.
+	return cfg.Internal, cfg.Internal, nil
+}
+
 // createNetwork is used by new network callbacks and persistent network cache
 func (d *driver) createNetwork(config *configuration) (bool, error) {
 	foundExisting := false
@@ -225,6 +233,11 @@ func parseNetworkOptions(id string, option options.Generic) (*configuration, err
 		return nil, fmt.Errorf("loopback interface is not a valid macvlan parent link")
 	}
 
+	// With no parent interface, the network is "internal".
+	if config.Parent == "" {
+		config.Internal = true
+	}
+
 	config.ID = id
 	return config, nil
 }