feat(network): support --aux-address on network create

cmd/nerdctl/network/network_create.go

@@ -49,6 +49,7 @@ func createCommand() *cobra.Command {
 	cmd.Flags().StringArray("subnet", nil, `Subnet in CIDR format that represents a network segment, e.g. "10.5.0.0/16"`)
 	cmd.Flags().StringArray("gateway", nil, "IPv4 or IPv6 Gateway for the master subnet")
 	cmd.Flags().StringArray("ip-range", nil, `Allocate container ip from a sub-range`)
+	cmd.Flags().StringArray("aux-address", nil, "Auxiliary IPv4 or IPv6 addresses used by Network driver, as name=IP pairs. The IPs are reserved and never assigned to containers")
 	cmd.Flags().StringArray("label", nil, "Set metadata for a network")
 	cmd.Flags().Bool("ipv4", true, "Enable IPv4 networking (set to false together with --ipv6 for an IPv6-only network)")
 	cmd.Flags().Bool("ipv6", false, "Enable IPv6 networking")
@@ -93,6 +94,10 @@ func createAction(cmd *cobra.Command, args []string) error {
 	if err != nil {
 		return err
 	}
+	auxAddresses, err := cmd.Flags().GetStringArray("aux-address")
+	if err != nil {
+		return err
+	}
 	labels, err := cmd.Flags().GetStringArray("label")
 	if err != nil {
 		return err
@@ -112,18 +117,19 @@ func createAction(cmd *cobra.Command, args []string) error {
 	}
 
 	return network.Create(types.NetworkCreateOptions{
-		GOptions:    globalOptions,
-		Name:        name,
-		Driver:      driver,
-		Options:     strutil.ConvertKVStringsToMap(opts),
-		IPAMDriver:  ipamDriver,
-		IPAMOptions: strutil.ConvertKVStringsToMap(ipamOpts),
-		Subnets:     subnets,
-		Gateway:     gateways,
-		IPRange:     ipRanges,
-		Labels:      labels,
-		IPv6:        ipv6,
-		IPv4:        &ipv4,
-		Internal:    internal,
+		GOptions:     globalOptions,
+		Name:         name,
+		Driver:       driver,
+		Options:      strutil.ConvertKVStringsToMap(opts),
+		IPAMDriver:   ipamDriver,
+		IPAMOptions:  strutil.ConvertKVStringsToMap(ipamOpts),
+		Subnets:      subnets,
+		Gateway:      gateways,
+		IPRange:      ipRanges,
+		AuxAddresses: auxAddresses,
+		Labels:       labels,
+		IPv6:         ipv6,
+		IPv4:         &ipv4,
+		Internal:     internal,
 	}, cmd.OutOrStdout())
 }

cmd/nerdctl/network/network_create_linux_test.go

@@ -256,6 +256,76 @@ func TestNetworkCreate(t *testing.T) {
 				}
 			},
 		},
+		{
+			Description: "with aux-address",
+			Setup: func(data test.Data, helpers test.Helpers) {
+				helpers.Ensure("network", "create", data.Identifier(),
+					"--subnet", "10.6.0.0/24",
+					"--gateway", "10.6.0.1",
+					"--aux-address", "router=10.6.0.5",
+					"--aux-address", "dns=10.6.0.6",
+				)
+			},
+			Cleanup: func(data test.Data, helpers test.Helpers) {
+				helpers.Anyhow("network", "rm", data.Identifier())
+			},
+			Command: func(data test.Data, helpers test.Helpers) test.TestableCommand {
+				return helpers.Command("network", "inspect", data.Identifier())
+			},
+			Expected: func(data test.Data, helpers test.Helpers) *test.Expected {
+				return &test.Expected{
+					ExitCode: expect.ExitCodeSuccess,
+					Output: func(stdout string, t tig.T) {
+						netw := nerdtest.InspectNetwork(helpers, data.Identifier())
+						var aux map[string]string
+						for _, c := range netw.IPAM.Config {
+							if c.Subnet == "10.6.0.0/24" {
+								aux = c.AuxiliaryAddresses
+							}
+						}
+						assert.Equal(t, aux["router"], "10.6.0.5")
+						assert.Equal(t, aux["dns"], "10.6.0.6")
+					},
+				}
+			},
+		},
+		{
+			Description: "aux-address is reserved",
+			Setup: func(data test.Data, helpers test.Helpers) {
+				helpers.Ensure("network", "create", data.Identifier(),
+					"--subnet", "10.6.1.0/24",
+					"--aux-address", "reserved=10.6.1.5",
+				)
+			},
+			Cleanup: func(data test.Data, helpers test.Helpers) {
+				helpers.Anyhow("network", "rm", data.Identifier())
+			},
+			Command: func(data test.Data, helpers test.Helpers) test.TestableCommand {
+				// The reserved address is carved out of the range, so requesting
+				// it explicitly must fail just as it does on Docker.
+				return helpers.Command("run", "--rm", "--net", data.Identifier(), "--ip", "10.6.1.5", testutil.CommonImage, "true")
+			},
+			Expected: test.Expects(expect.ExitCodeGenericFail, nil, nil),
+		},
+		{
+			Description: "an un-reserved address is allocatable",
+			Setup: func(data test.Data, helpers test.Helpers) {
+				helpers.Ensure("network", "create", data.Identifier(),
+					"--subnet", "10.6.2.0/24",
+					"--aux-address", "reserved=10.6.2.5",
+				)
+			},
+			Cleanup: func(data test.Data, helpers test.Helpers) {
+				helpers.Anyhow("network", "rm", data.Identifier())
+			},
+			Command: func(data test.Data, helpers test.Helpers) test.TestableCommand {
+				// Positive control: an address in the same subnet that is not
+				// reserved allocates fine, so the failure above is specific to the
+				// reserved IP rather than an unrelated --ip problem.
+				return helpers.Command("run", "--rm", "--net", data.Identifier(), "--ip", "10.6.2.7", testutil.CommonImage, "true")
+			},
+			Expected: test.Expects(expect.ExitCodeSuccess, nil, nil),
+		},
 	}
 
 	testCase.Run(t)

docs/command-reference.md

@@ -1279,12 +1279,13 @@ Flags:
 - :whale: `--subnet`: Subnet in CIDR format that represents a network segment, e.g. "10.5.0.0/16"
 - :whale: `--gateway`: IPv4 or IPv6 Gateway for the master subnet
 - :whale: `--ip-range`: Allocate container ip from a sub-range
+- :whale: `--aux-address`: Auxiliary IPv4 or IPv6 addresses, as `name=IP` pairs. Each IP is reserved and never assigned to a container. Repeatable, and matched to the subnet that contains it.
 - :whale: `--label`: Set metadata on a network
 - :whale: `--ipv4`: Enable IPv4. Enabled by default; set to false with `--ipv6` and an IPv6 subnet for an IPv6-only network. `--ipv4=false` is not supported on Windows.
 - :whale: `--ipv6`: Enable IPv6. Should be used with a valid subnet.
 - :whale: `--internal`: Restrict external access to the network.
 
-Unimplemented `docker network create` flags: `--attachable`, `--aux-address`, `--config-from`, `--config-only`, `--ingress`, `--scope`
+Unimplemented `docker network create` flags: `--attachable`, `--config-from`, `--config-only`, `--ingress`, `--scope`
 
 ### :whale: nerdctl network ls
 

pkg/api/types/network_types.go

@@ -33,8 +33,11 @@ type NetworkCreateOptions struct {
 	Subnets     []string
 	Gateway     []string
 	IPRange     []string
-	Labels      []string
-	IPv6        bool
+	// AuxAddresses holds "name=IP" auxiliary addresses (docker --aux-address).
+	// Each IP is reserved so IPAM never hands it out to a container.
+	AuxAddresses []string
+	Labels       []string
+	IPv6         bool
 	// IPv4 enables IPv4 on the network. A nil value defaults to enabled, so a
 	// directly-constructed NetworkCreateOptions keeps IPv4 on; setting it to
 	// false together with IPv6 yields an IPv6-only network.

pkg/cmd/network/create.go

@@ -41,6 +41,16 @@ func Create(options types.NetworkCreateOptions, stdout io.Writer) error {
 		return fmt.Errorf("IPv6-only network requires an IPv6 subnet, specify --subnet manually")
 	}
 	if len(options.Subnets) == 0 {
+		// Docker matches each aux-address to a subnet that contains it, so
+		// without any subnet there is nothing to match. Surface the same
+		// "no matching subnet for aux-address <ip>" error Docker returns.
+		aux, err := netutil.ParseAuxAddresses(options.AuxAddresses)
+		if err != nil {
+			return err
+		}
+		for _, ip := range aux {
+			return fmt.Errorf("no matching subnet for aux-address %s", ip)
+		}
 		if len(options.Gateway) > 0 || len(options.IPRange) > 0 {
 			return fmt.Errorf("cannot set gateway or ip-range without subnet, specify --subnet manually")
 		}

pkg/cmd/network/create_test.go

@@ -0,0 +1,35 @@
+/*
+   Copyright The containerd 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 network
+
+import (
+	"io"
+	"testing"
+
+	"gotest.tools/v3/assert"
+
+	"github.com/containerd/nerdctl/v2/pkg/api/types"
+)
+
+// TestCreateAuxAddressWithoutSubnet verifies that an aux-address given without
+// any subnet is rejected the same way Docker rejects it, before any CNI setup.
+func TestCreateAuxAddressWithoutSubnet(t *testing.T) {
+	err := Create(types.NetworkCreateOptions{
+		AuxAddresses: []string{"host=10.9.0.5"},
+	}, io.Discard)
+	assert.ErrorContains(t, err, "no matching subnet for aux-address 10.9.0.5")
+}

pkg/inspecttypes/dockercompat/dockercompat.go

@@ -1052,9 +1052,10 @@ func getUlimitsFromNative(sp *specs.Spec) ([]*units.Ulimit, error) {
 }
 
 type IPAMConfig struct {
-	Subnet  string `json:"Subnet,omitempty"`
-	Gateway string `json:"Gateway,omitempty"`
-	IPRange string `json:"IPRange,omitempty"`
+	Subnet             string            `json:"Subnet,omitempty"`
+	Gateway            string            `json:"Gateway,omitempty"`
+	IPRange            string            `json:"IPRange,omitempty"`
+	AuxiliaryAddresses map[string]string `json:"AuxiliaryAddresses,omitempty"`
 }
 
 type IPAM struct {
@@ -1196,7 +1197,20 @@ func NetworkFromNative(n *native.Network) (*Network, error) {
 	res.Name = sCNI.Name
 	for _, plugin := range sCNI.Plugins {
 		for _, ranges := range plugin.Ipam.Ranges {
-			res.IPAM.Config = append(res.IPAM.Config, ranges...)
+			// A range-set normally describes one subnet; an aux-address
+			// reservation splits it into several sub-ranges whose first entry
+			// carries the subnet, gateway, ip-range and aux-addresses. Report the
+			// first entry per distinct subnet so a split subnet collapses to one
+			// IPAM.Config like Docker, without dropping entries for different
+			// subnets in the same set.
+			seen := make(map[string]struct{}, len(ranges))
+			for _, r := range ranges {
+				if _, ok := seen[r.Subnet]; ok {
+					continue
+				}
+				seen[r.Subnet] = struct{}{}
+				res.IPAM.Config = append(res.IPAM.Config, r)
+			}
 		}
 	}
 

pkg/inspecttypes/dockercompat/dockercompat_test.go

@@ -605,6 +605,25 @@ func TestGetUlimitsFromNative(t *testing.T) {
 	}
 }
 
+func TestNetworkFromNative(t *testing.T) {
+	// The first range-set is one subnet split into sub-ranges by an aux-address
+	// reservation and must collapse to a single IPAM.Config carrying the aux; the
+	// second set holds two distinct subnets that must both be kept; the empty set
+	// contributes nothing.
+	cni := `{"name":"testnet","plugins":[{"ipam":{"ranges":[` +
+		`[{"Subnet":"10.6.0.0/24","Gateway":"10.6.0.1","AuxiliaryAddresses":{"router":"10.6.0.5"}},{"Subnet":"10.6.0.0/24"}],` +
+		`[{"Subnet":"10.7.0.0/24"},{"Subnet":"10.8.0.0/24"}],` +
+		`[]` +
+		`]}}]}`
+	got, err := NetworkFromNative(&native.Network{CNI: []byte(cni)})
+	assert.NilError(t, err)
+	assert.DeepEqual(t, []IPAMConfig{
+		{Subnet: "10.6.0.0/24", Gateway: "10.6.0.1", AuxiliaryAddresses: map[string]string{"router": "10.6.0.5"}},
+		{Subnet: "10.7.0.0/24"},
+		{Subnet: "10.8.0.0/24"},
+	}, got.IPAM.Config)
+}
+
 func TestNetworkSettingsFromNative(t *testing.T) {
 	tempStateDir, err := os.MkdirTemp(t.TempDir(), "rw")
 	if err != nil {

pkg/netutil/cni_plugin.go

@@ -34,6 +34,11 @@ type IPAMRange struct {
 	RangeEnd   string `json:"rangeEnd,omitempty"`
 	Gateway    string `json:"gateway,omitempty"`
 	IPRange    string `json:"ipRange,omitempty"`
+	// AuxiliaryAddresses records the reserved name=IP pairs for this subnet.
+	// host-local does not read it (reservation is done by splitting the range
+	// around each IP); it is nerdctl bookkeeping so `network inspect` can
+	// report AuxiliaryAddresses the way Docker does.
+	AuxiliaryAddresses map[string]string `json:"auxiliaryAddresses,omitempty"`
 }
 
 type IPAMRoute struct {