Configuring an additional network - Multiple networks | Networking

Approaches to managing an additional network
Configuration for an additional network attachment
- Configuration of an additional network through the Cluster Network Operator
- Configuration of an additional network from a YAML manifest
Configurations for additional network types
Configuration of IP address assignment for an additional network
Creating an additional network attachment with the Cluster Network Operator
Creating an additional network attachment by applying a YAML manifest

As a cluster administrator, you can configure an additional network for your cluster. The following network types are supported:

Approaches to managing an additional network

You can manage the life cycle of an additional network by two approaches. Each approach is mutually exclusive and you can only use one approach for managing an additional network at a time. For either approach, the additional network is managed by a Container Network Interface (CNI) plugin that you configure.

For an additional network, IP addresses are provisioned through an IP Address Management (IPAM) CNI plugin that you configure as part of the additional network. The IPAM plugin supports a variety of IP address assignment approaches including DHCP and static assignment.

Modify the Cluster Network Operator (CNO) configuration: The CNO automatically creates and manages the NetworkAttachmentDefinition object. In addition to managing the object lifecycle the CNO ensures a DHCP is available for an additional network that uses a DHCP assigned IP address.
Applying a YAML manifest: You can manage the additional network directly by creating an NetworkAttachmentDefinition object. This approach allows for the chaining of CNI plugins.

When deploying OKD nodes with multiple network interfaces on OpenStack with OVN SDN, DNS configuration of the secondary interface might take precedence over the DNS configuration of the primary interface. In this case, remove the DNS nameservers for the subnet id that is attached to the secondary interface:

$ openstack subnet set --dns-nameserver 0.0.0.0 <subnet_id>

Configuration for an additional network attachment

An additional network is configured by using the NetworkAttachmentDefinition API in the k8s.cni.cncf.io API group.

Do not store any sensitive information or a secret in the NetworkAttachmentDefinition object because this information is accessible by the project administration user.

The configuration for the API is described in the following table:

Table 1. `NetworkAttachmentDefinition` API fields
Field	Type	Description
`metadata.name`	`string`	The name for the additional network.
`metadata.namespace`	`string`	The namespace that the object is associated with.
`spec.config`	`string`	The CNI plugin configuration in JSON format.

Configuration of an additional network through the Cluster Network Operator

The configuration for an additional network attachment is specified as part of the Cluster Network Operator (CNO) configuration.

The following YAML describes the configuration parameters for managing an additional network with the CNO:

Cluster Network Operator configuration

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  # ...
  additionalNetworks: (1)
  - name: <name> (2)
    namespace: <namespace> (3)
    rawCNIConfig: |- (4)
      {
        ...
      }
    type: Raw

1	An array of one or more additional network configurations.
2	The name for the additional network attachment that you are creating. The name must be unique within the specified `namespace`.
3	The namespace to create the network attachment in. If you do not specify a value, then the `default` namespace is used.
4	A CNI plugin configuration in JSON format.

Configuration of an additional network from a YAML manifest

The configuration for an additional network is specified from a YAML configuration file, such as in the following example:

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: <name> (1)
spec:
  config: |- (2)
    {
      ...
    }

1	The name for the additional network attachment that you are creating.
2	A CNI plugin configuration in JSON format.

Configurations for additional network types

The specific configuration fields for additional networks is described in the following sections.

Configuration for a bridge additional network

The following object describes the configuration parameters for the bridge CNI plugin:

Table 2. Bridge CNI plugin JSON configuration object
Field	Type	Description
`cniVersion`	`string`	The CNI specification version. The `0.3.1` value is required.
`name`	`string`	The value for the `name` parameter you provided previously for the CNO configuration.
`type`	`string`
`bridge`	`string`	Specify the name of the virtual bridge to use. If the bridge interface does not exist on the host, it is created. The default value is `cni0`.
`ipam`	`object`	The configuration object for the IPAM CNI plugin. The plugin manages IP address assignment for the attachment definition.
`ipMasq`	`boolean`	Set to `true` to enable IP masquerading for traffic that leaves the virtual network. The source IP address for all traffic is rewritten to the bridge’s IP address. If the bridge does not have an IP address, this setting has no effect. The default value is `false`.
`isGateway`	`boolean`	Set to `true` to assign an IP address to the bridge. The default value is `false`.
`isDefaultGateway`	`boolean`	Set to `true` to configure the bridge as the default gateway for the virtual network. The default value is `false`. If `isDefaultGateway` is set to `true`, then `isGateway` is also set to `true` automatically.
`forceAddress`	`boolean`	Set to `true` to allow assignment of a previously assigned IP address to the virtual bridge. When set to `false`, if an IPv4 address or an IPv6 address from overlapping subsets is assigned to the virtual bridge, an error occurs. The default value is `false`.
`hairpinMode`	`boolean`	Set to `true` to allow the virtual bridge to send an Ethernet frame back through the virtual port it was received on. This mode is also known as reflective relay. The default value is `false`.
`promiscMode`	`boolean`	Set to `true` to enable promiscuous mode on the bridge. The default value is `false`.
`vlan`	`string`	Specify a virtual LAN (VLAN) tag as an integer value. By default, no VLAN tag is assigned.
`mtu`	`string`	Set the maximum transmission unit (MTU) to the specified value. The default value is automatically set by the kernel.

bridge configuration example

The following example configures an additional network named bridge-net:

{
  "cniVersion": "0.3.1",
  "name": "work-network",
  "type": "bridge",
  "isGateway": true,
  "vlan": 2,
  "ipam": {
    "type": "dhcp"
    }
}

Configuration for a host device additional network

Specify your network device by setting only one of the following parameters: device, hwaddr, kernelpath, or pciBusID.

The following object describes the configuration parameters for the host-device CNI plugin:

Table 3. Host device CNI plugin JSON configuration object
Field	Type	Description
`cniVersion`	`string`	The CNI specification version. The `0.3.1` value is required.
`name`	`string`	The value for the `name` parameter you provided previously for the CNO configuration.
`type`	`string`	The name of the CNI plugin to configure: `host-device`.
`device`	`string`	Optional: The name of the device, such as `eth0`.
`hwaddr`	`string`	Optional: The device hardware MAC address.
`kernelpath`	`string`	Optional: The Linux kernel device path, such as `/sys/devices/pci0000:00/0000:00:1f.6`.
`pciBusID`	`string`	Optional: The PCI address of the network device, such as `0000:00:1f.6`.

host-device configuration example

The following example configures an additional network named hostdev-net:

{
  "cniVersion": "0.3.1",
  "name": "work-network",
  "type": "host-device",
  "device": "eth1"
}

Configuration for an IPVLAN additional network

The following object describes the configuration parameters for the IPVLAN CNI plugin:

Table 4. IPVLAN CNI plugin JSON configuration object
Field	Type	Description
`cniVersion`	`string`	The CNI specification version. The `0.3.1` value is required.
`name`	`string`	The value for the `name` parameter you provided previously for the CNO configuration.
`type`	`string`	The name of the CNI plugin to configure: `ipvlan`.
`mode`	`string`	The operating mode for the virtual network. The value must be `l2`, `l3`, or `l3s`. The default value is `l2`.
`master`	`string`	The Ethernet interface to associate with the network attachment. If a `master` is not specified, the interface for the default network route is used.
`mtu`	`integer`	Set the maximum transmission unit (MTU) to the specified value. The default value is automatically set by the kernel.
`ipam`	`object`	The configuration object for the IPAM CNI plugin. The plugin manages IP address assignment for the attachment definition. Do not specify `dhcp`. Configuring IPVLAN with DHCP is not supported because IPVLAN interfaces share the MAC address with the host interface.

ipvlan configuration example

The following example configures an additional network named ipvlan-net:

{
  "cniVersion": "0.3.1",
  "name": "work-network",
  "type": "ipvlan",
  "master": "eth1",
  "mode": "l3",
  "ipam": {
    "type": "static",
    "addresses": [
       {
         "address": "192.168.10.10/24"
       }
    ]
  }
}

Configuration for a MACVLAN additional network

The following object describes the configuration parameters for the macvlan CNI plugin:

Table 5. MACVLAN CNI plugin JSON configuration object
Field	Type	Description
`cniVersion`	`string`	The CNI specification version. The `0.3.1` value is required.
`name`	`string`	The value for the `name` parameter you provided previously for the CNO configuration.
`type`	`string`	The name of the CNI plugin to configure: `macvlan`.
`mode`	`string`	Configures traffic visibility on the virtual network. Must be either `bridge`, `passthru`, `private`, or `vepa`. If a value is not provided, the default value is `bridge`.
`master`	`string`	The host network interface to associate with the newly created macvlan interface. If a value is not specified, then the default route interface is used.
`mtu`	`string`	The maximum transmission unit (MTU) to the specified value. The default value is automatically set by the kernel.
`ipam`	`object`	The configuration object for the IPAM CNI plugin. The plugin manages IP address assignment for the attachment definition.

If you specify the master key for the plugin configuration, use a different physical network interface than the one that is associated with your primary network plugin to avoid possible conflicts.

macvlan configuration example

The following example configures an additional network named macvlan-net:

{
  "cniVersion": "0.3.1",
  "name": "macvlan-net",
  "type": "macvlan",
  "master": "eth1",
  "mode": "bridge",
  "ipam": {
    "type": "dhcp"
    }
}

Configuration for an OVN-Kubernetes additional network

The Red Hat OpenShift Networking OVN-Kubernetes network plugin allows the configuration of secondary network interfaces for pods. To configure secondary network interfaces, you must define the configurations in the NetworkAttachmentDefinition custom resource definition (CRD).

Configuration for an OVN-Kubernetes additional network is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

The following sections provide example configurations for each of the topologies that OVN-Kubernetes currently allows for secondary networks.

Networks names must be unique. For example, creating multiple NetworkAttachmentDefinition CRDs with different configurations that reference the same network is unsupported.

OVN-Kubernetes network plugin JSON configuration table

The following table describes the configuration parameters for the OVN-Kubernetes CNI network plugin:

Table 6. OVN-Kubernetes network plugin JSON configuration table
Field	Type	Description
`cniVersion`	`string`	The CNI specification version. The required value is `0.3.1`.
`name`	`string`	The name of the network. This value must be unique across all `NetworkAttachmentDefinitions`. Failure to make this attribute unique might result in the merging of two networks with the same name. Merging two networks by sharing similar names is unsupported.
`type`	`string`	The name of the CNI plugin to configure. The required value is `ovn-k8s-cni-overlay`.
`topology`	`string`	The topological configuration for the network. The required value is `layer2`.
`subnets`	`string`	The subnet to use for the network across the cluster. When specifying `layer2` for the `topology`, only include the CIDR for the node. For example, `10.100.200.0/24`. For `"topology":"layer2"` deployments, IPv6 (`2001:DBB::/64`) and dual-stack (`192.168.100.0/24,2001:DBB::/64`) subnets are supported.
`mtu`	`string`	The maximum transmission unit (MTU) to the specified value. The default value, `1300`, is automatically set by the kernel.
`netAttachDefName`	`string`	The namespace and the network attachment name. The value must match the values specified for `namespace` and `name` when defining the network attachment definition object. For example, `ns1/l2-network` refers to the `ns1` namespace and the `l2-network` network attachment definition name.
`excludeSubnets`	`string`	A comma-separated list of CIDRs and IPs. IPs are removed from the assignable IP pool, and are never passed to the pods. When omitted, the logical switch implementing the network only provides layer 2 communication, and users must configure IPs for the pods. Port security only prevents MAC spoofing.

Configuration for a switched topology

The switched (layer 2) topology networks interconnect the workloads through a cluster-wide logical switch. This configuration can be used for IPv6 and dual-stack deployments.

Layer 2 switched topology networks only allow for the transfer of data packets between pods within a cluster.

The following NetworkAttachmentDefinition custom resource definition (CRD) YAML describes the fields needed to configure a switched secondary network.

    {
            "cniVersion": "0.3.1",
            "name": "ns1-l2-network",
            "type": "ovn-k8s-cni-overlay",
            "topology":"layer2",
            "subnets": "10.100.200.0/24",
            "mtu": 1300,
            "netAttachDefName": "ns1/l2-network",
            "excludeSubnets": "10.100.200.0/29"
    }

Configuring pods for additional networks

You must specify the secondary network attachments through the k8s.v1.cni.cncf.io/networks annotation.

The following example provisions a pod with two secondary attachments, one for each of the attachment configurations presented in this guide.

apiVersion: v1
kind: Pod
metadata:
  annotations:
    k8s.v1.cni.cncf.io/networks: l2-network
  name: tinypod
  namespace: ns1
spec:
  containers:
  - args:
    - pause
    image: k8s.gcr.io/e2e-test-images/agnhost:2.36
    imagePullPolicy: IfNotPresent
    name: agnhost-container

Configuring pods with a static IP address

The following example provisions a pod with a static IP address.

You can only specify the IP address for a pod’s secondary network attachment for layer 2 attachments.
Specifying a static IP address for the pod is only possible when the attachment configuration does not feature subnets.

apiVersion: v1
kind: Pod
metadata:
  annotations:
    k8s.v1.cni.cncf.io/networks: '[
      {
        "name": "l2-network", (1)
        "mac": "02:03:04:05:06:07", (2)
        "interface": "myiface1", (3)
        "ips": [
          "192.0.2.20/24"
          ] (4)
      }
    ]'
  name: tinypod
  namespace: ns1
spec:
  containers:
  - args:
    - pause
    image: k8s.gcr.io/e2e-test-images/agnhost:2.36
    imagePullPolicy: IfNotPresent
    name: agnhost-container

1	The name of the network. This value must be unique across all `NetworkAttachmentDefinitions`.
2	The MAC address to be assigned for the interface.
3	The name of the network interface to be created for the pod.
4	The IP addresses to be assigned to the network interface.

Configuration of IP address assignment for an additional network

The IP address management (IPAM) Container Network Interface (CNI) plugin provides IP addresses for other CNI plugins.

You can use the following IP address assignment types:

Static assignment.
Dynamic assignment through a DHCP server. The DHCP server you specify must be reachable from the additional network.
Dynamic assignment through the Whereabouts IPAM CNI plugin.

Static IP address assignment configuration

The following table describes the configuration for static IP address assignment:

Table 7. `ipam` static configuration object
Field	Type	Description
`type`	`string`	The IPAM address type. The value `static` is required.
`addresses`	`array`	An array of objects specifying IP addresses to assign to the virtual interface. Both IPv4 and IPv6 IP addresses are supported.
`routes`	`array`	An array of objects specifying routes to configure inside the pod.
`dns`	`array`	Optional: An array of objects specifying the DNS configuration.

The addresses array requires objects with the following fields:

Table 8. `ipam.addresses[]` array
Field	Type	Description
`address`	`string`	An IP address and network prefix that you specify. For example, if you specify `10.10.21.10/24`, then the additional network is assigned an IP address of `10.10.21.10` and the netmask is `255.255.255.0`.
`gateway`	`string`	The default gateway to route egress network traffic to.

Table 9. `ipam.routes[]` array
Field	Type	Description
`dst`	`string`	The IP address range in CIDR format, such as `192.168.17.0/24` or `0.0.0.0/0` for the default route.
`gw`	`string`	The gateway where network traffic is routed.

Table 10. `ipam.dns` object
Field	Type	Description
`nameservers`	`array`	An array of one or more IP addresses for to send DNS queries to.
`domain`	`array`	The default domain to append to a hostname. For example, if the domain is set to `example.com`, a DNS lookup query for `example-host` is rewritten as `example-host.example.com`.
`search`	`array`	An array of domain names to append to an unqualified hostname, such as `example-host`, during a DNS lookup query.

Static IP address assignment configuration example

{
  "ipam": {
    "type": "static",
      "addresses": [
        {
          "address": "191.168.1.7/24"
        }
      ]
  }
}

Dynamic IP address (DHCP) assignment configuration

The following JSON describes the configuration for dynamic IP address address assignment with DHCP.

Renewal of DHCP leases

A pod obtains its original DHCP lease when it is created. The lease must be periodically renewed by a minimal DHCP server deployment running on the cluster.

To trigger the deployment of the DHCP server, you must create a shim network attachment by editing the Cluster Network Operator configuration, as in the following example:

Example shim network attachment definition

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  additionalNetworks:
  - name: dhcp-shim
    namespace: default
    type: Raw
    rawCNIConfig: |-
      {
        "name": "dhcp-shim",
        "cniVersion": "0.3.1",
        "type": "bridge",
        "ipam": {
          "type": "dhcp"
        }
      }
  # ...

Table 11. `ipam` DHCP configuration object
Field	Type	Description
`type`	`string`	The IPAM address type. The value `dhcp` is required.

Dynamic IP address (DHCP) assignment configuration example

{
  "ipam": {
    "type": "dhcp"
  }
}

Dynamic IP address assignment configuration with Whereabouts

The Whereabouts CNI plugin allows the dynamic assignment of an IP address to an additional network without the use of a DHCP server.

The following table describes the configuration for dynamic IP address assignment with Whereabouts:

Table 12. `ipam` whereabouts configuration object
Field	Type	Description
`type`	`string`	The IPAM address type. The value `whereabouts` is required.
`range`	`string`	An IP address and range in CIDR notation. IP addresses are assigned from within this range of addresses.
`exclude`	`array`	Optional: A list of zero or more IP addresses and ranges in CIDR notation. IP addresses within an excluded address range are not assigned.

Dynamic IP address assignment configuration example that uses Whereabouts

{
  "ipam": {
    "type": "whereabouts",
    "range": "192.0.2.192/27",
    "exclude": [
       "192.0.2.192/30",
       "192.0.2.196/32"
    ]
  }
}

Creating an additional network attachment with the Cluster Network Operator

The Cluster Network Operator (CNO) manages additional network definitions. When you specify an additional network to create, the CNO creates the NetworkAttachmentDefinition object automatically.

Do not edit the NetworkAttachmentDefinition objects that the Cluster Network Operator manages. Doing so might disrupt network traffic on your additional network.

Prerequisites

Install the OpenShift CLI (oc).
Log in as a user with cluster-admin privileges.

Procedure

Optional: Create the namespace for the additional networks:
```
$ oc create namespace <namespace_name>
```
To edit the CNO configuration, enter the following command:
```
$ oc edit networks.operator.openshift.io cluster
```

Modify the CR that you are creating by adding the configuration for the additional network that you are creating, as in the following example CR.

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  # ...
  additionalNetworks:
  - name: tertiary-net
    namespace: namespace2
    type: Raw
    rawCNIConfig: |-
      {
        "cniVersion": "0.3.1",
        "name": "tertiary-net",
        "type": "ipvlan",
        "master": "eth1",
        "mode": "l2",
        "ipam": {
          "type": "static",
          "addresses": [
            {
              "address": "192.168.1.23/24"
            }
          ]
        }
      }

Save your changes and quit the text editor to commit your changes.

Verification

Confirm that the CNO created the NetworkAttachmentDefinition object by running the following command. There might be a delay before the CNO creates the object.
```
$ oc get network-attachment-definitions -n <namespace>
```
where:

<namespace>

Specifies the namespace for the network attachment that you added to the CNO configuration.
Example output
```
NAME                 AGE
test-network-1       14m
```

Creating an additional network attachment by applying a YAML manifest

Prerequisites

Install the OpenShift CLI (oc).
Log in as a user with cluster-admin privileges.

Procedure

Create a YAML file with your additional network configuration, such as in the following example:

apiVersion: k8s.cni.cncf.io/v1
kind: NetworkAttachmentDefinition
metadata:
  name: next-net
spec:
  config: |-
    {
      "cniVersion": "0.3.1",
      "name": "work-network",
      "type": "host-device",
      "device": "eth1",
      "ipam": {
        "type": "dhcp"
      }
    }

To create the additional network, enter the following command:
```
$ oc apply -f <file>.yaml
```
where:

<file>

Specifies the name of the file contained the YAML manifest.