Configuring a bridge network - Multiple networks | Networking

Creating an additional network attachment with the bridge CNI plug-in
- Configuration for bridge
- Configuration for ipam CNI plug-in
Next steps

As a cluster administrator, you can configure an additional network for your cluster using the bridge Container Network Interface (CNI) plug-in. When configured, all Pods on a node are connected to a virtual switch. Each Pod is assigned an IP address on the additional network.

Creating an additional network attachment with the bridge CNI plug-in

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

Do not edit the NetworkAttachmentDefinition CRs 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

To create an additional network for your cluster, complete the following steps:

Edit the CNO CR by running 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 you are creating, as in the following example CR.

The following YAML configures the bridge CNI plug-in:

apiVersion: operator.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  additionalNetworks: (1)
  - name: test-network-1
    namespace: test-1
    type: Raw
    rawCNIConfig: '{
      "cniVersion": "0.3.1",
      "name": "test-network-1",
      "type": "bridge",
      "ipam": {
        "type": "static",
        "addresses": [
          {
            "address": "191.168.1.7"
          }
        ]
      }
    }'

1	Specify the configuration for the additional network attachment definition.

Save your changes and quit the text editor to commit your changes.
Optional: Confirm that the CNO created the NetworkAttachmentDefinition CR by running the following command. There might be a delay before the CNO creates the CR.
```
$ oc get network-attachment-definitions -n <namespace>
```
Example output
```
NAME                 AGE
test-network-1       14m
```

Configuration for bridge

The configuration for an additional network attachment that uses the bridge Container Network Interface (CNI) plug-in is provided in two parts:

Cluster Network Operator (CNO) configuration
CNI plug-in configuration

The CNO configuration specifies the name for the additional network attachment and the namespace to create the attachment in. The plug-in is configured by a JSON object specified by the rawCNIConfig parameter in the CNO configuration.

The following YAML describes the configuration parameters for the CNO:

Cluster Network Operator YAML configuration

name: <name> (1)
namespace: <namespace> (2)
rawCNIConfig: '{ (3)
  ...
}'
type: Raw

1	Specify a name for the additional network attachment that you are creating. The name must be unique within the specified `namespace`.
2	Specify the namespace to create the network attachment in. If you do not specify a value, then the `default` namespace is used.
3	Specify the CNI plug-in configuration in JSON format, which is based on the following template.

The following object describes the configuration parameters for the bridge CNI plug-in:

bridge CNI plug-in JSON configuration object

{
  "cniVersion": "0.3.1",
  "name": "<name>", (1)
  "type": "bridge",
  "bridge": "<bridge>", (2)
  "ipam": { (3)
    ...
  },
  "ipMasq": false, (4)
  "isGateway": false, (5)
  "isDefaultGateway": false, (6)
  "forceAddress": false, (7)
  "hairpinMode": false, (8)
  "promiscMode": false, (9)
  "vlan": <vlan>, (10)
  "mtu": <mtu> (11)
}

1	Specify the value for the `name` parameter you provided previously for the CNO configuration.
2	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`.
3	Specify a configuration object for the ipam CNI plug-in. The plug-in manages IP address assignment for the network attachment definition.
4	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`.
5	Set to `true` to assign an IP address to the bridge. The default value is `false`.
6	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.
7	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`.
8	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`.
9	Set to `true` to enable promiscuous mode on the bridge. The default value is `false`.
10	Specify a virtual LAN (VLAN) tag as an integer value. By default, no VLAN tag is assigned.
11	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:

name: bridge-net
namespace: work-network
type: Raw
rawCNIConfig: '{ (1)
  "cniVersion": "0.3.1",
  "name": "work-network",
  "type": "bridge",
  "isGateway": true,
  "vlan": 2,
  "ipam": {
    "type": "dhcp"
    }
}'

1	The CNI configuration object is specified as a YAML string.

Configuration for ipam CNI plug-in

The ipam Container Network Interface (CNI) plug-in provides IP address management (IPAM) for other CNI plug-ins. You can configure ipam for either static IP address assignment or dynamic IP address assignment by using DHCP. The DHCP server you specify must be reachable from the additional network.

The following JSON configuration object describes the parameters that you can set.

Static IP address assignment configuration

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

Static assignment configuration

{
  "ipam": {
    "type": "static",
    "addresses": [ (1)
      {
        "address": "<address>", (2)
        "gateway": "<gateway>" (3)
      }
    ],
    "routes": [ (4)
      {
        "dst": "<dst>" (5)
        "gw": "<gw>" (6)
      }
    ],
    "dns": { (7)
      "nameservers": ["<nameserver>"], (8)
      "domain": "<domain>", (9)
      "search": ["<search_domain>"] (10)
    }
  }
}

1	An array describing IP addresses to assign to the virtual interface. Both IPv4 and IPv6 IP addresses are supported.
2	An IP address that you specify.
3	The default gateway to route egress network traffic to.
4	An array describing routes to configure inside the Pod.
5	The IP address range in CIDR format.
6	The gateway where network traffic is routed.
7	Optional: DNS configuration.
8	An of array of one or more IP addresses for to send DNS queries to.
9	The default domain to append to a host name. For example, if the domain is set to `example.com`, a DNS lookup query for `example-host` is rewritten as `example-host.example.com`.
10	An array of domain names to append to an unqualified host name, such as `example-host`, during a DNS lookup query.

Dynamic IP address 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
    rawCNIConfig: |-
    {
      "name": "dhcp-shim",
      "cniVersion": "0.3.1",
      "type": "bridge",
      "master": "ens5",
      "ipam": {
        "type": "dhcp"
      }
    }

DHCP assignment configuration

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

Static IP address assignment configuration example

You can configure ipam for static IP address assignment:

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

Dynamic IP address assignment configuration example using DHCP

You can configure ipam for DHCP:

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

Next steps

Attach a Pod to an additional network.