Configuring a bridge network

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 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

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

  1. Edit the CNO CR by running the following command:

    1. $ oc edit networks.operator.openshift.io cluster

  2. 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:

    1. apiVersion: operator.openshift.io/v1
    2. kind: Network
    3. metadata:
    4.   name: cluster
    5. spec:
    6.   additionalNetworks: (1)
    7.   - name: test-network-1
    8.     namespace: test-1
    9.     type: Raw
    10.     rawCNIConfig: '{
    11.       "cniVersion": "0.3.1",
    12.       "name": "test-network-1",
    13.       "type": "bridge",
    14.       "ipam": {
    15.         "type": "static",
    16.         "addresses": [
    17.           {
    18.             "address": "192.168.1.23/24"
    19.           }
    20.         ]
    21.       }
    22.     }'
    1Specify the configuration for the additional network attachment definition.

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

  4. Confirm that the CNO created the NetworkAttachmentDefinition object by running the following command. Replace <namespace> with the namespace that you specified when configuring the network attachment. There might be a delay before the CNO creates the object.

    1. $ oc get network-attachment-definitions -n <namespace>

    Example output

    1. NAME                 AGE
    2. 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

  1. name: <name> (1)
  2. namespace: <namespace> (2)
  3. rawCNIConfig: '{ (3)
  4.   ...
  5. }'
  6. type: Raw
1Specify a name for the additional network attachment that you are creating. The name must be unique within the specified namespace.
2Specify the namespace to create the network attachment in. If you do not specify a value, then the default namespace is used.
3Specify 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

  1. {
  2.   "cniVersion": "0.3.1",
  3.   "name": "<name>", (1)
  4.   "type": "bridge",
  5.   "bridge": "<bridge>", (2)
  6.   "ipam": { (3)
  7.     ...
  8.   },
  9.   "ipMasq": false, (4)
  10.   "isGateway": false, (5)
  11.   "isDefaultGateway": false, (6)
  12.   "forceAddress": false, (7)
  13.   "hairpinMode": false, (8)
  14.   "promiscMode": false, (9)
  15.   "vlan": <vlan>, (10)
  16.   "mtu": <mtu> (11)
  17. }
1Specify the value for the name parameter you provided previously for the CNO configuration.
2Specify 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.
3Specify a configuration object for the ipam CNI plug-in. The plug-in manages IP address assignment for the network attachment definition.
4Set 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.
5Set to true to assign an IP address to the bridge. The default value is false.
6Set 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.
7Set 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.
8Set 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.
9Set to true to enable promiscuous mode on the bridge. The default value is false.
10Specify a virtual LAN (VLAN) tag as an integer value. By default, no VLAN tag is assigned.
11Set 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:

  1. name: bridge-net
  2. namespace: work-network
  3. type: Raw
  4. rawCNIConfig: '{ (1)
  5.   "cniVersion": "0.3.1",
  6.   "name": "work-network",
  7.   "type": "bridge",
  8.   "isGateway": true,
  9.   "vlan": 2,
  10.   "ipam": {
  11.     "type": "dhcp"
  12.     }
  13. }'
1The 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 use the following methods for IP address assignment:

  • 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 plug-in.

Static IP address assignment configuration

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

Static assignment configuration

  1. {
  2.   "ipam": {
  3.     "type": "static",
  4.     "addresses": [ (1)
  5.       {
  6.         "address": "<address>", (2)
  7.         "gateway": "<gateway>" (3)
  8.       }
  9.     ],
  10.     "routes": [ (4)
  11.       {
  12.         "dst": "<dst>", (5)
  13.         "gw": "<gw>" (6)
  14.       }
  15.     ],
  16.     "dns": { (7)
  17.       "nameservers": ["<nameserver>"], (8)
  18.       "domain": "<domain>", (9)
  19.       "search": ["<search_domain>"] (10)
  20.     }
  21.   }
  22. }
1An array describing IP addresses to assign to the virtual interface. Both IPv4 and IPv6 IP addresses are supported.
2An 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.
3The default gateway to route egress network traffic to.
4An array describing routes to configure inside the pod.
5The IP address range in CIDR format, such as 192.168.17.0/24, or 0.0.0.0/0 for the default route.
6The gateway where network traffic is routed.
7Optional: DNS configuration.
8An of array of one or more IP addresses for to send DNS queries to.
9The 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.
10An array of domain names to append to an unqualified hostname, 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
  1. apiVersion: operator.openshift.io/v1
  2. kind: Network
  3. metadata:
  4.   name: cluster
  5. spec:
  6.   …
  7.   additionalNetworks:
  8.   - name: dhcp-shim
  9.     namespace: default
  10.     type: Raw
  11.     rawCNIConfig: |-
  12.       {
  13.         “name”: “dhcp-shim”,
  14.         “cniVersion”: “0.3.1”,
  15.         “type”: “bridge”,
  16.         “ipam”: {
  17.           “type”: “dhcp”
  18.         }
  19.       }

DHCP assignment configuration

  1. {
  2.   "ipam": {
  3.     "type": "dhcp"
  4.   }
  5. }

Dynamic IP address assignment configuration with Whereabouts

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

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

Whereabouts assignment configuration

  1. {
  2.   "ipam": {
  3.     "type": "whereabouts",
  4.     "range": "<range>", (1)
  5.     "exclude": ["<exclude_part>, ..."], (2)
  6.   }
  7. }
1Specify an IP address and range in CIDR notation. IP addresses are assigned from within this range of addresses.
2Optional: Specify a list of IP addresses and ranges in CIDR notation. IP addresses within an excluded address range are not assigned.

Static IP address assignment configuration example

You can configure ipam for static IP address assignment:

  1. {
  2.   "ipam": {
  3.     "type": "static",
  4.       "addresses": [
  5.         {
  6.           "address": "191.168.1.7"
  7.         }
  8.       ]
  9.   }
  10. }

Dynamic IP address assignment configuration example using DHCP

You can configure ipam for DHCP:

  1. {
  2.   "ipam": {
  3.     "type": "dhcp"
  4.   }
  5. }

Dynamic IP address assignment configuration example using Whereabouts

You can configure ipam to use Whereabouts:

  1. {
  2.   "ipam": {
  3.     "type": "whereabouts",
  4.     "range": "192.0.2.192/27",
  5.     "exclude": [
  6.        "192.0.2.192/30",
  7.        "192.0.2.196/32"
  8.     ]
  9.   }
  10. }

Next steps