1.7. Network topology
OVN-Kubernetes provides an overlay-based networking implementation. This overlay includes an OVS-based implementation of Service and NetworkPolicy resources.
The overlay network uses the Geneve (Generic Network Virtualization Encapsulation) tunnel protocol. The pod maximum transmission unit (MTU) for the Geneve tunnel is set to the default route MTU if it is not configured.
To configure the MTU, you must set an equal-to or less-than value than the MTU of the physical interface on the host. A less-than value for the MTU makes room for the required information that is added to the tunnel header before it is transmitted.
The MTU value of the OVN overlay networking in MicroShift must be 100 bytes smaller than the MTU value of the base network. If no MTU value is configured, MicroShift autoconfigures the value using the MTU value of the default gateway (Internet Protocol version 4 (IPv4) or Internet Protocol version 6 (IPv6)) of the host. If the auto-configuration does not work correctly, the MTU value can be configured manually. For example, if the MTU value of the network is 9000, the OVN MTU size must be set to 8900.
OVS runs as a systemd service on the MicroShift node. The OVS RPM package is installed as a dependency to the microshift-networking RPM package. OVS starts immediately when the microshift-networking RPM is installed.
Red Hat build of MicroShift network topology
1.7.1. Description of the OVN logical components of the virtualized network
- OVN node switch
A virtual switch named
<node-name>. The OVN node switch is named according to the hostname of the node.-
In this example, the
node-nameismicroshift-dev.
-
In this example, the
- OVN cluster router
A virtual router named
ovn_cluster_router, also known as the distributed router.-
In this example, the node network is
10.42.0.0/16.
-
In this example, the node network is
- OVN join switch
-
A virtual switch named
join. - OVN gateway router
-
A virtual router named
GR_<node-name>, also known as the external gateway router. - OVN external switch
-
A virtual switch named
ext_<node-name>.
1.7.2. Description of the connections in the network topology figure
-
The north-south traffic between the network service and the OVN external switch
ext_microshift-devis provided through the host kernel by the gateway bridgebr-ex. -
The OVN gateway router
GR_microshift-devis connected to the external network switchext_microshift-devthrough the logical router port 4. Port 4 is attached with the node IP address 192.168.122.14. The join switch
joinconnects the OVN gateway routerGR_microshift-devto the OVN cluster routerovn_cluster_router. The IP address range is 100.62.0.0/16.-
The OVN gateway router
GR_microshift-devconnects to the OVN join switchjointhrough the logical router port 3. Port 3 attaches with the internal IP address 100.64.0.2. -
The OVN cluster router
ovn_cluster_routerconnects to the join switchjointhrough the logical router port 2. Port 2 attaches with the internal IP address 100.64.0.1.
-
The OVN gateway router
-
The OVN cluster router
ovn_cluster_routerconnects to the node switchmicroshift-devthrough the logical router port 1. Port 1 is attached with the OVN cluster network IP address 10.42.0.1. -
The east-west traffic between the pods and the network service is provided by the OVN cluster router
ovn_cluster_routerand the node switchmicroshift-dev. The IP address range is 10.42.0.0/24. -
The east-west traffic between pods is provided by the node switch
microshift-devwithout network address translation (NAT). -
The north-south traffic between the pods and the external network is provided by the OVN cluster router
ovn_cluster_routerand the host network. This router is connected through theovn-kubernetesmanagement portovn-k8s-mp0, with the IP address 10.42.0.2. All the pods are connected to the OVN node switch through their interfaces.
-
In this example, Pod 1 and Pod 2 are connected to the node switch through
Interface 1andInterface 2.
-
In this example, Pod 1 and Pod 2 are connected to the node switch through
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