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openshift-docs/modules/nw-about-multicast.adoc

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// Module included in the following assemblies:
//
// * networking/openshift_sdn/enabling-multicast.adoc
// * networking/ovn_kubernetes_network_provider/enabling-multicast.adoc
ifeval::["{context}" == "openshift-sdn-enabling-multicast"]
:openshift-sdn:
:sdn: OpenShift SDN
endif::[]
ifeval::["{context}" == "ovn-kubernetes-enabling-multicast"]
:ovn:
:sdn: OVN-Kubernetes
endif::[]
:_mod-docs-content-type: CONCEPT
[id="nw-about-multicast_{context}"]
= About multicast
With IP multicast, data is broadcast to many IP addresses simultaneously.
[IMPORTANT]
====
* At this time, multicast is best used for low-bandwidth coordination or service discovery and not a high-bandwidth solution.
* By default, network policies affect all connections in a namespace. However, multicast is unaffected by network policies. If multicast is enabled in the same namespace as your network policies, it is always allowed, even if there is a `deny-all` network policy. Cluster administrators should consider the implications to the exemption of multicast from network policies before enabling it.
====
Multicast traffic between {product-title} pods is disabled by default. If you are using the {sdn} network plugin, you can enable multicast on a per-project basis.
ifdef::openshift-sdn[]
When using the OpenShift SDN network plugin in `networkpolicy` isolation mode:
* Multicast packets sent by a pod will be delivered to all other pods in the project, regardless of `NetworkPolicy` objects. Pods might be able to communicate over multicast even when they cannot communicate over unicast.
* Multicast packets sent by a pod in one project will never be delivered to pods in any other project, even if there are `NetworkPolicy` objects that allow communication between the projects.
When using the OpenShift SDN network plugin in `multitenant` isolation mode:
* Multicast packets sent by a pod will be delivered to all other pods in the
project.
* Multicast packets sent by a pod in one project will be delivered to pods in
other projects only if each project is joined together and multicast is enabled
in each joined project.
endif::openshift-sdn[]
ifeval::["{context}" == "openshift-sdn-enabling-multicast"]
:!openshift-sdn:
endif::[]
ifeval::["{context}" == "ovn-kubernetes-enabling-multicast"]
:!ovn:
endif::[]
ifdef::sdn[]
:!sdn:
endif::sdn[]