// Module included in the following assemblies:
//
// * networking/multiple_networks/primary_networks/about-user-defined-networks.adoc

:_mod-docs-content-type: CONCEPT
[id="cudn-transport-considerations_{context}"]
= Considerations for ClusterUserDefinedNetwork transport

[role="_abstract"]
Unlike the `UserDefinedNetwork` (UDN) custom resource (CR), the `ClusterUserDefinedNetwork` CR gives you more control over how pod traffic is carried on the cluster infrastructure and how it relates to networks outside the cluster.

By default, pod-to-pod traffic on the CUDN CR uses a Geneve overlay.
Pod IP addresses are not directly reachable from outside of the cluster.
When workload traffic leaves the cluster through the designated egress gateway, source addresses are masqueraded to the node IP address of the node that forwards the traffic, similar to other pod networks.

You can use route advertisements and the `RouteAdvertisements` CR so that routes for the CUDN are advertised on the provider network by using Border Gateway Protocol (BGP). Collectively, this configuration makes pod IP addresses reachable from outside the cluster. For information, see "About route advertisements".

Additionally, you can set `spec.network.transport` to `NoOverlay` to route layer 3 pod traffic on the underlay with BGP instead of Geneve encapsulation, or to `EVPN` to attach a primary CUDN to an external BGP EVPN fabric instead of using only the default overlay behavior. Configuring either transport requires additional objects and node networking beyond the CUDN CR. For more information, see "Improve east-west performance by routing pods on the underlay with BGP" and "About BGP EVPN for primary cluster user-defined networks".