istio.io/content/en/docs/reference/glossary/namespace-sameness.md

title	test
Namespace Sameness	n/a

Within a multicluster mesh, namespace sameness applies and all namespaces with a given name are considered to be the same namespace. If multiple clusters contain a Service with the same namespaced name, they will be recognized as a single combined service. By default, traffic is load-balanced across all clusters in the mesh for a given service.

Ports that match on number must also have the same port name to be considered as a combined service port.