# Relay limitations

> Understand the constraints and boundaries of the Relay service.

The underlying Relay service within the Multiplayer Services SDK has the following limitations:

* Relay is engine agnostic. If you use Relay with Unity, the recommended best practice is to use the [Multiplayer Services SDK](https://docs.unity3d.com/Packages/com.unity.services.multiplayer@latest). Use `SessionOptions` with [`WithRelayNetwork`](https://docs.unity3d.com/Packages/com.unity.services.multiplayer@2.2/api/Unity.Services.Multiplayer.SessionOptionsExtensions.html#Unity_Services_Multiplayer_SessionOptionsExtensions_WithRelayNetwork__1___0_System_String_) to configure a session to use Relay networking.

* Players can only connect with other players within the same session.

* Currently, there's no region-locking functionality; anyone can request an allocation in any [region](../pages/networking/locations-and-regions) if the region has enough capacity to support the request.

* The Relay service routes all communication through a single [region](../pages/networking/locations-and-regions) selected by the host. As a result, cross-region communication might not offer optimal latency.

* A maximum of 150 players can join the host in the same session. Not all game types will scale to that high amount of players without the use of a dedicated game server. Carefully consider the impact on the host player when attempting high player count sessions with Relay. This limit's aligned with the maximum number of players allowed in a Lobby.