# Configure PIM

You can configure dynamic multicast routing using a variant of the PIM protocol on Engines, Virtual Engines, and Engine Clusters.

## Before you begin

We recommend that you first create elements for configuring dynamic routing.

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Three variants of PIM are supported: PIM sparse mode (PIM-SM), PIM dense mode (PIM-DM), and PIM source-specific multicast (PIM-SSM), and the mode can be set separately for different multicast groups. The variant to use depends on many factors, such as the network topology, the number of recipients, and what the existing infrastructure supports.

- Use PIM-SM when multicast traffic needs to travel greater logical distances; over WAN links, for example. There is usually intermittent multicast traffic.
- Use PIM-DM when there are a lot of potential recipients and the logical distances are short; within a WAN, for example. There is usually a high, constant load of multicast traffic. Messages are flooded over the network, so this is not always the most efficient use of bandwidth.
- Use PIM-SSM when you want receivers to be able to specify the source IP address of the requested multicast stream. This is the most efficient use of bandwidth, but all devices and client applications must have support for IGMPv3 and this variant of PIM. However, SSM mapping allows IGMPv2 requests to be converted into IGMPv3 requests.