This configures, per route, in which direction or directions multicast traffic is forwarded: none, Ethernet-to-Satellite only, Satellite-to-Ethernet only, or both directions. This per-route granularity is what lets a hub site forward multicast content downlink to remotes while a remote site instead only forwards local multicast uplink toward the hub, rather than being forced into a single global multicast-forwarding behavior for every route on the box. A hub site distributing a multicast video feed to many remotes would set this to satToEthRouting(3), or the value covering both directions, on the relevant route so the feed actually reaches those downstream sites' Ethernet networks.