Some devices implement a form of IGMP proxying whereby
memberships learned on the interface represented by this
row, cause IGMP Host Membership Reports to be sent on the
interface whose ifIndex value is given by this object. Such
a device would implement the igmpV2RouterMIBGroup only on
its router interfaces (those interfaces with non-zero
igmpInterfaceProxyIfIndex). Typically, the value of this
object is 0, indicating that no proxying is being done.