This integer identifies the interface, using the same value as the standard ifIndex, to which the receive-address table entry's address applies. Admins use it to tie a specific accepted address, found in ifExtnsRcvAddress, back to the interface that recognizes it, useful when auditing which addresses a multi-address-capable interface is filtering for. A row with ifExtnsRcvAddrIfIndex of 5 describes an address accepted only by interface 5, not other interfaces on the box.