This INTEGER marks whether the filter applies to packets arriving (in) or leaving (out) on this virtual interface. Getting the direction right matters operationally because the same access-list entry can be meant to police only inbound abuse or only outbound leaks, and applying it to the wrong direction silently filters the wrong traffic. For instance, on VI 4 facing the Frame Relay uplink an admin blocking inbound telnet attempts would set this filter's direction to 'in' rather than 'out'.