This Counter32 reports the current number of ESP-encrypted inbound SAs currently active for this Virtual Interface, per its description, a live gauge rather than a lifetime running total. An admin watches this to see right now how many ESP inbound security associations are actually up on the tunnel, useful for confirming a tunnel carrying multiple SAs (e.g. per-subnet) is fully established rather than partially negotiated. For example, an admin who expects four ESP inbound SAs on VI 15 used for dialup client tunnels but sees this counter reading only two would know some subnet pairs failed to negotiate ESP setup.