The ifIndex of the interface on which this entry was
discovered.
The ifIndex is an 'external value' that identifies a
physical component associated with the Alias entry.
This object can be used to identify the physical
location of the interface in the ifTable [RFC2863].
The possibility of ifIndex value re-assignment must be
accommodated by a management application whenever the
value of sysUpTime is reset to zero.
Since ifIndex values in different 'naming scopes' are
not related to one another, the interface to physical
component associations are relative to the same
logical entity within the agent. For more discussion
of naming scopes, see the ENTITY-MIB [RFC2037]