The ifIndex value of the local interface.
For 802.3 Repeaters on which the repeater ports do not
have ifIndex values assigned, this value is a unique
value for the port, and greater than any ifIndex value
supported by the repeater; in this case, the specific
port is indicated by corresponding values of
cdpInterfaceGroup and cdpInterfacePort, where these
values correspond to the group number and port number
values of RFC 1516.