The cHsrpExtIfStandbyEntry allows an HSRP group
interface to track one or more standby interfaces.
To create a new cHsrpExtIfStandbyEntry row, a
management station should choose the ifIndex of
the interface which is to be added as part of an
HSRP group. Also, an HSRP group number and a
cHsrpExtIfStandbyIndex should be chosen.