The value of tmnxOamMcastTrCtlVRtrID specifies the virtual router to be
used for the test. The value specified must be the index of an active
row in TIMETRA-VRTR-MIB::vRtrConfTable.
tmnxOamTrCtlVRtrID (i.e. the equivalent object in the parent table) is
irrelevant when the test type is 'mcastTraceRoute'.
When directing an 'mcastTraceRoute' test to use a virtual router
associated with a VPRN service, the virtual router can be specified
using tmnxOamMcastTrCtlVRtrID (with the VPRN's virtual router number)
or tmnxOamTrCtlServiceId (with the VPRN's service number).
tmnxOamTrCtlServiceId is preferred, because service numbers are
constant across an SROS reboot (while virtual routers may be
renumbered). If non-default values are specified for both
tmnxOamMcastTrCtlVRtrID and tmnxOamTrCtlServiceId,
tmnxOamTrCtlServiceId is used.