This value identifies the functional role this internal interface plays as seen from the Fabric Interconnect side, for example whether it's serving as a chassis-facing internal port. It matters on the same internal chassis backplane link, but the record kept on the Fabric Interconnect (switch) side rather than the IOM/server side because the switch-side role determines which fault and traffic-handling rules the fabric interconnect applies to this specific backplane port. An ifRole confirming a chassis-facing role on this link's fabric-interconnect side tells an admin this particular fabric-interconnect port exists specifically to serve chassis 1's backplane traffic.