This Gauge32 is the chassis number this internal link connects to, as tracked from the Fabric Interconnect side. 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 fabric interconnect terminates internal links from multiple chassis, and this field is what tells an admin which chassis a given switch-side link record actually belongs to. A chassisId of 4 on this link's fabric-interconnect side tells an admin this specific switch-side record describes the fabric interconnect's connection into chassis 4, not any other chassis in the domain.