This is the distinguished name of the object on the far end of this internal backplane link, i.e. the corresponding SwitchIntFIo record on the fabric-interconnect side. It matters on the internal Ethernet link that carries a blade's traffic from the chassis I/O Module up to a Fabric Interconnect over the backplane because a link problem often needs to be diagnosed from both ends, and peerDn is what lets an admin jump straight to the matching record on the fabric interconnect instead of searching for it. Following peerDn from this backplane link is how an admin confirms whether a reported link-down condition is also visible on the fabric-interconnect side, which would rule out a purely local IOM issue.