This is the distinguished name of the corresponding VLAN object on the peer fabric interconnect, the other side, A or B, for this specific VLAN. Because UCS VLANs are normally created symmetrically on both fabric sides, this field on this row is what lets you jump directly to this VLAN's counterpart definition on the other fabric, useful for confirming both sides are configured consistently, e.g. same sharing type, same transport. If peerDn here points to a VLAN object with a mismatched sharing or transport setting compared to this row, that inconsistency between fabric A and B for this specific VLAN would explain intermittent connectivity depending on which fabric a server is currently using.