
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/fcoe/ b_Cisco_Nexus_5000_Series_NX-OS_Fibre_Channel_over_Ethernet_Configuration_Guide_/ Cisco_Nexus_5000_Series_NX-OS_Fibre_Channel_over_Ethernet_Configuration_Guide__chapter3.html You can prevent data corruption due to cross-fabric talk by configuring an FC-Map that identifies the Fibre Channel fabric for this Cisco Nexus device. When the FC-Map is configured, the switch discards the MAC addresses that are not part of the current fabric.
switch(config)# fcoe fcmap fabric-map Configures the global FC-Map. The default value is 0E.FC.00. The range is from 0E.FC.00 to 0E.FC.FF.
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/fcoe/513_n1_1/b_Cisco_n5k_fcoe_co