In the end-host mode, Fabric Interconnect does not work as a traditional layer 2 switch. In this mode, UCS Fabric Interconnect is presented to the northbound LAN switch as an end host with many adapters. Traffic from individual servers' vNICs is mapped to a specific Fabric Interconnect uplink port or port channel. This mapping of Ethernet traffic is known as LAN pin groups.
Pin groups can be configured as a static or dynamic pin group. The default configuration is dynamic pin groups.
This is the default pin group setting. In dynamic pinning, Fabric Interconnect automatically binds server vNICs to uplink FI ports. The mapping of server vNICs to uplink FI ports depends upon the total number of active uplinks configured, which could be either 1, 2, 4, or 8 (for older 6100 series FIs, uplinks could only be 1, 2, and 4).