The Cisco Nexus 1000V implements a loop detection mechanism that is based on source and destination MAC addresses and drops packets that are coming in on uplink ports if the source MAC address is already present on a local vEthernet interface. As a result, such protocols as the Virtual Router Redundancy Protocol (VRRP), the Common Address Redundancy Protocol (CARP), the Hot Standby Router Protocol (HSRP), and other similar protocols fail on Virtual Machines (VMs) that are associated to the Cisco Nexus 1000V.
Disabling loop detection provides a flexible way of supporting these protocols on VMs that are associated to the Cisco Nexus 1000V. By disabling the loop detection mechanism, you can configure any combination of the above mentioned protocols on a port profile or a vEthernet interface. As a result, you can run multiple protocols on the same VM.