The first control plane communication that we are concerned with is from the NSX Manager to each ESXi host via TCP port 5671. This port is reserved for the Rabbit MQ Message bus to the vsfwd daemon running on each host after the VMware Service Insertion Platform (VSIP) VIB installation, which is the Distributed Firewall kernel module. The NSX Manager uses the message bus to publish firewall rules down to each ESXi host. The ESXi host then applies them to vNICs of virtual machines that are running on top of its hypervisor.