Abstract: A controller may fulfill hardware address requests that are sent by source end hosts in a network to discover hardware addresses of destination end hosts. The controller may use network topology information to determine how to process the hardware address requests. The controller may retrieve a requested hardware address from a database of end hosts. If the controller is able to retrieve the hardware address of a destination end host from the database of end hosts, the controller may provide the source end host with a reply packet that contains the requested hardware address. If the controller is unable to retrieve the requested hardware address, the controller may form request packets to discover the address of the second end host and/or to discover a packet forwarding path between the source end host and the destination end host.

Abstract: A network of switches that forwards network packets between end hosts may be controlled by a controller. The controller may maintain information that identifies subsets of the end hosts that are associated with respective broadcast domains. The controller may configure the switches in the network to identify broadcast network packets and to forward the broadcast network packets to the controller. The controller may identify which broadcast domain is associated with a received broadcast network packet based on information such as source information retrieved from the broadcast network packet. The controller may identify switches that are coupled to the end hosts of a broadcast domain associated with the received broadcast network packet. The controller may forward the broadcast network packet to the identified switches through network control paths and may direct the identified switches to forward the broadcast network packet to end hosts of the associated broadcast domain.

Abstract: A network may include network switches with network switch ports that may be coupled to end hosts. The network switches may be controlled by a controller such as a controller server. Virtual switches may be formed using the controller from groups of the network switch ports and the end hosts. Each virtual switch may include virtual interfaces associated with end hosts or network switches. Virtual links may be formed that define network connections between the virtual interfaces and end hosts or between two virtual interfaces. Virtual network policies such as selective packet forwarding, packet dropping, packet redirection, packet modification, or packet logging may be implemented at selected virtual interfaces to control traffic through the communications network. The controller may translate the virtual network policies into network switch forwarding paths that satisfy the virtual network policies.

Abstract: A network of switches that forwards network packets between end hosts may be controlled by a controller. The controller may maintain information that identifies subsets of the end hosts that are associated with respective broadcast domains. The controller may use network topology information to determine which of the switches are coupled in a forwarding tree formed from network paths between the end hosts of a broadcast domain. The controller may be used to configure the switches with an identifier that identifies which broadcast domain is associated with each subset of end hosts. The controller may configure switches of a given forwarding tree that are coupled to end hosts of an associated broadcast domain to modify broadcast network packets received from the end hosts with the identifier and to forward the modified broadcast network packets along the forwarding tree exclusively to end hosts of the associated broadcast domain.

Abstract: Network policies that control the flow of traffic through a network may be implemented using a controller server that controls a network of switches. Based on network packet attributes, the controller server may identify network policies that are associated with the network traffic. The controller server may identify dependencies between the network policies based on priorities that are associated with the network policies and overlap between the network policies. The controller server may provide the switches with packet forwarding rules based on the identified dependencies between the network policies, network switch attributes, and network switch capabilities. The packet forwarding rules may implement network policies for current network traffic and future network traffic.

Abstract: A network may include network switches with network switch ports that may be coupled to end hosts. The network switches may be controlled by a controller such as a controller server. Virtual switches may be formed using the controller from groups of the network switch ports and the end hosts. Each virtual switch may include virtual interfaces associated with end hosts or network switches. Virtual links may be formed that define network connections between the virtual interfaces and end hosts or between two virtual interfaces. Virtual network policies such as selective packet forwarding, packet dropping, packet redirection, packet modification, or packet logging may be implemented at selected virtual interfaces to control traffic through the communications network. The controller may translate the virtual network policies into network switch forwarding paths that satisfy the virtual network policies.