Method and apparatus for implementing a flexible virtual local area network

An apparatus for configuring a virtual local area network in a first level system of local virtual local area networks (VLANs) over an underlying second level network of global VLANs, to transmit data frames between a plurality of VLANs in said first level of local VLANs, each of the global VLANs including one or more hosts and a plurality of switches, each of the switches serving one or more of the local VLANs, and wherein the hosts migrate across boundaries of the local VLANs, the apparatus comprising:

• a determining unit of a computer system configured to determine, in response to detecting that one of the hosts enters into a first of the local virtual local area networks served by a first of the switches, one of the global virtual local area networks to which the one of the hosts belongs, for transmitting a data frame from said first of the local VLANs to a second of the local VLANs by transmitting the data frame, over the one global VLANs, from the one of the hosts to at least a second of the switches, wherein the second switch serves one or more second ones of the local virtual local area networks, including to query a directory server for one of the global VLANs to which the one of the hosts belongs;
• an adding unit of the computer system configured to add an address of the first switch to the directory server for said one of the global VLANs to correspond to an address of the one of the hosts stored on the directory server;
• and
• the apparatus configured to create a mapping record at the first switch if the one of the hosts is a first one of the hosts in the first local virtual local area network, to record a correspondence relationship between an identifier of the first local virtual local area network and an identifier of the determined one of the global virtual local area networks.