Abstract:
A method for transferring information between a first network comprising first-network-stations operating under an Ethernet protocol and a second network comprising second-network-stations operating under a Fibre Channel (FC) protocol, including grouping the first-network-stations into virtual local area networks (VLANs) which each transfer a respective VLAN-data-frame within the VLAN, and grouping the second-network-stations into FC zones which each transfer a respective zone-data-frame within the zone. The method further includes coupling the networks together using a gateway to convey data between the networks, configuring the gateway with an association mapping a primary VLAN and a primary zone, and translating in the gateway between a primary VLAN-data-frame and a primary zone-data-frame, responsive to the association, so as to convey primary-data between the primary VLAN and the primary zone via the gateway.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to data transfer, and specifically to data transfer between regions of networks operating under differing protocols. 
   BACKGROUND OF THE INVENTION 
   Methods for transferring data within networks, such as local area networks (LANs), metropolitan area networks (MANs), and storage area networks (SANs), rely on standard protocols describing how the data is transferred. Typically the data for a specific network is transferred as data-frames having a format defined by the protocol governing the functioning of the network. Two protocols which are used for transferring data at gigabit/s (Gbps) rates are an IEEE 802.3(Z) Ethernet protocol, issued by the Institute of Electrical and Electronics Engineers, Inc., New Jersey, and an FC-PH Fibre Channel protocol, issued by the American National Standards Institute, Washington, D.C. The Ethernet protocol transfers data-frames over a common bus by ensuring that no data collision occurs when the frames are on the bus. The Fibre Channel protocol transfers data-frames via a switching fabric controlled by a management facility. The facility sets up a path through the fabric between source and destination ports, and the data-frames are routed along the path, ensuring there are no collisions. 
   Stations within a LAN or MAN operating according to the IEEE 802.3(Z) Ethernet protocol are often grouped together to form a virtual LAN (VLAN), the VLAN being a sub-set of all stations comprised in the area network. The grouping is a virtual grouping, which may relatively easily be changed, since there is no change in physical connections of the LAN when a VLAN is formed. VLANs are implemented by tagging data-frames transmitted from stations of the VLAN, according to the IEEE 802.1q tagging standard, also issued by the Institute of Electrical and Electronics Engineers, Inc. A station can belong to more than one VLAN. However, stations which do not belong to the same VLAN cannot directly transfer data between themselves. 
   Zoning is a method used in a Fibre Channel SAN to provide separation between groups of stations of the SAN, similar to the VLANs of the Ethernet network. In contrast to VLANs, where the grouping of the sub-sets is determined by tagging of frames of stations within the sub-sets, the grouping of stations within a zone is implemented by the Fibre Channel management facility. The FC-PH Fibre Channel protocol supports zoning when a station is attached to the Fibre Channel fabric, or when an attached station performs a request. In either event, the station receives a list of all the stations belonging to at least one of the requesting station zones. Another method of Fibre Channel zoning, not supported by the FCPH standard but known in the art, uses a programmed hardware filtering table comprised in a switch of the Fibre Channel fabric. For each frame arriving at a switch port, the switch forwards the frame only if the table indicates that the source FC address in the frame belongs to a zone that belongs to an output port. 
   Methods for transferring data between networks operating under different protocols operating at Gbps rates are known in the art. Dell Computer Corporation of Round Rock, Tex., provides a PowerVault Fibre Channel family of products which may be configured to transfer data between a Fibre Channel network and a gigabit Ethernet (GBE) network. Data transfer between the networks requires a suitably-adapted server. 
   In an article by Sherri Azgomi, which can be found at http://www.csdmag.com/main/1999/11/9911feat3.htm, and which is incorporated herein by reference, the author describes content addressable memories (CAMs) and gives a number of uses of CAMs. In contrast to a random access memory (RAM), wherein an address is supplied and data at that address is read, data is supplied to a CAM and the address where that data resides is read. An illustration of the use of a CAM in a network switch is given, wherein the CAM extracts and processes address information in incoming data packets. In order to switch the packet to a correct outgoing port, the CAM compares the destination address with a table of addresses stored within the CAM. On-chip implementations of CAM in the form of embedded functions are available as high-density programmable logic devices (PLDs), for example, as an Altera 10K100E device, produced by Altera Corporation of San Jose, Calif. 
   U.S. Pat. No. 6,032,209 to Mros et al., whose disclosure is incorporated herein by reference, describes a hot-swappable high speed point-to-point interface. The interface incorporates circuitry to eliminate electromagnetic interference when the interface is hot-swapped. The interface provides a connection between a high speed transmitter on a transmitter card, and a high speed receiver on another card. Both transmitter and receiver are able to operate at rates of the order of Gbps, and under GBE or Fibre Channel protocols. 
   SUMMARY OF THE INVENTION 
   It is an object of some aspects of the present invention to provide an improved method and apparatus for transferring data between locally grouped stations of networks operating under different protocols. 
   In preferred embodiments of the present invention, a gateway couples two area network communication systems, one system operating under a first protocol, most preferably an Ethernet protocol, the other operating under a second protocol, most preferably a Fibre Channel (FC) protocol. Both systems support Internet protocol (IP) frames. The gateway is implemented so that it is transparent to stations using both systems, and is most preferably comprised within a hub of the FC system. Most preferably, both systems comprise networks operating at a rate of at least 1 gigabit/s (Gbps). The Ethernet network has stations within its network formed into one or more subsets termed virtual local area networks (VLANs). The FC network has stations within its network formed into one or more subsets termed zones. 
   A “combination” grouping is formed by associating a specific VLAN with a specific zone, and data transfers between the VLAN and the zone of the combination grouping via the coupling gateway. The association is stored in the gateway. From the point of view of a VLAN station in the combination, all stations in the combination appear as native VLAN stations. From the point of view of an FC station within the combination, all stations appear as native FC zone stations. The gateway may store a multiplicity of associations, i.e., combination groupings, each combination grouping comprising a one-to-one mapping between a specific VLAN and a specific zone. Stations in the Ethernet network and in the FC network, within a specific combination grouping, may transfer data between themselves via the gateway. Allocating stations in networks operating under Ethernet and FC protocols to be part of one or more combination groupings increases flexibility of station grouping and simplifies security deployment in the infrastructure of the networks. 
   When an FC device in the FC zone of a specific combination grouping sends an IP FC frame to an Ethernet device in the VLAN of the grouping, the frame is sent to a gateway port, corresponding to a “next hop” destination media access control (MAC) address, which may typically correspond to a default router. The destination identity address is set according to the combination grouping. At the gateway, the frame is translated to an IP Ethernet frame with a VLAN identity corresponding to the source identity address of the FC device. The translated frame is then transmitted from the gateway to the destination Ethernet device. 
   In the reverse direction, i.e., sending from the VLAN to the FC zone, the gateway uses a source identity address (SID) as a means to explicitly carry the identity of the VLAN in the FC frame. A destination device can make security decisions based on this information. A domain part of the SID receives a “virtual” switch identity which tells the destination device that the SID area is actually the frame&#39;s VLAN. An IP frame from a VLAN source is directed by a router in the area network to the gateway port. The frame contains the VLAN identity and an identity for a destination device in the FC zone. On arrival at the gateway, the gateway, acting as the virtual switch, decides how to process the frame according to the VLAN identity and the destination identity. If the zone corresponding to the VLAN is allowed at the destination device, the incoming Ethernet frame is translated to an FC frame and is forwarded to the destination device. (Prior to transfer of a first frame of a specific VLAN to a specific destination device, a connection must be established between the port in the virtual switch that represents the VLAN and the destination device port.) 
   Each gateway is implemented using industry-standard devices and/or one or more custom or semi-custom devices such as application specific integrated circuits (ASICs), most preferably as a component which couples to an industry-standard hub operative in one of the systems. 
   In some preferred embodiments of the present invention, a content addressable memory (CAM) comprised in the gateway is used in order to quickly translate addresses. Most preferably, the CAM “learns” the addresses of stations after installation of the gateway, by analyzing data transferred as it is received. The CAM uses the learned addresses to build a look-up table for converting addresses between the two systems. 
   There is therefore provided, according to a preferred embodiment of the present invention, a method for transferring information between a first network including first-network-stations operating under an Ethernet protocol and a second network including second-network-stations operating under a Fibre Channel (FC) protocol, including: 
   grouping the first-network-stations into one or more virtual local area networks (VLANs), each of the VLANs including one or more of the first-network-stations which transfer a respective VLAN-data-frame within the VLAN; 
   grouping the second-network-stations into one or more FC zones, each of the zones including one or more of the second-network-stations which transfer a respective zone-data-frame within the zone; 
   coupling the first and the second networks together using a gateway to convey data between the networks; 
   configuring the gateway with a primary association mapping a primary VLAN chosen from the VLANs and a primary zone chosen from the zones, the primary VLAN transferring a primary VLAN-data-frame including primary-data, included in the data, therein, and the primary zone transferring a primary zone-data-frame including the primary-data therein; and 
   translating in the gateway between the primary VLAN-data-frame and the primary zone-data-frame, responsive to the primary association, so as to convey the primary-data between the primary VLAN and the primary zone via the gateway. 
   Preferably, configuring the gateway with the primary association includes storing the primary association in a memory included in the gateway, the memory including a content addressable memory which uses the primary association to perform the translation. 
   Preferably, translating in the gateway between the primary VLAN-data-frame and the primary zone-data-frame includes transferring the primary-data transparently between the primary VLAN and the primary zone so that the primary VLAN and the primary zone are not aware of translations performed in the gateway. 
   Preferably, the method further includes: 
   configuring the gateway with a secondary association mapping a secondary VLAN chosen from the VLANs and a secondary zone chosen from the zones, the secondary VLAN transferring a secondary VLAN-data-frame including secondary-data, included in the data, therein, and the secondary zone transferring a secondary zone-data-frame including the secondary-data therein; and 
   translating in the gateway between the secondary VLAN-data-frame and the secondary zone-data-frame, responsive to the secondary association, so as to convey the secondary-data between the secondary VLAN and the secondary zone via the gateway. 
   Further preferably, the method includes restricting the secondary VLAN and the secondary zone from accessing the primary-data. 
   Preferably, the method further includes: 
   providing a joint second-network-station, chosen from the second-network-stations, implemented to be in the primary zone and the secondary zone; 
   conveying the primary-data between the joint second-network-station and the primary VLAN, responsive to the primary association; and 
   conveying the secondary-data between the joint second-network-station and the secondary VLAN, responsive to the secondary association. 
   Preferably, the method further includes: 
   providing a joint first-network-station, chosen from the first-network-stations, implemented to be in the primary VLAN and the secondary VLAN; 
   conveying the primary-data between the joint first-network-station and the primary zone, responsive to the primary association; and 
   conveying the secondary-data between the joint first-network-station and the secondary zone, responsive to the secondary association. 
   Preferably, configuring the gateway includes allocating a virtual port of the gateway to the primary association, and translating in the gateway includes operating the gateway as a virtual switch so as to check a connection between the virtual port and a destination first-network-station included in the primary VLAN. 
   Further preferably, translating in the gateway includes translating an identity of the primary VLAN in the primary VLAN-data-frame to a virtual source identity in the primary zone-data-frame, for data conveyed from the first network to the second network. 
   Preferably, translating in the gateway includes translating a virtual destination identity included in the primary zone-data-frame to an identity of the primary VLAN in the primary VLAN-data-frame, for data conveyed from the second network to the first network. 
   There is further provided, according to a preferred embodiment of the present invention, apparatus for transferring information between a first network operating under an Ethernet protocol and including first-network-stations grouped into one or more VLANs, each VLAN including one or more of the first-network-stations which transfer a respective VLAN-data-frame within the VLAN, and a second network operating under a Fibre Channel (FC) protocol and including one or more second-network-stations grouped into one or more zones, each zone including one or more of the second-network-stations which transfer a respective zone-data-frame within the zone, the apparatus including: 
   a gateway which is adapted to couple the first and the second network and to map a primary association between a primary VLAN chosen from the VLANs and a primary zone chosen from the zones, the primary VLAN transferring a primary VLAN-data-frame including primary-data therein, and the primary zone transferring a primary zone-data-frame including the primary-data therein, and to translate between the primary VLAN-data-frame and the primary zone-data-frame, responsive to the primary association, so as to convey the primary-data between the primary VLAN and the primary zone. 
   Preferably, the gateway includes a content addressable memory wherein the primary association is stored and which is adapted to perform the translation. 
   Preferably, translating in the gateway between the primary VLAN-data-frame and the primary zone-data-frame includes transferring the primary-data transparently between the primary VLAN and the primary zone so that the primary VLAN and the primary zone are not aware of translations performed in the gateway. 
   Preferably, the gateway is adapted to map a secondary association between a secondary VLAN chosen from the VLANs and a secondary zone chosen from the zones, the secondary VLAN transferring a secondary VLAN-data-frame including secondary-data therein, and the secondary zone transferring a secondary zone-data-frame including the secondary-data therein, and to translate between the secondary VLAN-data-frame and the secondary zone-data-frame, responsive to the secondary association, so as to convey the secondary-data between the secondary VLAN and the secondary zone. 
   Further preferably, the gateway is adapted to restrict the secondary VLAN and the secondary zone from accessing the primary-data. 
   Preferably, the apparatus includes a joint second-network-station, chosen from the second-network-stations, implemented to be in the primary zone and the secondary zone, so that the primary-data is conveyed between the joint second-network-station and the primary VLAN responsive to the primary association, and the secondary-data is conveyed between the joint second-network-station and the secondary VLAN responsive to the secondary association. 
   Preferably, the apparatus includes a joint first-network-station, chosen from the first-network-stations, implemented to be in the primary VLAN and the secondary VLAN, so that the primary-data is conveyed between the joint first-network-station and the primary zone responsive to the primary association, and the secondary-data is conveyed between the joint first-network-station and the secondary zone responsive to the secondary association. 
   Preferably, the gateway includes a virtual port allocated to the primary association, and the gateway is adapted to operate as a virtual switch so as to check a connection between the virtual port and a destination first-network-station comprised in the primary VLAN. 
   Further preferably, the gateway is adapted to translate an identity of the primary VLAN in the primary VLAN-data-frame to a virtual source identity in the primary zone-data-frame, for data conveyed from the first network to the second network. 
   Further preferably, the gateway is adapted to translate a virtual destination identity comprised in the primary zone-data-frame to an identity of the primary VLAN in the primary VLAN-data-frame, for data conveyed from the second network to the first network. 
   The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a compound network coupling a Fibre Channel (FC) fabric and an Ethernet Wide Area Network (WAN), according to a preferred embodiment of the present invention; 
       FIG. 2  shows structures of Internet protocol (IP) data-frames transmitted via an Ethernet protocol, and IP data-frames transmitted via a Fibre Channel protocol, according to a preferred embodiment of the present invention; 
       FIG. 3  is a flowchart showing steps comprised in transferring data from the FC fabric to the WAN of the network of  FIG. 1 , according to a preferred embodiment of the present invention; 
       FIG. 4  is a flowchart showing steps comprised in transferring data from the WAN to the FC fabric of the network of  FIG. 1 , according to a preferred embodiment of the present invention; and 
       FIG. 5  is a schematic diagram of a compound network coupling the FC fabric and the Ethernet WAN of  FIG. 1 , according to an alternative preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Reference is now made to  FIG. 1 , which is a schematic diagram of a compound network  10  coupling a Fibre Channel (FC) fabric  11  and an Ethernet Wide Area Network (WAN)  26 , according to a preferred embodiment of the present invention. FC fabric  11  operates according to the FC-PH Fibre Channel protocol, and WAN  26  operates according to the IEEE 802.3(Z) Ethernet protocol, as described in the Background of the Invention. WAN  26  comprises generally similar Ethernet stations  36 ,  38 ,  40 , and  42 , herein assumed to be hosts, also respectively termed herein hosts A, B, C, and D. Within WAN  26  a first virtual local area network (VLAN)  32  comprises hosts  36  and  38  and a second VLAN  34  comprises hosts  40  and  42 . VLANs  32  and  34  comprise subsets of stations within WAN  26 , and are also herein referred to respectively as VLAN A and VLAN B. WAN  26  also comprises a router  30 , which operates within WAN  26  so as, inter alia, to transfer data-frames generated within the WAN between stations of the WAN. Hosts A, B, C, and D, are each allocated an Internet protocol (IP) address, so that they are able to transfer IP data-frames between themselves, subject to the VLAN limitations stated above. Most preferably, an operator of network  10  allocates the IP addresses. The addresses must be locally unique in order to implement IP communication between hosts A, B, C, and D. 
   Fabric  11  comprises generally similar FC stations  16 ,  18 ,  23 , and  24 , herein assumed to be servers, also herein termed respectively servers A, B, C, and D. A server  20  is used as a management facility for FC fabric  11 . A first FC zone  12  of fabric  11  comprises servers  16  and  18 , and a second FC zone  13  of the fabric comprises servers  23  and  24 . Zones  12  and  13  comprise FC stations which are subsets of fabric  11 , and are also herein termed respectively zones A and B. Fabric  11  comprises a gateway  22 , which is most preferably comprised within a hub of the fabric. Gateway  22  is coupled to router  30 , so that the gateway is able to receive data-frames from both fabric  11  and WAN  26  according to their respective protocols. Furthermore, gateway  22  is adapted to convert the data-frames between protocol formats, and to transmit in either format, so that the gateway acts as a data-frame transfer and conversion conduit. aServers A, B, C, and D, are each allocated an IP address, so that they are able to transfer IP data-frames between themselves, subject to the zoning limitations stated above. Most preferably, the operator of network  10  allocates the IP addresses via management server  20 . The addresses must be locally unique in order to implement IP communication between servers A, B, C, and D. 
   Most preferably, at the installation of gateway  22 , the operator of network  10  makes associations between specific VLANs and specific zones to form combination zones, each combination zone comprising one VLAN and one FC zone. Herein VLAN A and zone A are associated to form combination zone  46 , and VLAN B and zone B are associated to form combination zone  48 . Combination zones  46  and  48  are also referred to herein as combination zones A and B respectively. Alternatively, the associations are made after gateway  22  has been installed. As described in more detail below, the gateway acts as a coupling for combination zones A and B, forming a (VLAN A, zone A) couple and a (VLAN B, zone B) couple. Once each association has been implemented, Ethernet stations in a specific combination zone see all stations in the combination as native Ethernet stations, and FC stations see all stations in the combination as native FC stations. 
   When the association is made, a virtual port address is allocated to each couple associated by the gateway. The virtual port addresses are used by FC stations as a source zone identification. Most preferably, the virtual port addresses are chosen from a virtual switch domain, i.e., addresses of a fictitious switch in fabric  11 . Alternatively, the virtual port addresses are chosen from addresses in the gateway domain, i.e., addresses allocated to the gateway. 
     FIG. 2  shows structures of Internet protocol (IP) data-frames transmitted via an Ethernet protocol, and IP data-frames transmitted via a Fibre Channel protocol, according to a preferred embodiment of the present invention. An Ethernet data-frame  80  operating under IP comprises a header section  81  and a data section  90 . Header section  81  comprises a frame destination address (DA)  82  and a frame source address (SA)  84 , both most preferably being media access control (MAC) identifiers of the respective addresses. Header section  81  also comprises an identifier  86  for a VLAN within which the frame is transferred. Frame  80  comprises an IP header  88  containing an initial source address and a final destination address of the frame. Frame  90  also comprises a data section  90 , and a cyclic redundancy code (CRC) error-checking and end-of-frame (EOF) section  93 . It will be appreciated that during transfer of frame  80  within an Ethernet network, DA MAC address  82  and SA MAC address  84  may change, depending on the routing of the frame within the VLAN. VLAN identifier  86 , IP header  88  and the data section  90  are substantially unchanged as the frame traverses the VLAN. 
   A Fibre Channel data-frame  92  operating under IP comprises a header section  91  and a data section  104 . Header section  91  comprises a destination identification (DID) address  94 , a source identification (SID) address  96 , a MAC destination address  98 , and a MAC source address  100 . Frame  92  further comprises an IP header  102 , which, as for IP header  88 , comprises an initial source address and a final destination address of the frame. Data section  104  is substantially similar in construction to section  90 . Frame  92  further comprises a CRC/EOF section  105 , generally similar to section  93 . In contrast to data-frame  80 , as data-frame  92  transfers through an FC zone there is substantially no change in header section  91 , since the routing of the frame, is performed by elements of the FC fabric such as switches and hubs. 
   When a data-frame is converted by gateway  22  from an Ethernet data-frame to a Fibre Channel data-frame, or vice versa, data in respective sections  88 ,  90  and  102 ,  104  are substantially identical. For conversion from an Ethernet data-frame to a Fibre Channel data-frame, section  81  is converted to header section  91 . For conversion from a Fibre Channel data-frame to an Ethernet data-frame, header section  91  is converted to header section  81 . 
     FIG. 3  is a flowchart showing steps comprised in transferring data from fabric  11  to WAN  26 , for stations which are comprised in combination zone A, according to a preferred embodiment of the present invention. Server A in zone A is assumed to send data to host A in VLAN A. 
   In a first step, server A constructs FC data-frame  92 , and incorporates in header  102  the IP address of server A as the source IP address, and the IP address of host A as the destination IP address. DID address  94  and DA MAC address  98  are determined using an Address Resolution Protocol (ARP). DID address  94  is set to be the virtual port of gateway  22  associated with couple (VLAN A, zone A), and DA MAC address  98  is set to be the MAC address of router  30 . SID address  96  is the address of server A, which was determined at a fabric connection phase. SA MAC address  100  is set to be the physical address of server A. 
   In a second step, server A performs a connection with the virtual port of the gateway, i.e., with the port corresponding to DID address  94 . FC data-frame  92  is then transmitted into fabric  11 . 
   In a third step, gateway  22  receives data-frame  92 , and translates the data-frame to Ethernet data-frame  80 . At the gateway, DA MAC address  82  and SA MAC address  84  are respectively copied from DA MAC address  98  and SA MAC address  100 . DID address  94  is translated to the identifier of VLAN A, and is written into VLAN section  86  of the Ethernet data-frame. IP header address section  88  is written to be substantially the same as IP header address section  102 . Ethernet data-frame  80  is then transmitted from gateway  22  into WAN  26 . 
   In a final step, Ethernet data-frame  80  is transferred via router  30  to host A, which is able to receive the data-frame since host A is in VLAN A. During the transfer router  30  changes the DA MAC and SA MAC addresses, written into sections  82  and  84 , to correspond respectively to the physical address of host A and the physical address of the router. 
   In the transfer process described with reference to  FIG. 4 , the IP header in sections  102  and  88  and the data in sections  104  and  90  are maintained substantially unchanged. 
     FIG. 4  is a flowchart showing steps comprised in transferring data from WAN  26  to fabric  11 , for stations which are comprised in combination zone A, according to a preferred embodiment of the present invention. Host A in VLAN A is assumed to send data to server A in zone A. 
   In a first step, host A constructs Ethernet data-frame  80 , and incorporates in header  88  the IP address of host A as the source IP address, and the IP address of server A as the destination IP address. DA MAC address  82  is set to be the physical address of router  30 , and SA MAC address  84  is set to be the physical address of host A. The identifier of VLAN A is written into VLAN section  86  of the data-frame. Data-frame  80  is then transmitted into WAN  26 . 
   In a second step, router  30  transfers data-frame  80  to gateway  22 , changing DA MAC section  82  to be the physical address of server A, and SA MAC section  84  to be the physical address of the router. The remainder of data-frame  80  is substantially unchanged. 
   In a third step, gateway  22  receives Ethernet data-frame  80 , and uses the VLAN identifier in section  86  and the destination IP address comprised in header  88  to check the connection between the VLAN and the destination IP. The gateway assumes the role of a virtual switch to make the check about the connection between the virtual port of the gateway associated with the (VLAN A, zone A) couple and server A, identified from the destination IP address. There are three possible outcomes of the check:
         The connection is active. In this case the process continues at a fifth step below.   The connection is forbidden. A forbidden connection might occur, for example, if server A is not in zone A. In this case data-frame  80  is dropped.   The connection is not active. In this case the process continues in a fourth step, wherein a CPU in the gateway implements the connection, and then delivers the delayed frame.       

   In the fifth step, FC data-frame  92  is generated from Ethernet data-frame  80 . DID address  94  is most preferably generated from the destination IP address in header  88  using a CAM in gateway  22  such as CAM  56  ( FIG. 1 ). SID address  96  is set to be the virtual port address associated with the (VLAN A, zone A) couple. DA MAC address  98  and SA MAC address  100  are copied from the Ethernet frame. 
   In a final step, FC data-frame  92  is conveyed, by the connection set up in the third and/or fourth step, to server A. 
     FIG. 5  is a schematic diagram of a compound network  100  coupling Fibre Channel (FC) fabric  11  and Ethernet Wide Area Network (WAN)  26 , according to an alternative preferred embodiment of the present invention. Apart from the differences described below, the operation of network  120  is generally similar to that of network  10  ( FIG. 1 ), so that elements indicated by the same reference numerals in both networks  120  and  10  are generally identical in construction and in operation. Compound network  120  comprises, in fabric  11 , a server  122 , also referred to herein as server E. Server E is implemented to be in both zone A and zone B, so acting as a “joint” server. Thus, server E is able to communicate within zone A with servers A and B, and within zone B with servers C and D. 
   Since server E is in zone A, it is also in combination zone A, and is thus able to communicate with VLAN A and hosts A and B. Thus, server E is able to send data to host A substantially as described above ( FIG. 3 ) for server A sending data to host A, using the virtual port of gateway  22  associated with couple (VLAN A, zone A) as DID address  94 . Host A is able to send data to server E substantially as described above ( FIG. 4 ) for host A sending data to server A. As described therein, gateway  22  uses the VLAN A identifier in section  86  and the destination IP address of server E, comprised in header  88 , to check the connection between VLAN A and server E. 
   Since server E is also in zone B, it is also in combination zone B, and is thus able to communicate with VLAN B and hosts C and D. Thus, server E can send data to host C using the virtual port of gateway  22  associated with couple (VLAN B, zone B) as DID address  94 . Host C is also able to send data to server E substantially as described above, gateway  22  using the VLAN B identifier in section  86  and the destination IP address of server E, comprised in header  88 , to check the connection between VLAN B and server E. 
   It will be appreciated that a host  124  in WAN  26 , also referred to herein as host E, and which is implemented to be in both VLAN A and VLAN B, is able to communicate within combination zone A with servers in zone A, and within combination zone B with servers in zone B. 
   Data transfer implemented by preferred embodiments of the present invention is transparent, in both directions of transfer, to sources and destinations of the data. In other words, a station originating data in a VLAN in WAN  26  is not aware of any of the translation processes performed in gateway  22  and involved in transferring the data, via the gateway, to a zone in FC fabric  11 . Similarly, a station transferring data from a zone in fabric  11  to a VLAN in WAN  26  is not aware of gateway  22 , or of translations performed in the gateway. 
   It will be understood that the scope of the present invention is not limited to the number of VLANs, FC zones, and combination zones described above with respect to  FIG. 1 . IEEE 802.3(Z) Ethernet protocol supports up to 4096 VLANs, so that preferred embodiments of the present invention operating under the above-referenced protocol can comprise up to 4096 combination zones, each combination zone comprising an association between one VLAN and one FC zone. 
   It will be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.