Patent Publication Number: US-9432754-B2

Title: Maintaining a fabric name across a distributed switch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-pending U.S. patent application Ser. No. 14/058,545, filed Oct. 21, 2013. The aforementioned related patent application is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Embodiments of the present disclosure generally relate to the field of computer networks. 
     Computer systems often use multiple computers that are coupled together in a common chassis. The computers may be separate servers that are coupled by a common backbone within the chassis. Each server is a pluggable board that includes at least one processor, an on-board memory, and an Input/Output (I/O) interface. Further, the servers may be connected to a switch to expand the capabilities of the servers. For example, the switch may permit the servers to access additional Ethernet networks or Peripheral Component Interconnect Express (PCIe) slots as well as permit communication between servers in the same or different chassis. In addition, multiple switches may also be combined to create a distributed network switch. 
     Fibre Channel (FC) can be used to connect these servers and computing resources, including connecting computer systems to storage devices such as storage area network (SAN) devices. Fibre Channel is a high speed medium primarily used for data transfer and storage, but may also be used to connect other devices, servers, printers, etc. Fibre Channel is essentially a serial data channel, often created over fiber optic cabling, that provides a logical bi-directional, point-to-point connection between a host and a device. 
     BRIEF SUMMARY 
     Embodiments of the present disclosure provide a method, product, and system for performing an operation for distributing a switch name in a distributed Fibre Channel fabric or a distributed FCoE fabric in which FC frames are encapsulated in Ethernet frames. The operation includes instantiating a switch link between a controlling FCoE forwarder (cFCF) of the distributed Fibre Channel fabric and a first FCoE data-plane forwarder (FDF). The distributed Fibre Channel fabric may include a set of FDFs and the cFCF. The operation further includes receiving, from the cFCF, a distributed switch membership distribution (DFMD) message. The DFMD message may contain a fabric name identifying with the distributed Fibre Channel fabric. The operation includes modifying the first FDF to join the distributed Fibre Channel fabric based on the fabric name contained in the DFMD. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       So that the manner in which the above recited aspects are attained and can be understood in detail, a more particular description of embodiments of the present disclosure, briefly summarized above, may be had by reference to the appended drawings. 
       It is to be noted, however, that the appended drawings illustrate only typical embodiments of this present disclosure and are therefore not to be considered limiting of its scope, for the present disclosure may admit to other equally effective embodiments. 
         FIG. 1  illustrates a system architecture that includes a distributed network switch, according to one embodiment of the present disclosure. 
         FIG. 2  illustrates the distributed network switch configured for Fibre Channel switching, according to one embodiment of the present disclosure. 
         FIGS. 3A and 3B  are sequence diagrams depicting a method for distributing a fabric name in the distributed network switch, according to one embodiment of the present disclosure. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. The drawings referred to here should not be understood as being drawn to scale unless specifically noted. Also, the drawings are often simplified and details or components omitted for clarity of presentation and explanation. The drawings and discussion serve to explain principles discussed below, where like designations denote like elements. 
     DETAILED DESCRIPTION 
     Devices may be connected on Fibre Channel systems using various interconnection topologies and devices, such as switches, hubs, and bridges, to allow scalability based on users&#39; needs. As Fibre Channel networks get larger and network demands increase, switching may be implemented. A switched Fibre Channel network is referred to herein a “fabric.” A fabric is simply the underlying switching architecture used by a Fibre Channel switch. A fabric may contain many loops interconnected with switches. 
     Fibre Channel over Ethernet (FCoE) refers to a technology used for transporting Fibre Channel (FC) frames over Ethernet, which is standardized at the Technical Committee for Fibre Channel (T11) of the International Committee for Information Technology Standards (INCITS). The transported FC frames used are based on an FC architecture for storage networking purposes. The FC-BB-6 and FC-SW-6 working groups of the T11 Fibre Channel standards committee are working to develop a distributed switch model with associated protocols. In conjunction with the technology used for transporting FC frames over Ethernet, a distributed switch model and associated protocols of the current state of the art may be applied to both FCoE switches or standard FC switches. 
     A Fibre Channel switch uses a unique identifier, referred to as a World Wide Name (WWN) to identify a fabric. End points log into the fabric, i.e., establish a connection with the switch, in order to communicate with other endpoints on the fabric. For a standalone switch, assigning the fabric name may be simple. The fabric name is the WWN of the switch controlling the fabric, and endpoints connected to any port on the switch will see the same fabric name. However, this approach becomes problematic when implementing a distributed switch with multiple discrete switches, each having a unique WWN. The fabric must present the same name to an endpoint, regardless of the switch unit that owns the port where the endpoint is attached. Conventional techniques require a fabric name to be manually configured and entered into each element of an FCoE fabric. As result, configuration errors are commonplace and efficiency and productivity may be reduced. 
     In contrast, and to address the inefficiencies and performance issues previously described, the illustrated embodiments provide mechanisms for Fibre Channel forwarder fabric initialization sequence in a Fibre Channel switch environment, where a controlling Fibre Channel Forwarder (cFCF) is separated from a Fibre Channel over Ethernet (FCoE) data forwarder (FDF). The mechanisms, by way of example only, transmits a distributed switch membership distribution (DFMD) message which contains the WWNs of all switching elements in the fabric, and in addition, contain the WWN of the fabric itself. 
     In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice aspects of the present disclosure. Furthermore, although embodiments of the present disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the present disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     As will be appreciated by one skilled in the art, aspects of the present disclosure may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Aspects of the present disclosure are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the present disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
       FIG. 1  illustrates a system architecture  100  that includes a distributed network switch  180 , according to one embodiment of the present disclosure. The computer system  100  includes first and second servers  105 ,  106  connected to the distributed network switch  180 . In one embodiment, the first server  105  may include at least one processor  109  coupled to a memory  110 . The processor  109  may represent one or more processors (e.g., microprocessors) or multi-core processors. The memory  110  may represent random access memory (RAM) devices comprising the main storage of the server  105 , as well as supplemental levels of memory, e.g., cache memories, non-volatile or backup memories (e.g., programmable or flash memories), read-only memories, and the like. In addition, the memory  110  may include memory storage physically located in the server  105  or on another computing device coupled to the server  105 . The server  105  may operate under the control of an operating system (not shown) and execute various computer software applications, components, programs, objects, modules, and data structures, such as virtual machines  111 . 
     The server  105  may include network adapters  115 , sometimes referred to as converged network adapters (CNAs). A converged network adapter may include single root I/O virtualization (SR-IOV) adapters such as a Peripheral Component Interconnect Express (PCIe) adapter that supports Converged Enhanced Ethernet (CEE). Another embodiment of the system  100  may include a multi-root I/O virtualization (MR-IOV) adapter. The network adapters  115  may further be used to implement a Fibre Channel over Ethernet (FCoE) protocol, RDMA over Ethernet, Internet small computer system interface (iSCSI), and the like. In general, a network adapter  115  transfers data using both an Ethernet and PCI based communication method and may be coupled to one or more of the virtual machines  111 . In particular, Ethernet may be used as the protocol to the distributed network switch, while PCI may be used as the protocol to transfer data to/from main memory to the network adapter  115 . Additionally, the adapters may facilitate shared access between the virtual machines  111 . While the adapters  115  are shown as being included within the server  105 , in other embodiments, the adapters may be physically distinct devices that are separate from the server  105 . 
     As shown in  FIG. 1 , the second server  106  may include a processor  109  coupled to a memory  110  which includes one or more virtual machines  111  similar to those found in the first server  105 . The memory  110  of server  106  may include a hypervisor  113  configured to manage data shared between different virtual machines  111 . The hypervisor  113  may include a virtual bridge  114  that allows direct communication between connected virtual machines  111  rather than requiring the virtual machines  111  to use the bridge elements  120  or switching layer  130  to transmit data to other virtual machines  111  communicatively coupled to the hypervisor  113 . 
     In one embodiment, each network adapter  115  may include a converged adapter virtual bridge (not shown) that facilitates data transfer between the adapters  115  by coordinating access to the virtual machines  111 . Each converged adapter virtual bridge may recognize data flowing within its domain (i.e., addressable space). A recognized domain address may be routed directly without transmitting the data outside of the domain of the particular converged adapter virtual bridge. 
     Each network adapter  115  may include one or more Ethernet ports that are coupled to one of the bridge elements  120 , also referred to herein as bridging elements. Additionally, to facilitate PCIe communication, the server may have a PCI Host Bridge  117 . The PCI Host Bridge  117  may connect to an upstream PCI port  122  on a switch element in the distributed network switch  180 . The data is then routed via the switching layer  130  to the correct downstream PCI port  123  which may be located on the same or different switch module as the upstream PCI port  122 . The data may then be forwarded to the PCIe device  152 . 
     The distributed network switch  180  includes a plurality of bridge elements  120  that may be located on a plurality of a separate, though interconnected, hardware components. In one embodiment, the bridge elements  120  may be configured to forward data frames throughout the distributed network switch  180 . The bridge elements  120  forward the data frames transmitted by the network adapter  115  to the switching layer  130 . The bridge elements  120  may include a lookup table that stores address data used to forward the received data frames. For example, the bridge elements  120  may compare address data associated with a received data frame to the address data stored within the lookup table. Thus, the network adapters  115  do not need to know the network topology of the distributed network switch  180 . From the perspective of the network adapters  115 , the distributed network switch  180  acts like one single switch even though the distributed network switch  180  may be composed of multiple switches that are physically located on different components, such as on different chassis or racks. Distributing the operations of the network switch  180  into multiple bridge elements  120  provides redundancy in case of failure. 
     Each of the bridge elements  120  may be connected to one or more transport layer modules  125  that translate received data frames to the protocol used by the switching layer  130 . For example, the transport layer modules  125  may translate data received using either an Ethernet or PCI communication method to a generic data type (i.e., a cell) that is transmitted via the switching layer  130  (i.e., a cell fabric). Thus, the switch modules comprising the distributed network switch  180  are compatible with at least two different communication protocols—e.g., the Ethernet and PCIe communication standards. That is, at least one switch module has the necessary logic to transfer different types of data on the same switching layer  130 . 
     In one embodiment, the switching layer  130  may comprise a local rack interconnect (LRI) which connects bridge elements  120  located within the same chassis and rack, as well as links that connect to bridge elements  120  in other chassis and racks. After routing the cells, the switching layer  130  may communicate with transport layer modules  125  that translate the cells back to data frames that correspond to their respective communication protocols. A portion of the bridge elements  120  may facilitate communication with an Ethernet network  155  which provides access to a LAN or WAN (e.g., the Internet). Moreover, PCI data may be routed to a downstream PCI port  123  that connects to a PCIe device  152 . The PCIe device  152  may be a passive backplane interconnect, as an expansion card interface for add-in boards, or common storage that can be accessed by any of the servers connected to the distributed network switch  180 . 
     An Input/Output Management Controller (IOMC)  140  (i.e., a special purpose processor) is coupled to at least one bridge element  120  which provides the IOMC  140  with access to the switching layer  130 . One function of the IOMC  140  may be to receive commands from an administrator to configure the different hardware elements of the distributed network switch  180 . In one embodiment, these commands may be received from a separate switching network from the switching layer  130 . Although one IOMC  140  is shown, the system  100  may include a plurality of IOMCs  140 . In one embodiment, IOMCs  140  may be arranged in a hierarchy such that one IOMC  140  is chosen as a master while the others are delegated as members. In another embodiment, the IOMCs  140  may be arranged in a peer-to-peer layout where the IOMCs  140  collaborate to administer and manage the elements of the distributed network switch  180 . 
     In one embodiment, distributed network switch  180  may be configured to act as a FCoE Forwarder (FCF)  150 , which is a Fibre Channel switching element that is able to forward FCoE frames across one or more switch ports to connected endpoints (i.e., servers  105 ,  106 , storage devices). One example of an FCoE Forwarder is further described in the Fibre Channel Backbone 5 (FC-BB-5) standard published by T11 working group of the International Committee for Information Technology Standards (INCITS). The IOMC  140  is depicted in  FIG. 1  having an instance of a FCF  150  that manages execution of FCF functionality across the bridge elements  120  of the distributed network switch  180 . In one embodiment, the FCF  150  may be a distributed FCF where a controlling FCF element provides FC services to a large number of endpoints through many intermediate switches. An example of a distributed FCF is shown in  FIG. 2 . 
       FIG. 2  illustrates the distributed network switch  180  having a plurality of bridge elements  120  connected to the server  105 , according to one embodiment of the present disclosure. As shown in  FIG. 2 , the bridge elements  120  are organized into a plurality of switch modules  200  (e.g.,  200 - 1 ,  200 - 2 ,  200 - 3 ,  200 - 4 ). The distributed network switch  180  disclosed herein is configured to provide distributed FCoE switching via multiple switch modules  200 , the switching layer  130  interconnecting the switch modules  200 , and management firmware executing on a management controller, e.g., IOMC  140 . 
     A switch module  200  (sometimes referred to as a chassis interconnect elements or CIE) may be a physical switch unit configured to provide network bridging for the distributed network switch  180 . In one embodiment, the switch modules  200  are hardware components (e.g., PCB boards, FPGA boards, system on a chip, etc.) that provide physical support and connectivity between the network adapters  115  and the bridge elements  120 . Each switch module  200  may include a logical or physical grouping of bridge elements  120 . Each bridge element  120  may be a distributed Virtual Ethernet bridge (dVEB) configured to forward data frames throughout the distributed network switch  180 , including data frames comprising FCoE frames. In one embodiment, each bridge element  120  may have at least two ports, one port connecting to the switching layer  130  and another port connected to the servers  105  and  106  (e.g., via network adapters  115 ). The bridge elements  120  may forward data frames transmitted by the network adapter  115  to the switching layer  130 . In one implementation, a network adapter  115  and bridge element  120  may be connected using two 40 Gbit Ethernet connections or one 100 Gbit Ethernet connection. 
     According to one embodiment, the distributed network switch  180  may be a distributed FCF having a set of FCoE Data Forwarders  202  (FDFs) associated with at least one controlling FCF  204 ,  206  that controls the operations of the set of FDFs. The cFCFs  204 ,  206  defines a control plane for managing the distributed FCF and the FDFs  202  define a data plane for forwarding FCoE frames. The cFCFs and FDFs operate together to behave as a single distributed FCF such that a FCoE frame ingressing on a port in one switch module  200  may be routed to egress from a port in any other switch module  200 . From an external point of view (i.e., from the perspective of the server  105 ), the distributed FCF behaves as an FCF. In particular, the distributed FCF supports instantiation of VN_Port to VF_Port virtual links  210  with ENode MAC addresses (i.e., CNAs  115 ), and instantiation of VE_Port to VE_Port virtual links (not shown) with FCF-MACs. A VN_Port is a Virtual N_Port and refers to a port in an Enhanced Ethernet node (ENode), and a VF_Port is a Virtual Fort a port in an FCoE-capable Ethernet switch. A VE_Port is a Virtual E_port and refers to an inters-witch link port. From an internal point of view (i.e., from the perspective of the FCF), the distributed FCF may instantiate VA_port to VA_port virtual links  212  to enable FCoE frame forwarding between the cFCFs  204 ,  206  and FDFs  202 , as well as between FDFs  202 . A VA_port is an instance of the FC-2V sublevel of Fibre Channel that connects to another VA_port, and which is dynamically instantiated together with an FCoE_LEP on successful completion of a FIP_ELP Exchange. VA_port to VA_port virtual links  212  may also be used to exchange control information between cFCFs  204 ,  206  and FDFs  202 , as described in greater detail later. 
     In one embodiment, each switch module  200  may instantiate a FDF  202  (FDF), which are simplified FCoE switching entities that forward FC frames among ports through the distributed network switch  180 . In one embodiment, a FDF  202  is a simplified FCoE switching element configured to forward FC frames among VA_ports and VF_ports through a Fibre Channel data-plane forwarder (FCDF) switching element. In some embodiments, an FDF  202  is functionally composed of a FCDF switching element with at least one Lossless Ethernet MAC (FDF-MAC), which may be physical or virtual ports of a switch module  200 . The FDF  202  may support instantiation of VA_Ports and VF_Ports over its FDF-MACs. 
     In one embodiment, at least one of the switch modules  200  includes a primary controlling FCoE forwarder  204 ,  206  (sometimes referred to as a controlling FCF, cFCF, or primary controlling switch). The cFCFs are configured to control and manage FDFs  202  to provide fabric services, through the FDFs  202  on each switch module  200 , to all endpoints (e.g., server  105 ) connected to the switch ports. In the embodiment shown in  FIG. 2 , the switch modules  200  include a primary cFCF  204  that controls the FDFs  202 , and a secondary cFCF  206  that synchronizes state with the primary cFCF  204  and is able to resume operation in case of failure of the primary cFCF  204 . Examples of FDFs and cFCFs are described in the Fibre Channel Backbone-6 (FC-BB-6) and the Fibre Channel Switch Fabric 6 (FC-SW-6) standards published by T11 working group of the International Committee for Information Technology Standards (INCITS). 
     To operate as a single distributed fabric, each of the FCoE switching elements (i.e., FDFs, cFCFs) share a fabric name, such as a World Wide Name (WWN), that identifies the fabric to connected entities. The fabric is configured to present the same name to an endpoint, regardless of the switch module  200  that owns the port where the endpoint is attached. Accordingly, embodiments of the present disclosure provide a mechanism for distributing a fabric name to elements of a distributed Fibre Channel (e.g., FCoE) switch. In one embodiment, the mechanism modifies and extends a Distributed Switch Membership Distribution (DFMD) message to include a descriptor that contains the fabric name. DFMD messages are used by controlling switches (e.g., cFCFs) to communicate to an FDF the identities of the primary cFCF and secondary cFCF and all of the FDFs that comprise the distributed network switch  180 . 
       FIGS. 3A and 3B  are flowcharts depicting a method  300  for distributing a fabric name to switch elements of a distributed FCF, according to one embodiment of the present disclosure.  FIG. 3A  illustrates how an FDF  202  (e.g., FDF 1 ) and a cFCF  204  discover each other within the distributed network switch  180  and instantiate a virtual link between switching elements through a FCoE Initialization Protocol (FIP) discovery protocol, although it should be appreciated that other protocols may be used. In one example scenario, the FDF 1  may be a switch module  200  that was newly added to the distributed network switch  180 . In another example, the FDF 1  may be a switch module  200  that was previously offline and is now coming online. 
     As shown, the method  300  begins at step  302 , where the cFCF  204  transmits a multicast (MC) discovery solicitation message to all switching elements (e.g., FDFs  202 ) within distributed network switch  180  to identify any FDFs that may already be up. In one embodiment, the cFCF  204  periodically broadcasts an FCoE Initialization Protocol (FIP) Discovery Solicitation message to an “All-FCF-MACs” group address listened to by switching elements within the distributed network switch. 
     cFCFs and FDFs may periodically transmit messages advertising their status and exchange parameters related to joining the fabric. At step  304 , the cFCF  204  transmits a discovery advertisement to switching elements (e.g., FDFs  202 ) within the distributed network switch  180 . In some embodiments, the cFCF  204  broadcasts (e.g., via multicast) a FIP Discovery Advertisement message to the “All-FCF-MACS” group addressed listened to by FDFs within the distributed network switch. 
     In one embodiment, a Discovery Advertisement message may include a priority descriptor used by endpoints to select a FCF to which to perform a FIP login, a MAC address descriptor, a name identifier descriptor, a fabric descriptor, and a period descriptor (i.e., FKA_ADV_Period) which species periodic reception and transmission of keep alive messages. Table 1 illustrates one embodiment of a fabric descriptor used in FIP operations. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Example FIP Fabric Descriptor Format 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Bit 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Word 
                 31 
                 30 
                 29  
                 28 
                 27  
                 26  
                 25  
                 24 
                 23  
                 22 
                 21 
                 20 
                 19 
                 18 
                 17  
                 16  
                 15  
                 14 
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                 10  
                 9 
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                 6  
                 5  
                 4 
                 3  
                 2 
                 1 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 0 
                 Type = 05h 
                 Length = 04h  
                 Reserved 
                 VF_ID 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 Reserved 
                 (MSB)  
                   
                   
                   
                   
                   
                   
                   
                 FC-MAP 
                   
                   
                   
                   
                   
                   
                 (LSB) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 2 
                 (MSB) 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 Fabric Name  
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 3 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 (LSB) 
                   
               
               
                   
               
            
           
         
       
     
     As shown, in one embodiment, the fabric descriptor includes a virtual fabric identifier (VF_ID) field that specifies a value that uniquely identifies a virtual fabric among all the virtual fabrics that share a set of switches and ports, a Fibre Channel Mapped Address Prefix (FC-MAP) field that specifies the value to be used as the most significant 24 bits in Fabric Provided MAC Addresses (FPMAs), and a fabric name which identifies the fabric. According to one embodiment, discovery advertisements may contain only a single Fabric descriptor, and all discovery advertisements from an FCF in a VLAN may contain the same single Fabric descriptor. The VF_ID field in the fabric descriptor may be set to the VF_ID identifying the advertised fabric. If a VF_ID field is not defined for the advertised fabric, the VF_ID field may be set to zero. The FC-MAP field in the fabric descriptor may be set to the FC-MAP value the FCF is using. If the FC-MAP value is not administratively configured, then the FC-MAP value may be set to a default FC-MAP value. According to one embodiment, the fabric name field in the fabric descriptor is set to the fabric name for the originating FCF. 
     As such, the discovery advertisement transmitted by the cFCF  204  may contain the fabric name, i.e., the fabric WWN. In one embodiment, the fabric name contained within the discovery advertisement may be name identifier associated with the fabric and that is unique within the fabric. In one implementation, fabric names as referred to herein may have a 48-bit address similar to a 48-bit IEEE Standard 802.1a Universal LAN MAC Address format, although other formats may be utilized. 
     At step  306 , the FDF  202  transmits a discovery advertisement to switching elements (e.g., FDFs  202 ) within the distributed network switch  180 . In one embodiment, an FDF is part of a distributed FCF internal topology if the initialization exchanges with the cFCF  204  are completed. If an FDF is not (yet) part of a distributed FCF internal topology, all VA_port capable FDF-MACs on that FDF shall transmit Discovery Advertisements with the fabric name of the fabric descriptor set to zero. Further, if the FDF is not (yet) part of the distributed FCF internal topology, all VF_port-capable FDF-MACs on that FDF may not transmit Discovery Advertisements. In one embodiment, if an FDF  202  is part of a distributed FCF internal topology, all VA_port capable and VF_port-capable FDF-MACs on that FDF may have the fabric name received from the cFCF  204  in the fabric name of the fabric descriptor in all transmitted discovery advertisements. For example, as shown in  FIG. 3A , the FDF  202  is configured to transmit discovery advertisements that do not contain the fabric name, until the FDF is part of the fabric. In some embodiments, the discovery advertisement message transmitted by the FDF contains a zero or null value for the fabric name. 
     At step  308 , responsive to receiving the discovery advertisement from the FDF  202 , the cFCF  204  transmits a unicast discovery solicitation to the FDF  202  to initiate a handshake process that establishes parameters for communicating between the cFCF  204  and the FDF  202  and parameters of the fabric. For example, the cFCF  204  transmits a unicast FIP Discovery Solicitation messages may include a maximum FCoE PDU (protocol data unit) size the cFCF  204  intends to use for FCoE traffic. In some embodiments, upon receiving the Discovery Advertisement, the cFCF  204  may verify whether that the FC-MAP value in the Fabric descriptor in the Discovery Advertisement is the same as the FC-MAP value of the recipient FCF. If not, the cFCF  204  may discard the Discovery Advertisement. In some embodiments, upon receiving Discovery Advertisements, the FCoE controller of a VE_port-capable FCF-MAC (e.g., cFCF  204 ) may create an entry per FCF-MAC in an internal FCF list. Each entry in the internal FCF list of the cFCF may include a Max FCoE Size Verified bit set to zero for entries created from unsolicited multicast Discovery Advertisements, or set to one when a solicited unicast Discovery Advertisement is received. 
     At step  310 , responsive to receiving the unicast discovery solicitation from the cFCF  204 , the FDF  202  (e.g., FDF 1 ) transmits a unicast FIP Discovery Advertisement to the cFCF  204 . In some embodiments, after receiving the (unicast) Discovery Solicitation originated by an FCF (i.e., cFCF), the FDF 1  may perform a verification check by verifying that the FC-MAP value in the FC-MAP descriptor in the Discovery Solicitation is the same as the FC-MAP value of the recipient FCF. If the verification check is false, the Discovery Solicitation may be discarded. 
     Responsive to receiving the solicited unicast Discovery Advertisement from the FDF 1 , the cFCF may set the ‘Max FCoE Size Verified’ bit to one in the entry for that FDF 1  in the internal FCF list of the cFCF  204 . At step  312 , the cFCF  204  requests establishment of a port-to-port link between the cFCF  204  and the FDF  202 . In some embodiments, the cFCF  204  transmits a FIP Exchange Link Parameters (ELP) request to the FDF  202 . At step  314 , the FDF  202  accepts the ELP request, instantiating a virtual link between at least one port associated with the FDF  202  and at least one port associated with the cFCF  204 , and transmits a FIP ELP reply back to the cFCF  204 . At this point, the instantiated link becomes part of the distributed switch internal topology (i.e., the set of links internal to the distributed switch). 
     Upon instantiating a link with the FDF  202 , the cFCF  204  initiates a FDF reachability notification (FDRN) with the backup (i.e., secondary) cFCF  206 , if available, to keep the state synchronized and communicate to the secondary cFCF  206  that cFCF  204  has instantiated a link with another FDF. 
       FIG. 3B  illustrates operations of the FDF  202  (e.g., FDF 1 ) becoming functional within the fabric of the distributed network switch  180 . Upon completion of the FDRN exchange, the cFCF  204  may provide to the now-joined FDF 1  membership information associated with the distributed switch. At step  316 , responsive to instantiating a link with the FDF 1 , the cFCF  204  transmits a distributed switch membership distribution (DFMD) message to communicate to an FDF  202  (i.e. FDF 1 ) the identities of the primary cFCF  204  and secondary cFCF  206 , if any, and of all the FDFs  202  that compose the distributed switch. In one implementation, the DFMD message contains WWNs of all fabric members and the fabric name for the distributed FCF. In some embodiments, the DFMD payload may be integrity protected by a cryptographic hash; in such an embodiment, the involved entities are provided with a shared key. If the primary cFCF  204  does not have a link with the destination FDF, the DFMD message may be relayed to the destination FDF by the intermediate FDFs. An example of DFMD message payload is shown in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Example Distributed Switch Membership Distribution (DFMD) 
               
            
           
           
               
               
            
               
                 Item 
                 Size (Bytes) 
               
               
                   
               
               
                 Switch Fabric Internal Link Services (SW_ILS) 
                 4 
               
               
                 Code = XX00 0008h 
                   
               
               
                 Destination FDF Switch_Name 
                 8 
               
               
                 Originating Controlling Switch Switch_Name 
                 8 
               
               
                 Descriptor List Length 
                 4 
               
               
                 Fabric_Name 
                 8 
               
               
                 Membership Set Descriptor 
                 Variable 
               
               
                 Integrity Descriptor 
                 Variable 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, the DFMD message may include a Destination FCDF Switch_Name which contains the Switch_Name of the destination FDF, an Originating Controlling Switch Switch_Name which contains the Switch_Name of the originating cFCF, a Descriptor List Length which contains the length in bytes of the subsequent list of descriptors, a Membership set descriptor which contains list of switch names for the Primary cFCF, the secondary cFCF, and the set of FDFs in the switch, and integrity descriptors which contains cryptographic information that protects the integrity of the DFMD payload. According to one embodiment, the DFMD message further includes a Fabric_Name which contains the Fabric Name of the distributed FCF. In one implementation, the Fabric_Name may be an 8-byte 16-digit hexadecimal value that is the WWN associated with the distributed FC switch fabric. 
     At step  318 , the FDF 1  receives, processes the DMFD message to extract the fabric name and other parameters contained within the DMFD message, and transmits a message (i.e., ACC DFMD) indicating acceptance of the DMFD message. In one embodiment, the FDF  202  learns the fabric WWN and modifies operation to join the fabric based on the fabric name contained in the DFMD message. In some embodiments, FDF  202  modifies to the internal state of the FDF to indicate the FDF has successfully joined a fabric associated with the fabric name. Responsive to joining the fabric, the FDF  202  may transmit discovery advertisement messages based on the modified internal state as described below. 
     In one embodiment, the cFCF  204  may re-compute the N_Port_ID routes and distributed the recomputed routes to each FDF belonging to the distributed switch through N_Port_ID Route Distribution (NPRD) exchanges. At step  320 , the cFCF transmits a NPRD message to FDF 1  that lists endpoints (e.g., server  105 ) logged in to other FDFs  202 . In one embodiment, the FDF 1  learns how to route frames to the cFCF based on information contained with the NPRD message. At step  322 , the FDF 1  transmits acceptance of the NPRD message (i.e., ACC NPRD). 
     At this point, the FDF 1  considers itself part of the fabric and includes the fabric WWN in discovery advertisements. At step  324 , the FDF 1  broadcasts a FIP multicast Discovery Advertisement message which contains the WWN of the fabric to the “All-FCF-MACs” group address listened to by switching elements within the distributed network switch, for example, another FDF (e.g., FDF 2 ) and cFCF  204 . It should be recognized that even though the FDF 1  may know that FDF 2  is a fabric member, the FDF 1  may be unable to send the FDRN required after virtual link instantiation until this point. At step  326 , the FDF 1  broadcasts a FIP multicast Discovery Advertisement message which contains the WWN of the fabric to an “All-ENode-MACs” group address listened to by endpoints logged into the distributed network switch, including the CNA  115  of the server  105 . It should be appreciated that communication between the FDF 1  and endpoints (e.g., CNA  115 ) may include a fabric login (FLOGI) from the endpoint device. Because the FDF 1  may have been unable to perform FLOGI processing until this point, it should be further recognized that few benefits may be gained from the FDF 1  advertising the fabric with the fabric name prior to this point. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.