Abstract:
An isolation switch blade Fibre Channel switch presents F_ports to form a first Fibre Channel fabric and N_ports to a second Fibre Channel fabric to appear as node devices. The isolation switch blade may be used to connect a plurality of blade servers to a Fibre Channel fabric. Fabric events engendered by the insertion or removal of hot-pluggable devices are handled by the isolation switch blade and “event storms” on the Fibre Channel fabric are avoided. The isolation switch blade presents the blade servers to the FC fabric as a virtualized N_port.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 12/987,475, now U.S. Pat. No. 8,055,794, entitled “Isolation Switch for Fibre Channel Fabrics in Storage Area Networks” by Santosh Shanbhag, Richard L. Hammons, Balakumar N. Kaushik, and Vincent W. Guan and filed on Jan. 10, 2011, which is a continuation of U.S. patent application Ser. No. 12/722,022, now U.S. Pat. No. 7,877,512, issued Jan. 25, 2011, entitled “Isolation Switch for Fibre Channel Fabrics in Storage Area Networks” by Santosh Shanbhag, Richard L. Hammons, Balakumar N. Kaushik, and Vincent W. Guan and filed on Mar. 11, 2010, which is a continuation of U.S. patent application Ser. No. 10/767,405, now U.S. Pat. No. 7,707,309, issued Apr. 27,2010, entitled “Isolation Switch for Fibre Channel Fabrics in Storage Area Networks” by Santosh Shanbhag, Richard L. Hammons, Balakumar N. Kaushik, and Vincent W. Guan and filed on Jan. 29, 2004, all of which are hereby incorporated by reference and to which priority is claimed. This patent application is related to U.S. Pat. Nos. 7,577,134, entitled “Port Expander for Fibre Channel Fabrics in Storage Area Networks” by Manjunath A. Gopal Gowda and Richard L. Hammons and 7,760,717, entitled “Interface Switch for Use with Fibre Channel Fabrics in Storage Area Networks” by Michael Atkinson and U.S. patent applications Ser. Nos. 12/500,441, entitled “Port Expander for Fibre Channel Fabrics in Storage Area Networks” by Manjunath A. Gopal Gowda and Richard L. Hammons and filed on Jul. 9, 2009; 12/785,129, entitled “Interface Switch for Use with Fibre Channel Fabrics in Storage Area Networks” by Michael Atkinson and filed on May 21, 2010; and 10/356,392, entitled “Method and Apparatus for Routing between Fibre Channel Fabrics” by Chris Del Signore, Vineet Abraham, Sathish Gnanasekaran, Pranab Patnaik, Vincent W. Guan and Balakumar N. Kaushik. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to storage area networking using the Fibre Channel protocol. More particularly, it relates to storage area networks connected to blade-type file servers. 
     2. Description of the Related Art 
     The scaling of dynamic Fibre Channel fabrics is a challenging problem. When switches are added to or removed from a fabric they tend to precipitate high volumes of control traffic, causing the CPUs of the constituent switches to get overloaded, and often result in production data disruption due to fabric re-configurations. Fabrics also tend to become unstable while handling large volumes of fabric events. These issues are further exacerbated by the growing trend to blade servers. The host processor blades in the blade servers are intended to be hot-pluggable. Further, any Fibre Channel switch located on a blade would also be intended to be hot-pluggable. This makes fabrics even more dynamic and places increasingly higher scalability requirements on Fibre Channel fabrics. The hot-plug capabilities of these, possibly large, numbers of host and switch blades increases the probability of “event storms,” resulting in loading or disrupting the enterprise fabrics they are connected to. These problems may ultimately result in loss of service (e.g., host bus adapter logins may timeout) under heavy load conditions in the fabric. It would be desirable to be able to use host blades and switch blades in blade servers without having the problems discussed above. 
     SUMMARY OF THE INVENTION 
     An isolation switch blade according to the present invention presents the façade of a switch to a fabric formed of the host processor blades and that of a host to the enterprise fabric and performs controlled mediation of data and control traffic between the blade fabric and the enterprise fabric. The multiplexing of multiple streams of traffic between the N_ports on the host processor blades and the enterprise fabric is accomplished by a feature in certain Fabric Operating Systems (FOS) called “N_port Virtualization” (NPV). One particular NPV mechanism is described in U.S. patent application Ser. No. 10/356,659 filed Jan. 31, 2003 and entitled “Method and Apparatus for Providing Virtual Ports with Attached Virtual Devices in a Storage Area Network” and in U.S. patent application Ser. No. 10/209,743 filed Jul. 31, 2002 and entitled “Method and Apparatus for Virtualizing Storage Devices inside a Storage Area Network Fabric.” Further information is provided in U.S. patent application Ser. No. 10/201,331 filed Jul. 23, 2002 and entitled “Fibre Channel Virtual Host Bus Adapter.” The disclosures of these three patent applications are incorporated herein by reference. Using the NPV mechanism, the number of host processor blades that can simultaneously be plugged in, and to which virtual N_port identifiers can be assigned, is 255 (using a one-byte port id), which is a sufficiently large number to accommodate the number of blades in present day blade server chassis. 
     An isolation switch blade according to the present invention can be connected to multiple enterprise fabrics, so the N_port identifiers within the enterprise fabrics may be mapped to proxy addresses that are scoped by the fabric. All control traffic address mappings between virtual and physical addresses may be mediated and translated by the CPU of the isolation switch blade and address mappings for data traffic performed at wire speed. 
     The use of N_port virtualization also enables the isolation switch blade to act as an initiator, which is advantageous as this allows partitioning of fabrics and isolation of the enterprise fabric from exchanges originating from the host processor blades. Since the host processor blades are not directly connected to the enterprise fabric, the enterprise fabric is isolated from large amounts of fabric activity due to host processor blades being swapped in and out. This isolation promotes scalability within the enterprise fabric. Since the isolation switch blade may preferably be a single conduit into the enterprise fabric, it is also a good point to enforce perimeter defenses (similar to a firewall) against attacks, either intentional or resulting from misbehaviors. The isolation switch blade may also act as a throttle by controlling the host processor blade access into the enterprise fabric. Further, the isolation switch blade may act as a protocol gateway. In addition, the use of the N_port connection increases interoperability, as compared to using an E_port connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of an isolation switch blade in logical communication with four host blades and an enterprise fabric according to the present invention. 
         FIG. 2  is a schematic representation of a system in which four host blades are connected to a pair of isolation switch blades according to the present invention. 
         FIG. 3  is a schematic representation of a Fibre Channel enterprise fabric in logical communication with a firewall/intrusion detector in an isolation switch blade according to the present invention. 
         FIG. 4  is a schematic representation of a dual connected host-target configuration according to the present invention. 
         FIG. 5  is a schematic representation of an isolation switch blade with path fail over according to the present invention. 
         FIG. 6A  is a representation of frame flow from a host blade to a target in the enterprise fabric according to the present invention. 
         FIGS. 6B and 6C  are blocks of exemplary isolation switch blades according to the present invention. 
         FIG. 6D  is an illustration of the software modules in an isolation switch blade according to the present invention. 
         FIG. 7  depicts a fabric initialization and login procedure according to the present invention. 
         FIG. 8  is an exemplary PID mapping table according to the present invention. 
         FIG. 9  depicts a device registration and discovery procedure according to the present invention. 
         FIG. 10  depicts zoning in an enterprise fabric according to the present invention. 
         FIG. 11  shows load balancing and fail over with two isolation switch blades according to the present invention. 
         FIG. 12  shows the use of a Fibre Channel authentication protocol according to the present invention. 
         FIG. 13  shows an alternative embodiment with the connection of an isolation switch blade to an enterprise fabric as an E_Port according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Many organizations have begun consolidating their file servers into centralized data centers, looking to use physical, application or data consolidation as a means of reducing the challenges and costs associated with administering many small file servers scattered across the enterprise. To date, physical consolidation has generally involved replacing bulky tower servers with slender 1U or 2U rack systems. Such rack systems take less space and put the servers and infrastructure within easy reach of the network administrator, rather than spread across a large area. 
     These servers enable organizations to reap many benefits of consolidation, yet because each server requires its own infrastructure—including, e.g., cables for power, Ethernet, systems management, power distribution units (PDUs), keyboard/video/mouse (KVM) switches and Fibre Channel switches—they present challenges of their own. A rack of 1U servers can have hundreds of cables strung throughout the rack, making it difficult to determine which cables attach where and complicating the addition and removal of servers to and from the rack. In addition, the PDUs and switches consume valuable rack sidewall space. A blade server eliminates many of these complications, thus providing an effective alternative to 1U and 2U servers. 
     The term “blade server” refers to a rack-optimized server that can hold a number of hot-swappable devices called blades. There is a range of blade server designs—from ultra-dense, low-voltage, lesser-performing servers to high-performance, lower density servers to proprietary, customized rack solutions that include some blade features. 
     An isolation switch blade (ISB) according to the present invention may be a Fibre Channel (FC) switch in the blade form factor that is housed in a chassis that may include Ethernet switch modules, Fibre Channel switch modules, KVM management modules, power supply modules, a midplane and host blades (all not shown). An example of such a device is the IBM eServer BladeCenter. In addition to providing FC switching capabilities, the isolation switch blade may also incorporate advanced capabilities for providing failure and security isolation, and can facilitate enterprise fabric scaling. Another benefit of the isolation switch blade is that it can be interoperable with a variety of switches since it can connect to the fabric as an N_port rather than as an E_port in the preferred embodiment. 
     This disclosure describes the architecture of an isolation switch blade according to the present invention. The role of an isolation switch blade is to enable Fibre Channel fabrics to behave well when blade servers are connected to them. Fibre Channel fabrics comprise one or more Fibre Channel switches connected in some networked topology. 
     Blade servers introduce a level of service distribution (distribution of applications across blades to scale out) that is not as common in current ‘monolithic’ servers, which are typically configured to run an enterprise application running on a single server. Furthermore, misbehaving host bus adapters (HBAs) might induce control traffic, e.g. repeatedly doing FLOGIs (fabric logins, a process by which a node makes a logical connection to a fabric switch) and, with the introduction of a large number of blades, the probability of such misbehavior increases. As a result, there is a greater likelihood of a larger number of data and control traffic exchanges being initiated from multiple sources and it is critical to insulate the fabric from misbehaviors and/or malicious attacks. 
     An isolation switch blade is similar to a conventional switch blade in that it presents standard F_ports (fabric ports to which N_ports attach) to the host blades, but different in that it connects to the enterprise fabric as N_ports (rather than as E_ports) in the preferred embodiment. The isolation switch blade partitions the enterprise storage area network (SAN) into two separate fabrics such that the blade server is connected to the “blade fabric” and other servers and devices are connected to the “enterprise fabric.”  FIG. 1  shows a possible deployment of the isolation switch blade in a blade chassis  102  with a series of host blades  104  which illustrates how two distinct logical fabrics, the blade fabric  106  and the enterprise fabric  108 , are being constructed. The purpose of the blade fabric  106  is to isolate the enterprise fabric  108  and provide controlled access to it from host blades  104 . 
     The isolation switch blade  100  replicates some of the functionality of a Fibre Channel fabric bridge. However the isolation switch blade  100  is quite different from, and consequently simpler than, a fabric bridge. 
     As illustrated in  FIG. 2 , one may dual-connect each host blade  104  to multiple isolation switch blades  100 A,  100 B in order to eliminate a single point of failure. This dual-connect is conventional in existing SANs and the isolation switch blade allows such a configuration to be maintained. 
     Fabric scalability is about ensuring that the Fabric OS can reasonably handle the peak load conditions induced by ever-larger fabrics during periods of intense demand and activity. Such peak loads generally involve fabric-wide events that affect many of the Fabric OS components. Fabric reconfiguration takes place with the introduction and removal of switches into the fabric. The reconfiguration process involves computation-intensive activities such as rebuilding of fabrics, re-computation of routes, etc. With the introduction of bladed servers and switches, fabrics are expected to become increasingly more dynamic, resulting in an increase in the rate at which these fabric-wide events and fabric reconfigurations occur. Hence, the scalability issues may be further exacerbated. 
     When an embedded switch in a blade server chassis joins the fabric, the introduction of the embedded switch typically requires a domain id assignment, routes to be recomputed, zone merges to be done and so on. Since the key capability provided by blade servers is the ability to scale out and provide modularity, the plugging in and out of blades may be a norm rather than an exception and these fabric reconfigurations are more likely to take place more frequently. 
     When a number of blade servers attempt to FLOGI to an embedded switch&#39;s F_port, a large number of updates to the switch&#39;s login database may be triggered. A Fibre Channel Protocol (FCP) daemon in the Fabric OS may start probing the N_ports and send “update area” messages to the name server. A large number of probes and name server updates may be triggered, followed by the name server sending Registered State Change Notifications (RSCNs), a switch function that allows notification to registered nodes if a change occurs in the fabric. Similarly, a blade being removed from the chassis may trigger updates to the switch login database and name server database and may cause more RSCNs to be sent out to registered devices. A large amount of such internal fabric activity results in a large amount of processing burden on switch CPUs and this may result in device-initiated exchanges timing out, resulting in devices not being able to receive proper service. 
     Aspects of the present invention involve isolating blade servers from the enterprise fabric via the isolation switch blade  100 . This provides a high level of isolation between the host blades  104  and the enterprise fabric  108 . Scalability is enhanced due to isolation provided by the isolation switch blades  100  to enterprise fabrics  108  such that the enterprise fabric  108  is not directly impacted when host blades  104  are swapped in and out of the blade fabric  106  and can hence provide a more controlled environment to the enterprise fabric  108 . 
     Connecting as an N_port using the NPV mechanism enables the isolation switch blade  100  to be connected to non-proprietary enterprise fabrics  108  and does not have potential interoperability issues of proprietary E_port implementations. 
     Since the isolation switch blade  100  places itself in the control path of any traffic that originates on the host blades  104  and may be intended for the enterprise fabric  108 , the isolation switch blade  100  is a viable base for hosting software that can perform port and Logical Unit Number (LUN) filtering, zoning enforcement, stateful inspection, checking for malformed packets, probing for buffer overflows in the FOS copies in the blade center fabric, and performing overall in-band intrusion detection. In other words, the isolation switch blade  100  can fulfill a secondary purpose of providing enhanced security at the perimeter of the enterprise fabric  108  by acting in the role of a “firewall” by selectively filtering out frames that match certain criteria of deviant behavior.  FIG. 3  shows one such implementation in schematic form wherein a firewall/intrusion detection system is hosted on isolation switch blade  100 C. 
     With this location, the isolation switch blade  100  may also act as a protocol gateway, such as iSCSI to FCP and so on. 
       FIG. 4  depicts a typical deployment architecture with a pair of isolation switch blades (ISB 1  100 A and ISB 2  100 B) providing dual connectivity for four host blades (host blade  1  to host blade  4   104 A to  104 D) to two fabrics (A  108 A and B  108 B). This configuration can be similarly extended to any number of host blades, isolation switch blades or enterprise fabrics. For a 16 port isolation switch blade connected to two fabrics with dual connectivity, up to 14 host blades may be connected to the isolation switch blade. 
     The isolation switch blade  100  may be designed to provide path fail-over capability.  FIG. 5  shows an isolation switch blade configuration with path fail over. If one path to a fabric  108 A or  108 B is lost due to a link going down between the isolation switch blade  100 A or  100 B and the fabric  108 A,  108 B, the isolation switch blade  100 A,  100 B may automatically switch the outgoing traffic to the other port and fill the appropriate SID on the frames, as long as this port is zoned to the target, if it is port zoned, based on which port the frames are sent through. 
     A simplified architecture makes certain assumptions regarding the behavior of host blade host bus adapters. The assumptions are: a) the host blades  104  can handle or respond to RSCNs when notified about changes to devices connected to the enterprise fabric  108 ; and, b) in the case where servers are connected to the same enterprise fabric  108  across multiple isolation switch blades  100 , it is assumed that the servers have the ability to handle multi-pathing for load balancing or fail over appropriately. In a more complex architecture the isolation switch blade can handle these functions if needed. 
     A detailed example of the transfer of frames using an isolation switch blade is shown in  FIG. 6A . The isolation switch blade  100  is connected to a switch  200 , which is representative of the enterprise fabric  108 , and to a host blade  104 . In the illustrated example, port  1   208  of the isolation switch blade  100  is connected to the host blade  104 . The port  1   208  is configured in F_port mode. Similarly, port  4   212  of the isolation switch blade  100  is connected to a port  9   214  of switch  200 , a switch in the enterprise fabric  108 . The port  4   212  is configured in NPV_port mode, while the port  9   214  is configured in F_port mode. A tape drive unit  204  is connected to port  5   218  of switch  200 . It is presumed that the switch  200  is domain 1 in fabric  108 , and the isolation switch blade  100  is domain 0 in blade fabric  106 . 
     Port  4   212  is connected by a private intraswitch link  224  to port  5   210 . Port  5   210  is connected to port  1   208  by a private intraswitch link  225 . Port  5   210  is configured in loopback mode. This is done because in the preferred embodiment public and private translations are only performed on the external receiver portion of a port, so an intervening port is needed to perform address translation. In alternate embodiments each port can do the necessary address translations and this intermediate port is not needed. The host blade  104  and the tape unit  204  have phantom addresses on the private links  224  and  225 . In the illustrated embodiment, the address 04 is provided to the tape unit  204  and the address 02 is provided for the host blade  104 . Thus private to public translations occur at port  5   210  and public to private translations occur at port  1   208  and port  4   212 . For more detail on performing these translations, please refer to U.S. Pat. No. 6,401,128 entitled “System and Method for Sending and Receiving Frames Between a Public Device and a Private Device,” which is hereby incorporated by reference. 
     In the illustrated embodiment the tape unit  204  receives private address 04 and the host blade  104  receives private address 02. Port  5   210  is assigned an address 010900, while port  4   212  is assigned an address of 010500. Thus the host blade  104  will address the tape drive  204  by providing a destination address of 010904 that is a full public address. This address of 010904 is converted by port  1   208  to a private address of 04. This private address of 04 in turn is translated by port  5   210  to an address of 0105EF, which is the actual address of the tape unit  204  in fabric  108 . The source address of the host blade  104  is 000101 and is converted to 02 by port  1   208  and then to 010902 by port  5   210 . For the tape unit  204  to address the host blade  104 , a destination address of 010902 is used. This address of 010902 is converted by port  4   212  into a private address of 02. Packets transmitted from port  5   210  to the port  1   208  are then converted from this private address of 02 to the desired address of 000101 for the host blade  104  by port  5   210 . Similarly, port  4   212  converts the tape unit  204  source address of 0105EF to 04 and port  5   210  converts this address to 010904. 
     If public to private address translation as described above is not available, other suitable address translation techniques which allow full wire speed operation may be used. 
       FIG. 6B  illustrates a block diagram of an isolation switch blade  100  according to the preferred embodiment. In switch  100  a processor unit  402  that includes a high performance CPU, preferably a PowerPC, and various other peripheral devices including an Ethernet module, is present. Receiver/driver circuitry  440  for a serial port is connected to the processor unit  402 , as is a PHY  406  used for an Ethernet connection. A flash memory  410  is connected to the processor  402  to provide permanent memory for the operating system and other routines of the interfabric switch  120 , with DRAM  408  also connected to the processor  402  to provide the main memory utilized in the isolation switch blade  100 . A PCI bus  412  is provided by the processor  402  and to it is connected a Fabric Channel miniswitch  414 . The Fibre Channel miniswitch  414  is preferably developed as shown in U.S. patent application Ser. No. 10/123,996, entitled, “Fibre Channel Zoning By Device Name In Hardware,” by Ding-Long Wu, David C. Banks, and Jieming Zhu, filed on Apr. 17, 2002 which is hereby incorporated by reference. This application also describes a hardware filtering mechanism that can be used for filtering, zoning, malformed packet detection, intrusion detection and other aspects of the isolation switch blade  100 C. The miniswitch  414  is thus effectively a 16 port switch. Fourteen ports of the miniswitch  414  are connected to a series of serializers  418 , which are then connected to media unit  420 . Twelve of the media units  420  are for connection to host blades  104  and two media units  420  are for connections to enterprise fabric or fabrics  108 . Two of the ports of the miniswitch  414  are configured in loopback mode such as in port  5   210  in  FIG. 6A . There are two loopbacks in this embodiment to match the number of enterprise fabric ports. In the preferred embodiment, if two separate enterprise fabrics  108  are connected to the isolation switch blade  100 , for example as shown in  FIG. 4 , an additional loopback port may be needed to provide an additional address translation for one of the fabrics should the connected domains of the enterprise fabrics be the same. This case would reduce the number of available host blade connections to eleven. 
       FIG. 6C  is an embodiment of an isolation switch blade  100 ′ with a larger number of connections for host blades  104 . In this embodiment there are two miniswitches  414 A and  414 B. Miniswitch  414 B is preferably an eight port device. In this embodiment two ports of miniswitch  414 A are connected to two ports of miniswitch  414 B. Each miniswitch  414 A and  414 B has only one port configured in loopback mode. Each miniswitch  414 A,  414 B is configured to have one enterprise fabric connection, with the remainder available for host blades, so that the embodiment provides connections for up to 16 host blades  104 . In this embodiment preferably the two interswitch links would be configured as private links to minimize the number of hops from an enterprise fabric to a host blade. Thus, if the host blade and the enterprise fabric were connected to the same miniswitch, the loopback port for that miniswitch would be used for address translation. However, if the enterprise fabric and host blade were connected to different miniswitches, the ports of the interswitch link would handle the address translation. In the case described above where the connected domains of the enterprise fabrics are the same, the interswitch links would handle the additionally needed address translation so no additional loopback ports would be needed. 
     Proceeding then to  FIG. 6D , a general block diagram of the isolation switch blade  100  hardware and software is shown. Block  300  indicates the hardware as previously described. Block  302  is the basic software architecture of the virtualizing switch. Generally think of this as the isolation switch blade fabric operating system and all of the particular modules or drivers that are operating within that embodiment. Modules operating on the operating system  302  are Fibre Channel, switch and diagnostic drivers  304 ; port modules  306 , if appropriate; a driver  308  to work with the Fibre Channel miniswitch ASIC; and a system module  310 . Other switch modules include a fabric module  312 , a configuration module  314 , a phantom module  316  to handle private-public address translations, an FSPF or Fibre Shortest Path First routing module  320 , an AS or alias server module  322 , an MS or management server module  324 , a name server module  326  and a security module  328 . Additionally, the normal switch management interface  330  is shown including web server, SNMP, telnet and API modules. 
     Three additional modules are present according to the present invention. A firewall/intrusion detection module  334  performs those features as described. A PID mapping table  342  is present and accessible by any of the modules as needed. Finally, a virtual node port module  338  performs the node port virtualization function. This module  338  is included in the drivers  304  in the preferred embodiment. 
     The link initialization protocol between a host blade  104  and the isolation switch blade  100  and between the isolation switch blade  100  and enterprise fabrics  108  is the same as that of a normal F_port as described in the FC-PH and FC-FS standards. Once link initialization is complete, the N_port or virtual N_port and F_port are in the active state. The link initialization between the host blade  104  and isolation switch blade  100  and between the isolation switch blade  100  and the F_ports of the enterprise fabrics  108  can happen independently of each other. 
     The introduction of the first host blade  104  into the blade chassis  102  causes an FLOGI into the isolation switch blade  100 . This results in the isolation switch blade  100  performing a FLOGI into the enterprise fabric  108  and subsequently performing FDISC requests into the enterprise fabric  108  for each host blade  104  that is in the blade chassis  102  to get virtual port id (PID) assignments for the host blades  104 . This process is described more completely in U.S. patent application Ser. No. 10/291,331 incorporated by reference above. Within the blade center fabric  108 , the isolation switch blade  100  receives a domain id (though in most cases the isolation switch blade  100  would generally be the single and thus principal switch in the blade fabric), after which time the host blades  104  can login to the blade fabric  106 . 
     After link initialization is complete, the blade server&#39;s N_port sends its first FLOGI to the isolation switch blade&#39;s F_port in the blade center fabric  106 . At some point after the isolation switch blade  100  has done an FLOGI into the enterprise fabric  108  and received an N_port id, the isolation switch blade  100  may perform an FDISC on behalf of all currently connected host blade N_ports and receive their virtual N_port ids in the FDISC LS_ACC. The name server of the enterprise fabric will thus be populated with the virtual N_port ids representative of the host blade  104  N_ports. A mapping of the NPV pid to the N_port pid is maintained by the isolation switch blade  100  as described below. Since the enterprise fabric  108  may not be ready to respond to the FLOGI from the isolation switch blade  100 , the isolation switch blade  100  must retry the FLOGI some number of times until successful or disable the port. 
     The isolation switch blade  100  has to present a facade of a switch to the host blades  104  and of a host to the enterprise fabrics  108  and be able to propagate any control traffic/management requests between the blade center fabric  106  and the enterprise fabrics  108 . This is described below. 
     During the initial switch and fabric bring-up phases, a large number of activities occur simultaneously. The isolation switch blade  100  decouples the fabric bring up of the enterprise fabric  108  from the blade center fabric  106  and, as a result, the blade center fabrics  106  and enterprise  108  fabrics may be brought up in any order and independently of each other. The two bring up scenarios are described below 
     1. Bringing up the enterprise fabrics before the blade center fabric: 
     Referring now to  FIG. 7 , consider enterprise fabrics A and B  108 A and  108 B being brought up first such that these fabrics are built, zoning starts doing zone merges, and edge devices connected to these fabrics try to do FLOGI and then query the name server (NS). When an isolation switch blade  100  is connected to fabrics A and B  108 A and  108 B, it can now FLOGI into these fabrics. However, if the switches in fabrics A and B  108 A and  108 B have not completed fabric initialization at this time, the isolation switch blade  100  is connected to them (i.e. not yet obtained their domain IDs), they may disable the port on which they receive the FLOGI. Once the domain id has been assigned, they may re-enable the port. As a result, the enterprise fabrics  108  have an opportunity to quiesce before they respond to the isolation switch blade  100  FLOGIs, since the isolation switch blade  100  is attempting to connect as a device and not as a switch. Eventually, the switch may send an LS_ACC responding to the FLOGI with an N_port id for the isolation switch blade  100  port that performed the FLOGI. The isolation switch blade  100  then queries the enterprise fabric  108  name server and uses the responses to develop a name server for the blade fabric  106 . Alternatively, the isolation switch blade  100  may forward the name server query from the host blade  104  to the enterprise fabric  108  and return the responses back to the host blade  104  after performing the necessary address translation of the name server response payload. 
     Subsequently, when a host blade  104 , is plugged into the blade chassis  102  and a FLOGI is performed from N_port  1  (NP1) into the isolation switch blade  100 , the isolation switch blade  100  may then send an FDISC to the enterprise fabric  108  for host blade  104  and may receive a virtual N_port id for N_port  1 . In an alternate embodiment, the virtual N_port ids can be assigned a priori (i.e. before the host blade  104  is plugged in) to a given slot id so that a virtual PID is assigned before the host blade  104  is plugged into the slot. This may provide further independence between the blade fabric  106  and enterprise fabric  108  operations. However, this approach may result in unnecessary NS entries being created in the enterprise fabric  108  if the host blades  104  do not exist. Also, Port Logins (PLOGI&#39;s) to these virtual N_ports may have to be rejected in cases where the host blade  104  does not exist or the isolation switch blade  100  may have to handle these exchanges. 
     The host blade  104  N_port  1  may then register with the name server on the isolation switch blade  100 . Once name server entries from enterprise Fabrics A and B  108 A and  108 B are imported into the isolation switch blade- 100 , N_port  1  can do a PLOGI into devices and continue with other operations as usual. 
     2. Bringing up the blade fabric before the enterprise fabrics: 
     If the isolation switch blade  100  is brought up first, it may be the principal switch and assign itself a domain id. When the host blade  104  is plugged into the blade server before fabrics A and B  108 A and  108 B are brought up, N_port  1  may FLOGI into F_port  1  (FP 1 ) of the isolation switch blade  100  and register with the name server on the isolation switch blade  100 . However, name server entries from enterprise fabrics  108 A and  108 B may not yet be available to perform FC operations to targets within the enterprise fabrics  108 A and  108 B. Subsequently, Fabrics A and B  108 A and  108 B may be brought up and the isolation switch blade  100  may perform FLOGI and FDISC to get a virtual address assignment for N_port  1  and export name server entries to the isolation switch blade  100 , after which N_port  1  can PLOGI into devices and perform other operations as usual. Other host blades like host blade  104  can FLOGI into the isolation switch blade  104  while Fabrics A and B  108 A and  108 B are coming up. 
     Since the blade fabric  106  and enterprise fabric  108  are brought up independently of each other, service parameters assigned to N_ports during the fabric login process may be different. The service parameters of importance are the time out values. It is important that the isolation switch blade  100  provide the host blades  104  in the blade fabric  106  with timeout values (E_D_TOV and RA_TOV) that are equal to or less than the timeout values provided by the enterprise fabrics  108  to the virtual N_ports of the isolation switch blade  100 . It is possible to enforce this if the enterprise fabrics  108  are brought up before the blade fabric  106  is brought up. However, in the case that the blade fabric  106  is brought up first, and the timeout values assigned to the host blade  104  ports happen to be higher than those assigned to the virtual N_ports by the enterprise fabric  108 , the host blades  104  should be forced to log out and log into the isolation switch blade  100  again. 
     After receiving a LS_ACC for its FLOGI request, each host blade  104  can register for RSCN, perform a N_port login with the name server of the isolation switch blade  100  and register with the isolation switch blade&#39;s  100  name server. FCP probing may also be triggered following the FLOGI and the isolation switch blade&#39;s  100  name server may be updated. The host blades  104  may also want to query the name server database and perform N_port login with target devices in the enterprise fabric  108 . In order to do this, proxy addresses for the union of name server entries within the enterprise fabrics  108  need to be assigned and the proxy addresses exposed to the host blades  104 . As mentioned earlier, a mapping table may be maintained by the isolation switch blade  100 . In addition to the mappings between the virtual N_port and physical N_port identifiers, mappings between the proxy addresses and enterprise addresses  108  may be maintained in the mapping table. 
     If the host blades  104  complete their login and registration and the isolation switch blade  100  has not yet completed the link initialization, login and FDISC to the enterprise fabrics  108 , the host blades  104  may not yet be able to see the targets connected to enterprise fabrics  100  in the isolation switch blade&#39;s  100  name server. The host blade  104  may be able to subsequently PLOGI only when the targets become visible. This enables the enterprise fabric  108  build to be completed (all domains are reachable) and routes to be established before the host blades  104  start querying about or attempt to PLOGI into the devices connected to the enterprise fabric  108 . 
     On the other hand, if the isolation switch blade  100  has already completed FLOGI and FDISC with the blade fabrics  106  and enterprise fabric  108  devices have been registered with the NS, the host blades  104  can discover devices by querying the isolation switch blade&#39;s  100  NS for the targets. This isolation between the target devices within the enterprise fabrics  108  and host blades  104  enables the enterprise fabrics  108  to be insulated from a large amount of simultaneous activity. 
     The addition of an additional host blade  104  into the blade chassis  102  may trigger a new FDISC to the enterprise fabric  108  and the assignment of a virtual N_port id and not a FLOGI. Since FDISC does not trigger FCP probing and NS updates, this process may be less disruptive to the enterprise fabric  108 . The isolation switch blade  100  may handle FCP probing of the host blades  104  and perform NS updates to its NS database based on the probes. 
     In  FIG. 8 , PNP 1 -A is the virtual PID assigned for N_port  1  by Fabric A  108 A and PNP 1 -B is the virtual PID assigned by Fabric B  108 B for N_port  1 . Since PNP 1 -A and PNP 1 -B are assigned by two independent fabrics, they could be identical and the mapping should be able to handle this. Similarly, the PIDs of devices in Fabric A and B  108 A and  108 B may collide and proxy addresses may have to be maintained to provide a unique address space that is scoped by fabric. 
     In order to create separate namespaces for PIDs per enterprise fabric  108  that are connected to the isolation switch blade  100 , each enterprise fabric  108  is assigned a unique identifier by the isolation switch blade  100 , known as the “proxy domain identifier.” The proxy domain identifier may be filled into the “domain” field of the SID/DID for frames that are initiated from/targeted to switches/devices in the enterprise fabrics  108 A and  108 B and the remaining 16 bits of the address may be used to uniquely identify ports in each of the fabrics  108 A and  108 B. 
     Similarly, the virtual PIDs, assigned via NPV, may be used to address the isolation switch blade  100  and host blades  104  within the blade fabric  106 . The isolation switch blade  100  may map these proxy and virtual addresses to physical addresses as described below. 
     Since the isolation switch blade  100  serves as a proxy between the blade server and enterprise fabrics  108 , it has to map between virtual N_port ids assigned by the enterprise fabric  108  and N_port ids assigned by the blade fabric  106 . Similarly, it has to map between the virtual proxy addresses for devices in the enterprise fabric  108  and physical addresses. These mappings may be maintained in a separate PID mapping table. 
     The PID mapping table contains mappings between physical and virtual host blade N_port ids and also between physical and proxy enterprise fabric  108  device N_port ids. When control or data frames from the host blade  104  are targeted to a device in the enterprise fabric  108 , the SID may be mapped to the virtual N_port id at the isolation switch blade  100 . The DID may be mapped from the proxy address to the physical address and sent to the right isolation switch blade  100  egress port. These mappings are performed using a PID mapping table. An exemplary PID mapping table is shown in  FIG. 8 . This table is used to populate the public to private and private to public address translation tables in the isolation switch blade  100  ports. 
     The table may be divided into sections that are indexed by the proxy domain identifier and the address of the isolation switch blade  100  virtual N_port connected to the enterprise fabrics  108 . The Proxy Domain column uniquely identifies the enterprise fabric  108  to which frames from the blade fabric  106  get routed. The domain portion of the DID of all frames targeted to devices in the enterprise fabrics  108  may carry the proxy domain id. The PID mapping table partitions the PID namespace so that there is no possibility of PID conflicts. PID 1 , PID 2  etc. are the physical addresses of ports in the enterprise fabric  108  and PID 1 ′, PID 2 ′ etc. are the corresponding proxy addresses assigned by the isolation switch blade  100 . 
     The isolation switch blade  100  queries the NS of both Fabric A and B  108 A and  108 B and populates the physical addresses and the isolation switch blade  100  assigns unique logical proxy addresses pre-fixed with a proxy domain id. The isolation switch blade  100  “listens” for device detected RSCNs from these fabrics  108 A and  108 B and updates its mapping table. The mapping table also contains mappings between all the physical addresses (N_port  1 , N_port  2  etc.) to virtual N_port id (PNP 1 -A, PNP 2 -A etc.) for N_ports of the host blades  104 . 
     For frames destined to enterprise fabrics  108 , the Proxy Domain (PD 0 , PD 1 ) field in the DID is used to perform the mapping table lookup. For frames destined from enterprise fabrics  108  to host blades  104 , the lookup is performed based on isolation switch blade  100  virtual N_port (NPV 1 , NPV 2 ). 
     Host blade  104  may send a frame to a virtual target PID in Fabric A  108 A from N_port  1 . isolation switch blade  100  may check to see if the virtual PID is within the table partition associated with PD 0  or PD 1  and translate the proxy address to a physical address. Similarly, frames from the enterprise fabric  108 A to the host blade  104  may be scoped by the virtual N_port (NPVI or NPV 2 ) and the virtual N_port ids mapped to a physical N_port id from the table. 
     The blade server N_port (N_port  1 ) initiates a PLOGI to a target using the blade fabric  106  N_port id as the SID and the isolation switch blade  100  maps the SID to the virtual N_port Id of the enterprise fabric  108 . Responses are directed to the virtual N_ports as DIDs and the DIDs are mapped to the blade fabric  106  N_port ids using the mappings in the PID mapping table. Similarly, the PIDs contained in the data traffic may require a wire-speed mapping of PIDs. Mapping control traffic from the host blades  104  and the enterprise fabric  108  (such as FLOGIs or PLOGIs to the NS) and traffic from the enterprise fabric  108  to the host blades  104  is mediated by the isolation switch blade  100  processor, and the mapping is implemented using a logical PID mapping table. The SID/DID used in management frames for the host blade  104  N_port may be the virtual PIDs. Some control traffic, such as certain types of ELS and NS responses, carry PIDs in their payload. In these cases the addresses in the payloads must also be mapped using the PID mapping table. 
     The PID mapping table entry may be updated when a PID is assigned by the blade fabric  106  to a host blade  104  N_port and updated whenever a corresponding virtual N_port id is returned by the enterprise fabric  108  in response to an FDISC (in the case of pre-provisioned virtual PIDs described earlier, a new entry may be created with the creation of a new virtual PID). Removal of a host blade  104  may cause removal of the corresponding virtual N_port id from NS and removal of the PID mapping table entry. 
     Only those devices in the enterprise fabric  108  that are zoned to one or more of the host blade  104  ports in the blade fabric  106  may have an entry in the blade fabric&#39;s NS and the PID mapping table. Hence the number of entries in the isolation switch blade&#39;s  100  PID mapping table may be equal to the sum of the total number of devices in the enterprise fabrics  108  that are zoned to one or more of the host blade  104  ports in the blade fabric  106  and the total number of host blades  104 . 
     As an example, consider a frame initiated from physical address N_port  1  of the host blade  104 , to target physical address PID 1  in enterprise fabric A  108 A. The SID/DID fields in the frame headers are: 
     At host blade  104 : SID=N_port  1 , DID=PID 1 ′ 
     At isolation switch blade  100 : SID=PNP 1 -A, DID=PID 1  (based on lookup indexed by proxy domain id field of DID, PD 0 ). 
     In Fabric A  108 : SID=PNPI-A, DID=PID 1   
     Now consider a frame targeted to physical address N_port  1  of host blade  104  from physical address PID 1  of initiator in enterprise fabric A  108 A. The SID/DID fields in the frame headers are: 
     In Fabric A  108 A: SID=PID 1 , DID=PNP 1 -A 
     At isolation switch blade  100 : SID=PID 1 ′, DID=N_port  1  (based on lookup indexed by isolation switch blade ingress virtual N_port, NPV 1 ). 
     At host blade  104 : SID=PID 1 ′, DID=N_port  1   
     Following the login and initialization process described above, the enterprise fabric&#39;s  108  name server may retrieve new and deleted NPV device bitmaps from the switch driver of the switch that was involved in the NPV. Since device entries for all devices in enterprise fabrics  108  are maintained in the PID mapping table, response to all host blade  104  requests may be performed by the isolation switch blade  100  and do not need to trigger queries to the NS on the enterprise fabric  108 . The isolation switch blade  100  may update its own NS based on the registration and deregistration of host blades  104  and respond to any host blade  104  related NS queries. It may register for RSCNs in order to update its mapping table when devices enter and leave the enterprise fabric  108 . When host blades  104  are pulled out, the NPV ports will send corresponding FLOGOs to the enterprise fabric  108  and the isolation switch blade  100  will flush the addresses of the removed host blades  104  from its name server and from its PID mapping table. Such registration and discovery is illustrated schematically in  FIG. 9 . 
     The isolation switch blade  100  does not impact Worldwide Named (WWN) based zoning. For domain, port based zoning, virtual N_port ids may be mapped to PIDs using the PID mapping table. To add a host blade  104  N_port to a zone, the virtual PID may be looked up in the PID mapping table and used as the PID for this port to be zoned. Such zoning is illustrated in  FIG. 10  wherein host blades  104 A and  104 B connect to Fabric A  108  via the isolation switch blade  100 . 
     In order to provide fault tolerance and better link utilization that can reduce the possibility of congestion, isolation switch blade  100  configurations may be able to support multiple paths from a host blade  104  to a target in the enterprise fabric  108 . Depending on the capabilities of the host blade  104 , it is possible to perform load balancing and/or fail over. 
       FIG. 11  shows a dual isolation switch blade  100  configuration. This configuration allows a host blade  104  to be connected to two fabrics A and B  108 A and  108 B, over separate isolation switch blades  100 A and  100 B. If the multipathing firmware in the host blade  104  supports load balancing, it is possible for the host blade  104  to send frames to Fabric A  108 A or Fabric B  108 B on both N_port  1  and N_port  2 . 
     If the multipathing software is capable of supporting failover, the host blade  104  can send frames from N_port  2  if the path from N_port  1  to the target is not available for any reason, such as link going down or isolation switch blade  104 A failing. The isolation switch blades  100 A,  100 B support fail over in that if isolation switch blade  100 A fails, it results in isolation switch blade  100 B taking over and the enterprise fabrics  108  are not subjected to disruption. 
     In order to support in-band fabric management, for queries via CT pass thru from the host bus adapter, management CT frames may be allowed through the isolation switch blade  100  into enterprise fabrics  108 . In order to support dynamic queries to the host bus adapter using FDMI-2, CT frames from enterprise fabric  108  switches may be allowed through the host bus adapter to the host blades  104 . CT frames may be directed to the isolation switch blade&#39;s  100  management server and the isolation switch blade  100  may have the same level of management capabilities as the management server on any other switch. As mentioned earlier, the isolation switch blade&#39;s  100  CPU is responsible for the address mappings of these CT frames. 
     In-band discovery from enterprise fabrics  108  may result in the isolation switch blade  100  being discovered as a node that is connected to that enterprise fabric  108  and hence may result in a partial view of the topology. The discovered N_port ids of the host blades  104  may be used to perform zoning. 
     In band discovery with the isolation switch blade  100  as a proxy may result in discovery of switches and devices in the enterprise fabrics  108  as well as the discovery of host blades  104  and may result in a complete topology discovery. 
     From an element management perspective, the isolation switch blade  100  should be treated as a new type of switch that exposes F_ports and N_ports. In order to enforce frame filtering at the isolation switch blade  100 , the isolation switch blade  100  may be configured with access control policies. 
     In the NPV implementation described in above references, the SID/DID validation in the miniswitch is turned off since NPV requires a PID to be assigned by the enterprise fabric  108 . Hence the DID field in the transmitted frames and the SID fields in the received frames that are expected to match at the enterprise fabric&#39;s F_port, do not match in the case of NPV. This opens up security threats since the main purpose of the SID/DID checking is to prevent spoofing of authorized devices by unauthorized devices by using the PID of the authorized device. However, since the isolation switch blade  100  is acting as an intermediary in this case, it can prevent rogue devices from spoofing since the SID/DID checking happens at the F_port of the isolation switch blade  100 . Further, the security threats can be mitigated using zones of trust. 
     The FCAP protocol, as explained in U.S. patent application Ser. No. 10/062,125 filed Jan. 31, 2002 entitled “Network Security and Applications to the Fabric Environment” which is hereby incorporated by reference, is used by Secure FabOS to establish zones of trust. Host blades  104  and the isolation switch blade  100  are part of the blade fabric  106  and may be part of that fabric&#39;s zone of trust. Similarly, the isolation switch blade  100  may be part of the enterprise fabric&#39;s  108  zone of trust.  FIG. 12  is a schematic representation showing FCAP between host blade  104  and the isolation switch blade  100  and between the isolation switch blade  100  and Fabric A  108 . 
     Secure FabOS also has the notion of security policies that limit access to the fabric. One set of policies, the Device Connection Control (DCC) policies, may be used to determine which host blades  104  are allowed to connect to F_ports within the enterprise fabric  108 . DCC policies may be exported from the enterprise fabrics  108  to the isolation switch blade  100  and enforced at the isolation switch blade  100 . 
     Due to the unique placement of the isolation switch blade  100  at the edge of the enterprise fabric  108 , it can further bolster the capabilities of Secure FabOS. Rules can be defined and enforced at the isolation switch blade  100  such that certain frames are filtered out and not allowed access into the enterprise fabric  108 . These rules might take the form of access control policies or the form of policies that detect patterns in an attempt to differentiate legitimate traffic from intrusions. 
     As shown schematically in  FIG. 13 , another possible implementation of an isolation switch blade  100 A,  100 B, is to connect to the enterprise fabric  108  as an E_port. The advantage that this provides over the NPV isolation switch blade  100  is the ability to trunk E_ports. However, this configuration needs to virtualize the Fabric OS and run multiple copies as described in U.S. patent application Ser. No. 10/209,743. Connecting as an E_port also has the disadvantage of possible lack of interoperiability due to the general proprietary nature of E-ports. Because of these complexities, the potential advantages provided by trunking are generally outweighed and the preferred embodiment is as described above, though N_port trunking could provide the benefits without the disadvantages. 
     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.