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Versions: 00 01 02 03 04 05 06 rfc2625                                  
IP and ARP Over FC Working Group                       Murali Rajagopal
INTERNET-DRAFT                                              Raj Bhagwat
<draft-ietf-ipfc-fibre-channel-02.txt>                    Wayne Rickard
(Expires Apr 1, 1999)                                (Gadzoox Networks)


                           IP and ARP over Fibre Channel

Status of this Memo

   This document is an Internet-Draft. Internet-Drafts are working
   documents of the Internet Engineering Task Force (IETF), its areas,
   and  its working groups. Note that other groups may also distribute
   working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as Reference
   material  or to cite them other than as ``work in progress''.

   To view the entire list of current Internet-Draft, please check
   the``1id-abstracts.txt'' listing contained in the Internet-Drafts
   Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net ( Northern
   Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific
   Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).

Abstract

   Fibre Channel (FC) is a high speed serial interface technology that
   supports several higher layer protocols including Small Computer
   System Interface (SCSI) and Internet Protocol(IP). Until now, SCSI
   has been the only widely used protocol over FC. Existing FC standards
   [3] do not adequately specify how IP packets may be transported over
   FC and how IP addresses are resolved to FC addresses. The purpose of
   this document is to specify a way of encapsulating IP and Address
   Resolution Protocol(ARP) over Fibre Channel and also to describe a
   mechanism(s) for IP address resolution.

Contents

   Status of this Memo ...........................................  1
   Abstract .......................................................  1

   1. Introduction ...............................................  3

   2. Problem Statement ..........................................  4

   3. IP and ARP Encapsulation ...................................  4
      3.1 FC Frame Format ........................................  4
      3.2 MTU ....................................................  5
      3.3 FC Port and Node Network Addresses .....................  6
      3.4 FC Payload Format ......................................  7
      3.5 ARP Packet Format ......................................  8




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   4. Address Resolution ......................................... 10
      4.1 Problem Description .................................... 10
      4.2 ARP layer Mapping and Operation ........................ 10
          4.2.1 ARP Broadcast in a Point-to-Point Topology ....... 11
          4.2.2 ARP Broadcast in a Private Loop Topology ......... 11
          4.2.3 ARP Broadcast in a Public Loop Topology .......... 11
          4.2.4 ARP Operation in a Fabric Topology ............... 12

   5. Mechanism for Maintaining FC Layer Mappings ................ 13
      5.1 Use of Name Server ..................................... 13
      5.2 FARP ................................................... 13

   6. FC Layer Address Validation ................................ 18
      6.1 General Discussion ..................................... 19
      6.2 FC Layer Address Validation in a Point-to-Point Topology 19
      6.3 FC Layer Address Validation in a Private Loop Topology . 19
      6.4 FC Layer Address Validation in a Public Loop Topology .. 20
      6.5 FC layer Address Validation in a Fabric Topology ....... 20

   7. Exchange Management ........................................ 20
      7.1 Exchange Origination ................................... 20
      7.2 Exchange Termination ................................... 20

   8. Summary of Supported Features .............................. 21
      8.1 FC-4 Header ............................................ 21
      8.2 R_CTL .................................................. 21
      8.3 F_CTL .................................................. 22
      8.4 Sequences .............................................. 23
      8.5 Exchanges .............................................. 24
      8.6 ARP .................................................... 24
      8.7 Extended Link Services (ELS) ........................... 25
      8.8 Login Parameters ....................................... 25
          8.8.1 Common Service Parameters  - FLOGI ............... 25
          8.8.2 Common Services Parameters - PLOGI ............... 26
          8.8.3 Class Service Parameters - PLOGI ................. 26

   9. Security Considerations .................................... 26

   10. Acknowledgements .......................................... 26

   11. References ................................................ 26

   12. Authors' Addresses ........................................ 27

   Appendix A: Fibre channel Overview ............................ 28
      A.1 Brief Tutorial ......................................... 28
      A.2 Fibre Channel Header Fields ............................ 29
      A.3 Acronyms and Glossary of FC Terms ...................... 32

   Appendix B: Fibre Channel Protocol Considerations.............. 34
      B.1 Reliability in Class 3 ................................. 34
      B.2 Continuously Increasing SEQ_CNT ........................ 34

   Appendix C: Other Mechanisms for FC layer Mappings ............ 35



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      C.1 Login on cached Mapping Information .................... 35
      C.2 Login on ARP parsing ................................... 35
      C.3 Login to Everyone ...................................... 36
      C.4 Static Table ........................................... 38


1. Introduction

   FC is a gigabit speed networking technology primarily used for
   Storage Area Networking (SAN). FC is standardized under American
   National Standards Institute (ANSI)and has specified a number of
   documents describing its protocols,  operations, and services.

   Need:

   Currently, Fibre Channel is predominantly used for communication
   between storage devices and servers using the SCSI protocol, with
   most  of the servers still communicating with each other over LANs.
   Although, the Fibre Channel standard [3] has architecturally defined
   support for IP encapsulation and address resolution, it is
   inadequately specified. ([3] prohibits broadcasts thus loops are not
   covered; [10] has no support for Class 3)

   This has lead to a nonstandard way of using IP over FC in the past.
   Once such a standard method is completely specified, servers can
   directly communicate with each other using IP over FC, possibly
   boosting performance in Server host-to-host communications.  This
   technique will be especially useful in a Clustering  Application.

   Objective:

   The major objective of this specification is to promote  inter-
   operable implementations of IP over Fibre Channel. This
   specification describes a method for encapsulating IPv4 and Address
   Resolution Protocol (ARP) packets  over Fibre Channel. This
   specification accommodates any FC topology  (loop, fabric, or point-
   to-point) and any FC class of service (1, 2  or 3). Use of IEEE 802.2
   LLC/SNAP encapsulation for IP and ARP as  specified in this document
   shall not preclude the use of same  encapsulation technique for other
   protocol stacks (e.g.  IPX, AppleTalk).

   Organization:

   Section 2 states the problem that is solved in this  specification.
   Section 3 describes the techniques used for encapsulating  IP and ARP
   packets in a FC sequence. Section 4 discusses ARP (IP address to MAC
   address) and the required mappings and operation. Section  5
   discusses the FC Layer mappings (MAC address to Port_ID). Section 6
   provides a discussion on validation of the FC-layer mapping for the
   different FC topologies. Section 7 describes the "Exchange"
   Management in FC. Section 8 is a summary section and provides a quick
   summary of the FC header settings, FC Link Service Commands, and a
   summarized reference to features supported in ARP, FC Sequences, FC
   Exchanges, and FC Login Parameters.



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   Appendix A provides a brief overview of the FC Protocols and Networks
   along with a list of acronyms and a glossary of FC Terms used in this
   specification. Appendix B addresses reliability in Class 3.

2. Problem Statement

   This draft addresses two problems:
     - A sequence format definition and encapsulation mechanism for IP
       and ARP packets over FC
     - A mechanism(s) Address Resolution

   As noted earlier, the existing FC Standards [3], [10] are inadequate.
   A solution to both problems has been proposed by the Fibre Channel
   Association (FCA)[1]. FCA is a industry consortium of Fibre Channel
   vendor companies and not a standards body.  This draft specification
   is largely based on the proposed solution in [1] and is an attempt to
   provide a standardized specification addressing both the above stated
   problems.

3. IP and ARP Encapsulation

3.1 FC Frame Format

   All FC frames have a standard format much like LAN 802.x protocols.
   (See Appendix A for Fibre Channel related Acronyms and Glossary of
   Terms.) However, the exact size of each frame varies depending on the
   sizes of  the variable fields. The FC frame structure is shown in
   Fig. 1.

         +-------+--------+-----------+----//-------+-----+-----+
         | SOF   |Frame   |Optional   |   Payload   |CRC  | EOF |
         | (4B)  |Header  |Header     |             |(4B) |(4B) |
         |       |(24B)   |<----------------------->|     |     |
         |       |        |       (0-2112B)         |     |     |
         +-------+--------+-----------+----//-------+-----+-----+

                          Fig. 1 FC Frame Format

   The Start of Frame (SOF) and End of Frame (EOF) are both 4 bytes long
   and act as frame delimiters.

   The CRC is 4 bytes long and uses the same 32-bit polynomial used in
   FDDI and is specified in ANSI X3.139 Fiber Distributed Data
   Interface.

   The Frame Header is 24 bytes long and has several fields associated
   with identification and control of the payload. The values and
   options for the fields that are relevant to the IP and ARP payloads
   will be discussed later.

   A FC Optional Header allows up to 4 optional header fields:

        - An Expiration Security Header (16 bytes)
        - Network (16 bytes)



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        - Association (32 bytes)
        - Device (up to 64 bytes).

   The IP and ARP FC sequences are required to carry the Network_Header
   optional header field which is 16 bytes long. Other types of optional
   headers are prohibited.  The use of the Network_Header for the IP and
   ARP payload encapsulation is described below.

   In FC, an application level payload is called a Sequence. Typically,
   a Sequence consists of more than one frame. Larger user data is
   segmented and reassembled using two methods: Sequence Count and
   Relative Offset. Use of Sequence Count is straight forward and data
   blocks are sent using frames with increasing sequence counts (modulo
   16). With Relative Offset, frames could temporally arrive out of
   order.

   When IP and ARP form the FC payload then only the First Frame of the
   logical Sequence shall include the FC Network_Header. (Care should
   exercised when this is the case. Note that the physical temporal
   ordering of the frames can be different as a result of traversing
   through a "Fabric".)  Fig. 2 shows the logical First Frame and
   logical subsequent frames

                   First Frame of a Logical FC Sequence
   ---+------------+---------------------------+----------//----------+---
      |  FC Header |     FC Network Header     | FC Sequence Data     |
   ---+------------+---------------------------+---------//-----------+---

                Subsequent Frames of a Logical FC Sequence
                   --+-----------+----------//------+--
                     | FC Header | FC Sequence Data |
                   --+-----------+----------//------+--

               Fig. 2 FC Network Header in a Frame Sequence

   The SOF, CRC, EOF control fields and other optional headers have been
   omitted in the figure for clarity.

3.2 MTU

   The Maximum Transmission Unit (MTU) for IP is defined as the length
   of the IP packet, including IP headers. The theoretical maximum size
   of an IP Packet is 65,535 bytes. In FC-4 the transmission unit is a
   "Information Unit" and not frames. An N_Port may transmit an
   Information Unit using multiple frames. The receiving N_Port will
   assemble the frames to reconstruct the sent Information Unit. The
   size of a single Information Unit is limited to 2^32-1, which is very
   large. However, restricting the IP over FC MTU helps in buffer
   resource allocation at N_Ports. A MTU of 65,280 bytes allows for up
   to 256 bytes of overhead. The IEEE 802.2 LLC/SNAP headers requires 8
   bytes, leaving the rest 248 bytes for future uses.

   There shall be a one-to-one mapping between an IP packet and a FC
   sequence. In other words, one IP packet shall always map to only one



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   FC Sequence.

   Note that, although the FC physical frame MTU is limited to 2112
   bytes, it is hidden from IP and does not affect the IP MTU at FC-4.

3.3 FC Port and Node Network Addresses

   FC devices are identified by Nodes and Ports. A Node is a collection
   of one or more Ports identified by a unique nonvolatile 64-bit World
   Wide Node name (WW_NN). Each Port in a node, is identified with a
   unique nonvolatile 64-bit World Wide Port name (WW_PN), and a
   volatile Port_ID.

   Port_ID are 24-bits. In a FC frame header, the Port_ID is referred to
   as S_ID (Source ID) to identify the port originating a frame, and
   D_ID to identify the destination port. The Port_ID of a given port is
   volatile. (The mechanism(s) by which a Port_ID may change in a FC
   topology is outside the scope of this document.)

   FC specifies a Network Address Authority (NAA) to distinguish between
   the various name registration authorities that may be used to
   identify the WW_PN and the WW_NN. A 4-bit NAA identifier, 12-bit
   field set to 0x000 and an IEEE 48-bit MAC address together make the
   64-bit WW_NN or the WW_PN addresses [2]. In a single port Node, the
   WW_NN and the WW_PN may be identical.

   The WW_PN names of the source and destinations are carried in the FC
   Network Header. The format of the FC Network Header is shown in Fig.
   3 and defined in the FC standards [2]. The Network header  is
   normally optional in FC but mandatory in this specification. The 4
   most significant bits in each address denotes the Network Address
   Authority (NAA) type. In this specification, the source and
   destination NAA binary pattern '0001' indicates the IEEE-48 bit MAC
   address and is the only code point that is valid.  This NAA field
   value allows FC networks to be bridged with other FC networks or
   traditional LANs.  The Source (Destination) MAC address occupies the
   lower 48 bits of the Network_Source_Address (Network_Dest_Address),
   and the upper 12 bits are set to 0x000.

            +--------+---------------------------------------+
            | D_NAA  |Network_Dest_Address (High-order bits) |
            |(4 bits)|              (28 bits)                |
            +--------+---------------------------------------+
            |      Network_Dest_Address (Low-order bits)     |
            |                       (32 bits)                |
            +--------+---------------------------------------+
            | S_NAA  |Network_Source_Address(High-order bits)|
            |(4 bits)|              (28 bits)                |
            +--------+---------------------------------------+
            |      Network_Source_Address (Low-order bit)    |
            |                       (32 bits)                |
            +--------+---------------------------------------+

                 Fig. 3 Format of the Network Header Field



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3.4 FC Payload Format

   The payload of an FC sequence carrying an IP packet shall use the
   format shown in Fig. 4. Fig. 5 shows the format when the payload is
   an ARP packet. However, both formats use the 8-byte LLC/SNAP header.

     +-----------------+-----//----------+-------------//------------+
     | LLC/SNAP Header | IP Header       |         IP Data           |
     |   (8 bytes)     | (20 bytes min.) | (65280 -IP Header) bytes  |
     +-----------------+-----//----------+-------------//------------+

             Fig. 4 Format of FC Sequence Payload carrying IP

                  +-----------------+-------------------+
                  | LLC/SNAP Header |   ARP Packet      |
                  |   (8 bytes)     |   (28 bytes)      |
                  +-----------------+-------------------+

             Fig. 5 Format of FC Sequence Payload carrying ARP

   As noted earlier, since FC frames belonging to the same Sequence can
   be delivered out of order over a Fabric, the IP Header must appear in
   the frame that has relative offset of 0.

   A Logical Link Control (LLC) field along with a Sub Network Access
   Protocol (SNAP) field is a method used to identify routed and bridged
   non-OSI protocol PDUs and is defined in IEEE 802.2 and applied to IP
   in [8]. In LLC Type 1 operation (i.e., unacknowledged connectionless
   mode), the LLC header is 3-bytes long and consists of a 1-byte
   Destination Service Access Point (DSAP)field, a 1-byte Source Service
   Access Point (SSAP)field, and a 1-byte Control field as shown in Fig.
   6.

                     +----------+----------+----------+
                     |   DSAP   |   SSAP   |   CTRL   |
                     | (1 byte) | (1 byte  | (1 byte) |
                     +----------+----------+----------+

                                Fig. 6 LLC Format

   The LLC's DSAP and SSAP values of 0xAA indicate that a IEEE 802.2
   SNAP header follows. The LLC's CTRL value equal to 0x03 specifies
   Unnumbered Information Command PDU. The LLC header value shall be
   0xAA-AA-03. Other values of DSAP/SSAP indicate support for other
   protocols but are prohibited in this specification.

   The SNAP header is 5 bytes long and consists of a 3-byte
   Organizationally Unique Identifier (OUI) field and a 2-byte Protocol
   Identifier as shown in Fig. 7

                      +------+------+-------+------+------+
                      |         OUI         |     PID     |
                      |      ( 3 bytes)     |  (2 bytes)  |
                      +------+------+-------+------+------+



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                               Fig. 7 SNAP Format

   SNAP was invented to "encapsulate" LAN frames within the payload.
   The SNAP OUI value 0x00-00-00 specifies that the PID is an EtherType
   (i.e., routed non-OSI protocol). An OUI value of 0x00-80-C2 indicates
   Bridged Protocols.

   When the OUI value equals 0x00-00-00, the SNAP PID value of 0x08-00
   indicates IP and a SNAP PID value of 0x08-06 indicates ARP. The
   complete LLC/SNAP header is shown in Fig. 8.

    +----------+----------+----------+-------+-------+-------+-------+------+
    |   DSAP   |   SSAP   |   CTRL   |          OUI          |      PID     |
    | (1 byte) | (1 byte) | (1 byte) |      ( 3 bytes)       |  (2 bytes    |
    +----------+----------+----------+-------+-------+-------+-------+------+

                             Fig. 8 LLC/SNAP Header

3.5 ARP Packet Format

   The format of the encapsulated ARP packet is based on [9] and is
   shown in Fig. 9.

   The 'HW Type' field shall be set to 0x00-01

   Note: Technically, the correct HW Type value should be set to 0x00-06
   according to RFC 1700 indicating IEEE 802 networks. However, as a
   practical matter a HW Type value of 0x00-06 is known to cause
   rejections from some Ethernet end stations when FC is bridged to
   Ethernet. Translational bridges are normally expected to change this
   field from Type 6 to 1 and vice versa under these configurations but
   many do not. It is because of this reason the Type Code is set to 1
   rather than 6. However, both HW Type values of 0x00-01 and 0x00-06
   shall be accepted.

   The 'Protocol' field shall be set to 0x08-00 indicating IP protocol.

   The 'HW Addr Length' field shall be set to 0x06 indicating 6 bytes of
   HW address.

   The 'Protocol Addr Length' field shall be set to 0x04 indicating 4
   bytes of IP address.

   The 'Operation' Code field shall be either 0x00-01 for Request or
   0x00- 02 for Reply.

   The 'HW Addr of Sender' field shall be the 6 byte IEEE MAC address of
   the sender.

   The 'Protocol Addr of Sender' field shall be the 4 byte IP address of
   the sender.

   The 'HW Addr of Target' field shall be set to zero if the 'Operation
   Code' field is set to 1.  Otherwise, it shall be set to the 6 byte



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   IEEE MAC address of the original sender of the ARP request.

   The 'Protocol Addr of Target' field shall be set to the 4 byte IP
   address of the target.

                        +-------------------------+
                        | HW Type                 | 2 bytes
                        +-------------------------+
                        | Protocol                | 2 bytes
                        +-------------------------+
                        | HW Addr Length          | 1 byte
                        +-------------------------+
                        | Protocol Addr Length    | 1 byte
                        +-------------------------+
                        | Op Code                 | 2 bytes
                        +-------------------------+
                        | HW Addr of Sender       | 6 bytes
                        +-------------------------+
                        | Protocol Addr of Sender | 4 bytes
                        +-------------------------+
                        | HW Addr of Target       | 6 bytes
                        +-------------------------+
                        | Protocol Addr of Target | 4 bytes
                        +-------------------------+
                                             Total 28 bytes
                         Fig. 9 ARP Packet Format


   The ARP packet is 28 bytes long in this particular application. The
   difference between an ARP Request Packet and an ARP Reply Packet is
   given below:

     1. ARP Request packet: 'Operation' Code field = 0x00-01 and the 'HW
        Addr of Target' is set to 0x00-00-00-00-00-00.

     2. ARP Reply packet: 'Operation' Code field = 0x00-02 and the 'HW
        Addr of Target' is appropriately set to the extracted 'HW Addr
        of Sender' field from the ARP Request packet; similarly, the
        'Protocol Addr of Target' is set to the  extracted 'Protocol
        Addr of Sender' field from the ARP Request packet

   An ARP Request message is defined as a FC broadcast sequence carrying
   the ARP Request packet. The exact mechanism used to broadcast a FC
   sequence depends on the topology and will be discussed in the next
   section. Compliant ARP broadcast messages shall include Network
   Headers.

   An ARP Reply message is defined as an ARP Reply packet encapsulated
   in a FC sequence. Compliant ARP Reply messages shall include Network
   Headers.







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4. Address Resolution

4.1 Problem Description

   Address Resolution is concerned with associating IP addresses with FC
   Port addresses. As described earlier, FC device ports have two
   addresses:
      - a non-volatile unique 64-bit address called World Wide Port_Name
        (WW_PN)

      - a volatile 24-bit address called a Port_ID (see Appendix A for a
        definition of Port_ID)

   The Address Resolution mechanism therefore will need two levels of
   mapping:

       1. A mapping from IP address to the WW_PN address(i.e., IEEE
          48-bit MAC address)

       2. A mapping from WW_PN to the Port_ID

   The address resolution problem is compounded by the fact that the
   Port_ID is volatile and the second mapping has to be validated before
   use. Moreover, this validation process can be different depending on
   the FC network topology used.

   Architecturally, the first level of mapping and control operation is
   handled by the ARP layer, and the second level of mapping and control
   by the FC layer.

4.2 ARP Layer Mapping and Operation

   Whenever a source FC port with a designated IP address wishes to send
   IP data to a destination FC port also with a designated IP address
   then, the following steps are taken:
     1. The source port shall consult its local mapping tables to
        determine the <destination IP address, destination WW_PN>.
        (Since the NAA= b'0001' the WW_PN address and 48-bit MAC address
        conceptually mean the same thing in this discussion.)

     2. If such a mapping is found, then the source shall send the IP
        data to the port whose WW_PN address was found in the table.

     3. If such a mapping is not found, then the source shall send an
        ARP broadcast message to its connected FC network in
        anticipation of getting a reply from the correct destination
        along with its WW_PN address.

     4. When an ARP broadcast message is received by the destination it
        shall generate an ARP response. Since the ARP response must be
        addressed to a specific destination Port_ID, the FC layer
        mapping between the MAC address and Port_ID (of the ARP Request
        orginator) must be valid before the reply is sent.




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4.2.1 ARP Broadcast in a Point-to-Point Topology

     The ARP Request (Broadcast) and Reply mechanism described in
     Section 3.5 and 4.2 still applies, although there is only one node
     that receives this.

4.2.2 ARP Broadcast in a Private Loop Topology

     In a private loop, the ARP broadcast message is sent using the
     broadcast method specified in the FC-AL [7]standard.

        1. The source port shall first send an Open Broadcast
           Replicate primitive (OPN(fr))Signal forcing all the ports in
           the loop (except itself), to replicate the frames that they
           receive while examining the frame header's Destination_ID
           field.

        2. The source port shall remove this OPN(fr) signal when it
           returns to it.

        3. The loop is now ready to receive the ARP broadcast message
           and is sent as a broadcast sequence, that is using FC
           frames.

        4. The source shall now send a FC frame containing the ARP
           Request (ARP broadcast message), as a sequence in a Class 3
           frame with the following FC Header D_ID field and F_CTL bits
           in the FC header set to:

               Destination  ID<Word 0, bit 0:23>: D_ID = 0xFF-FF-FF

               Sequence Initiative <Word 2, bit23>: SI=0

               Last Sequence <Word 2, bit 20>: LS=1

               End Sequence <Word 2, bit 19>: ES=1.

               The above FCTL settings apply to single-frame broadcasts,
               as used in ARP sequences. This information is provided to
               clarify ARP Broadcast usage only, and should not be
               interpreted as prohibiting the use of multiframe sequence
               broadcasts for other applications.

      5. Compliant ARP broadcast sequences shall include Network Headers
         with destination MAC address in the Network Header set to
         0xFF-FF-FF-FF-FF-FF and NAA = b'0001'
      6. The destination port recognizing its IP address in the ARP
         packet shall respond with an ARP Reply message.

4.2.3 ARP Broadcast in a Public Loop Topology

   The following steps will be followed when a port is configured in a
   public loop:




Rajagopal, Bhagawat, Rickard                                   [Page 11]


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      1. A public loop device attached to a fabric through an FL_Port
         shall not use the OPN(fr) signal primitive. Rather, it shall
         send the broadcast sequence to the FL_Port at AL_PA = 0x00.

      2. A fabric shall propagate the broadcast to all other ports
         including the FL_Port which the broadcast arrived on. This
         includes all F_Ports, and other FL_Ports.

      3. On each FL_Port, the fabric shall first propagate the
         broadcast by first using the primitive signal OPNfr, in order
         to prepare the loop to receive the broadcast sequence.

      4. A broadcast sequence is now sent on all ports (all FL_ports,
         F_Ports)in Class 3 frame with:

               Destination ID <Word 0, bit 23:0>: D_ID = 0xFF-FF-FF

               Sequence Initiative <Word 2, bit23>: SI=0

               Last Sequence <Word 2, bit 20>: LS=1

               End Sequence <Word 2, bit 19>: ES=1.

      5. Compliant ARP broadcast sequences shall include Network Headers
         with destination MAC address in the Network Header set to
         0xFF-FF-FF-FF-FF-FF and NAA = b'0001'

      6. The destination port recognizing its IP address in the ARP
         packet shall respond with an ARP Reply message.

4.2.4 ARP Operation in a Fabric Topology

      1. Nodes directly attached to fabric do not require the OPN(fr)
         primitive signal.

      2. A broadcast sequence is now sent on all ports (all FL_ports,
         F_Ports)in Class 3 frame with:

               Destination ID <Word 0, bit 23:0>: D_ID = 0xFF-FF-FF

               Sequence Initiative <Word 2, bit23>: SI=0

               Last Sequence <Word 2, bit 20>: LS=1

               End Sequence <Word 2, bit 19>: ES=1.

      3. Compliant ARP broadcast sequences shall include Network Headers
         with destination MAC address in the Network Header set to
         0xFF-FF-FF-FF-FF-FF and NAA = b'0001'

      4. The destination port recognizing its IP address in
         the ARP packet shall respond with an ARP Reply





Rajagopal, Bhagawat, Rickard                                   [Page 12]


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5.  Mechanisms for Maintaining FC Layer Mappings

   FC layer mapping between the WW_PN and the Port_ID is independent of
   the ARP mechanism and is more closely associated with the details of
   the FC protocols. Two main mechanisms - Name Server and FARP that may
   be used to create and maintain WW_PN to Port_ID tables are described
   here.  Other less formal mechanisms are described in Appendix C.  The
   preferred method is a configuration and administration issue, and may
   be implementation-dependent.

5.1 Use of Name Server

   This method is used in environments where a Name Server is
   available[4].

       1. A Name Server may be referenced to resolve unmapped WW_PN
          addresses.

       2. Any upper layer send request for which there is not a Port_ID
          to WW_PN mapping can trigger a query to a name server. The
          WW_PN must be re-formatted in the 64-bit WW_PN format before
          the query is issued.

       3. The format of the Name Server query and response is outside
          the scope of this document. See[4] for a typical example and
          [14] for a Name Server implementation.

       4. The query response from the Name Server must contain the
          Port_ID associated with the WW_PN specified in the query.

       5. Normal Port Login procedures follow at this point before
          packets can be forwarded to a port.

5.2 FARP

   The Fibre Channel Address Resolution Protocol (FARP) is a method
   using ELS commands to resolve <WW_PN, D_ID> mapping in environments
   without a Name Server. That is, when the WW_PN is known, but not the
   D_ID and a Name Server service doesn't exist. This situation arises,
   for instance, when Login tables entries expire.

   The FARP-REQ Extended Link Service Broadcast Request command shall
   resolve Port_IDs of communicating Fibre Channel devices.  A FARP-REQ
   can be used to retrieve a specific N_Port's current Port_ID given the
   unique WW_PN and WW_NN. This is accomplished by requesting either a
   FARP-REPLY ELS Unicast command, or by indicating that the Responder
   N_Port shall perform a login with the FARP-REQ Requester. No sequence
   initiatives is transferred with the FARP-REQ and therefore no Reply
   (ACCEPT or REJECT) is sent as a response. Reception of a FARP-REQ
   causes a higher level entity at the responding host to send a FARP-
   REPLY, which is an ELS command that transfers sequence initiative and
   therefore expects an ELS response (ACCEPT or REJECT).

   Protocol:



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        FARP-REQ (ELS broadcast) Request Sequence

             No Reply Sequence

        FARP-REPLY (ELS command) Sequence

             Accept Reply Sequence

   Format: FT-1

   Addressing:

      - For a FARP-REQ, The S_ID designates the Requester
        N_Port requesting addressing information. The D_ID is the
        broadcast identifier, 0xFF-FF-FF.

      - For a FARP-REPLY, the S_ID designates the N_Port ID of the
        device matching the Responder Address Information in the FARP
        Request. The D_ID is the N_Port ID of the device that initiated
        the FARP request.

   Payload:  There are 2 formats of the FARP-REQ payload depending on
   the address information carried.


    +-----------------------------------------------------------------+
    |                  FARP-REQ Payload                               |
    +-----------------------------+---------+-------------------------+
    |         Field               | Size    |                         |
    |                             |(Bytes)  |          Remarks        |
    +-----------------------------+---------+-------------------------+
    | 0x54-00-00-00               |   4     |                         |
    +-----------------------------+---------+-------------------------+
    | Match Address Code Points   |   1     |                         |
    +-----------------------------+---------+-------------------------+
    | Port_ID of Requester        |   3     |                         |
    +-----------------------------+---------+-------------------------+
    | Responder Flags             |   1     |                         |
    +-----------------------------+---------+-------------------------+
    | Port_ID of Responder        |   3     | set to 0x00-00-00       |
    +-----------------------------+---------+-------------------------+
    |WW_PN of Requester           |   8     |                         |
    |(FARP-REQ)                   |         |                         |
    +-----------------------------+---------+-------------------------+
    |WW_NN of Requester           |   8     |                         |
    |(FARP-REQ)                   |         |                         |
    +-----------------------------+---------+-------------------------+
    |WW_PN of Responder           |   8     |                         |
    +-----------------------------+---------+-------------------------+
    |WW_NN of Responder           |   8     |                         |
    +-----------------------------+---------+-------------------------+






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    +-----------------------------------------------------------------+
    |                  FARP-REQ Payload                               |
    +-----------------------------+---------+-------------------------+
    |         Field               | Size    |                         |
    |                             |(Bytes)  |          Remarks        |
    +-----------------------------+---------+-------------------------+
    | 0x54-00-00-00               |   4     |                         |
    +-----------------------------+---------+-------------------------+
    | Match Address Code Points   |   1     |                         |
    +-----------------------------+---------+-------------------------+
    | Port_ID of Requester        |   3     |                         |
    +-----------------------------+---------+-------------------------+
    | Responder Flags             |   1     |                         |
    +-----------------------------+---------+-------------------------+
    | Port_ID of Responder        |   3     | set to 0x00-00-00       |
    +-----------------------------+---------+-------------------------+
    |IP Address of Requester      |   16    |IPv4 Add.= lower 32 bits |
    | (FARP-REQ)                  |         |                         |
    |                             |         |IPv6 Add.= all 128 bits  |
    +-----------------------------+---------+-------------------------+
    |IP Address of Responder      |   16    |IPv4 Add.= lower 32 bits |
    |                             |         |                         |
    |                             |         |IPv6 Add.= all 128 bits  |
    +-----------------------------+---------+-------------------------+

   Both formats carry common fields: command code, Match Address Code
   Point, Port_ID of Requester, Responder Flags, and Port_ID of
   Responder.

   The first format carries the WW_PN and WW_NN of both the Requester
   and Responder while the second format carries the IP addresses of
   Requester and Responder. Note that the NAA is implicitly assumed to
   be defined to be equal to b'0001' indicating IEEE-48-bit MAC
   addresses are contained in World Wide Port and Node Names.

   In the first format the "WW_PN of Responder" and "WW_NN of Responder"
   fields should be filled in with the Node and Port Names of the
   desired Responder.

   The Match Address Code Points define what addresses to match based on
   these code points.

   The Responder Flags define what Responder action if the result of the
   Match Address Code Points is successful.

   In the first format, the FARP-REQ Requester supplies the WW_PN of the
   Responder, the WW_NN of the Responder, or both.

   WW_PN in FARP is the 8-byte WW_PN of the Requester/ Responder to the
   FARP-REQ.

   WW_NN in FARP is the 8-byte WW_NN of the Requester/ Responder to the
   FARP-REQ.




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   In the second format, the FARP-REQ Requester supplies either a 32-bit
   IPv4 Address or a 128-bit IPv6 address of the Requester and
   Responder.

   Port_ID of Requester: is the 24-bit Port_ID used in the S_ID field of
   the FARP-REQ header.

   Port_ID of Responder: is the 24-bit Port_ID used in the S_ID field of
   the FARP-REPLY header.

   Responder Flags: is an 8-bit field (bits 0-7) that defines the action
   of the Responder.  This field is only valid in a FARP-REQ.

   FARP-REQ is an ELS broadcast command.  You do not have to be logged
   in to issue a FARP request.

   Possible Responder Actions:

      Port Login (P_LOGI)
          Sent to the Port Identified by " Requester Port_ID" field
          when responder bit 0 (INIT_PLOGI) == binary '1'

      FARP-REPLY Sequence

          Sent to the Port Identified by "Requester Port_ID" field
          when responder bit 1 (INIT_FARP-REPLY) == binary '1'

   Bits 0 (INIT-PLOGI) = binary '1' and Bit 1 (INIT_FARP-REPLY) = binary
   '1' at the same time is prohibited. Recipients of the FARP Request
   ELS shall not issue a Service Reject (LS_RJT) if FARP is not
   supported.

   Table below  indicates the action performed for each bit.  If no bits
   are set, the Responder will take no action.

   +----------+-------------------------------------------------------+
   |          |                 FARP Responder Flag                   |
   +----------+----------------+--------------------------------------+
   | Bit      | Bit Name       |            Action                    |
   | Position |                |                                      |
   +----------+----------------+--------------------------------------+
   |    0     | INIT_PLOGI     | Initiate P_LOGI to the Requester     |
   +----------+----------------+--------------------------------------+
   |    1     | INIT_FARP-REPLY| Send FARP_RES message to Requester   |
   +----------+----------------+--------------------------------------+
   | 2 to 7   | Reserved       |                                      |
   +----------+----------------+--------------------------------------+

   For each recipient of the FARP-REQ Broadcast ELS, the recipients
   match one or more addresses based on the encoded bits of the "FARP
   Match Address Code Points" field. This is shown in the following
   table:





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   +------------------------------------------------------------------+
   |                FARP Match Address Code Points                    |
   +------------------------------------------------------------------+
   |   LSBits  |     Bit name     |         Action                    |
   +-----------+------------------+-----------------------------------+
   |   0000    | Reserved         |                                   |
   +-----------+------------------+-----------------------------------+
   |   0001    | MATCH_WW_PN      | Match on WW_PN of Responder       |
   +-----------+------------------+-----------------------------------+
   |   0010    | MATCH_WW_NN      | Match on WW_NN of Responder       |
   +-----------+------------------+-----------------------------------+
   |   0011    | MATCH_WW_PN &    | Match on both WW_PN and           |
   |           | MATCH_WW_NN      | WW_NN of Responder                |
   +-----------+------------------+-----------------------------------+
   |   0100 to | Reserved         |                                   |
   |   1000    |                  |                                   |
   +-----------+------------------+-----------------------------------+
   |   1001    | MATCH_IPv4       | Match on IPv4 Address of Responder|
   +-----------+------------------+-----------------------------------+
   |   1010    | MATCH_IPv6       | Match on IPv6 Address of Responder|
   +-----------+------------------+-----------------------------------+
   |   1011 to | Reserved         |                                   |
   |   1111    |                  |                                   |
   +-----------+------------------+-----------------------------------+

   Note that bit-3 of the LSB differentiates between World_Wide Names
   and IP addresses.

   If a Node receives a FARP-REQ with MATCH_WW_PN (0001) or MATCH_WW_NN
   (0001) or both (0011) Match Address Code Points, then it may issue a
   response according to the FARP Responder Flag.

       - Support for the MATCH_WW_PN is mandatory.
       - Support for the MATCH_WW_NN is optional.
       - Support for both MATCH_WW_PN and MATCH_WW_NN at the same time
         is optional

   If a Node receives a FARP_REQ with MATCH_IPv4 (1001) or MATCH_IPv6
   (1010) Match Address Code Points, then it may issue a response
   according to the FARP Responder Flag.

       - Support for MATCH_IPv4 is optional.
       - Support for MATCH_IPv6 is optional.

   If there are no matches or support is optional then a silent behavior
   from the Responder is valid.

   FARP-REPLY is an ELS command directed to the Port_ID of the FARP-REQ
   Requester. You do not have to be logged in to the FARP-REQ Requester
   to issue a FARP-REPLY. The format of the FARP-REPLY payload is as
   follows:






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   +---------------------------------------------------------------------+
   |               FARP-REPLY Payload with WW-Names                      |
   +-------------------------------------+---------+---------------------+
   |               Field                 | Size    |   Remarks           |
   |                                     | (Bytes) |                     |
   +-------------------------------------+---------+---------------------+
   | 0x55-00-00-00                       |   4     |                     |
   +-------------------------------------+---------+---------------------+
   | Match Address Code Points           |   1     |                     |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Requester                |   3     |                     |
   +-------------------------------------+---------+---------------------+
   | Responder Flags                     |   1     |  Not used           |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Responder                |   3     |                     |
   +-------------------------------------+---------+---------------------+
   |WW_PN of Requester (FARP-REQ)        |   8     |                     |
   +-------------------------------------+---------+---------------------+
   |WW_NN of Requester (FARP-REQ)        |   8     |                     |
   +-------------------------------------+---------+---------------------+
   |WW_PN of Responder                   |   8     |                     |
   +-------------------------------------+---------+---------------------+
   |WW_NN of Responder                   |   8     |                     |
   +-------------------------------------+---------+---------------------+

   +---------------------------------------------------------------------+
   |                 FARP-REPLY Payload with IP Addresses                |
   +-------------------------------------+---------+---------------------+
   |               Field                 | Size    |                     |
   |                                     | (Bytes) |   Remarks           |
   +-------------------------------------+---------+---------------------+
   | 0x55-00-00-00                       |   4     |                     |
   +-------------------------------------+---------+---------------------+
   | Match Address Code Points           |   1     |                     |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Requester                |   3     |                     |
   +-------------------------------------+---------+---------------------+
   | Responder Flags                     |   1     |  Not used           |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Responder                |   3     |                     |
   +-------------------------------------+---------+---------------------+
   |IP Address of Requester (FARP-REQ)   |   16    |IPv4 Add.=low 32 bits|
   |                                     |         |IPv6 Add.=128 bits   |
   +-------------------------------------+---------+---------------------+
   |IP Address of Responder              |   16    |IPv4 Add.=low 32 bits|
   |                                     |         |IPv6 Add.=128 bits   |
   +-------------------------------------+---------+---------------------+

6.  FC Layer Address Validation

   At all times, the <MAC Address, Port_ID> mapping has to be validated
   before use. There are many events that can invalidate this mapping.
   The following discussion addresses conditions when such a validation
   is required.



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6.1 General Discussion

   After a link interruption occurs, the Port_ID of a port may change.
   After the interruption, the Port_IDs of all other ports that have
   previously performed PLOGI (N_Port Login) with this port may have
   changed, and its own Port_ID may have changed.

   Because of this, address validation is required after a LIP in a loop
   topology [7]or after NOS/OLS in a point-to-point topology [6].

   Port_IDs will not change as a result of Link Reset(LR),thus address
   validation is not required.

   In addition to actively validating devices after a link interruption,
   if a port receives any FC-4 data frames (other than broadcast
   frames), from a port that is not currently logged in, then it shall
   send an explicit Extended Link Service (ELS) Request logout (LOGO)
   command to that port.

   ELS commands (Requests and Replies) are used by an N_Port to solicit
   a destination port (F_Port or N_Port) to perform some link-level
   function or service.) The LOGO Request is used to request
   invalidation of the service parameters and Port_ID of the recipient
   N_Port.

   The level of initialization and subsequent validation and recovery
   reported to the upper (FC-4) layers is implementation-specific.

   In general, an explicit Logout (LOGO) shall be sent whenever the FC-
   Layer mapping between the Port_ID and WW_PN of a remote port is
   removed.

   The effect of power-up or re-boot on the mapping tables is outside
   the scope of this specification.

6.2 FC Layer Address Validation in a Point-to-Point Topology

   No validation is required after LR. In a point-to-point topology,
   NOS/OLS causes implicit logout of each port and after a NOS/OLS, each
   port must perform a PLOGI [2].

6.3 FC Layer Address Validation in a Private Loop Topology

   After a LIP, a port shall not transmit any link data to another port
   until the address of the other port has been validated. The
   validation consists of completing either ADISC or PDISC. (See
   Appendix A)

   ADISC (Address Discovery) is an ELS command for discovering the hard
   addresses - the 24-bit identifier- of NL_Ports [5], [6].

   PDISC (Discover Port) is an ELS command for exchanging service
   parameters without affecting login state [5], [6].




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   As a requester, this specification prohibits PDISC and requires
   ADISC.

   As a responder, an implementation may need to respond to both ADISC
   and PDISC for compatibility with other FC specifications.

   If the three addresses, Port_ID, WW_PN, WW_NN, exactly match the
   values prior to the LIP, then any active exchanges may continue.

   If any of the three addresses have changed, then the node must be
   explicitly logged out [4], [5].

   If a port's N_Port ID changes after a LIP, then all active Port-ID to
   WW_PN mappings at this port must be explicitly logged out.

6.4 FC Layer Address Validation in a Public Loop Topology

   A FAN (Fabric Address Notification) ELS command is sent by the fabric
   to all known previously logged in  ports following an initialization
   event. Therefore, after a LIP, hosts may wait for this notification
   to arrive or they may perform a FLOGI.

   The WW_PN and WW_NN of the fabric FL_Port contained in the FAN ELS or
   FLOGI response must exactly match the values before the LIP. In
   addition, the AL_PA obtained by the port must be the same as the one
   before the LIP.

   If the above conditions are met, the port may resume all exchanges.
   If not, then FLOGI (Fabric login) must be performed with the fabric
   and all nodes must be explicitly logged out.

   A public loop device will have to perform the private loop
   authentication to any nodes on the local loop which have an Area +
   Domain Address == 0x00-00-XX

6.5 FC Layer Address Validation in a Fabric Topology

   No validation is required after LR (link reset).

   After NOS/OLS, a port must perform FLOGI. If, after FLOGI, the S_ID
   of the port, the WW_PN of the fabric, and the WW_NN of the fabric are
   the same as before the NOS/OLS, then the port may resume all
   exchanges. If not, all nodes must be explicitly, logged out [2].

7. Exchange Management

7.1 Exchange Origination

   FC Exchanges shall be established to transfer data between ports.
   Frames on IP exchanges shall not transfer Sequence Initiative.

7.2 Exchange Termination

   With the exception of the recommendations in Appendix B, "Reliability



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   in Class 3", the mechanism for aging or expiring exchanges based on
   activity, timeout, or other method is outside the scope of this
   document.

   Exchanges may be terminated by either port.

   The Exchange Originator may terminate Exchanges by setting the LS
   bit, following normal FC standard FC-PH [2] rules. This specification
   prohibits the use of the NOP ELS with LS set for Exchange
   termination.

   Exchanges may be torn down by the Exchange Originator or Exchange
   Responder by using the ABTS_LS protocol. The use of ABTS_LS for
   terminating aged exchanges or error recovery is outside the scope of
   this document.

   The termination of IP exchanges by Logout is discouraged, since this
   may terminate active exchanges on other FC-4s.

8. Summary of Supported Features

   Note: 'Required' means the feature support is mandatory, 'Prohibited'
   means the feature support is not valid, and 'Settable' means support
   is as specified in the relevant standard.

8.1 FC-4 Header
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | Type Code ( = 5) ISO8802-2 LLC/SNAP           | Required   |   2   |
   | Network Headers                               | Required   |   3   |
   | Other Optional Headers                        | Prohibited |       |
   +--------------------------------------------------------------------+
   Notes:

       1. This table applies only to FC-4 related data, such as IP and
          ARP packets. This table does not apply to link services and
          other non-FC-4 sequences (PLOGI, for example) that must occur
          for normal operation.

       2. The TYPE field in the FC Header (Word 2 bits 31-24) must
          indicate ISO 8802-2 LLC/SNAP Encapsulation (Type 5). This
          revision of the document focuses solely on the issues related
          to running IP and ARP over FC. All other issues are outside
          the scope of this document, including full support for IEEE
          802.2 LLC.

       3. DF_CTL field (Word 3, bits 23-16 of FC-Header)must indicate
          the presence of a Network Header (0010 0000) on the First
          logical Frame of FC-4 sequences.

8.2 R_CTL

   R_CTL in FC-Header: Word 0, bits 31-24



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   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | Information Category (R_CTL Routing):         |            |       |
   |      FC-4 Device Data                         | Required   |   1   |
   |      Extended Link Data                       | Required   |   2   |
   |      FC-4 Link Data                           | Prohibited |       |
   |      Video Data                               | Prohibited |       |
   |      Basic Link Data                          | Required   |   3   |
   |      Link Control                             | Required   |   4   |
   | R_CTL information                             |            |       |
   |      Uncategorized                            | Prohibited |       |
   |      Solicited Data                           | Prohibited |       |
   |      Unsolicited Control                      | Required   |   2   |
   |      Solicited Control                        | Required   |   2   |
   |      Unsolicited Data                         | Required   |   1   |
   |      Data Descriptor                          | Prohibited |       |
   |      Unsolicited Command                      | Prohibited |       |
   |      Command Status                           | Prohibited |       |
   +--------------------------------------------------------------------+
   Notes:
       1. This is required for FC-4 (IP and ARP) packets
          - Routing bits of R_CTL field must indicate Device Data
            frames (0000).
          - Information Category of R_CTL field must indicate
            Unsolicited Data (0100).
       2. This is required for Extended Link Services.

       3. This is required for Basic Link Services.

       4. This is required for Link Control frames.

8.3 F_CTL

   F_CTL in FC-Header: Word 2, bits 23-0
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | Exchange Context                              | Settable   |       |
   | Sequence Context                              | Settable   |       |
   | First / Last / End Sequence (FS/LS/ES)        | Settable   |       |
   | Chained Sequence                              | Prohibited |       |
   | Sequence Initiative (SI)                      | Settable   |   1   |
   | X_ID Reassigned / Invalidate                  | Prohibited |       |
   | Unidirectional Transmit                       | Settable   |       |
   | Continue Sequence Condition                   | Required   |   2   |
   | Abort Seq. Condition -continue and single seq.| Required   |   3   |
   | Relative Offset - Unsolicited Data            | Settable   |   4   |
   | Fill Bytes                                    | Settable   |       |
   +--------------------------------------------------------------------+
   Notes:
       1. For FC-4 frames, each N_Port shall have a dedicated OX_ID for
          sending data to each N_Port in the network and a dedicated
          RX_ID for receiving data from each N_Port as well. Exchanges



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          are used in a unidirectional mode, thus setting sequence
          initiative is not valid for FC-4 frames. Sequence initiative
          is valid when using Extended Link Services.
       2. This field is required to be 00, no information.
       3. Sequence error policy is requested by an exchange originator
          in the F_CTL Abort Sequence Condition bits in the first data
          frame of the exchange. For classes 1 and 2, ACK frame is
          required to be "continuous sequence".
       4. Relative offset prohibited on all other types (Information
          Category) of frames.

8.4 Sequences
   +---------------------------------------------------------------------+
   |                      Feature                    |   Support  |Notes |
   +---------------------------------------------------------------------+
   | Class 2 open sequences / exchange               |     1      |   1  |
   | Length of seq. not limited by end-to-end credit | Required   |   2  |
   | Maximum sequence size - IP sequences            |   65536    |   3  |
   | Maximum sequence size - ARP sequences           |    532     |   4  |
   | Capability to receive sequence of maximum size  | Optional   |   5  |
   | Sequence Streaming                              | Prohibited |   6  |
   | Stop Sequence Protocol                          | Prohibited |      |
   | ACK_0 support                                   | Optional   |   7  |
   | ACK_1 support                                   | Required   |   7  |
   | ACK_N support                                   | Prohibited |      |
   | Class of Service for transmitted sequences      | 1, 2 or 3  |   8  |
   | Continuously Increasing Sequence Count          | Optional   | 9,10 |
   +---------------------------------------------------------------------+
   Notes:
       1. Only one active sequence per exchange is optional.

       2. A sequence initiator shall be capable of transmitting
          sequences containing more frames than the available credit
          indicated by a sequence recipient at login. FC-PH [2] end-to
          end flow control rules will be followed when transmitting such
          sequences.

       3. Maximum sequence size is 65535 bytes. Thus if the maximum IP
          packet size (MTU) is limited to 65280 bytes, then after
          accounting for 8 bytes of LLC/SNAP, we still have
          (65535 - 65280 -8 = 247 bytes) for header overhead.

       4. Maximum size ARP packet is 532 bytes (including LLC/SNAP
          headers).

       5. Some OS environments may not handle the max MTU of 65535. It
          is up to the administrator to configure the Max MTU for all
          systems.

       6. All class 3 sequences are assumed to be non-streamed.

       7. Only applies for Class 1 and 2. Use of ACK_1 is default,
          ACK_0 used if indicated by sequence recipient at login.




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       8. The administrator configured class of service is used, except
          where otherwise specified (e.g. Broadcasts are always sent in
          class 3).

       9. Review Appendix B, "Reliability in Class 3".

      10. The first frame of the first sequence of anew exchange must
          have SEQ_CNT = 0 [2].

8.5 Exchanges
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | X_ID interlock support                        | Optional   |   1   |
   | OX_ID=FFFF                                    | Prohibited |       |
   | RX_ID=FFFF                                    | Optional   |   2   |
   | Action if no exchange resources available     | P_RJT      |   3   |
   | Long Lived Exchanges                          | Optional   |   4   |
   | Reallocation of Idle Exchanges                | Optional   |       |
   +--------------------------------------------------------------------+
   Notes:
       1. Only applies to Classes 1 and 2, supported by the exchange
          originator. A Port shall be capable of interoperating with
          another Port that requires X_ID interlock. The exchange
          originator facility within the Port shall use the X_ID
          Interlock protocol in such cases.

       2. An exchange responder is not required to assign RX_IDs. If a
          RX_ID of FFFF is assigned, it is identifying exchanges based
          on S_ID / D_ID / OX_ID only.

       3. In Classes 1 and 2, a Port shall reject a frame that would
          create a new exchange with a P_RJT containing reason code
          "Unable to establish exchange". In Class 3, the frame would be
          dropped.

       4. When an exchange is created between 2 Ports for IP/ARP data,
          it remains active while the ports are logged in with each
          other. An exchange shall not transfer Sequence Initiative
          (SI). Broadcasts and ELS commands may use short lived
          exchanges.

8.6 ARP
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | ARP Server Support                            | Prohibited |   1   |
   | Response to ARP requests                      | Required   |   2   |
   | ARP requests transmitted as broadcast message | Required   |       |
   | Class of Service for ARP requests             |     3      |   3   |
   | Class of Service for ARP replies              | 1, 2 or 3  |   4   |
   +--------------------------------------------------------------------+
   Notes:
      1. Well-known Address FFFFFC is not used for ARP requests. Frames



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         from Well-known Address FFFFFC are not considered to be ARP
         frames. Broadcast support is required for ARP.

      2. The IP Address is mapped to a specific MAC address with ARP.

      3. An ARP request is a broadcast message, thus Class 3 is always
         used.

      4. An ARP reply is a normal sequence, thus the administrator
         configured class of service is used.

8.7 Extended Link Services (ELS)
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | Class of service for ELS commands / responses |  1,2 or 3  |   1   |
   | Explicit N-Port Login                         | Required   |       |
   | Explicit F-Port Login                         | Required   |       |
   | FLOGI ELS command                             | Required   |       |
   | PLOGI ELS command                             | Required   |       |
   | ADISC ELS command                             | Required   |       |
   | PDISC ELS command                             | Optional   |   2   |
   | FAN ELS command                               | Required   |   6   |
   | LOGO ELS command                              | Required   |       |
   | FARP-REQ ELS command                          | Required   |   3   |
   | FARP-REPLY ELS command                        | Required   |   4   |
   | Other ELS command support                     | Optional   |   5   |
   +-----------------------------------------------+------------+-------+
   Notes:
       1. The administrator configured class of service is used.

       2. PDISC is prohibited as requester. ADISC should be used
          instead. As a responder, an implementation may need to respond
          to both ADISC and PDISC for compatibility with other
          specifications.

       3. Sending a FARP-REQ is optional as Requester, however, support
          for receiving a FARP-REQ is Required at the Responder

       4. Sending FARP-REPLY is required for MATCH_WW_PN, support for
   all
          other Match Address Code Points is optional.

       5. If other ELS commands are received an LS_RJT may be sent. NOP
          is not required by this specification, and should not be used
          as a mechanism to terminate exchanges.

       6. Required for FL_Ports

8.8 Login Parameters

   Unless explicitly noted here, a compliant implementation shall use
   the login parameters as described in [4].




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8.8.1 Common Service Parameters - FLOGI

        - FC-PH Version, lowest version may be 0x09 to indicate
          'minimum 4.3'.

        - Can't use BB_Credit=0 for N_Port on a switched Fabric
          (F_Port).

8.8.2 Common Service Parameters - PLOGI

        - FC-PH Version, lowest version may be 0x09 to indicate
          'minimum 4.3'.
        - Can't use BB_Credit=0 for N_Port in a Point-to-Point
          configuration

        - Random Relative Offset is optional.

        - Note that the 'Receive Data Field Size' fields specified in
          the PLOGI represent both optional headers and payload.

        - The MAC Address can therefore be extracted from the 6 lower
          bytes of the WW_PN field (when the IEEE 48-bit Identifier
          format is chosen as the NAA) during PLOGI or ACC payload
          exchanged during Fibre Channel Login [2].

        - The MAC Address can also be extracted from the WW_PN field in
          the Network Header during ADISC (and ADISC ACC), or PDISC
          (and PDISC ACC).

8.8.3 Class Service Parameters - PLOGI

        - Discard error policy only.

9. Security Considerations

   There are no known security issues raised by this document.

10. Acknowledgement

   This specification is based on FCA IP Profile, Version 3.3.  The FCA
   IP Profile was a joint work of the Fibre Channel Association (FCA)
   vendor community.  The following companies and organizations have
   contributed to the creation of the FCA IP Profile: Adaptec, Ancor,
   Brocade, Clariion, Crossroads, emf Associates, Emulex, Finisar,
   Gadzoox, Hewlett Packard, Interphase, Jaycor, LLNL, McData, Migration
   Associates, Orca Systems, Prisa, Q-Logic, Symbios, Systran,
   Tektronix, Univ. of Minnesota, Univ. of New Hamshire. Jon Infante
   from Emulex deserves special mention for his extensive comments.

11. References

   [1] FCA IP Profile, Revision 3.3, May 15, 1997

   [2] Fibre Channel Physical and Signaling Interface (FC-PH) , ANSI



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       X3.230-1994

   [3] Fibre Channel Link Encapsulation (FC-LE), Revision 1.1, June 26,
       1996

   [4] Fibre Channel Fabric Loop Attachment (FC-FLA), Rev. 2.7, August
       12, 1997

   [5] Fibre Channel Private Loop SCSI Direct Attach (FC-PLDA),
       Rev. 2.1, September 22, 1997

   [6] Fibre Channel Physical and Signaling Interface-2 (FC-PH-2),
       Rev. 7.4, ANSI X3.297-1996

   [7] Fibre Channel Arbitrated Loop (FC-AL), ANSI X3.272-1996

   [8] Postel, J. and Reynolds, J., "A standard for the Transmission of
       IP Datagrams over IEEE 802 Networks". RFC 1042, ISI, Feb, 1988

   [9] Plummer, D. "An Ethernet Address Resolution Protocol -or-
       Converting Network Addresses to 48-bit Ethernet Address for
       Transmission on Ethernet Hardware", STD 37, RFC 826, MIT, Nov
       1982.

   [10] FCSI IP Profile, FCSI-202, Revision 2.1, September 8, 1995

   [11] Fibre Channel Physical and Signaling Interface -3 (FC-PH-3),
        Rev. 9.3, ANSI X3.xxx-199x

   [12] Fibre Channel-The Basics, "Gary R. Stephens and Jan V. Dedek",
        Ancot Corporation

   [13] Fibre Channel -Gigabit Communications and I/O for Computers
        Networks "Alan Benner", McGraw-Hill, 1996, ISBN 0-07-005669-2

   [14] Fibre Channel Generic Services -2 (FC-GS-2), Rev. 5.2
   X3.288-199x

12. Authors' Addresses
   Murali Rajagopal
   Gadzoox Networks, Inc.
   711 Kimberly Avenue, Suite 100
   Placentia, CA 92870

   Phone: +1 714 577 6805
   Fax: +1 714 524 8508
   Email: murali@gadzoox.com

   Raj Bhagwat
   Gadzoox Networks, Inc.
   711 Kimberly Avenue, Suite 100
   Placentia, CA 92870

   Phone: +1 714 577 6806



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   Fax: +1 714 524 8508
   Email: raj@gadzoox.com

   Wayne Rickard
   Gadzoox Networks, Inc.
   711 Kimberly Avenue, Suite 100
   Placentia, CA 92870

   Phone: +1 714 577 6803
   Fax: +1 714 524 8508
   Email: wayne@gadzoox.com

APPENDIX A: Fibre Channel Overview

A.1 Brief Tutorial

   FC standard [2] defines 5 "levels" (not layers) for its protocol
   description: FC-0, FC-1, FC-2, FC-3, and FC-4. The first three levels
   (FC-0, FC-1, FC-2) are largely concerned with the physical formatting
   and control aspects of the protocol. FC-3 is architecturally defined
   but not unspecified at this time. FC-4 is meant for supporting profiles
   of higher protocols such as IP and Small Computer System Interface (SCSI)
   and supports a relatively small set of higher level protocols compared to
   LAN protocols such as IEEE 802.3.

   FC devices are called "Nodes", each of which has at least one "Port" to
   connect to other ports. A Node may be a workstation, a disk drive or
   disk array, a camera, a display unit, etc. The set of hardware components,
   and transceivers, connecting two or more node ports is called a topology.

   A "Link" is two unidirectional paths flowing in opposite directions and
   connecting two Ports within adjacent Nodes.

   FC Nodes communicate using higher layer protocols such as SCSI and IP
   and are configured to operate using one of the following
   networking topologies:
       - Point-to-Point
       - Private Loop
       - Public Loop (attachment to a Fabric)
       - Fabric
   The point-to-point is the simplest of the four topologies, where only
   two nodes communicate with each other. The private loop may connect a
   number of devices (max 126) in a logical ring much like Token Ring and
   is distinguished from a public loop by the absence of a Fabric Node
   participating in the loop. The Fabric topology is a switched network
   where any attached node can communicate with any other.

   Table below summarizes the usage of port types depending on its location
   [12]. Note that E-Port is not relevant to any discussion in this
   specification but is included below for completeness.

   +-----------+-------------+-----------------------------------------+
   | Port Type |  Location   |      Topology Associated with           |
   +-----------+-------------+-----------------------------------------+



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   | N_Port    |   Node      |      Point-to-Point or Fabric           |
   +-----------+-------------+-----------------------------------------+
   | NL_Port   |   Node      |In N_Port mode -Point-to-Point or Fabric |
   |           |             |In NL_Port mode - Arbitrated Loop        |
   +-----------+-------------+-----------------------------------------+
   | F_Port    |   Fabric    |                   Fabric                |
   +-----------+-------------+-----------------------------------------+
   | FL_Port   |   Fabric    | In F_Port mode - Fabric                 |
   |           |             | In FL_Port mode - Arbitrated Loop       |
   +-----------+-------------+-----------------------------------------+
   | E_Port    |   Fabric    |     Internal Fabric Expansion           |
   +-----------+-------------+-----------------------------------------+


   A.2 Fibre Channel Header Fields

   Fibre Channel Frame Header, Network Header, and payload carrying IP Packet

   +---+----------------+----------------+----------------+--------------+
   |Wrd|    <31:24>     |    <23:16>     |    <15:08>     |    <07:00>   |
   +---+----------------+----------------+----------------+--------------+
   |0  |    R_CTL       |                     D_ID                       |
   +---+----------------+----------------+----------------+--------------+
   |1  |    CS_CTL      |                     S_ID                       |
   +---+----------------+----------------+----------------+--------------+
   |2  |    TYPE        |                     F_CTL                      |
   +---+----------------+----------------+----------------+--------------+
   |3  |   SEQ_ID       |  DF_CTL        |          SEQ_CNT              |
   +---+----------------+----------------+----------------+--------------+
   |4  |             OX_ID               |              RX_ID            |
   +---+--------+-------+----------------+----------------+--------------+
   |5  |        Parameter (Control or Relative Offset for Data )         |
   +---+-----------------------------------------------------------------+
   |6  |  NAA   |        Network_Dest_Address (Hi order bits)            |
   +---+--------+-------+----------------+----------------+--------------+
   |7 |                  Network_Dest_Address (Lo order bits)            |
   +---+--------+-------+----------------+----------------+--------------+
   |8  |  NAA   |        Network_Src_Address (Hi order bits)             |
   +---+--------+-------+----------------+----------------+--------------+
   |9  |                 Network_Src_Address (Lo order bits)             |
   +---+----------------+----------------+----------------+--------------+
   |10 |     DSAP       |     SSAP       |      CTRL      |     OUI      |
   +---+----------------+----------------+----------------+--------------+
   |11 |               OUI               |               PID             |
   +---+----------------+----------------+----------------+--------------+
   |12 |                   IP Packet Data                                |
   +---+----------------+----------------+----------------+--------------+
   |13 |                           ...                                   |
   +---+----------------+----------------+----------------+--------------+

   The FC header as shown in the above diagrams contains routing and other
   control information to manage frames, sequences, and exchanges. The
   frame header is sent as 6 transmission words immediately following an SOF
   delimiter and before the data field.



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   D_ID and S_ID:

       FC uses destination address routing [12], [13]. Frame routing in
       a point-to-point topology is trivial.

       For the Arbitrated Loop topology, with the destination NL_Port on
       the same AL, the source port must pick the destination port,
       determine its AL Physical Address, and "Open" the destination
       port. The frames must pass through other NL_Ports or the FL_Port
       on the loop between the source and destination, but these ports
       do not capture the frames. They simply repeat and transmit the
       frame. Either communicating port may "Close" the circuit.

       When the destination port is not on the same AL, the source

       NL_Port must open the FL_Port attached to a Fabric. Once in the
       Fabric, the Fabric routes the frames again to the destination.

       In a Fabric topology, the Fabric looks into the frame header,
       extracts the destination address (D_ID), searches its own routing
       tables, and sends the frame to the destination port along the path
       chosen. The process of choosing a path may be performed at each
       fabric element or switch until the F_Port attached to the destination
       N_Port is reached.

   R_CTL (Routing Control) and TYPE(data structure):

       Frames for each FC-4 can be easily distinguished from the others
       at the receiving port using the R_CTL (Routing Control) and TYPE
       (data structure) fields in the frame header.

       The R_CTL has two sub-fields: Routing bits and Information category.
       The Routing bits sub-field has specific values that mean FC-4 data
       follows and the Information Category tells the receiver the "Type"
       of data contained in the frame. The R_CTL and TYPE code points are
       shown in the diagrams.

   Other Header fields:

       F_CTL (Frame Control) and SEQ_ID (Sequence Identification),
       SEQ_CNT (Sequence Count), OX_ID (Originator exchange Identifier),
       RX_ID (Responder exchange Identifier), and Parameter fields are
       used to manage the contents of a frame, and mark information
       exchange boundaries for the destination port.

   F_CTL(Frame Control):

       The FC_CTL field is a 3-byte field that contains information
       relating to the frame content. Most of the other frame header
       fields are used for frame identification. Among other things,
       bits in this field indicate the first sequence, last sequence, or
       end sequence. Sequence Initiative bit is used to pass control of
       the next sequence in the exchange to the recipient.




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   SEQ_ID (Sequence Identifier) and SEQ_CNT (Sequence Count):

       This is used to uniquely identify sequences within an Exchange.
       The <S_ID, D_ID, SEQ_ID> uniquely identifies any active sequence.
       SEQ_CNT is used to uniquely identify frames within a Sequence to
       assure sequentiality of frame reception, and to allow unique
       correlation of link control frames with their related data frames.

   Originator Exchange Identifier (OX_ID) and Responder Exchange
   Identifier (RX_ID):

       The OX_ID value provides association of frames with specific
       Exchanges originating at a particular N_Port. The RX_ID field
       provides the same function that the OX_ID provides for the
       Exchange Originator. The OX_ID is meaningful on the Exchange
       Originator, and the RX_ID is meaningful on the Responder.

   DF_CTL (Data Field Control):

        The DF_CTL field specifies the presence or absence of optional
        headers between the Frame header and Frame Payload

   PARAMETER:

       The Parameter field has two meanings, depending on Frame type.
       For Link Control Frames, the Parameter field indicates the
       specific type of Link Control frame. For Data frames, this
       field contains the Relative Offset value. This specifies an
       offset from an Upper Layer Protocol buffer from a base address.

               Code Points for FC Frame with IP  packet Data
   +---+----------------+----------------+----------------+--------------+
   |Wrd|    <31:24>     |    <23:16>     |    <15:08>     |    <07:00>   |
   +---+----------------+----------------+----------------+--------------+
   | 0 |    0x04        |                     D_ID                       |
   +---+----------------+----------------+----------------+--------------+
   | 1 |    0x00        |                     S_ID                       |
   +---+----------------+----------------+----------------+--------------+
   | 2 |    0x05        |                     F_CTL                      |
   +---+----------------+----------------+----------------+--------------+
   | 3 |   SEQ_ID       |     0x20       |          SEQ_CNT              |
   +---+----------------+----------------+----------------+--------------+
   | 4 |             OX_ID               |              RX_ID            |
   +---+----------------+----------------+----------------+--------------+
   | 5 |           0xXX-XX-XX-XX Parameter Relative Offset               |
   +---+------+----------------------------------------------------------+
   | 6 | 0001 |        0x000             | Dest. MAC (Hi order bits)     |
   +---+------+---------+----------------+----------------+--------------+
   | 7 |                      Dest. MAC (Lo order bits)                  |
   +---+------+----------+----------------+------------------------------+
   | 8 | 0001 |        0x000             | Src. MAC  (Hi order bits)     |
   +---+------+---------+----------------+----------------+--------------+
   | 9 |                 Src. MAC (Lo order bits)                        |
   +---+----------------+----------------+----------------+--------------+



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   |10 |     0xAA       |     0xAA       |      0x03      |     0x00     |
   +---+----------------+----------------+----------------+--------------+
   |11 |           0x00-00               |             0x08-00           |
   +---+----------------+----------------+----------------+--------------+
   |12 |                   IP Packet Data                                |
   +---+----------------+----------------+----------------+--------------+
   |13|                        ...                                      |
   +---+----------------+----------------+----------------+--------------+

   The Code Points for FC Frames with ARP packets are very similar to IP
   packets with the exception of PID value in Word 11 which is set to
   0x08-06. Also, the Network Header as shown above appears only in the
   first logical FC Sequence carrying IP. In the case, where FC frames
   carry ARP packets it is always present because these are single frame
   sequences.

A.3 Acronyms and Glossary of FC Terms

   It is assumed that the reader is familiar with the terms and acronyms
   used in the FC protocol specification [2]. The following is provided for
   easy reference.

   First Frame: The frame that contains the SOFi field. This means a logical
   first and may not necessarily be the first frame temporally received in a
   sequence.

   Code Point: The coded bit pattern associated with control fields in frames
   or packets.

   PDU: Protocol Data Unit

   ABTS_LS: Abort Sequence Protocol - Last Sequence. A protocol for
   aborting an exchange based on the ABTS recipient setting the
   Last_Sequence bit in the BA_ACC ELS to the ABTS

   ADISC: Discover Address. An ELS for discovering the Hard Addresses (the
   24 bit NL_Port Identifier) of N_Ports

   D_ID: Destination ID

   ES: End sequence. This FCTL bit in the FC header indicates this frame is
   the last frame of the sequence.

   FAN: Fabric Address Notification. An ELS sent by the fabric to all known
   previously logged in ports following an initialization event.

   FLOGI: Fabric Login.

   LIP: Loop Initialization. A primitive sequence used by a port to detect
   if it is part of a loop or to recover from certain loop errors.

   Link: Two unidirectional paths flowing in opposite directions and
   connecting two Ports within adjacent Nodes.




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   LOGO: Logout.

   LR: Link reset. A primitive sequence transmitted by a port to initiate
   the link reset protocol or to recover from a link timeout.

   LS: Last sequence of Exchange. This FCTL bit in the FC header indicates
   the sequence is the last sequence of the exchange.

   Network Address Authority: A 4-bit field specified in Network Headers
   that distinguishes between various name registration authorities that
   may be used to identify the WW_PN and the WW_NN. NAA=b'0001' indicates
   IEEE-48-bit MAC addresses

   Node: A collection of one or more Ports identified by a unique World
   Wide Node Name (WW Node Name).

   NOS: Not Operational. A primitive sequence transmitted to indicate that
   the port transmitting this sequence has detected a link failure or is
   offline, waiting for OLS to be received.

   OLS: Off line. A primitive sequence transmitted to indicate that the
   port transmitting this sequence is either initiating the link
   initialization protocol, receiving and recognizing NOS, or entering the
   offline state.

   PDISC: Discover Port. An ELS for exchanging Service Parameters without
   affecting login state.

   Primitive Sequence: A primitive sequence is an Ordered Set that is
   transmitted repeatedly and continuously.

   Private Loop Device: A device that does not attempt fabric login (FLOGI)
   and usually adheres to PLDA.  The Area and Domain components of the
   NL_Port ID must be 0x0000. These devices cannot communicate with any
   port not in the local loop.

   Public Loop Device: A device whose Area and Domain components of the
   NL_Port ID cannot be 0x0000. Additionally, to be FLA compliant, the
   device must attempt to open AL_PA 0x00 and attempt FLOGI. These devices
   communicate with devices on the local loop as well as devices on the
   other side of a Fabric.

   Port: The transmitter, receiver and associated logic at either end of a
   link within a Node. There may be multiple Ports per Node. Each Port is
   identified by a unique Port_ID, which is volatile, and a unique World
   Wide Port Name (WW Port Name), which is unchangeable. In this document,
   the term "port" may be used interchangeably with NL_Port or N_Port.

   Port_ID: Fibre Channel ports are addressed by unique 24-bit Port_IDs. In
   a Fibre Channel frame header, the Port_ID is referred to as S_ID (Source
   ID) to identify the port originating a frame, and D_ID to identify the
   destination port. The Port_ID of a given port is volatile (changeable).
   The mechanisms through which a Port_ID may change in a Fibre Channel
   topology are outside the scope of this document.



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   PLOGI: Port Login.

   SI: Sequence Initiative

   World Wide Port_Name (WW_PN): Fibre Channel requires each Port to have
   an unchangeable WW_PN. Fibre Channel specifies a Network Address
   Authority (NAA) to distinguish between the various name registration
   authorities that may be used to identify the WW_PN. A 4-bit NAA
   identifier, 12-bit field set to 0x0 and an IEEE 48-bit MAC address
   together make this a 64-bit field.

   World Wide Node_Name (WW_NN): Fibre Channel identifies each Node with a
   unchangeable WW_NN. In a single port Node, the WW_NN and the WW_PN may be
   identical.


APPENDIX B: Fibre Channel Protocol Considerations

B.1 RELIABILITY IN CLASS 3

   Problem:
   Sequence ID reuse in Class 3 can conceivably result in missing frame
   aliasing with no corresponding detection at the FC2 level.

   Prevention:
   This specification requires one of the following methods if Class 3 is
   used.

        - Continuously increasing Sequence Count (new Login Bit) - both
          sides must set When an N_Port sets the PLOGI login bit for
          continuously increasing SEQ_CNT, it is guaranteeing that it
          will transmit all frames within an exchange using a continuously
          increasing SEQ_CNT (see description below).

        - After using all SEQ_IDs (0-255) once, must start a new Exchange.
          It is recommended that a minimum of 4 Exchanges be used before
          an OX_ID can be reused.

        - Note: If an implementation is not checking the OX_ID when
          reassembling sequences, the problem can still occur. Cycling
          through some number of SEQ_IDs, then jumping to a new exchange
          does not solve the problem. SEQ_IDs must still be unique between
          two N_Ports, even across exchanges.

        - Use only single-frame Sequences.

B.2 CONTINUOUSLY INCREASING SEQ_CNT

   This method allows the recipient to check incoming frames, knowing
   exactly what SEQ_CNT value to expect next. Since the SEQ_CNT will not
   repeat for 65,536 frames, the aliasing problem is significantly reduced.

   A login bit (PLOGI) is used to indicate that a device always uses a
   continuously increasing SEQ_CNT, even across transfers of sequence



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   initiative. This bit is necessary for interoperability with some
   devices, and it provides other benefits as well.

   In the FC-PH-3 [11], the following is supported:

         Word 1, bit 17 - SEQ_CNT (S)
         0 = Normal FC-PH rules apply
         1 = Continuously Increasing SEQ_CNT

   Any N_Port that sets Word 1, Bit 17 = 1, is guaranteeing that it will
   transmit all frames within an exchange using a continuously increasing
   SEQ_CNT. Each exchange shall start with SEQ_CNT = 0 in the first frame,
   and every frame transmitted after that shall increment the previous
   SEQ_CNT by one, even across transfers of sequence initiative. Any frames
   received from the other N_Port in the exchange shall have no effect on
   the transmitted SEQ_CNT.

APPENDIX C: Other Mechanisms for FC Layer Mappings

   Each method should have some mechanism to ensure PLOGI has completed
   successfully before data is sent. A related concern in large networks is
   limiting concurrent logins to only those ports with active IP traffic.

C.1 Login on Cached Mapping Information

   This method insulates the level performing LOGIN from the level
   interpreting ARP. It is more accommodating of non-ARP mechanisms for
   building the FC-layer mapping table.

       1. Broadcast messages that carry a Network Header contain
          the S_ID on the FC-header and WW_PN in the Network-header.
          Caching this information provides a correlation of Port_ID to
          WW_PN. If the received Broadcast message is compliant with this
          specification, the WW_PN will be the MAC Address.

       2. The WW_PN is "available" if Login has been performed to the
          Port_ID and flagged. If login has not been performed, the
          WW_PN is "unavailable".

       3. If an outbound packet is destined for a port that is
          "unavailable", the cached information (from broadcast) is used
          to look up the Port_ID.

       4. After sending an ELS PLOGI command (Port Login) to the Port (from
          a higher level entity at the host), waiting for an outbound packet
          before sending this Port Login conserves resources for only for
          those ports which wish to establish communication.

       5. After Port Login completes (ACC received), the outbound packet
          can be forwarded. At this point in time, both ends have the
          necessary information to complete their <IP address,
          MAC Address, Port_ID> association.

C.2 Login on ARP Parsing



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   This method performs LOGIN sooner by parsing ARP before passing it up to
   higher levels for IP/MAC Address correlation. It requires a low-level
   awareness of the IP address, and is therefore protocol-specific.

       1. When an ARP Broadcast Message is received, the S_ID is extracted
          from the FC header and the corresponding Network_Source_Address
          from the Network Header.

       2. The ARP payload is parsed to determine if (a) this host is the
          target of the ARP request (Target IP Address match), and (b) if
          this host is currently logged in with the port (Port_ID = S_ID)
          originating the ARP broadcast.

       3. The ARP is passed to higher level for ARP Response generation.

       4. If a Port Login is required, an ELS PLOGI command (Port Login)
          is sent immediately to the Port originating the ARP Broadcast.

       5. After Port Login completes, an ARP response can be forwarded.
          Note that there are two possible scenarios:

          - The ACC to PLOGI returns before the ARP reply is processed
            and the ARP Reply is immediately forwarded.

          - The ARP reply is delayed, waiting for ACC (successful
            Login).

       6. At this point in time, both ends have the necessary
          information to complete their
          <IP address, MAC Address, Port_ID> association.

C.3 Login to Everyone

   In Fibre Channel topologies with a limited number of ports, it may be
   efficient to unconditionally login to each port. This method is
   discouraged in fabric and public loop environments.

   After Port Login completes, the MAC Address to Port_ID Address tables
   can be constructed.

C.4 Static Table

   In some loop environments with a limited number of ports, a static
   mapping from a MAC Address to Port_ID (D_ID or AL_PA) may be maintained.
   The FC layer will always know the destination Port_ID based on the
   table. The table is typically downloaded into the driver at
   configuration time. This method scales poorly, and is therefore not
   recommended.

   [draft-ietf-ipfc-fibre-channel-02.txt]
   [This INTERNET DRAFT expires on April 1, 1999]






Rajagopal, Bhagawat, Rickard                                   [Page 36]


Internet-Draft        IP and ARP over Fibre Channel           Oct 1 1998



























































Rajagopal, Bhagawat, Rickard                                   [Page 37]