tech-invite   World Map
3GPP     Specs     Glossaries     UICC       IETF     RFCs     Groups     SIP     ABNFs       T+       Search     Home

RFC 2625

 
 
 

IP and ARP over Fibre Channel

Part 3 of 3, p. 40 to 63
Prev RFC Part

 


prevText      Top      Up      ToC       Page 40 
Appendix B: InARP

B.1 General Discussion

   Inverse ARP (InARP) is a mechanism described in RFC 1293/2390 [15,
   16], which is useful when a node desires to know the protocol address
   of a target node whose hardware address is known. Situations where
   this could occur are described in [15, 16]. The motivation for using
   InARP in FC is to allow a node to learn the IP address of another
   node with which it has performed a Port Login (PLOGI).  PLOGI is a
   normal FC process that happens between nodes, independent of this
   standard. PLOGI makes it possible for a node to discover the WW_PN
   and the Port_ID of the other node but not its IP address. A node in
   this way may potentially obtain the IP address of all nodes with
   which it can PLOGI.

   Note that the use of the InARP mechanism can result in resolving all
   WW_PN to IP addresses and ARP may no longer be required. This can be
   beneficially applied in cases where a particular FC topology makes it
   inefficient to send out an ARP broadcast.

B.2 InARP Protocol Operation

   InARP uses the same ARP Packet format but with different 'Op Codes',
   one for InARP Request and another for InARP Reply.

   The InARP protocol operation is very simple. The requesting node
   fills the hardware address (WW_PN) of the target device and sets the
   protocol address to 0x00-00-00-00. Because, the request is sent to a
   node whose WW_PN and Port_ID are known, there is no need for a
   broadcast. The target node fills in its Protocol address (IP address
   in this case) and sends an InARP Reply back to the sender.  A node
   may collect, all such WW_PN and IP addresses pairs in a similar way.

B.3 InARP Packet Format

   Since the InARP protocol uses the same packet format as the ARP
   protocol, much of the discussion on ARP formats given in Section 4
   applies here.

   The InARP is 28-bytes long in this application and uses two packet
   types:  Request and Reply. Like ARP, the InARP Packet fields are
   common to both InARP Requests and InARP Replies.

   InARP Request and Reply Packets are encapsulated in a single frame FC
   Sequence much like ARP. Compliant InARP Request and Reply FC
   Sequences SHALL include Network_Headers.

Top      Up      ToC       Page 41 
   The 'HW Type' field SHALL be set to 0x00-01.

   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 set as follows:

           0x00-08 for InARP Request
           0x00-09 for InARP Reply

   The 'HW Addr of Sender' field SHALL be the 6-byte IEEE MAC address of
   the Requester (InARP Request) or Responder (InARP Reply).

   The 'Protocol Addr of Sender' field SHALL be the 4-byte IP address of
   the Requester (InARP Request) or Responder (InARP Reply).

   The 'HW Addr of Target' field SHALL be set to the 6-byte MAC address
   of the Responder in an InARP Request and to the 6-byte MAC address of
   the Requester in an InARP Reply.

   The 'Protocol Addr of Target' field SHALL be set to 0x00-00-00-00 in
   an InARP Request and to the 4-byte IP address of the Requester in an
   InARP Reply.

B.4 InARP Support Requirements

   Support for InARP is OPTIONAL. If a node does not support InARP and
   it receives an InARP Request message then a silent behavior is
   specified.

Top      Up      ToC       Page 42 
APPENDIX C: Some Informal Mechanisms for FC Layer Mappings

   Each method SHALL have some check 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 contain 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 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

   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.

Top      Up      ToC       Page 43 
      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 a 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.

Top      Up      ToC       Page 44 
Appendix D:  FC Layer Address Validation

D.1 General Discussion

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

   After a FC 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.

Top      Up      ToC       Page 45 
D.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].

D.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 G.)

   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].

   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.

D.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.

   If the WW_PN and WW_NN of the fabric FL_Port contained in the FAN ELS
   or FLOGI response exactly match the values before the LIP, and if the
   AL_PA obtained by the port is the same as the one before the LIP,
   then 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.

Top      Up      ToC       Page 46 
   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

D.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].

Top      Up      ToC       Page 47 
APPENDIX E: Fibre Channel Overview

E.1 Brief Tutorial

   The 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 has been architected to
   provide a place holder for functions that might need to be performed
   after the upper layer protocol has requested the transmission of an
   information unit, but before FC-2 is asked to deliver that piece of
   information by using a sequence of frames [18]. At this time, no FC-3
   functions have been defined.  FC-4 is meant for supporting profiles
   of Upper Layer Protocols (ULP) such as IP and Small Computer System
   Interface (SCSI), and supports a relatively small set 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.  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 Point-to-Point, Private Loop,
   Public Loop (attachment to a Fabric), or Fabric network topologies.

   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. For a
   detail description of FC topologies refer to [18].

   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.

Top      Up      ToC       Page 48 
  +-----------+-------------+-----------------------------------------+
  | Port Type |  Location   |      Topology Associated with           |
  +-----------+-------------+-----------------------------------------+
  | 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           |
  +-----------+-------------+-----------------------------------------+

E.2 Exchange, Information Unit, Sequence, and Frame

   The FC 'Exchange' is a mechanism used by two FC ports to identify and
   manage an operation between them [18]. An Exchange is opened whenever
   an operation is started between two ports. The Exchange is closed
   when this operation ends.

   The FC-4 Level specifies data units for each type of application
   level payload called 'Information Unit' (IU). Each protocol carried
   by FC has a defined size for the IU. Every operation must have at
   least one IU.  Lower FC levels map this to a FC 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 [18]. With the use of Sequence Count, data blocks
   are sent using frames with increasing sequence counts (modulo 65536)
   and it is quite straightforward to detect the first frame that
   contains the Network_Header.  When Relative Offset is used, as frames
   arrive, some computation is required to detect the first frame that
   contains the Network_Header. Sequence Count and Relative Offset field
   control information, is carried in the FC Header.

   The FC-4 Level makes a request to FC-3 Level when it wishes it to be
   delivered.  Currently, there are no FC-3 level defined functions, and
   this level simply converts the Information Unit delivery request into
   a 'Sequence' delivery request and passes it on to the FC-2 Level.
   Therefore, each FC-4 Information Unit corresponds to a FC-2 Level
   Sequence.

   The maximum data carried by a FC frame cannot exceed 2112-bytes [2].
   Whenever, the Information Unit exceeds this value, the FC-2 breaks it
   into multiple frames and sends it in a sequence.

Top      Up      ToC       Page 49 
   There can be multiple Sequences within an Exchange. Sequences within
   an Exchange are processed sequentially. Only one Sequence is active
   at a time. Within an Exchange information may flow in one direction
   only or both. If bi-directional then one of the ports has the
   initiative to send the next Sequence for that Exchange. Sequence
   Initiative can be passed between the ports on the last frame of
   Sequence when control is transferred. This amounts to half-duplex
   behavior.

   Ports may have more than one Exchange open at a time. Ports can
   multiplex between Exchanges. Exchanges are uniquely identified by
   Exchange IDs (X_ID). An Originator OX_ID and a Responder RX_ID
   uniquely identify an Exchange.

E.3 Fibre Channel Header Fields

   The FC header as shown in the diagrams below 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.

   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.

Top      Up      ToC       Page 50 
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 ...                            |
 +---+----------------+----------------+----------------+--------------+

   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.

Top      Up      ToC       Page 51 
   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.

   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.

Top      Up      ToC       Page 52 
E.4 Code Points for FC Frame

E.4.1 Code Points with IP and ARP Packets

   The Code Points for FC Frames with IP and ARP Packets are very
   similar with the exception of PID value in Word 11 which is set to
   0x08-00 for IP and 0x08-06 for ARP. Also, the Network_Header appears
   only in the first logical frame of a FC Sequence carrying IP. In the
   case, where FC frames carry ARP packets it is always present because
   these are single frame Sequences.

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

Top      Up      ToC       Page 53 
              Code Points for FC Frame with ARP 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)                      |
 +---+----------------+----------------+----------------+------------+
 |10 |     0xAA       |     0xAA       |      0x03      |     0x00   |
 +---+----------------+----------------+----------------+------------+
 |11 |           0x00-00               |             0x08-06         |
 +---+----------------+----------------+----------------+------------+
 |12 |                   ARP Packet Data                             |
 +---+----------------+----------------+----------------+------------+
 |13|                        ...                                     |
 +---+----------------+----------------+----------------+------------+

   The Code Points for a FARP-REQ for a specific Match Address Code
   Point MATCH_WW_PN_NN ( b'011') is shown below. In particular, note
   the IP addresses field of the Requester set to a valid address and
   that of the responder set to '0'. Note also the setting of the D_ID
   address and the Port_ID of the Responder.

   The corresponding code point for a FARP-REPLY is also shown below.
   In particular, note the setting of the Port_ID of Responder and the
   IP address setting of the Responder.

Top      Up      ToC       Page 54 
E.4.2 Code Points with FARP Command

     Code Points for FC Frame with FARP-REQ Command for MATCH_WW_PN_NN
 +---+----------------+----------------+----------------+------------+
 |Wrd|    <31:24>     |    <23:16>     |    <15:08>     |    <07:00> |
 +---+----------------+----------------+----------------+------------+
 | 0 |    0x04        |                     D_ID =                   |
 |   |                |    0xFF             0xFF              0xFF   |
 +---+----------------+----------------+----------------+------------+
 | 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 |     0x54       |     0x00       |     0x00       |    0x00    |
 +---+----------------+----------------+----------------+------------+
 | 7 |           Port_ID  of Requester = S_ID           |Match Addr. |
 |   |                                                  |Code Points |
 |   |                                                  | xxxxx011   |
 +---+----------------+----------------+----------------+------------+
 | 8 |           Port_ID  of Responder   =              |Responder   |
 |   |     0x00              0x00            0x00       |Flags       |
 +---+----------------+----------------+----------------+------------+
 | 9 | 0001 |        0x000             |WW_PN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |10 |         WW_PN Src. MAC (Lo order bits)                        |
 +---+------+----------+---------------+-----------------------------+
 |11 | 0001 |        0x000             |WW_NN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |12 |         WW_NN Src. MAC (Lo order bits)                        |
 +---+----------------+----------------+----------------+------------+
 |13 | 0001 |        0x000             |WW_PN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |14 |         WW_PN Dest. MAC (Lo order bits)                       |
 +---+------+----------+---------------+-----------------------------+
 |15 | 0001 |        0x000             |WW_NN Dest.MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |16 |         WW_NN Dest. MAC (Lo order bits)                       |
 +---+----------------+----------------+----------------+------------+
 |17 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |18 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+

Top      Up      ToC       Page 55 
 |19 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |20 |     set to a valid IPv4 Address by Requester if Available     |
 +--------------------+----------------+---------+-------------------+
 |21 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |22 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |23 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |   |                           0x00-00-00-00                       |
 |24 |       set to a valid IPv4 Address of Responder if available   |
 +--------------------+----------------+---------+-------------------+

Top      Up      ToC       Page 56 
            Code Points for FC Frame with FARP-REPLY Command
 +---+----------------+----------------+----------------+------------+
 |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 |     0x55       |     0x00       |     0x00       |    0x00    |
 +---+----------------+----------------+----------------+------------+
 | 7 |           Port_ID  of Requester = D_ID           | xxxxx011   |
 +---+----------------+----------------+----------------+------------+
 | 8 |           Port_ID  of Responder = S_ID           |Resp. Flag  |
 +---+----------------+----------------+----------------+------------+
 | 9 | 0001 |        0x000             |WW_PN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |10 |         WW_PN Src. MAC (Lo order bits)                        |
 +---+------+----------+---------------+-----------------------------+
 |11 | 0001 |        0x000             |WW_NN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |12 |         WW_NN Src. MAC (Lo order bits)                        |
 +---+----------------+----------------+----------------+------------+
 |13 | 0001 |        0x000             |WW_PN Src. MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |14 |         WW_PN Dest. MAC (Lo order bits)                       |
 +---+------+----------+---------------+-----------------------------+
 |15 | 0001 |        0x000             |WW_NN Dest.MAC(Hi order bits)|
 +---+------+---------+----------------+----------------+------------+
 |16 |         WW_NN Dest. MAC (Lo order bits)                       |
 +---+----------------+----------------+----------------+------------+
 |17 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |18 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |19 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |20 |       set to a valid IPv4 Address by Requester                |
 +--------------------+----------------+---------+-------------------+
 |21 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+

Top      Up      ToC       Page 57 
 |22 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |23 |                           0x00-00-00-00                       |
 +--------------------+----------------+---------+-------------------+
 |24 |        set to a valid IPv4 Address by Responder               |
 +--------------------+----------------+---------+-------------------+

Top      Up      ToC       Page 58 
APPENDIX F: Fibre Channel Protocol Considerations

F.1 Reliability In Class 3

   Problem: Sequence ID reuse in Class 3 can conceivably result in
   missing frame aliasing, which could result in delivery of corrupted
   (incorrectly-assembled) data, with no corresponding detection at the
   FC 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 in Section
          B.1 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.

F.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
   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

Top      Up      ToC       Page 59 
   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.

Top      Up      ToC       Page 60 
Appendix G: 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.

   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.

Top      Up      ToC       Page 61 
   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_NN).

   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_PN), 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).

   PLOGI: Port Login.

Top      Up      ToC       Page 62 
   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.

Top      Up      ToC       Page 63 
Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.