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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-04.txt>                    Wayne Rickard
(Expires July 15, 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 ...................................  5
      3.1 FC Frame Format ........................................  5
      3.2 MTU ....................................................  6
          3.2.1 IP MTU ...........................................  6
          3.2.2 Maximally Minimum IPv4 packet ....................  7
          3.2.3 ARP MTU ..........................................  7
          3.2.4 FC Payload containing FARP Packet ................  8



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      3.3 FC Port and Node Network Addresses .....................  8
      3.4 FC Payload Format ......................................  9

   4. ARP .........................................................10
      4.1 Address Resolution  .................................... 10
      4.2 ARP Packet Format ...................................... 11
      4.3 ARP Layer Mapping and Operation ........................ 13
      4.4 ARP Broadcast in a Point-to-Point Topology ............. 13
      4.5 ARP Broadcast in a Private Loop Topology ............... 13
      4.6 ARP Broadcast in a Public Loop Topology ................ 14
      4.7 ARP Operation in a Fabric Topology ..................... 14

   5. FARP ....................................................... 15
      5.1 Scope .................................................. 15
      5.2 FARP Overview .......................................... 15
      5.3 FARP Command Format .................................... 16
      5.4 Match Address Code Points .............................. 19
      5.5 Responder Flags ........................................ 19
      5.6 FARP Support Requirements .............................. 20

   6. Exchange Management ........................................ 21
      6.1 Exchange Origination ................................... 21
      6.2 Exchange Termination ................................... 21

   7. Summary of Supported Features .............................. 21
      7.1 FC-4 Header ............................................ 21
      7.2 R_CTL .................................................. 22
      7.3 F_CTL .................................................. 22
      7.4 Sequences .............................................. 23
      7.5 Exchanges .............................................. 24
      7.6 ARP  and InARP ......................................... 25
      7.7 Extended Link Services (ELS) ........................... 25
      7.8 Login Parameters ....................................... 26
          7.8.1 Common Service Parameters  - FLOGI ............... 26
          7.8.2 Common Services Parameters - PLOGI ............... 26
          7.8.3 Class Service Parameters - PLOGI ................. 26

   8. Security Considerations .....................................27

   9. Acknowledgements ........................................... 27

   10. References ................................................ 27

   11. Authors' Addresses ........................................ 28

   Appendix A: Additional Matching Mechanisms in FARP ............ 29

   Appendix B: InARP ............................................. 32
      B.1 General Discussion ..................................... 32
      B.2 InARP Protocol Operation ............................... 32
      B.3 InARP Packet Format .................................... 32
      B.4 InARP Support Requirements ............................. 33

   Appendix C: Some Informal Mechanisms for FC Layer Mappings .....33



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      C.1 Login on cached Mapping Information .................... 33
      C.2 Login on ARP parsing ................................... 34
      C.3 Login to Everyone ...................................... 34
      C.4 Static Table ........................................... 35

   Appendix D: FC Layer Address Validation........................ 35
      D.1 General Discussion ..................................... 35
      D.2 FC Layer Address Validation in a Point-to-Point Topology 35
      D.3 FC Layer Address Validation in a Private Loop Topology . 36
      D.4 FC Layer Address Validation in a Public Loop Topology .. 36
      D.5 FC layer Address Validation in a Fabric Topology ....... 36

   Appendix E: Fibre channel Overview ............................ 37
      E.1 Brief Tutorial ......................................... 37
      E.2 Exchange, Information Unit, Sequence, and Frame ........ 38
      E.3 Fibre Channel Header Fields ............................ 38
      E.4 Code Points for FC Frame ............................... 41
           E.4.1 With IP and ARP Packet .......................... 41
           E.4.2 With FARP Command ............................... 43

   Appendix F: Fibre Channel Protocol Considerations.............. 45
      F.1 Reliability in Class 3 ................................. 45
      F.2 Continuously Increasing SEQ_CNT ........................ 45

   Appendix G: Acronyms and Glossary of FC Terms ................. 46



1. Introduction

   Fibre Channel is a gigabit speed networking technology primarily used
   for Storage Area Networking (SAN). FC is standardized under American
   National Standard for Information Systems of the National Committee
   for Information Technology Standards (NCITS) 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, there exists a Fibre Channel Standard [3] that 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.





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   Objective and Scope:

   The major objective of this specification is to promote  inter-
   operable implementations of IPv4 over FC. This  specification
   describes a method for encapsulating IPv4 and Address Resolution
   Protocol (ARP) packets  over FC. This specification accommodates any
   FC topology  (loop, fabric, or point-to-point) and any FC class of
   service (1, 2  or 3). This specification also describes a FC Address
   Resolution Protocol(FARP) for associating MAC addresses to FC Port
   identifiers.

   A secondary objective of this specification is to describe other
   optional FARP mechanisms that directly build IPv4 address and FC Port
   Identifier (Port_ID) associations.  Inverse ARP (InARP) is another
   optional mechanism that is described which allows learning the IP
   address of a remote node given its MAC address and Port_ID.

   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 the ARP protocol(IP
   address to MAC address). Section 5 discusses the FARP protocol used
   in FC Layer mappings (MAC address to Port_ID).  Section 6 describes
   the "Exchange" Management in FC. Section 7 is a summary section and
   provides a quick reference to FC header settings, FC Link Service
   Commands, supported features in ARP, FARP, InARP, FC Sequences, FC
   Exchanges, and FC Login Parameters.  Section 8 discusses any security
   considerations. Section 9 acknowledges the technical contributors of
   this document. Section 10 provides a list of references, and Section
   11 provides the authors' addresses.

   Appendix A discusses other FARP mechanisms that are optional.
   Appendix B discusses the Inverse ARP protocol(MAC address to IP
   address) as an alternate and optional way to build MAC and IP address
   associations. Appendix C lists some informal mechanisms for FC Layer
   Mappings.  Appendix D provides a discussion on validation of the FC-
   layer mappings for the different FC topologies.  Appendix E provides
   a brief overview of the FC Protocols and Networks.  Appendix F
   addresses reliability in Class 3 and Sequence Count FC Protocol
   issues.  Appendix G provides a list of acronyms and a glossary of FC
   Terms used in this specification.

2. Problem Statement

   This draft addresses two problems:

     - A format definition and encapsulation mechanism for IPv4
       and ARP packets over FC
     - Mechanisms for Address Resolution

   As noted earlier, the existing FC Standards [3], [10] are inadequate
   to solve these problem. A solution to both problems was first
   proposed by the Fibre Channel Association (FCA)[1]. FCA is a industry



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   consortium of FC vendor companies and not a standards body.  This
   draft specification is based on the proposed solution in [1] and
   builds on it.

   Address Resolution is concerned with resolving IP addresses to MAC
   address and MAC addresses to FC Port Identifiers (Port_ID). ARP
   provides a solution to the first resolution problem and FARP the
   second.

   An optional FARP mechanism resolves IP address directly to FC
   Port_IDs. This is useful in some upper layer applications.

   InARP is another optional mechanism that resolves MAC and Port_IDs to
   an IP address.  InARP is useful when a node after performing a PLOGI
   with a remote node knows its WW_PN and Port_ID, but not its IP
   address.

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 E and F).  However, the exact size of each frame varies
   depending on the sizes of  the variable fields.  The size of the
   variable fields ranges from 0 to 2111 bytes as shown in the FC frame
   structure 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. Some of the values
   and options for the fields that are relevant to the IP and ARP
   payloads are discussed in Section 7.

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

        - An Expiration Security Header (16 bytes)
        - Network (16 bytes)
        - Association (32 bytes)
        - Device (up to 64 bytes).



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   The IP and ARP FC Sequences shall carry only the Network_Header
   optional header field which is 16 bytes long. Other types of optional
   headers are prohibited.  The role of the Network_Header in the IP and
   ARP payload encapsulation is described below.

   An application level payload such as IP in FC is called a Information
   Unit at the FC-4 Level. Lower FC levels map this to what is called as
   a FC Sequence.  (See Appendix E.2 for a description of Sequences and
   Information Units.)  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 and described in Appendix E.

   In FC, the physical temporal ordering of the frames as it arrives at
   a destination can be different from the order sent as a result of
   traversing through a FC Network.

   When IP forms the FC payload then only the first frame of the logical
   Sequence shall include the FC Network_Header. Fig. 2 shows the
   logical First Frame and logical subsequent frames. Since frames may
   arrive out of order, detection of the first frame of the logical FC
   Sequence is necessary.

   ARP packets map to a single frame FC Sequence and shall always carry
   the FC Network Header.

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

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

               Fig. 2 FC Network Header in a Frame Sequence

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

3.2 MTU

3.2.1 IP MTU

   An FC Information Unit specific to each protocol data such as IP is
   defined in FC-4. This defines the upper bound on the size of the
   information that can be transported.



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   Each IP or ARP Packet is mapped to a single FC Information Unit,
   which is in turn mapped to a single FC Sequence. Therefore there
   shall be a one-to-one mapping between an IP or ARP packet and a FC
   Sequence.

   Fibre Channel limits the size of a single Information Unit to 2^32-1,
   which is very large [2].  However, since the Maximum Transmission
   Unit (MTU) size of an IPv4 packet does not exceed 65,536 bytes, the
   resulting FC Payload size is far below its maximum limit. The FC
   Payload includes the FC Network Header (16 bytes), the LLC/SNAP
   Header (8 bytes), and the IP packet.

   IPv4 Packet definition includes the IP Payload and IP Headers - both
   fixed and optional.  The corresponding FC Payload includes the FC
   Network Header, the LLC/SNAP Header, and the IPv4 Packet.

   As noted above, the greatest length allowed for an IPv4 Packet
   including any optional headers and independent of this standard is
   65,536 bytes. However, limiting the IP MTU size to 65,280 bytes helps
   in buffer resource allocation at N_Ports and also allows for up to
   255 bytes of overhead. Since the FC Network Header requires 16 bytes
   and the IEEE 802.2 LLC/SNAP header requires 8 bytes, it leaves 232
   bytes for future use.

   All implementations shall restrict the IP MTU size to 65,280 bytes
   and the corresponding FC MTU size to 65536 bytes.

3.2.2 Maximally Minimum IPv4 Packet

   In order to avoid fragmentation in FC, it is useful to specify a
   minimum size FC Payload size.  This is relevant when a minimum size
   IP Packet with a fixed size IP Header and a zero byte IP Payload is
   carried in the FC Payload. More importantly is the case when, the FC
   Payload carries a maximally minimum size IP Packet, which is defined
   as an IP packet with a zero byte payload, a fixed size IP Header (20
   bytes), and the maximum size optional IP Header (48 bytes) [19].

   All implementations shall support a maximally minimum sized FC
   Payload of 92 bytes, which is required to support 68 bytes of a
   maximally minimum size IP Packet, 16 bytes of the FC Network Header,
   and 8 bytes of the LLC/SNAP Header.

3.2.3 ARP MTU

   The ARP packet has a fixed size of 28 bytes. All implementations
   shall support a FC Payload size of 52 bytes, which is required to
   support 28 bytes of an ARP Packet, 16 bytes of the FC Network Header,
   and 8 bytes of the LLC/SNAP Header. Note that the minimum MTU
   requirement for ARP is covered by the minimum MTU requirement for IP
   but it is mentioned here for completeness.

   The InARP packet is identical in size to the ARP and the same MTU
   requirements apply.




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3.2.4 FC Payload containing FARP Packet

   The FARP Command is a FC Extended Link Service (ELS) command and maps
   directly to a FC payload without the LLC/SNAP or the FC Network
   Header. The FARP Command has a fixed size of 76 bytes.  Because FARP
   operates purely in the FC space, it places no special MTU
   requirements in this specification.

3.3 FC Port and Node Network Addresses

   FC devices are identified by Nodes and their 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 Identifier (Port_ID).

   Port_IDs are 24-bits long. A FC frame header carries a Source Port_ID
   (S_ID) and the Destination Port_ID (D_ID). 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. See Appendix D).

   The FC Network Header is generally optional in FC Standards, but
   mandatory in this specification.  FC Network Headers carry source and
   destination WW_PNs. A WW_PN consists of a 60-bit Network Address and
   a upper 4-bit Network Address Authority (NAA) field as shown in Fig.
   3.  The 4-bit NAA field is used to distinguish between the various
   name registration authorities used to define the Network Address [2].

   In this specification, both the Source and Destination 4-bit NAA
   identifiers shall be set to binary '0001' indicating that an IEEE
   48-bit MAC address is contained the lower 48 bits of the network
   address fields. The high order 12 bits in the network address fields
   shall be set to 0x0000. This NAA field value allows FC networks to be
   bridged with other FC networks or traditional LANs.

            +--------+---------------------------------------+
            | 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

   FC Payload with IP:

   The payload of a FC sequence carrying an IP and ARP packet shall use
   the formats shown in Fig. 4 and 5 respectively. Both formats use the
   8-byte LLC/SNAP header.

   +-----------------+-----------+------------+-------------//----------+
   | LLC/SNAP Header | IP Header | Opt. IPHdr.|         IP Data         |
   |   (8 bytes)     | (20 bytes)| (48 bytes  | (65280 -IP Header       |
   |                 |           |   Max)     |   - Opt. Hdr.) bytes    |
   +-----------------+-----------+------------+-------------//----------+

             Fig. 4 Format of FC Sequence Payload carrying IP

   FC Payload with ARP:

   As noted earlier, FC frames belonging to the same Sequence may be
   delivered out of order over a Fabric. If the Relative Offset method
   is used to identify FC payload fragments, then the IP Header must
   appear in the frame that has a relative offset of 0.

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

             Fig. 5 Format of FC Sequence Payload carrying ARP

   FC payload with FARP:

   FARP Protocol commands are directly mapped to a FC payload and do not
   carry the LLC/SNAP or FC Network Header. FARP commands are 76 bytes
   long.

   LLC:

   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 by 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




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

   SNAP:

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

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

                            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).

   The SNAP OUI value of 0x00-80-C2 indicates Bridged Protocols.

   With the OUI value set to 0x00-00-00, the SNAP PID value of 0x08-00
   indicates IP and a PID value of 0x08-06 indicates ARP (or InARP).

   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

4. ARP

4.1 Address Resolution

   Address Resolution in this specification is concerned with
   associating IP addresses with FC Port addresses. As described
   earlier, FC device ports have two types of addresses:

      - a non-volatile unique 64-bit address called World Wide Port_Name
        (WW_PN) - a volatile 24-bit address called a Port_ID

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

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



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       2. A mapping from the WW_PN to the Port_ID (see Appendix F for a
       definition of Port_ID)

   The address resolution problem is compounded by the fact that the
   Port_ID is volatile and the second mapping has to be valid before
   use. Moreover, this validation process can be different depending on
   the FC network topology used. Appendix D provides a discussion on
   validation for the different FC topologies.

   Architecturally, the first level of mapping and control operation is
   handled by the Address Resolution Protocol (ARP), and the second
   level by the FC Address Resolution Protocol (FARP). FARP is described
   in Section 5.

   Another optional mechanism in FARP which directly maps IP addresses
   to Port_IDs is described in Appendix A.

   The Inverse Address Resolution Protocol (InARP) is yet another method
   that resolves MAC and Port_IDs to IP addresses. InARP is described
   Appendix B.

4.2 ARP Packet Format

   The Address Resolution Protocol (ARP) was designed to be a general
   purpose protocol, and to work with many network technologies, and
   with many upper layer protocols [9]. Fig 9 shows the ARP packet
   format where the upper layer protocol uses a 4 octet IP address and
   the network technology uses six-octet MAC address.

   The ARP consists of two packet types - Request and Reply  - and the
   ARP Packet is 28 bytes long in this application. The ARP Packet
   fields are common to both ARP Requests and ARP Replies. The format of
   the encapsulated ARP packet is based on [9].

   The LLC/SNAP encapsulated ARP Request Packet is mapped to a FC
   broadcast sequence and the exact mechanism used to broadcast a FC
   Sequence depends on the FC topology. This is discussed later in this
   section. Compliant ARP Request broadcasts shall include Network
   Headers.

   The LLC/SNAP encapsulated ARP Reply Packet is mapped to a FC
   Sequence. Compliant ARP Replys shall include Network Headers.

   Note that in all discussions to follow, the WW_PN and the 48-bit MAC
   address conceptually mean the same thing.

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

   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



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   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 IPv4 address.

   The 'Operation' Code field shall be set as follows:

            0x00-01 for ARP Request
            0x00-02 for ARP Reply

   The 'HW Addr of Sender' field shall be the 6 byte IEEE MAC address of
   the sender. It is either the Requester (ARP Request) or the Responder
   (ARP Reply) address.

   The 'Protocol Addr of Sender' field shall be the 4 byte IP address of
   the Requester (ARP Request) or that of the Responder (ARP Reply).

   The 'HW Addr of Target' field shall be set to zero during an ARP
   Request and to the 6 byte MAC address of the Requester (ARP Request)
   in an ARP Reply.

   The 'Protocol Addr of Target' field shall be set to the 4-byte IP
   address of the Responder (ARP Reply) in a ARP Request, and to the
   4-byte IP address of the Requester (ARP Request) in an ARP Reply.

                        +-------------------------+
                        | 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




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4.3 ARP Layer Mapping and Operation

   Whenever a FC port wishes to send IP data to another FC port, 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>.

     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 Request broadcast to its connected FC network in
        anticipation of getting a reply from the correct destination
        along with its WW_PN.

     4. When an ARP Request broadcast frame is received by a node with
        the matching IP address, then it shall generate an ARP Reply.
        Since the ARP Reply 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.

     5. If no node has the matching IP address, it results in a silent
        behavior.

4.4 ARP Broadcast in a Point-to-Point Topology

     The ARP Request (Broadcast) and Reply mechanism described above
     still apply, although there is only one node that receives the ARP
     Request.

4.5 ARP Broadcast in a Private Loop Topology

     In a private loop, the ARP Request broadcast frame 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.
           The source now sends the ARP Request as a single-frame
           broadcast Sequence in a Class 3 frame with the following
           FC Header D_ID field and F_CTL bits setting:

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

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



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

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

      4. A compliant ARP broadcast sequence frame shall include the
         Network Header with destination MAC address set to
         0xFF-FF-FF-FF-FF-FF and with NAA = b'0001'

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

4.6 ARP Broadcast in a Public Loop Topology

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

      1. A public loop device attached to a fabric through a 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 FC 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. A compliant ARP broadcast sequence frame shall include the
         Network Header with destination MAC address set to
         0xFF-FF-FF-FF-FF-FF and with NAA = b'0001'

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

4.7 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:




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               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. A compliant ARP broadcast sequence frame shall include the
         Network Header with destination MAC address set to
         0xFF-FF-FF-FF-FF-FF and with NAA = b'0001'

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

5.  FARP

5.1 Scope

   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. Name Server and FARP are two formal mechanisms that
   can be used to create and maintain WW_PN to Port_ID tables.

   The FC Address Resolution Protocol (FARP) is a method using Extended
   Link Service (ELS) commands that resolves <WW_PN, Port_ID> mappings.
   The WW_PN to Port_ID address resolution using FARP is especially
   useful for instance when the Login table entries at a node expire and
   a Name Server is not available.  It is outside the scope of this
   document to describe Name Server. (See [4].)

   Additional address matching mechanisms that resolve <WW_NN, Port_ID>
   and <IP addr., Port_ID> mapping have been added to FARP. These
   additional mechanisms are optional and described in Appendix A.
   Direct IP address to Port_ID mapping may be desirable in some
   applications where there is no visibility of the MAC address.

   Other less formal FC Layer Mapping mechanisms are described in
   Appendix C.

   Since Port_IDs are volatile, all mapped Port_IDs  at all times have
   to be valid before use. There are many events that can invalidate
   this mapping. Appendix D discusses conditions when such a validation
   is required.

5.2 FARP Overview

   The FARP protocol uses two ELS commands - FARP-REQ and FARP-REPLY.

   Note: In the following discussion 'Requester' means the node
         issuing the FARP-REQ ELS message; 'Responder' means the
         node replying to the request by sending the FARP-REPLY
         command.




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   The FARP-REQ ELS Broadcast Request command is used to retrieve a
   specific node's current Port_ID given its unique WW_PN. This Port_ID
   is sent in a FARP-REPLY unicast command.

   The FARP-REQ may indicate that the Responder:

          - Perform only a Login with it (Requester)

          - Send only a FARP-REPLY

          - Perform a Login and send a FARP-REPLY.

   No sequence initiative is transferred with the FARP-REQ and therefore
   no Reply (ACCEPT or REJECT) follows this command.

   Since a Sequence Initiative is transferred with the FARP-REPLY,
   either a ACCEPT or REJECT follows this command as a response.

   Reception of a FARP-REQ may require a higher level entity at the
   responding node to send a FARP-REPLY or perform a Port Login.

   You do not have to be logged in to issue a FARP Request. Also, you do
   not have to be logged in to the FARP Requester to issue a FARP-REPLY.

   The FARP Protocol Steps:

        FARP-REQ (ELS broadcast) Request Sequence

             (No Reply Sequence)

        FARP-REPLY (ELS command) Sequence

             Accept/Reject Reply Sequence

   The FARP Protocol Format [2]:

             FT_1

   The FARP Protocol Addressing:

          - In a FARP-REQ, the S_ID in the FC Header designates the
          Requester's Port ID. The D_ID in the FC Header is the
          broadcast identifier, 0xFF-FF-FF.

          - In a FARP-REPLY, the S_ID in the FC Header designates the
          Responder's Port_ID. The D_ID in the FC Header is the
          Requester's Port_ID.

5.3 FARP Command Format

   FARP-REQ and FARP REPLY commands have identical formats and fields
   but use different command codes. See tables below.





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   +---------------------------------------------------------------------+
   |                         FARP-REQ Command                            |
   +-------------------------------------+---------+---------------------+
   |               Field                 | Size    |   Remarks           |
   |                                     | (Bytes) |                     |
   +-------------------------------------+---------+---------------------+
   | 0x54-00-00-00                       |   4     | Request Command Code|
   +-------------------------------------+---------+---------------------+
   | Match Address Code Points           |   1     | Indicates Address   |
   |                                     |         | Matching  Mechanism |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Requester                |   3     | Supplied by         |
   |                                     |         | Requester =         |
   |                                     |         | S_ID in FC Header   |
   +-------------------------------------+---------+---------------------+
   | Responder Flags                     |   1     | Response Action to  |
   |                                     |         | be taken            |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Responder                |   3     | Set to 0x00-00-00   |
   +-------------------------------------+---------+---------------------+
   | WW_PN of Requester                  |   8     |Supplied by Requester|
   +-------------------------------------+---------+---------------------+
   | WW_NN of Requester                  |   8     |OPTIONAL;            |
   |                                     |         |See Appendix A       |
   +-------------------------------------+---------+---------------------+
   | WW_PN of Responder                  |   8     |Supplied by Requester|
   +-------------------------------------+---------+---------------------+
   | WW_NN of Responder                  |   8     |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+
   | IP Address of Requester             |   16    |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+
   | IP Address of Responder             |   16    |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+

   Following is a brief description of the address fields in the FARP
   Commands.

   Port_ID of Requester:

   It is the 24-bit Port_ID used in the S_ID field of the FC Header of a
   FARP-REQ.  It is supplied by the Requester in FARP-REQ. It is
   retained in FARP-REPLY.

   Port_ID of Responder:

   It is the 24-bit Port_ID used in the S_ID field of the FC Header of a
   FARP-REPLY.  It is set to 0x00-00-00 in a FARP-REQ. It is supplied by
   the Responder in a FARP-REPLY.

   WW_PN:

   This address field is used with the b'001' (MATCH_WW_PN) Match
   Address Code Point. See Match Address Code Point Table below. The
   Requester supplies the unique 8-byte WW_PN of the Requester and the



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   Responder. It is retained in a FARP-REPLY.

   WW_NN:

   The WW_NN address field is used with Match Address Code Points
   b'010', b'011, and b'111', which are all optional. Its usage is fully
   described in Appendix A. When the WW_NN field is not used it shall be
   either set to '0' or a valid non-zero address.

   IPv4:

   The IPv4 address field is used with the MATCH_IPv4 Match Address Code
   Points b'100', b'101', and b'111', which are all optional. Its usage
   is fully described in Appendix A. When the IP Address field is not
   used it shall be either set to '0' or a valid IP address. A valid IP
   address consists of the 32-bit IPv4 Address with the upper 96 bits
   set to '0'.

   +---------------------------------------------------------------------+
   |                         FARP-REPLY Command                          |
   +-------------------------------------+---------+---------------------+
   |               Field                 | Size    |   Remarks           |
   |                                     | (Bytes) |                     |
   +-------------------------------------+---------+---------------------+
   | 0x55-00-00-00                       |   4     | Reply Command Code  |
   +-------------------------------------+---------+---------------------+
   | Match Address Code Points           |   1     | Not Used and        |
   |                                     |         | Unchanged from the  |
   |                                     |         | FARP-REQ            |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Requester                |   3     | Extracted from      |
   |                                     |         | FARP-REQ            |
   +-------------------------------------+---------+---------------------+
   | Responder Flags                     |   1     | Not Used  and       |
   |                                     |         | Unchanged from the  |
   |                                     |         | FARP-REQ            |
   +-------------------------------------+---------+---------------------+
   | Port_ID of Responder                |   3     | Supplied by         |
   |                                     |         | Responder =         |
   |                                     |         | S_ID in FC Header   |
   +-------------------------------------+---------+---------------------+
   |WW_PN of Requester                   |   8     |Supplied by Requester|
   +-------------------------------------+---------+---------------------+
   |WW_NN of Requester                   |   8     |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+
   |WW_PN of Responder                   |   8     |Supplied by Requester|
   +-------------------------------------+---------+---------------------+
   |WW_NN of Responder                   |   8     |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+
   |IP Add. of Requester                 |   16    |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+
   |IP Address of Responder              |   16    |OPTIONAL; see App. A |
   +-------------------------------------+---------+---------------------+




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5.4 Match Address Code Points

   For each receipt 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 shown in the table below. FARP operation
   with the Match Address Code Point equal to b'001' is described in
   this section. Other code points are optional and discussed in
   Appendix A. The upper 5 bits of the Match Address Code Point byte are
   unused their use not defined.

   When a node receives a FARP-REQ with Code Point b'001', it checks its
   WW_PN against the one set in 'WW_PN of Responder' field of the FARP-
   REQ command.  If there is a match, then the node issues a response
   according to the action indicated by the FARP Responder Flag. See
   table below.

   WW_NN and IPv4 address fields are not used with the b'001' Code Point
   operation.  They shall be set to '0' or a valid address either by the
   Requester or the Requester and the Responder.

   +------------------------------------------------------------------+
   |                     Match Address Code Points                    |
   +------------------------------------------------------------------+
   |   LSBits  |     Bit name       |           Action                |
   +-----------+--------------------+---------------------------------+
   |    000    | Reserved           |                                 |
   +-----------+--------------------+---------------------------------+
   |    001    | MATCH_WW_PN        | If 'WW_PN of Responder' =       |
   |           |                    | Node's WW_PN then respond       |
   +-----------+--------------------+---------------------------------+
   |    010    | MATCH_WW_NN        | OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+
   |    011    | MATCH_WW_PN_NN     | OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+
   |    100    | MATCH_IPv4         | OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+
   |    101    | MATCH_WW_PN_IPv4   | OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+
   |    110    | MATCH_WW_NN_IPv4   | OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+
   |    111    | MATCH_WW_PN_NN_IPv4| OPTIONAL; see Appendix A        |
   +-----------+--------------------+---------------------------------+

5.5 Responder Flags

   The Responder Flags define what Responder action to take if the
   result of the Match Address Code Points is successful. 'Responder
   Flags' is an 8-bit field (bits 0-7) and is defined in the table
   below. This field is used only in a FARP-REQ.  This field is retained
   unchanged in a FARP-REPLY. If no bits are set, the Responder will
   take no action.






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   +----------+-------------------------------------------------------+
   |          |                 FARP Responder Flag                   |
   +----------+----------------+--------------------------------------+
   | Bit      | Bit Name       |            Action                    |
   | Position |                |                                      |
   +----------+----------------+--------------------------------------+
   |    0     | INIT_P_LOGI    | Initiate a P_LOGI to the Requester   |
   +----------+----------------+--------------------------------------+
   |    1     | INIT_REPLY     | Send FARP_REPLY to Requester         |
   +----------+----------------+--------------------------------------+
   | 2 to 7   | Reserved       |                                      |
   +----------+----------------+--------------------------------------+

   If INIT_P_LOGI bit is set then, a Login is performed with the port
   identified by "Port_ID of Requester" field.

   If INIT_REPLY is set then, a FARP-REPLY is sent to the Port
   Identified by "Port_ID of Requester" field

   If both bits are set at the same time, then, a FARP-REPLY is sent
   followed by a Login to the port identified by "Port_ID of Requester"
   field.

   All other bit patterns are undefined at this time and are reserved
   for possible future use.

5.6 FARP Support Requirements

   Responder action - FARP-REPLY and/or Port Login - for a successful
   MATCH_WW_PN is always required.

   Support for all other match Address Code Points is optional and a
   silent behavior from the Responder is valid when it is not supported.
   Recipients of the FARP-REQ ELS shall not issue a Service Reject
   (LS_RJT) if FARP options are not supported

   In all cases if there are no matches, then a silent behavior is
   valid.

   If an implementation issues a FARP-REQ with a Match Address Code
   Point that is optional, and fails to receive a response, then it may
   conclude that this particular option is either not supported or there
   are no address matches.

   If it concludes, that this Match Address Code Point may not be
   supported then, it may reattempt the FARP-REQ with the MATCH_WW_PN
   Code Point.

   Getting multiple FARP Replies corresponding to a single FARP-REQ
   should normally never occur.  It is beyond the scope of this document
   to specify conditions under which this error may occur or what the
   corrective action ought to be.





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6. Exchange Management

6.1 Exchange Origination

   FC Exchanges shall be established to transfer data between ports.
   Frames on IP exchanges shall not transfer Sequence Initiative. See
   Appendix E for a brief discussion on FC exchanges.

6.2 Exchange Termination

   With the exception of the recommendations in Appendix F, Section F.1,
   "Reliability 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.

7. 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.

7.1 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



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          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.

7.2 R_CTL

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

   +--------------------------------------------------------------------+
   |                      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.

7.3 F_CTL

   F_CTL in FC-Header: Word 2, bits 23-0




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   +--------------------------------------------------------------------+
   |                      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
          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.

7.4 Sequences

   +---------------------------------------------------------------------+
   |                      Feature                    |   Support  |Notes |
   +---------------------------------------------------------------------+
   | Class 2 open sequences / exchange               |     1      |   1  |
   | Length of seq. not limited by end-to-end credit | Required   |   2  |
   | IP and ARP Packet and FC Payload Sizes          | Required   |   3  |
   | Capability to receive sequence of maximum size  | Optional   |   4  |
   | Sequence Streaming                              | Prohibited |   5  |
   | Stop Sequence Protocol                          | Prohibited |      |
   | ACK_0 support                                   | Optional   |   6  |
   | ACK_1 support                                   | Required   |   6  |
   | ACK_N support                                   | Prohibited |      |
   | Class of Service for transmitted sequences      | 1, 2 or 3  |   7  |
   | Continuously Increasing Sequence Count          | Optional   | 8, 9 |
   +---------------------------------------------------------------------+
   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



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          sequences.

       3.  a) IP MTU size is 65280 bytes and resulting FC MTU size is
              65536 bytes.
           b) Maximally Min IP packet size is 68 bytes and resulting
              Maximally Min FC Payload size is 92 bytes.
           c) ARP packet (and InARP) is 28 bytes and resulting FC
              Payload size is 52 bytes.

       4. Some OS environments may not handle the max MTU of 65536. It
          is up to the administrator to configure the Max MTU for all
          systems.

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

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

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

       8. Review Appendix E, "Reliability in Class 3".

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

7.5 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.




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       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.

7.6 ARP and InARP
   +--------------------------------------------------------------------+
   |                      Feature                  |   Support  | Notes |
   +--------------------------------------------------------------------+
   | ARP Server Support                            | Prohibited |   1   |
   | Response to ARP requests                      | Required   |   2   |
   | Class of Service for ARP requests             |     3      |   3   |
   | Class of Service for ARP replies              | 1, 2 or 3  |   4   |
   | Response to InARP requests                    | Optional   |       |
   | Class of Service for InARP requests/replies   | 1, 2 or 3  |   5   |
   +--------------------------------------------------------------------+
   Notes:
      1. Well-known Address FFFFFC is not used for ARP requests. Frames
         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 Sequence, thus Class 3 is always
         used.

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

      5. An InARP Request or Reply is a normal sequence, thus an
         administrator configured class of service is used.

7.7 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   |   5   |
   | LOGO ELS command                              | Required   |       |
   | FARP-REQ/FARP-REPLY ELS commands              | Required   |   3   |
   | Other ELS command support                     | Optional   |   4   |
   +-----------------------------------------------+------------+-------+
   Notes:
       1. The administrator configured class of service is used.

       2. PDISC is prohibited as requester; ADISC should be used



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

       3. Responder action - FARP-REPLY and/or Port Login - for a
          successful MATCH_WW_PN is always required.
          Support for all other match Address Codes Points is optional;
          a silent behavior from the Responder is valid when it is not
          supported.
          Recipients of the FARP-REQ ELS shall not issue a Service
          Reject (LS_RJT) if FARP is not supported

       4. 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.

       5. Required for FL_Ports

7.8 Login Parameters

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

7.8.1 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).

7.8.2 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).

7.8.3 Class Service Parameters - PLOGI

        - Discard error policy only.



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8. Security Considerations

   FC frames are CRC protected for the header and payload using ANSI
   X3.139 specified 32-polynomial used with FDDI. Manipulation of header
   information without regenerating a new one will be easily detected.
   Independent of IP and ARP, Fibre Channel protocols do have special
   issues with security.  Use of IP or ARP over FC does not introduce
   new security threats and is for most part transparent.

   The <WW_PN, Port_ID> mappings should be valid at all times. There are
   many events that can invalidate this mapping. Appendix D discusses
   conditions when a validation is required. This type of validation is
   normally performed in FC and does not require special consideration
   in this document.

9. 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, 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 contributions to the
   FARP Protocol. The authors extend their thanks to all who provided
   comments.

10. References

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

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



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       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

   [15] RFC 1293: Inverse Address Resolution Protocol.
        T. Bradley, C. Brown. Jan. 1992, PROPOSED STD,
        Obsoleted by RFC 2390

   [16] RFC 2390: Inverse Address Resolution Protocol.
        T. Bradley, C. Brown, A. Malis Aug. 1992, DRAFT STD

   [17] RFC 791: Internet Protocol. J. Postel. Sep 01-1981.
        STANDRAD

   [18] The Fibre Channel Consultant: A Comprehensive Introduction,
        "Robert W. Kembel", Northwest Learning Associates, 1998

11. 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
   Fax: +1 714 524 8508
   Email: raj@gadzoox.com

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



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   Placentia, CA 92870

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


Appendix A: Additional Matching Mechanisms in FARP

   Section 5 described the FC Layer mapping between the WW_PN and the
   Port_ID using the FARP Protocol. This appendix describes other
   optional criteria for address matching and include:

     - WW_NN
     - WW_PN & WW_NN at the same time
     - IPv4
     - IPv4 & WW_PN at the same time
     - IPv4 & WW_PN & WW_NN at the same time

   Depending on the Match Address Code Points, the FARP protocol
   fundamentally resolves three main types of addresses to Port_IDs and
   is described in table below.

      - For Match Address Code Point b'001':
        WW_PN Names fields are used to resolve the WW_PN names to
        Port_IDs.
        WW_NN and IP address fields are not used with these Code Points
        and shall be set to either '0' or valid addresses by Requester
        or Requester and Responder.

      - For Match Address Code Point b'010':
        WW_NN Names fields are used to resolve the WW_NN names to
        Port_IDs.
        WW_PN and IP address fields are not used with these Code Points
        and shall be set to either '0' or valid addresses by Requester
        or Requester and Responder.

      - For Match Address Code Point b'100':
        IPv4 fields are used to resolve the IPv4 addresses to Port_IDs.
        WW_PN and WW_NN fields are not used with these Code Points and
        shall be set to either '0' or valid addresses by Requester or
        Requester and Responder.

      - For all other Match Address Code Points b'011', b'101',b'110',
        b'111', depending on set bits one or more addresses are jointly
        resolved to a Port_ID. See table below. If fields are not used,
        then they are set either to '0' or valid addresses

   The Responder Flags remain the same as before. Note that there can be
   utmost one FARP-REPLY per FARP-REQ.

   Tables showing FARP-REQ and FARP-REPLY and address fields setting are
   given below:




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   +--------------------------------------------------------------------+
   |                       Match Address Code Points                    |
   +--------------------------------------------------------------------+
   | LSBits|      Bit name      |             Action                    |
   +-------+--------------------+---------------------------------------+
   | 000   |   Reserved         |                                       |
   +-------+--------------------+---------------------------------------+
   | 001   | MATCH_WW_PN        | If 'WW_PN of Responder' =             |
   |       |                    | Node's WW_PN then respond             |
   +-------+--------------------+---------------------------------------+
   | 010   | MATCH_WW_NN        | If 'WW_NN of Responder' =             |
   |       |                    | Node's WW_NN then respond             |
   +-------+--------------------+---------------------------------------+
   | 011   | MATCH_WW_PN_NN     | If both 'WW_PN of Responder' &        |
   |       |                    | 'WW_NN of Responder' =                |
   |       |                    | Node's WW_PN & WW_NN then respond     |
   +-------+--------------------+---------------------------------------+
   | 100   | MATCH_IPv4         | If 'IPv4 Address of Responder' =      |
   |       |                    | Node's IPv4 Address then respond      |
   +-------+--------------------+---------------------------------------+
   | 101   | MATCH_WW_PN_IPv4   | If 'WW_PN & IPv4 of Responder' =      |
   |       |                    | Node's WW_PN and IPv4 then respond    |
   +-------+--------------------+---------------------------------------+
   | 110   | MATCH_WW_NN_IPv4   | If both 'WW_NN of Responder' &        |
   |       |                    | 'IPv4 Address of Responder' =         |
   |       |                    | Node's WW_NN & IPv4 then respond      |
   +-------+--------------------+---------------------------------------+
   | 111   |MATCH_WW_PN_NN_IPv4 | If 'WW_PN of Responder' &             |
   |       |                    | 'WW_NN of Responder' &                |
   |       |                    | 'IPv4 Address of Responder' =         |
   |       |                    | Nodes' WW_PN & WW_NN & IPv4           |
   |       |                    | then respond                          |
   +-------+--------------------+---------------------------------------+

   +---------------------------------------------------------------------+
   |                         FARP-REQ Command                            |
   +-------------------------------+---------+---------------------------+
   |               Field           | Size    |         Remarks           |
   |                               | (Bytes) |                           |
   +-------------------------------+---------+---------------------------+
   | 0x54-00-00-00                 |   4     | Request Command Code      |
   +-------------------------------+---------+---------------------------+
   | Match Address Code Points     |   1     | Indicates Address         |
   |                               |         | Matching Mechanism        |
   +-------------------------------+---------+---------------------------+
   | Port_ID of Requester          |   3     |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   | Responder Flags               |   1     |Response Action to be taken|
   +-------------------------------+---------+---------------------------+
   | Port_ID of Responder          |   3     | Set to 0x00-00-00         |
   +-------------------------------+---------+---------------------------+
   |WW_PN of Requester             |   8     | Supplied by Requester     |
   +-------------------------------+---------+---------------------------+
   |WW_NN of Requester             |   8     |OPTIONAL;                  |



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   |                               |         |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   |WW_PN of Responder             |   8     |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   |WW_NN of Responder             |   8     |OPTIONAL ;Supplied by      |
   |                               |         |Requester or Responder     |
   +-------------------------------+---------+---------------------------+
   |IP Add. of Requester           |   16    |OPTIONAL; Supplied by      |
   |                               |         |Requester                  |
   |                               |         |IPv4 Add.=low 32 bits      |
   +-------------------------------+---------+---------------------------+
   |IP Address of Responder        |   16    |OPTIONAL; Supplied by      |
   |                               |         |Requester or Responder     |
   |                               |         |IPv4 Add.=low 32 bits      |
   +-------------------------------+---------+---------------------------+

   +---------------------------------------------------------------------+
   |                         FARP-REPLY Command                          |
   +-------------------------------+---------+---------------------------+
   |               Field           | Size    |        Remarks            |
   |                               | (Bytes) |                           |
   +-------------------------------+---------+---------------------------+
   | 0x55-00-00-00                 |   4     |Reply Command Code         |
   +-------------------------------+---------+---------------------------+
   | Match Address Code Points     |   1     | Not Used and unchanged    |
   |                               |         |from the FARP-REQ          |
   +-------------------------------+---------+---------------------------+
   | Port_ID of Requester          |   3     |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   | Responder Flags               |   1     | Not Used and unchanged    |
   |                               |         |from the FARP-REQ          |
   +-------------------------------+---------+---------------------------+
   | Port_ID of Responder          |   3     |Supplied by Responder      |
   +-------------------------------+---------+---------------------------+
   |WW_PN of Requester             |   8     |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   |WW_NN of Requester             |   8     |OPTIONAL; Supplied by      |
   |                               |         |Requester                  |
   +-------------------------------+---------+---------------------------+
   |WW_PN of Responder             |   8     |Supplied by Requester      |
   +-------------------------------+---------+---------------------------+
   |WW_NN of Responder             |   8     |OPTIONAL; Supplied by      |
   |                               |         |Requester or Responder     |
   +-------------------------------+---------+---------------------------+
   |IP Add. of Requester           |   16    |OPTIONAL; Supplied by      |
   |                               |         |Requester                  |
   |                               |         |IPv4 Add.=low 32 bits      |
   +-------------------------------+---------+---------------------------+
   |IP Address of Responder        |   16    |OPTIONAL; Supplied by      |
   |                               |         |Requester or Responder     |
   |                               |         |IPv4 Add.=low 32 bits      |
   +-------------------------------+---------+---------------------------+





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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 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 messages:
   Request and Reply. Like ARP, the InARP Packet fields are common to
   both InARP Requests and InARP Replies.

   An InARP Request and Reply Packets are encapsulated in a  single
   frame FC sequence just like ARP. Compliant InARP Request and Reply FC
   Sequences shall include Network headers.

   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.



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   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
   acceptable.

APPENDIX C: Some Informal Mechanisms for FC Layer Mappings

   Each method should 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 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.



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       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

   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.




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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.

Appendix D.  FC Layer Address Validation

D.1 General Discussion

   At all times, the <WW_PN, Port_ID> mapping has to 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.

D.2 FC Layer Address Validation in a Point-to-Point Topology

   No validation is required after LR. In a point-to-point topology,



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   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.

   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



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   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].

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 [19]. 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 of 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. 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.




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   +-----------+-------------+-----------------------------------------+
   | 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 protocol called
   'Information Unit'. Each protocol (e.g. SCSI, IP) carried by FC has a
   defined size for the Information Unit. Every operation must have at
   least one Information Unit.

   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.

   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



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   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.

   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      |



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   +---+----------------+----------------+----------------+--------------+
   |11 |               OUI               |               PID             |
   +---+----------------+----------------+----------------+--------------+
   |12 |                   IP Packet Data                                |
   +---+----------------+----------------+----------------+--------------+
   |13 |                           ...                                   |
   +---+----------------+----------------+----------------+--------------+

   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.

   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.



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   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.

E.4 Code Points for FC Frame

E.4.1 Code Point 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                              |
   +---+----------------+----------------+----------------+------------+



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   |13 |                        ...                                    |
   +---+----------------+----------------+----------------+------------+

               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 that the setting of the Port_ID of Responder and
   the IP address setting of the Responder.

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   |
   +---+----------------+----------------+----------------+------------+



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   | 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                       |
   +--------------------+----------------+---------+-------------------+
   |19 |                           0x00-00-00-00                       |
   +--------------------+----------------+---------+-------------------+
   |20 |       set to a valid IPv4 Address by Requester                |
   +--------------------+----------------+---------+-------------------+
   |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   |
   +--------------------+----------------+---------+-------------------+

             Code Points for FC Frame with FARP-REPLY Command



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   +---+----------------+----------------+----------------+------------+
   |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                       |
   +--------------------+----------------+---------+-------------------+
   |22 |                           0x00-00-00-00                       |
   +--------------------+----------------+---------+-------------------+
   |23 |                           0x00-00-00-00                       |
   +--------------------+----------------+---------+-------------------+
   |24 |        set to a valid IPv4 Address by Responder               |
   +--------------------+----------------+---------+-------------------+




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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

   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



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   initiative. Any frames received from the other N_Port in the exchange
   shall have no effect on the transmitted SEQ_CNT.

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.

   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



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


   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.

   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.



Rajagopal, Bhagwat, Rickard                                    [Page 47]


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


   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.




   [draft-ietf-ipfc-fibre-channel-04.txt] [This INTERNET DRAFT expires
   on July 15, 1999]
















































Rajagopal, Bhagwat, Rickard                                    [Page 48]