rfc2625.txt

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



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RFC 2625             IP and ARP over Fibre Channel             June 1999


   With the OUI value set to 0x00-00-00, the SNAP PID value equal to
   0x08-00 indicates IP and a PID value equal to 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

3.5 Bit and Byte Ordering

   IP or ARP Packets are mapped to FC-4 Level using the big endian byte
   ordering, which corresponds to the standard network byte order or
   canonical form [20]. FC-4 Payload maps with no change in order to the
   FC-2 Level.

   FC-1 Level defines the method used to encode data prior to
   transmission and subsequently decode the data upon reception. The
   method encodes 8-bit bytes into 10-bit transmission characters to
   improve the transmission characteristics of the serial data stream.
   In Fibre Channel, data fields are aligned on word boundaries. See
   Appendix E.  A word in FC is defined as 4 bytes or 32 bits. The
   resulting transmission word after the 8-bit to 10-bit encoding
   consists of 40 bits.

   Data words or Ordered Sets (special FC-2 Level control words) from
   the FC-2 Level map to the FC-1 Level with no change in order and the
   bytes in the word are transmitted in the Most Significant Byte first
   to Least Significant Byte order. The transmission order of bits
   within each byte is the Least Significant Bit to the Most Significant
   Bit.

4. ARP

4.1 Address Resolution

   Address Resolution in this specification is primarily 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




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   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)

      2. A mapping from the WW_PN to the Port_ID (see Appendix G 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 MUST be valid before use.
   Moreover, this validation process can be different depending on the
   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.

   Other optional mechanisms in FARP that directly map an IP address to
   a Port_ID, or WW_NN to a Port_ID are described in Appendix A.

   The Inverse Address Resolution Protocol (InARP) is yet another
   optional mechanism that resolves WW_PN and Port_IDs to IP addresses.
   InARP is described in Appendix B.

4.2 ARP Packet Format

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

   The ARP uses two packet types - Request and Reply - and each type of
   packet is 28 -bytes long in this specification. The ARP Packet fields
   are common to both ARP Requests and ARP Replys.

   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.






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   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
   many do not. It is because of this reason that 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.






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

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 should first consult its local mapping tables to
         determine the <destination IP address, destination WW_PN>.

      2. If such a mapping is found, then the source sends 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 sends 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, it generates an ARP Reply.  Since the
         ARP Reply must be addressed to a specific destination Port_ID,
         the FC layer mapping between the WW_PN 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, the result is a silent
         behavior.





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RFC 2625             IP and ARP over Fibre Channel             June 1999


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 first sends 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 then removes 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

    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
         MUST NOT use the OPN(fr) signal primitive. Rather, it sends the
         broadcast sequence to the FL_Port at AL_PA = 0x00.





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RFC 2625             IP and ARP over Fibre Channel             June 1999


      2. A FC Fabric propagates 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 propagates 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