RFC 2625
IP and ARP over Fibre Channel
Appendix B: InARP
B.1 General Discussion
Inverse ARP (InARP) is a mechanism described in RFC 1293/2390 [15, 16], which is useful when a node desires to know the protocol address of a target node whose hardware address is known. Situations where this could occur are described in [15, 16]. The motivation for using InARP in FC is to allow a node to learn the IP address of another node with which it has performed a Port Login (PLOGI). PLOGI is a normal FC process that happens between nodes, independent of this standard. PLOGI makes it possible for a node to discover the WW_PN and the Port_ID of the other node but not its IP address. A node in this way may potentially obtain the IP address of all nodes with which it can PLOGI. Note that the use of the InARP mechanism can result in resolving all WW_PN to IP addresses and ARP may no longer be required. This can be beneficially applied in cases where a particular FC topology makes it inefficient to send out an ARP broadcast.B.2 InARP Protocol Operation
InARP uses the same ARP Packet format but with different 'Op Codes', one for InARP Request and another for InARP Reply. The InARP protocol operation is very simple. The requesting node fills the hardware address (WW_PN) of the target device and sets the protocol address to 0x00-00-00-00. Because, the request is sent to a node whose WW_PN and Port_ID are known, there is no need for a broadcast. The target node fills in its Protocol address (IP address in this case) and sends an InARP Reply back to the sender. A node may collect, all such WW_PN and IP addresses pairs in a similar way.B.3 InARP Packet Format
Since the InARP protocol uses the same packet format as the ARP protocol, much of the discussion on ARP formats given in Section 4 applies here. The InARP is 28-bytes long in this application and uses two packet types: Request and Reply. Like ARP, the InARP Packet fields are common to both InARP Requests and InARP Replies. InARP Request and Reply Packets are encapsulated in a single frame FC Sequence much like ARP. Compliant InARP Request and Reply FC Sequences SHALL include Network_Headers.
The 'HW Type' field SHALL be set to 0x00-01.
The 'Protocol' field SHALL be set to 0x08-00 indicating IP protocol.
The 'HW Addr Length' field SHALL be set to 0x06 indicating 6-bytes of
HW address.
The 'Protocol Addr Length' field SHALL be set to 0x04 indicating
4-bytes of IP address.
The 'Operation' Code field SHALL be set as follows:
0x00-08 for InARP Request
0x00-09 for InARP Reply
The 'HW Addr of Sender' field SHALL be the 6-byte IEEE MAC address of
the Requester (InARP Request) or Responder (InARP Reply).
The 'Protocol Addr of Sender' field SHALL be the 4-byte IP address of
the Requester (InARP Request) or Responder (InARP Reply).
The 'HW Addr of Target' field SHALL be set to the 6-byte MAC address
of the Responder in an InARP Request and to the 6-byte MAC address of
the Requester in an InARP Reply.
The 'Protocol Addr of Target' field SHALL be set to 0x00-00-00-00 in
an InARP Request and to the 4-byte IP address of the Requester in an
InARP Reply.
B.4 InARP Support Requirements
Support for InARP is OPTIONAL. If a node does not support InARP and
it receives an InARP Request message then a silent behavior is
specified.
APPENDIX C: Some Informal Mechanisms for FC Layer Mappings
Each method SHALL have some check to ensure PLOGI has completed successfully before data is sent. A related concern in large networks is limiting concurrent logins to only those ports with active IP traffic.C.1 Login on Cached Mapping Information
This method insulates the level performing Login from the level interpreting ARP. It is more accommodating of non-ARP mechanisms for building the FC-layer mapping table. 1. Broadcast messages that carry a Network_Header contain the S_ID on the FC-header and WW_PN in the Network-Header. Caching this information provides a correlation of Port_ID to WW_PN. If the received Broadcast message is compliant with this specification, the WW_PN will contain the MAC Address. 2. The WW_PN is "available" if Login has been performed to the Port_ID and flagged. If Login has not been performed, the WW_PN is "unavailable". 3. If an outbound packet is destined for a port that is "unavailable", the cached information (from broadcast) is used to look up the Port_ID. 4. After sending an ELS PLOGI command (Port Login) to the Port (from a higher level entity at the host), waiting for an outbound packet before sending this Port Login conserves resources for only those ports which wish to establish communication. 5. After Port Login completes (ACC received), the outbound packet can be forwarded. At this point in time, both ends have the necessary information to complete their <IP address, MAC Address, Port_ID> association.C.2 Login on ARP Parsing
This method performs Login sooner by parsing ARP before passing it up to higher levels for IP/MAC Address correlation. It requires a low- level awareness of the IP address, and is therefore protocol- specific. 1. When an ARP Broadcast Message is received, the S_ID is extracted from the FC-header and the corresponding Network_Source_Address from the Network_Header.
2. The ARP payload is parsed to determine if
(a) this host is the target of the ARP request (Target IP
Address match), and
(b) if this host is currently logged in with the port
(Port_ID = S_ID) originating the ARP broadcast.
3. The ARP is passed to a higher level for ARP Response
generation.
4. If a Port Login is required, an ELS PLOGI command (Port Login)
is sent immediately to the Port originating the ARP Broadcast.
5. After Port Login completes, an ARP response can be forwarded.
Note that there are two possible scenarios:
- The ACC to PLOGI returns before the ARP reply is processed
and the ARP Reply is immediately forwarded.
- The ARP reply is delayed, waiting for ACC (successful
Login).
6. At this point in time, both ends have the necessary
information to complete their
<IP address, MAC Address, Port_ID> association.
C.3 Login to Everyone
In Fibre Channel topologies with a limited number of ports, it may be
efficient to unconditionally Login to each port. This method is
discouraged in fabric and public loop environments.
After Port Login completes, the MAC Address to Port_ID Address tables
can be constructed.
C.4 Static Table
In some loop environments with a limited number of ports, a static
mapping from a MAC Address to Port_ID (D_ID or AL_PA) may be
maintained. The FC layer will always know the destination Port_ID
based on the table. The table is typically downloaded into the driver
at configuration time. This method scales poorly, and is therefore
not recommended.
Appendix D: FC Layer Address Validation
D.1 General Discussion
At all times, the <WW_PN, Port_ID> mapping MUST be valid before use. There are many events that can invalidate this mapping. The following discussion addresses conditions when such a validation is required. After a FC link interruption occurs, the Port_ID of a port may change. After the interruption, the Port_IDs of all other ports that have previously performed PLOGI (N_Port Login) with this port may have changed, and its own Port_ID may have changed. Because of this, address validation is required after a LIP in a loop topology [7] or after NOS/OLS in a point-to-point topology [6]. Port_IDs will not change as a result of Link Reset (LR),thus address validation is not required. In addition to actively validating devices after a link interruption, if a port receives any FC-4 data frames (other than broadcast frames), from a port that is not currently logged in, then it shall send an explicit Extended Link Service (ELS) Request logout (LOGO) command to that port. ELS commands (Requests and Replies) are used by an N_Port to solicit a destination port (F_Port or N_Port) to perform some link-level function or service.) The LOGO Request is used to request invalidation of the service parameters and Port_ID of the recipient N_Port. The level of initialization and subsequent validation and recovery reported to the upper (FC-4) layers is implementation-specific. In general, an explicit Logout (LOGO) SHALL be sent whenever the FC- Layer mapping between the Port_ID and WW_PN of a remote port is removed. The effect of power-up or re-boot on the mapping tables is outside the scope of this specification.
D.2 FC Layer Address Validation in a Point-to-Point Topology
No validation is required after LR. In a point-to-point topology, NOS/OLS causes implicit Logout of each port and after a NOS/OLS, each port must perform a PLOGI [2].D.3 FC Layer Address Validation in a Private Loop Topology
After a LIP, a port SHALL not transmit any link data to another port until the address of the other port has been validated. The validation consists of completing either ADISC or PDISC. (See Appendix G.) ADISC (Address Discovery) is an ELS command for discovering the hard addresses - the 24-bit identifier- of NL_Ports [5], [6]. PDISC (Discover Port) is an ELS command for exchanging service parameters without affecting Login state [5], [6]. As a requester, this specification prohibits PDISC and requires ADISC. As a responder, an implementation may need to respond to both ADISC and PDISC for compatibility with other FC specifications. If the three addresses, Port_ID, WW_PN, WW_NN, exactly match the values prior to the LIP, then any active exchanges may continue. If any of the three addresses have changed, then the node must be explicitly Logged out [4], [5]. If a port's N_Port ID changes after a LIP, then all active Port-ID to WW_PN mappings at this port must be explicitly Logged out.D.4 FC Layer Address Validation in a Public Loop Topology
A FAN (Fabric Address Notification) ELS command is sent by the fabric to all known previously logged in ports following an initialization event. Therefore, after a LIP, hosts may wait for this notification to arrive or they may perform a FLOGI. If the WW_PN and WW_NN of the fabric FL_Port contained in the FAN ELS or FLOGI response exactly match the values before the LIP, and if the AL_PA obtained by the port is the same as the one before the LIP, then the port may resume all exchanges. If not, then FLOGI (Fabric Login) must be performed with the fabric and all nodes must be explicitly Logged out.
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-XXD.5 FC Layer Address Validation in a Fabric Topology
No validation is required after LR (link reset). After NOS/OLS, a port must perform FLOGI. If, after FLOGI, the S_ID of the port, the WW_PN of the fabric, and the WW_NN of the fabric are the same as before the NOS/OLS, then the port may resume all exchanges. If not, all nodes must be explicitly, Logged out [2].
APPENDIX E: Fibre Channel Overview
E.1 Brief Tutorial
The FC Standard [2] defines 5 "levels" (not layers) for its protocol description: FC-0, FC-1, FC-2, FC-3, and FC-4. The first three levels (FC-0, FC-1, FC-2) are largely concerned with the physical formatting and control aspects of the protocol. FC-3 has been architected to provide a place holder for functions that might need to be performed after the upper layer protocol has requested the transmission of an information unit, but before FC-2 is asked to deliver that piece of information by using a sequence of frames [18]. At this time, no FC-3 functions have been defined. FC-4 is meant for supporting profiles of Upper Layer Protocols (ULP) such as IP and Small Computer System Interface (SCSI), and supports a relatively small set compared to LAN protocols such as IEEE 802.3. FC devices are called "Nodes", each of which has at least one "Port" to connect to other ports. A Node may be a workstation, a disk drive or disk array, a camera, a display unit, etc. A "Link" is two unidirectional paths flowing in opposite directions and connecting two Ports within adjacent Nodes. FC Nodes communicate using higher layer protocols such as SCSI and IP and are configured to operate using Point-to-Point, Private Loop, Public Loop (attachment to a Fabric), or Fabric network topologies. The point-to-point is the simplest of the four topologies, where only two nodes communicate with each other. The private loop may connect a number of devices (max 126) in a logical ring much like Token Ring, and is distinguished from a public loop by the absence of a Fabric Node participating in the loop. The Fabric topology is a switched network where any attached node can communicate with any other. For a detail description of FC topologies refer to [18]. Table below summarizes the usage of port types depending on its location [12]. Note that E-Port is not relevant to any discussion in this specification but is included below for completeness.
+-----------+-------------+-----------------------------------------+ | Port Type | Location | Topology Associated with | +-----------+-------------+-----------------------------------------+ | N_Port | Node | Point-to-Point or Fabric | +-----------+-------------+-----------------------------------------+ | NL_Port | Node |In N_Port mode -Point-to-Point or Fabric | | | |In NL_Port mode - Arbitrated Loop | +-----------+-------------+-----------------------------------------+ | F_Port | Fabric | Fabric | +-----------+-------------+-----------------------------------------+ | FL_Port | Fabric | In F_Port mode - Fabric | | | | In FL_Port mode - Arbitrated Loop | +-----------+-------------+-----------------------------------------+ | E_Port | Fabric | Internal Fabric Expansion | +-----------+-------------+-----------------------------------------+E.2 Exchange, Information Unit, Sequence, and Frame
The FC 'Exchange' is a mechanism used by two FC ports to identify and manage an operation between them [18]. An Exchange is opened whenever an operation is started between two ports. The Exchange is closed when this operation ends. The FC-4 Level specifies data units for each type of application level payload called 'Information Unit' (IU). Each protocol carried by FC has a defined size for the IU. Every operation must have at least one IU. Lower FC levels map this to a FC Sequence. Typically, a Sequence consists of more than one frame. Larger user data is segmented and reassembled using two methods: Sequence Count and Relative Offset [18]. With the use of Sequence Count, data blocks are sent using frames with increasing sequence counts (modulo 65536) and it is quite straightforward to detect the first frame that contains the Network_Header. When Relative Offset is used, as frames arrive, some computation is required to detect the first frame that contains the Network_Header. Sequence Count and Relative Offset field control information, is carried in the FC Header. The FC-4 Level makes a request to FC-3 Level when it wishes it to be delivered. Currently, there are no FC-3 level defined functions, and this level simply converts the Information Unit delivery request into a 'Sequence' delivery request and passes it on to the FC-2 Level. Therefore, each FC-4 Information Unit corresponds to a FC-2 Level Sequence. The maximum data carried by a FC frame cannot exceed 2112-bytes [2]. Whenever, the Information Unit exceeds this value, the FC-2 breaks it into multiple frames and sends it in a sequence.
There can be multiple Sequences within an Exchange. Sequences within an Exchange are processed sequentially. Only one Sequence is active at a time. Within an Exchange information may flow in one direction only or both. If bi-directional then one of the ports has the initiative to send the next Sequence for that Exchange. Sequence Initiative can be passed between the ports on the last frame of Sequence when control is transferred. This amounts to half-duplex behavior. Ports may have more than one Exchange open at a time. Ports can multiplex between Exchanges. Exchanges are uniquely identified by Exchange IDs (X_ID). An Originator OX_ID and a Responder RX_ID uniquely identify an Exchange.E.3 Fibre Channel Header Fields
The FC header as shown in the diagrams below contains routing and other control information to manage Frames, Sequences, and Exchanges. The Frame-header is sent as 6 transmission words immediately following an SOF delimiter and before the Data Field. D_ID and S_ID: FC uses destination address routing [12], [13]. Frame routing in a point-to-point topology is trivial. For the Arbitrated Loop topology, with the destination NL_Port on the same AL, the source port must pick the destination port, determine its AL Physical Address, and "Open" the destination port. The frames must pass through other NL_Ports or the FL_Port on the loop between the source and destination, but these ports do not capture the frames. They simply repeat and transmit the frame. Either communicating port may "Close" the circuit. When the destination port is not on the same AL, the source NL_Port must open the FL_Port attached to a Fabric. Once in the Fabric, the Fabric routes the frames again to the destination. In a Fabric topology, the Fabric looks into the Frame-header, extracts the destination address (D_ID), searches its own routing tables, and sends the frame to the destination port along the path chosen. The process of choosing a path may be performed at each fabric element or switch until the F_Port attached to the destination N_Port is reached.
Fibre Channel Frame Header, Network_Header, and Payload carrying IP
Packet
+---+----------------+----------------+----------------+--------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+--------------+
|0 | R_CTL | D_ID |
+---+----------------+----------------+----------------+--------------+
|1 | CS_CTL | S_ID |
+---+----------------+----------------+----------------+--------------+
|2 | TYPE | F_CTL |
+---+----------------+----------------+----------------+--------------+
|3 | SEQ_ID | DF_CTL | SEQ_CNT |
+---+----------------+----------------+----------------+--------------+
|4 | OX_ID | RX_ID |
+---+--------+-------+----------------+----------------+--------------+
|5 | Parameter (Control or Relative Offset for Data ) |
+---+-----------------------------------------------------------------+
|6 | NAA | Network_Dest_Address (Hi order bits) |
+---+--------+-------+----------------+----------------+--------------+
|7 | Network_Dest_Address (Lo order bits) |
+---+--------+-------+----------------+----------------+--------------+
|8 | NAA | Network_Src_Address (Hi order bits) |
+---+--------+-------+----------------+----------------+--------------+
|9 | Network_Src_Address (Lo order bits) |
+---+----------------+----------------+----------------+--------------+
|10 | DSAP | SSAP | CTRL | OUI |
+---+----------------+----------------+----------------+--------------+
|11 | OUI | PID |
+---+----------------+----------------+----------------+--------------+
|12 | IP Packet Data ... |
+---+----------------+----------------+----------------+--------------+
R_CTL (Routing Control) and TYPE(data structure):
Frames for each FC-4 can be easily distinguished from the others
at the receiving port using the R_CTL (Routing Control) and TYPE
(data structure) fields in the Frame-header.
The R_CTL has two sub-fields: Routing bits and Information
category. The Routing bits sub-field has specific values that mean
FC-4 data follows and the Information Category tells the receiver
the "Type" of data contained in the frame. The R_CTL and TYPE code
points are shown in the diagrams.
Other Header fields:
F_CTL (Frame Control) and SEQ_ID (Sequence Identification),
SEQ_CNT (Sequence Count), OX_ID (Originator exchange Identifier),
RX_ID (Responder exchange Identifier), and Parameter fields are
used to manage the contents of a frame, and mark information
exchange boundaries for the destination port.
F_CTL(Frame Control):
The FC_CTL field is a 3-byte field that contains information
relating to the frame content. Most of the other Frame-header
fields are used for frame identification. Among other things, bits
in this field indicate the First Sequence, Last Sequence, or End
Sequence. Sequence Initiative bit is used to pass control of the
next Sequence in the Exchange to the recipient.
SEQ_ID (Sequence Identifier) and SEQ_CNT (Sequence Count):
This is used to uniquely identify sequences within an Exchange.
The <S_ID, D_ID, SEQ_ID> uniquely identifies any active Sequence.
SEQ_CNT is used to uniquely identify frames within a Sequence to
assure sequentiality of frame reception, and to allow unique
correlation of link control frames with their related data frames.
Originator Exchange Identifier (OX_ID) and Responder Exchange
Identifier (RX_ID):
The OX_ID value provides association of frames with specific
Exchanges originating at a particular N_Port. The RX_ID field
provides the same function that the OX_ID provides for the
Exchange Originator. The OX_ID is meaningful on the Exchange
Originator, and the RX_ID is meaningful on the Responder.
DF_CTL (Data Field Control):
The DF_CTL field specifies the presence or absence of optional
headers between the Frame-header and Frame Payload
PARAMETER:
The Parameter field has two meanings, depending on Frame type.
For Link Control Frames, the Parameter field indicates the
specific type of Link Control frame. For Data frames, this field
contains the Relative Offset value. This specifies an offset from
an Upper Layer Protocol buffer from a base address.
E.4 Code Points for FC Frame
E.4.1 Code Points with IP and ARP Packets
The Code Points for FC Frames with IP and ARP Packets are very similar with the exception of PID value in Word 11 which is set to 0x08-00 for IP and 0x08-06 for ARP. Also, the Network_Header appears only in the first logical frame of a FC Sequence carrying IP. In the case, where FC frames carry ARP packets it is always present because these are single frame Sequences. Code Points for FC Frame with IP packet Data +---+----------------+----------------+----------------+------------+ |Wrd| <31:24> | <23:16> | <15:08> | <07:00> | +---+----------------+----------------+----------------+------------+ | 0 | 0x04 | D_ID | +---+----------------+----------------+----------------+------------+ | 1 | 0x00 | S_ID | +---+----------------+----------------+----------------+------------+ | 2 | 0x05 | F_CTL | +---+----------------+----------------+----------------+------------+ | 3 | SEQ_ID | 0x20 | SEQ_CNT | +---+----------------+----------------+----------------+------------+ | 4 | OX_ID | RX_ID | +---+----------------+----------------+----------------+------------+ | 5 | 0xXX-XX-XX-XX Parameter Relative Offset | +---+------+--------------------------------------------------------+ | 6 | 0001 | 0x000 | Dest. MAC (Hi order bits) | +---+------+---------+----------------+----------------+------------+ | 7 | Dest. MAC (Lo order bits) | +---+------+----------+----------------+----------------------------+ | 8 | 0001 | 0x000 | Src. MAC (Hi order bits) | +---+------+---------+----------------+----------------+------------+ | 9 | Src. MAC (Lo order bits) | +---+----------------+----------------+----------------+------------+ |10 | 0xAA | 0xAA | 0x03 | 0x00 | +---+----------------+----------------+----------------+------------+ |11 | 0x00-00 | 0x08-00 | +---+----------------+----------------+----------------+------------+ |12 | IP Packet Data | +---+----------------+----------------+----------------+------------+ |13 | ... | +---+----------------+----------------+----------------+------------+
Code Points for FC Frame with ARP packet Data
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+------+--------------------------------------------------------+
| 6 | 0001 | 0x000 | Dest. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 7 | Dest. MAC (Lo order bits) |
+---+------+----------+----------------+----------------------------+
| 8 | 0001 | 0x000 | Src. MAC (Hi order bits) |
+---+------+---------+----------------+----------------+------------+
| 9 | Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|10 | 0xAA | 0xAA | 0x03 | 0x00 |
+---+----------------+----------------+----------------+------------+
|11 | 0x00-00 | 0x08-06 |
+---+----------------+----------------+----------------+------------+
|12 | ARP Packet Data |
+---+----------------+----------------+----------------+------------+
|13| ... |
+---+----------------+----------------+----------------+------------+
The Code Points for a FARP-REQ for a specific Match Address Code
Point MATCH_WW_PN_NN ( b'011') is shown below. In particular, note
the IP addresses field of the Requester set to a valid address and
that of the responder set to '0'. Note also the setting of the D_ID
address and the Port_ID of the Responder.
The corresponding code point for a FARP-REPLY is also shown below.
In particular, note the setting of the Port_ID of Responder and the
IP address setting of the Responder.
E.4.2 Code Points with FARP Command
Code Points for FC Frame with FARP-REQ Command for MATCH_WW_PN_NN +---+----------------+----------------+----------------+------------+ |Wrd| <31:24> | <23:16> | <15:08> | <07:00> | +---+----------------+----------------+----------------+------------+ | 0 | 0x04 | D_ID = | | | | 0xFF 0xFF 0xFF | +---+----------------+----------------+----------------+------------+ | 1 | 0x00 | S_ID | +---+----------------+----------------+----------------+------------+ | 2 | 0x05 | F_CTL | +---+----------------+----------------+----------------+------------+ | 3 | SEQ_ID | 0x20 | SEQ_CNT | +---+----------------+----------------+----------------+------------+ | 4 | OX_ID | RX_ID | +---+----------------+----------------+----------------+------------+ | 5 | 0xXX-XX-XX-XX Parameter Relative Offset | +---+----------------+----------------+----------------+------------+ | 6 | 0x54 | 0x00 | 0x00 | 0x00 | +---+----------------+----------------+----------------+------------+ | 7 | Port_ID of Requester = S_ID |Match Addr. | | | |Code Points | | | | xxxxx011 | +---+----------------+----------------+----------------+------------+ | 8 | Port_ID of Responder = |Responder | | | 0x00 0x00 0x00 |Flags | +---+----------------+----------------+----------------+------------+ | 9 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)| +---+------+---------+----------------+----------------+------------+ |10 | WW_PN Src. MAC (Lo order bits) | +---+------+----------+---------------+-----------------------------+ |11 | 0001 | 0x000 |WW_NN Src. MAC(Hi order bits)| +---+------+---------+----------------+----------------+------------+ |12 | WW_NN Src. MAC (Lo order bits) | +---+----------------+----------------+----------------+------------+ |13 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)| +---+------+---------+----------------+----------------+------------+ |14 | WW_PN Dest. MAC (Lo order bits) | +---+------+----------+---------------+-----------------------------+ |15 | 0001 | 0x000 |WW_NN Dest.MAC(Hi order bits)| +---+------+---------+----------------+----------------+------------+ |16 | WW_NN Dest. MAC (Lo order bits) | +---+----------------+----------------+----------------+------------+ |17 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |18 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+
|19 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |20 | set to a valid IPv4 Address by Requester if Available | +--------------------+----------------+---------+-------------------+ |21 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |22 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |23 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ | | 0x00-00-00-00 | |24 | set to a valid IPv4 Address of Responder if available | +--------------------+----------------+---------+-------------------+
Code Points for FC Frame with FARP-REPLY Command
+---+----------------+----------------+----------------+------------+
|Wrd| <31:24> | <23:16> | <15:08> | <07:00> |
+---+----------------+----------------+----------------+------------+
| 0 | 0x04 | D_ID |
+---+----------------+----------------+----------------+------------+
| 1 | 0x00 | S_ID |
+---+----------------+----------------+----------------+------------+
| 2 | 0x05 | F_CTL |
+---+----------------+----------------+----------------+------------+
| 3 | SEQ_ID | 0x20 | SEQ_CNT |
+---+----------------+----------------+----------------+------------+
| 4 | OX_ID | RX_ID |
+---+----------------+----------------+----------------+------------+
| 5 | 0xXX-XX-XX-XX Parameter Relative Offset |
+---+----------------+----------------+----------------+------------+
| 6 | 0x55 | 0x00 | 0x00 | 0x00 |
+---+----------------+----------------+----------------+------------+
| 7 | Port_ID of Requester = D_ID | xxxxx011 |
+---+----------------+----------------+----------------+------------+
| 8 | Port_ID of Responder = S_ID |Resp. Flag |
+---+----------------+----------------+----------------+------------+
| 9 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|10 | WW_PN Src. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|11 | 0001 | 0x000 |WW_NN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|12 | WW_NN Src. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|13 | 0001 | 0x000 |WW_PN Src. MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|14 | WW_PN Dest. MAC (Lo order bits) |
+---+------+----------+---------------+-----------------------------+
|15 | 0001 | 0x000 |WW_NN Dest.MAC(Hi order bits)|
+---+------+---------+----------------+----------------+------------+
|16 | WW_NN Dest. MAC (Lo order bits) |
+---+----------------+----------------+----------------+------------+
|17 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|18 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|19 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|20 | set to a valid IPv4 Address by Requester |
+--------------------+----------------+---------+-------------------+
|21 | 0x00-00-00-00 |
+--------------------+----------------+---------+-------------------+
|22 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |23 | 0x00-00-00-00 | +--------------------+----------------+---------+-------------------+ |24 | set to a valid IPv4 Address by Responder | +--------------------+----------------+---------+-------------------+
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 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 Node: A collection of one or more Ports identified by a unique World Wide Node Name (WW_NN). NOS: Not Operational. A primitive Sequence transmitted to indicate that the port transmitting this Sequence has detected a link failure or is offline, waiting for OLS to be received. OLS: Off line. A primitive Sequence transmitted to indicate that the port transmitting this Sequence is either initiating the link initialization protocol, receiving and recognizing NOS, or entering the offline state. PDISC: Discover Port. An ELS for exchanging Service Parameters without affecting Login state. Primitive Sequence: A primitive Sequence is an Ordered Set that is transmitted repeatedly and continuously. Private Loop Device: A device that does not attempt Fabric Login (FLOGI) and usually adheres to PLDA. The Area and Domain components of the NL_Port ID must be 0x0000. These devices cannot communicate with any port not in the local loop. Public Loop Device: A device whose Area and Domain components of the NL_Port ID cannot be 0x0000. Additionally, to be FLA compliant, the device must attempt to open AL_PA 0x00 and attempt FLOGI. These devices communicate with devices on the local loop as well as devices on the other side of a Fabric. Port: The transmitter, receiver and associated logic at either end of a link within a Node. There may be multiple Ports per Node. Each Port is identified by a unique Port_ID, which is volatile, and a unique World Wide Port Name (WW_PN), which is unchangeable. In this document, the term "port" may be used interchangeably with NL_Port or N_Port. Port_ID: Fibre Channel ports are addressed by unique 24-bit Port_IDs. In a Fibre Channel frame header, the Port_ID is referred to as S_ID (Source ID) to identify the port originating a frame, and D_ID to identify the destination port. The Port_ID of a given port is volatile (changeable). PLOGI: Port Login.
SI: Sequence Initiative World Wide Port_Name (WW_PN): Fibre Channel requires each Port to have an unchangeable WW_PN. Fibre Channel specifies a Network Address Authority (NAA) to distinguish between the various name registration authorities that may be used to identify the WW_PN. A 4-bit NAA identifier, 12-bit field set to 0x0 and an IEEE 48-bit MAC address together make this a 64-bit field. World Wide Node_Name (WW_NN): Fibre Channel identifies each Node with a unchangeable WW_NN. In a single port Node, the WW_NN and the WW_PN may be identical.
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