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Versions: (draft-monia-ips-ifcp) 00 01 02 03
04 05 06 07 08 09 10 11 12 13 14 RFC 4172
IP Storage Working Group Charles Monia
INTERNET DRAFT Rod Mullendore
Expires November 2001 Josh Tseng
<draft-ietf-ips-ifcp-02.txt> Nishan Systems
Franco Travostino
Victor Firoiu
Nortel Networks
David Robinson
Sun Microsystems
Wayland Jeong
Troika Networks
Rory Bolt
Quantum/ATL
Paul Rutherford
ADIC
Mark Edwards
Eurologic
May 2001
iFCP - A Protocol for Internet Fibre Channel Storage Networking
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026 [1].
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed
at http://www.ietf.org/shadow.html.
Comments
Comments should be sent to the ips mailing list
(ips@ece.cmu.edu) or to the author(s).
Monia, et al. Standards Track 1
iFCP Revision 2 May 2001
Status of this Memo..............................................1
Comments.........................................................1
1. Abstract................................................4
2. About This Document.....................................4
2.1 Conventions used in this document.......................4
2.2 Purpose of this document................................4
3. iFCP Introduction.......................................4
3.1 Definitions.............................................5
3.2 The iFCP Network Model..................................6
3.3 The N_PORT Addressing Model.............................8
3.3.1 Operation in Address Transparent Mode.................11
3.3.2 Operation in Address Translation Mode.................12
3.4 iFCP Layered Services..................................16
3.4.1 Application Layer.....................................17
3.4.2 FC-4 Layer (FCP)......................................18
3.4.3 FC-2 Layer............................................18
3.4.4 iFCP Layer............................................18
4. iFCP Protocol..........................................19
4.1 Overview...............................................19
4.1.1 iFCP Transport Services...............................19
4.1.2 iFCP Support for Link Services........................19
4.2 Mandatory FC-2 Functionality...........................19
4.3 FC-2 Functionality Not Supported.......................19
4.4 Optional FC-2 Functionality............................20
5. TCP Stream Transport of iFCP Frames....................20
5.1 TCP Session Model......................................20
5.2 IFCP Session Management................................20
5.2.1 Creating an N_PORT Login Session......................20
5.2.2 Terminating an N_PORT Login Session...................21
5.3 TCP Port Numbers.......................................22
6. Encapsulation of Fibre Channel Frames..................23
6.1 Encapsulation Header Format............................23
6.1.1 Common Encapsulation Flags............................25
6.2 SOF and EOF Delimiter Fields...........................26
6.3 Frame Encapsulation and De-encapsulation...............27
7. Link Services..........................................28
7.1 Augmented Link Service Messages........................29
7.2 Augmented Link Services Requiring Payload Address
Translation.....................................................30
7.3 Augmented Link Services................................31
7.3.1 Abort Exchange (ABTX).................................32
7.3.2 Discover Address (ADISC)..............................33
7.3.3 Discover Address Accept (ADISC ACC)...................34
7.3.4 FC Address Resolution Protocol Reply (FARP-REPLY).....34
7.3.5 FC Address Resolution Protocol Request (FARP-REQ).....36
7.3.6 Logout (LOGO).........................................37
7.3.7 Port Login (PLOGI)....................................37
7.3.8 Read Exchange Concise.................................38
7.3.9 Read Exchange Concise Accept..........................39
7.3.10 Read Exchange Status Block (RES)....................40
7.3.11 Read Exchange Status Block Accept...................40
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7.3.12 Read Link Error Status (RLS)........................41
7.3.13 Read Sequence Status Block (RSS)....................42
7.3.14 Reinstate Recovery Qualifier (RRQ)..................43
7.3.15 Request Sequence Initiative (RSI)...................43
7.3.16 Third Party Process Logout (TPRLO)..................44
8. TCP Session Control Messages..........................45
8.1 Connection Bind (CBIND)...............................47
8.2 Unbind Connection (UNBIND)............................49
9. iFCP Error Detection..................................50
9.1 Overview..............................................50
9.2 Timer Definitions and Stale Frame Detection...........50
9.2.1 Error_Detect_Timeout (E_D_TOV).......................50
9.2.2 Resource Allocation Timeout (R_A_TOV.................51
10. Fabric Services Supported by an iFCP implementation...52
10.1 iFCP Support for the FC Broadcast Service.............53
11. Security..............................................54
11.1 Overview..............................................54
11.2 Physical Security.....................................54
11.3 Controlling Access....................................54
11.4 Authentication and Encryption.........................54
11.5 Storage Firewalls.....................................55
12. Quality of Service Considerations.....................55
12.1 Minimal requirements..................................55
12.2 High-assurance........................................55
13. References............................................57
13.1 Relevant SCSI (T10) Specifications....................57
10.2 Relevant Fibre Channel (T11) Specifications.........58
10.3 Relevant RFC Documents..............................58
10.4 Other Reference Documents...........................59
14. Author's Addresses....................................59
A. iFCP Support for Fibre Channel Link Services..........61
A.1 Basic Link Services...................................61
A.2 Link Services Processed Transparently.................61
A.3 Augmented Link Services...............................62
B. Performance of The Multi-Connection iFCP Session Model 64
B.1 Relationship of Throughput to Packet Losses...........64
B.2 Background............................................65
Full Copyright Statement.......................................67
Monia Standards Track 3
iFCP Revision 2 May 2001
1. Abstract
This document specifies an architecture and gateway-to-gateway
protocol for the implementation of Fibre Channel fabric
functionality on a network in which TCP/IP switching and
routing elements replace Fibre Channel components. The
protocol enables the attachment of existing Fibre Channel
storage products to an IP network by supporting the fabric
services required by such devices.
2. About This Document
2.1 Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
in RFC-2119 [2].
All frame formats are in big endian network byte order.
2.2 Purpose of this document
This is a standards-track document, which specifies a protocol
for the implementation of Fibre Channel transport services on
a TCP/IP network. Some portions of this document contain
material from standards controlled by NCITS T10 and T11. This
material is included here for informational purposes only. The
authoritative information is given in the appropriate NCITS
standards document.
The authoritative portions of this document specify the
protocol for mapping standards-compliant fibre Channel storage
and adapter implementations to TCP/IP. This mapping includes
sections of this document which describe the "iFCP Protocol"
(see section 4).
3. iFCP Introduction
iFCP is a gateway-to-gateway protocol, which provides Fibre
Channel fabric services to FCP-based Fibre Channel devices
over a TCP/IP network. iFCP uses TCP to provide congestion
control, error detection and recovery. iFCP's primary
objective is to allow interconnection and networking of
existing Fibre Channel devices at wire speeds over an IP
network.
The protocol and method of frame translation described in this
document permit the transparent attachment of Fibre Channel
Monia Standards Track 4
iFCP Revision 2 May 2001
storage devices to an IP-based fabric by means of lightweight
gateways.
The protocol achieves this transparency through an address
translation process that allows normal frame traffic to pass
through the gateway directly, with provisions for intercepting
and emulating the fabric services required by an FCP device.
3.1 Definitions
Terms needed to clarify the concepts presented in this
document are presented here.
Address-translation mode û A mode of gateway operation in
which the scope of N_PORT fabric addresses for locally
attached devices are local to the iFCP gateway.
Address-transparent mode û A mode of gateway operation in
which the scope of N_PORT fabric addresses for all
fibre channel devices are unique to the logical fabric
to which the gateway belongs.
Gateway Region û The portion of the storage network accessed
through an iFCP gateway. Devices in the region consist
of all fibre channel devices directly attached to the
gateway.
Logical Fabric û A collection of iFCP gateways configured to
interoperate together in address-transparent mode.
Fibre Channel Network - A native fibre channel fabric and all
attached Fibre Channel devices.
Fabric - The part of a Fibre Channel network that provides the
transport services defined in the FC-FS specification.
A fabric may be implemented in the IP framework by
means of the architecture and protocols discussed in
this document.
FC-2 - The Fibre Channel transport services layer described in
the FC-FS specification.
FCP Portal - An IP-addressable entity representing the point
at which a logical or physical iFCP device is attached
to the IP network.
N_PORT - An iFCP or Fibre Channel entity representing the
interface to Fibre Channel device functionality. This
interface implements the Fibre Channel N_PORT
semantics specified in the FC-FS standard [FC-FS].
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iFCP Revision 2 May 2001
N_PORT fabric address - The address of an N_PORT within the
Fibre Channel fabric.
N_PORT Network Address - The address of an N_PORT in the IP
fabric. This address consists of the IP address of
the FCP Portal and the N_PORT ID of the directly-
attached Fibre Channel device.
F_PORT - The interface used by an N_PORT to access Fibre
Channel fabric and fabric services functionality.
iFCP - The protocol discussed in this document.
Logical FCP Device - The abstraction representing a single
Fibre Channel device as it appears on an iFCP network.
iSNS - The protocol by which storage name services are
implemented. Resolution of Fibre Channel network
object names is provided by an iSNS name server.
N_PORT Session - An association created when two N_PORTS have
executed a PLOGI operation. It is comprised of the
N_PORTs and TCP connection that carries traffic
between them.
iFCP Frame - The frame inserted into the TCP stream which
contains the Fibre Channel frame and iFCP header.
Port Login (PLOGI) - The Fibre Channel Extended Link Service
(ELS) that establishes an N_PORT login session through
the exchange of identification and operation
parameters between an originating N_PORT and a
responding N_PORT.
DOMAIN_ID û The value contained in the high-order byte of a
24-bit N_PORT fibre channel address.
3.2 The iFCP Network Model
The purpose of the iFCP protocol is to enable the
implementation if Fibre Channel fabric functionality on an IP
network in which IP components and technology replace the
fibre channel infrastructure.
The following diagram shows a Fibre Channel fabric with
attached devices. These are connected to the fabric through
N_PORT and F_PORT interfaces, whose behavior is specified in
[FGS].
Within the Fibre Channel device domain, fabric-addressable
entities consist of other N_PORTs and devices internal to the
fabric that perform the fabric services defined in [FGS]. In
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iFCP Revision 2 May 2001
this case, the N_PORT Fibre Channel addresses are 24-bit
quantities that are unique within the scope of the FC fabric.
N_PORTs that perform fabric services are assigned well-known
addresses starting at the top end of the 24-bit Fibre Channel
address space.
Fibre Channel Network
+--------+ +--------+
| FC | | FC |
| Device | | Device |
|........| |........| Fibre Channel
| N_PORT |<------>| N_PORT | Device Domain
+---+----+ +----+---+ ^
| | |
+---+----+ +----+---+ |
| F_PORT | | F_PORT | |
==========+========+========+========+==============
| Fabric & | |
| Fabric Services | v
| | Fibre Channel
+--------------------------+ Fabric Domain
An iFCP Network with iFCP Gateways
Fibre Channel Devices Fibre Channel Devices
+--------+ +--------+ +--------+ +--------+
| FC | | FC | | FC | | FC |
| Device | | Device | Fibre | Device | | Device | Fibre
|........| |........| Channel |........| |........| Channel
| N_PORT | | N_PORT |<--------->| N_PORT | | N_PORT | Device
+---+----+ +---+----+ Traffic +----+---+ +----+---+ Domain
| | | | ^
+---+----+ +---+----+ +----+---+ +----+---+ |
| F_PORT | | F_PORT | | F_PORT | | F_PORT | |
=+========+==+========+===========+========+==+========+==========
| iFCP Layer |<--------->| iFCP Layer | |
|....................| ^ |....................| |
| FCP Portal | | | FCP Portal | v
+--------+-----------+ | +----------+---------+ IP
| Control | Fabric
| Data |
| |
| |
|<------Encapsulated Frames------->|
| +------------------+ |
| | | |
+------+ IP Network +--------+
| |
+------------------+
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iFCP Revision 2 May 2001
The above diagram shows the simplest implementation of an
equivalent iFCP fabric. Two gateway regions are shown. Each
consists of Fibre Channel devices directly connected to the
iFCP fabric through F_PORTs implemented as part of the edge
switch or gateway.
Looking into the F_PORT on the Fibre Channel side of the
gateway, the network appears as a Fibre Channel fabric. Here,
the gateway presents remote N_PORTs as directly attached
devices. Conversely, on the IP network side, the gateway
presents each locally connected N_PORT as a logical fibre
channel device.
An important property of this gateway architecture is that the
fabric configuration and topology within the gateway region
are opaque to the IP network. That is, the topology in the
fibre channel domain, whether it is loop- or switch-based, is
hidden from the IP network and from other gateways.
Consequently, support for such FC fabric topologies becomes a
gateway implementation option. In such cases, the gateway
incorporates whatever functionality is required to distil and
present locally attached N_PORTs (or NL_PORTs) as logical iFCP
devices.
N_PORT to N_PORT communications that traverse a TCP/IP network
require the intervention of the iFCP layer. This consists of
the following operations:
a) Execution of the frame addressing and mapping functions
described in section 3.3.
b) Execution of fabric-supplied link services addressed to
one of the well-known Fibre Channel N_PORT addresses.
c) Encapsulation of Fibre Channel frames for injection into
the TCP/IP network and de-encapsulate Fibre Channel frames
received from the TCP/IP network.
d) Establishment of an N_PORT login session in response to a
PLOGI directed to a remote device.
The following sections discuss the frame addressing mechanism
and the way in which it is used to achieve communications
transparency between N_PORTs.
3.3 The N_PORT Addressing Model
This section discusses the role of the N_PORT addressing model
in the routing of frames between locally and remotely attached
N_PORTs.
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iFCP Revision 2 May 2001
In the case of a remote N_PORT, where the frame traffic must
traverse the IP network, the gateway must perform this routing
transparently with respect to the locally attached N_PORT.
To provide such transparency, the gateway maintains an
association between the fibre channel address of a remote
N_PORT, as seen by a locally attached device, and the
corresponding address of the remote device on the IP network.
To establish this association the iFCP gateway assigns and
manages fibre channel N_PORT fabric addresses as described in
the following sections.
The fabric address of an N_PORT device is a 24-bit value
having the following format defined by the fibre channel
specification [FCS]:
Bit 23 16 15 8 7 0
+-----------+------------+----------+
| Domain ID | Area ID | Port ID |
+-----------+------------+----------+
Fibre Channel Address Format
Such addresses are volatile and subject to change based on
modifications in the fabric configuration.
In a fibre channel fabric, each switch element has a unique
Domain I/D assigned by a master switch. The value of the
Domain I/D ranges from 1 to 239 (0xEF). Each switch in turn
controls a 65K block of addresses divided into area and port
IDs. N_PORTs logging into the fabric receive a unique fabric
address consisting of the switchÆs Domain I/D concatenated
with switch-assigned area and port I/Ds.
These N_PORT addresses are carried in the fibre channel frame
as shown in the following diagram.
Bit 31 24 23 0
+--------+-----------------------------------+
Word 0 | | Destination N_PORT Address (D_ID) |
+--------+-----------------------------------+
Word 1 | | Source N_PORT Address (S_ID) |
+--------+-----------------------------------+
. | |
. | Control information |
. | and Payload |
Word 527 +--------------------------------------------+
(Max) Fibre Channel Address Fields within a Frame
The D_ID and S_ID fields represent the fabric addresses of the
source and destination N_PORTs respectively.
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iFCP Revision 2 May 2001
In an iFCP storage fabric, the iFCP gateway replaces the FC
switch element as the device responsible for N_PORT address
assignment and frame routing. Unlike an FC switch, however, an
iFCP gateway must route frames between N_PORTs within the
gateway region or to external devices attached to remote
gateways on the IP network.
In order to be FC-compatible, the gateway must route such
frames using only the embedded 24-bit address. By exploiting
its control of address allocation and access to frame traffic
entering or leaving the gateway region, it is able to achieve
the necessary transparency.
The gateway may allocate device addresses in one of two ways:
a) Address Transparent Mode û A mode of address assignment in
which several gateways collaborate to form a ælogical
fabricÆ. Each gateway in control of a region is responsible
for obtaining and distributing unique domain I/Ds from the
address assignment authority as described in section
3.3.1.1. Consequently, within the scope of the logical
fabric, the address of each N_PORT is unique. For that
reason, gateway-assigned aliases are not required to
represent remote N_PORTs.
b) Address Translation Mode û A mode of address assignment in
which the scope of all N_PORT device addresses, including
remote devices, is local to each gateway region. The
address of a remote device is represented by a gateway
assigned N_PORT alias.
All iFCP implementations MUST support operation in address
translation mode. Support for address transparent mode is
optional.
The choice of addressing mode involves the tradeoffs between
scalability, and transparency discussed below.
The scalability constraints are a consequence of the Fibre
Channel address allocation policy described above. As noted,
an IP fabric using this address allocation scheme is limited
to a combined total of 239 gateways and fibre channel switch
elements. As the system expands, an IP fabric may consist of
many switch elements distributed throughout the enterprise,
each of which controls a small number of devices. In this
case, the limitation in switch count may become a barrier to
extending and fully integrating the storage network.
Address Translation mode avoids this limitation by decoupling
N_PORT fabric addresses from the constraints of fabric-wide
address space management. Consequently, a virtually unlimited
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iFCP Revision 2 May 2001
number of iFCP gateways, Fibre Channel devices and switch
elements may be internetworked. This mode of address
allocation also simplifies management of the IP storage fabric
configuration by eliminating the need for a centralized
address-assignment authority.
A consequence of address translation mode is that the 24-bit
N_PORT address is no longer unique across the storage network.
As a result, when processing frame traffic to or from remote
N_PORTs, the gateway must intervene to translate the 24-bit
N_PORT addresses between the sending and receiving gateways.
These address operations involve:
a) Translating the N_PORT I/Ds in the frame header and
b) Translating N_PORT I/Ds carried in the payload of certain
extended link service messages.
The process of N_PORT I/D translation for the frame header is
described in section 3.3.2. The processing for link services
with frame addresses in the payload is described in section
7.1.
The details of the address transparent and address translation
operational modes are discussed in the following sections.
3.3.1 Operation in Address Transparent Mode
The use of address transparent mode is an alternative where
address transparency is desired. In addition to the
scalability limits discussed above, the following
considerations and requirements pertain to this mode of
operation:
a) There is increased dependency on the services of a central
address assignment authority, such as iSNS. If connectivity
with the server is lost, new DOMAIN_ID values cannot be
automatically allocated as gateways and fibre channel
switch elements are added to the logical fabric. As a
result, new gateways and switch elements cannot be
automatically added to the ip fabric. Of course, it is
always possible to add and manage such additional
components manually.
b) Coordination of iSNS servers is required. Multiple iFCP
gateways set up with independently-administered address
servers must be completely torn down and slaved under a
single iSNS name server before they can be configured into
the same logical fabric. In contrast, operation in address
translation mode requires only that the independent iSNS
servers import client attributes from other iSNS servers,
Monia Standards Track 11
iFCP Revision 2 May 2001
before clients under different iSNS authorities can be made
to interoperate.
c) iFCP gateways in transparent mode will not interoperate
with iFCP gateways that are not in transparent mode.
d) When interoperating with locally attached Fibre Channel
fabrics, the iFCP gateway MUST assume control of DOMAIN_ID
assignments in accordance with the appropriate Fibre
Channel standard or specification. As described in section
3.3.1.1, DOMAIN_ID values assigned to FC switches in
attached fabrics must be issued by the iSNS server or
manually assigned.
e) When operating in address transparent Mode, no fibre
channel address translation SHALL take place, and no link
service Messages shall be augmented with additional
information by the iFCP layer.
The process for establishing the TCP/IP context associated
with an N_PORT login session in this mode is similar to that
specified for address translation mode (section 3.3.2).
3.3.1.1 Transparent Mode Domain I/D Management
As described above, each gateway and fibre channel switch in a
logical fabric must have a unique domain I/D. In a gateway
region containing fibre channel switch elements, each element
obtains a domain I/D by querying a master switch element as
described in [FC-SW] -- in this case the iFCP gateway itself.
The gateway in turn may obtain domain I/Ds on demand from a
central address allocation authority, such as an iSNS name
server or manually from a pre-assigned block of IDs. In that
sense, the address authority (e.g., iSNS) assumes the role of
master switch for the logical fabric.
3.3.1.2 Incompatibility with Address Translation Mode
iFCP gateways in address transparent mode shall not originate
or accept frames that do not have the TRN bit set to one in
the iFCP flags field of the encapsulation header (see section
6.1). The iFCP gateway shall immediately terminate any N_PORT
sessions with the iFCP gateway from which it receives such
frames.
3.3.2 Operation in Address Translation Mode
This section summarizes the process for modifying FC frame
addresses embedded in the frame header.
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iFCP Revision 2 May 2001
As described above, the iFCP gateway is responsible for
assigning Fibre Channel N_PORT addresses to locally and
remotely attached N_PORTs.
For remotely attached N_PORTs, the gateway assigns an N_PORT
alias used in place of the N_PORT address assigned by the
remote gateway. To perform this function and enable the
appropriate routing, the gateway builds and maintains a table
that maps N_PORT aliases to the appropriate TCP/IP connection
and N_PORT ID of all external N_PORTs.
The gateway opportunistically builds the store of N_PORT
addresses and TCP/IP connections for remotely attached devices
in the IP fabric by:
a) Intercepting name service requests issued by locally-
attached N_PORTs as described below or,
b) Intercepting incoming N_PORT login requests from external
Fibre Channel devices and outgoing N_PORT login requests
directed to remote N_PORTs. Such requests are used to
establish the N_PORT login session as described in section
5.1.
In response to name server requests, the iSNS server returns
the IP address and N_PORT ID pair of the remote device. The IP
address is mapped to the connection context. After saving the
context and N_PORT ID, the iFCP layer creates the 24-bit
N_PORT alias that is returned to the local N_PORT as the Fibre
Channel address of the external device.
3.3.2.1 Translation Table Maintenance
The contents of the gatewayÆs address translation tables are
updated opportunistically, in response to the name service
queries and PLOGI requests described previously. There is no
need to invalidate entries in response to changes in the
fabric configuration, since any potentially stale entries
caused by such events are self-correcting as described below.
Once a fabric has achieved steady-state operation, any event
that causes a change in the fibre channel address of a device
also causes the device to terminate all N_PORT sessions. In
the process of resuming operation, the status of the device,
including its new address, is reflected in the name serverÆs
database. The new state of the device is advertised using the
appropriate state change notifications. These, in turn,
trigger the series of port login operations described below.
For inbound PLOGI requests, the iFCP gateway simply updates
the translation table, generates the N_PORT alias and forwards
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iFCP Revision 2 May 2001
the request to the local N_PORT for processing as described
above.
For outbound requests, a fabric-attached fibre channel device
usually precedes the PLOGI with a name server query to obtain
the deviceÆs new N_PORT address. At this point, the iFCP
gateway intercepts such a request, performs the necessary iSNS
query, creates the translation table entry and returns the
assigned N_PORT alias to the requester.
After issuing the PLOGI, the N_PORT verifies that it has
logged in with the expected device by checking the device name
returned in the PLOGI response.
An N_PORT that attempts to execute a PLOGI without first
querying the name server is still required to confirm the
device name as described above.
3.3.2.2 Frame Address Translation
For outbound frames, the table of external N_PORT network
addresses are referenced to map the Destination N_PORT alias
and Source N_PORT ID to a TCP connection identifier and the
N_PORT ID assigned by the remote gateway. The translation
process for outbound frames is shown below.
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iFCP Revision 2 May 2001
Raw Fibre Channel Frame
+--------+-----------------------------------+ +--------------+
| | Destination N_PORT Alias |--->| Lookup TCP |
+--------+-----------------------------------+ | connection |
| | Source N_PORT ID |--->| and N_PORT ID|
+--------+-----------------------------------+ +------+-------+
| | | TCP
| Control information | | Conn
| and Payload | | &
+--------------------------------------------+ | N_PORT
| ID
|
After Address Translation and TCP/IP Encapsulation |
+--------------------------------------------+ Conn |
| iFCP Encapsulation |<----------+
| Header | Context |
+========+===================================+ |
| | Destination N_PORT ID |<----------+
+--------+-----------------------------------+
| | Source N_PORT ID |
+--------+-----------------------------------+
| |
| Control information |
| and Payload |
+--------------------------------------------+
For inbound frames, the store regenerates the N_PORT alias
from the TCP connection context and N_PORT ID contained in the
encapsulated FC frame. The translation process for inbound
frames is shown below.
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Network Format of Inbound Frame
+--------------------------------------------+ Conn. +--------+
| iFCP Encapsulation Header |------>| N_PORT |
| |Context| Alias |
+========+===================================+ | Lookup |
| | Destination N_PORT ID | | |
+--------+-----------------------------------+ | |
| | Source N_PORT ID |------>| |
+--------+-----------------------------------+ +----+---+
| | |N_PORT
| Control information | |Alias
| and Payload | |
+--------------------------------------------+ |
|
|
|
Frame after Address Translation and De-encapsulation |
+--------+-----------------------------------+ |
| | Destination N_PORT ID | |
+--------+-----------------------------------+ |
| | Source N_PORT Alias |<-----------+
+--------+-----------------------------------+
| |
| Control information |
| and Payload |
+--------------------------------------------+
3.3.2.3 Incompatibility with Address Transparent Mode
iFCP gateways in address translation mode shall not originate
or accept frames that have the TRN bit set to one in the iFCP
flags field of the encapsulation header. The iFCP gateway
shall immediately abort any N_PORT login sessions with the
iFCP gateway from which it receives such frames as described
in section 5.2.2.2.
3.4 iFCP Layered Services
The following diagram shows the functional layers for host
devices that support FCP.
As shown, iFCP provides a set of layered services that
transparently provide the transport services required by FCP
devices. Using the iFCP framework, any existing host FCP
implementation will execute with no modifications required.
The iFCP protocol layer consists of the data transport
services and iFCP-specific Link Services. This layer provides
transport services specific to Fibre Channel devices as
specified in [FC-PH], [FC-PH-2], and [FC-PH-3].
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This is illustrated in the following diagram, which shows the
IP Fabric consisting of the TCP/IP network and the iFCP Layer.
The IP Fabric provides the transport services for FCP, and is
a direct replacement for the transport services provided by a
Fibre Channel fabric. Meanwhile, the components in the Fibre
Channel Device Domain remain unchanged.
+---------------------------------------+ - - - - - - -
| Storage & Backup Applications |
+---------------------------------------+
| Operating System | Application
+--------------------+ | Layer
| SCSI | |
+--------------------+ | - - - - - - -
| FCP | | FC-4 Layer
+------------+-------+------------------+ - - - - - - -
| | Link Services |
| +--------------------------+ FC-2 Layer ^
| | |
| N_PORT - F_PORT Interface | Fibre Channel
| | Device Domain
<=============================================================>
| | IP Fabric
| iFCP Data Transport Service | |
| | v
| +---------------+
| |iFCP Specific | iFCP Layer
| |Link Services |
+-----------------------+---------------+ - - - - - -
| |
| TCP | Transport
| | Layer
+---------------------------------------+ - - - - - -
| |
| IP | Network
| | Layer
+---------------------------------------+ - - - - - -
| |
| Physical Transport | Link Layer
| |
+---------------------------------------+ - - - - - -
In the figure shown above, each layer leverages the services
of the layer below it.
3.4.1 Application Layer
This includes the operating system, Storage and Backup
applications, and the SCSI driver. This layer interfaces with
FCP and Link Services in the FC-2 and FC-4 layers.
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3.4.2 FC-4 Layer (FCP)
FCP is the Fibre Channel FC-4 layer application protocol used
to communicate with devices implementing the SCSI-3 command
set and architectural model. Basically, FCP divides each SCSI
I/O operation into a series of information units to be
transferred between the initiator and target.
3.4.3 FC-2 Layer
The FC-2 Layer provides the facilities for Link Services and
transfer of Fibre Channel information units as described
below.
3.4.3.1 Link Service Messages
Fibre Channel defines a series of link services defined in
Fibre Channel Physical and Signaling Interface specification
(FC-PH, FC-PH-2, FC-PH-3). These Link Service Messages
provide a set of defined functions that allow a Fibre Channel
port to send control information, or to request another port
to perform a specific function. Some Link Service messages
reference services provided internally within the Fibre
Channel fabric.
3.4.3.2 N_PORT Interface
This is an interface which provides access to Fibre Channel
device functionality. The N_PORT interface is responsible for
segmentation and reassembly of information units from Fibre
Channel frames.
3.4.3.3 F_PORT Interface
This is the interface through which the N_PORT accesses the
Fibre Channel fabric.
3.4.4 iFCP Layer
The iFCP layer provides three essential services for FCP-based
storage products:
a) Transport of Fibre Channel frames and Link Service
messages between N_PORTs
b) Support for special Link Service messages needed by iFCP
to manage the transmission of storage data on a IP
network.
c) Augmentation of some Link Service messages with additional
data needed in the iFCP environment.
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The iFCP layer maps Fibre Channel frames to a predetermined
TCP connection for transport. Additionally, many link service
messages can similarly be transported without modification
over a TCP connection.
4. iFCP Protocol
4.1 Overview
4.1.1 iFCP Transport Services
The iFCP transport services map the Fibre Channel frames
comprising each FCP IU and Link Service message to a
predetermined TCP connection for transport across an IP
network. When receiving FCP-based storage data from the
network, the iFCP layer transports, and delivers each
resulting frame to the appropriate N_PORT. Except for the
augmented ELS requests in section 7.1, the iFCP layer never
interprets the contents of the frame payload.
For incoming iFCP frames with control data, iFCP interprets
the augmented information, modifies the frame content
accordingly, and may forward the resulting frame to the N_PORT
for further processing.
For out-bound Fibre Channel frames that require control data,
the iFCP layer creates the augmented information based on
frame content, modifies the frame content, then transmits the
resulting Fibre Channel frame with augmented data through the
appropriate TCP connection.
4.1.2 iFCP Support for Link Services
Some Link Service messages contain N_PORT addresses in the
payload. When a gateway operating in address translation mode
encounters such messages, it will augment the information in
the payload by adding additional information. The receiving
gateway will reference the augmented information in order to
reconstruct the original Link Service message. The
reconstructed frames are then forwarded to the receiving
N_PORT for further processing.
Section 7.1 describes augmented Link Services in detail.
4.2 Mandatory FC-2 Functionality
[To be specified]
4.3 FC-2 Functionality Not Supported
[To be specified]
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4.4 Optional FC-2 Functionality
[To be specified]
5. TCP Stream Transport of iFCP Frames
TCP connections MAY be established between FCP_Portals that
have discovered each other through a naming service or through
manual configuration. If a TCP connection is not maintained
between the FCP_Portals, then a change in the status of remote
N_PORTs must be discovered through a central name server
authority.
Multiple TCP connections may exist between pairs of FCP
Portals. Such connections are either "bound" or "unbound".
An unbound connection is a TCP connection that is not actively
supporting an N_PORT login session. Pre-existing TCP
connections between FCP Portals remain unbound and uncommitted
until a CBIND message (see section 7.2.2) has been transmitted
through them.
When the iFCP layer detects a Port Login (PLOGI) message
creating a login session between a pair of N_PORTs, it will
select an existing unbound TCP connection or establish a new
TCP connection, and send the CBIND message down that TCP
connection. This allocates the TCP connection to that PLOGI
login session. A TCP connection may not be bound to more than
one N_PORT login session.
5.1 TCP Session Model
iFCP uses a single TCP connection to transport all Fibre
Channel frames between unique pairs of N_PORTs. A TCP
connection may be used by one and only one N_PORT login
session.
5.2 IFCP Session Management
This section describes the protocols for establishing and
terminating an N_PORT login session. One and only one N_PORT
login session SHALL exist between an N_PORT pair.
5.2.1 Creating an N_PORT Login Session
The gateway SHALL initiate the creation of an N_PORT login
session in response to a PLOGI ELS directed to a remote N_PORT
from a locally attached N_PORT as described in the following
steps.
a) Allocate a TCP connection to the remote gateway. An
existing connection in the Unbound state may be used or a
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new connection may be created and placed in the Unbound
state.
b) If a connection cannot be allocated or created, the gateway
SHALL terminate the PLOGI with an LS_RJT response. The
Reason Code field in the LS_RJT message shall be set to
0x09 (Unable to Perform Command Request) and the Reason
Explanation SHALL be set to 0x29 (Insufficient Resources to
Support Login).
c) If an N_PORT login session already exists to the remote
N_PORT, the gateway SHALL forward the PLOGI ELS using the
existing session.
d) If the N_PORT login session does not exist, the gateway
SHALL issue a CBIND session control message (see section 0)
to allocate the connection and SHALL place the connection
in the Bound state if successful.
e) In the event that the CBIND message fails, the PLOGI shall
be terminated with an LS_REJ message. Depending on the
CBIND failure status, the Reason Code and Reason
Explanation SHALL be set as shown in the following table.
CBIND Failure LS_RJT Reason LS_RJT Reason Code
Status Code Explanation
------------- ------------- ------------------
Unspecified Unable to Perform No additional
Reason (0x10) Command Request explanation (0x00)
(0x0D)
No Such Device Unable to Perform Invalid N_PORT Name
(0x11) Command Request (0x0D).
(0x0D)
N_PORT Login Unable to Perform Invalid N_PORT Name
Session Already Command Request (0x0D).
Exists (0x12) (0x0D)
Lack of Unable to Perform Insufficient
Resources (0x13) Command Request Resources to Support
(0x0D). Login (0x29).
5.2.2 Terminating an N_PORT Login Session
An N_PORT login session SHALL be terminated or aborted in
response to one of the following events:
a) An LS_RJT response is returned to the gateway that issued
the PLOGI ELS. The gateway shall forward the LS_RJT to
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the local N_PORT and complete the session as described in
section 5.2.2.1.
b) An ACC received from a remote device in response to a
LOGO. The gateway shall forward the ACC to the local
N_PORT and complete the session as described in section
5.2.2.1.
c) For an FC frame received from the IP network, a gateway
detects a CRC error in the encapsulation header. The
gateway shall abort the session as described in section
5.2.2.2.
d) The TCP connection associated with the login session fails
for any reason. The gateway detecting the failed
connection shall abort the session as described in section
5.2.2.2.
5.2.2.1 N_PORT Login Session Completion
An N_PORT login session is completed in response to a rejected
PLOGI request or a successful LOGO ELS.
The gateway receiving one of the above responses shall issue
an Unbind session control ELS as described in section 8.2. An
Unbind error shall be considered a fatal gateway error.
In response to the Unbind message, either gateway may choose
to close the connection or return it to the pool of unbound
connections.
5.2.2.2 Aborting an N_PORT Login Session
An N_PORT login session SHALL be aborted if the TCP connection
is spontaneously terminated or for any other reason described
in this specification.
In any event, the TCP connection shall be closed. If the
local N_PORT has logged in to the remote N_PORT, the gateway
SHALL send a LOGO to the local N_PORT.
5.3 TCP Port Numbers
An FCP Portal uses a single port number to receive TCP
connection requests for iFCP over TCP. All TCP connections
established between FCP Portals must be directed to the
registered well known port number assigned by the IANA.
An FCP Portal may use any TCP port number consistent with its
implementation of the TCP/IP stack to initiate a TCP
connection, but each port number must be unique.
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6. Encapsulation of Fibre Channel Frames
This section describes the iFCP encapsulation of Fibre Channel
frames. The encapsulation is based on the common
encapsulation format defined in [ENCAP].
The format of an encapsulated frame is shown below:
+--------------------+
| Header |
+--------------------+-----+
| SOF | f |
+--------------------+ F r |
| FC frame content | C a |
+--------------------+ m |
| EOF | e |
+--------------------+-----+
Encapsulation Format
As shown, the encapsulation consists of a 7-word header, an
SOF delimiter word, the FC frame (including the fibre channel
CRC), and an EOF delimiter word. The header and delimiter
formats are described in the following sections.
6.1 Encapsulation Header Format
W|------------------------------Bit------------------------------|
o| |
r|3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 |
d|1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0| Protocol# | Version | -Protocol# | -Version |
+---------------+---------------+---------------+---------------+
1| Reserved (must be zero) |
+---------------+---------------+---------------+---------------+
2| LS_COMMAND | iFCP Flags | SOF | EOF |
+-----------+---+---------------+-----------+---+---------------+
3| Flags | Frame Length | -Flags | -Frame Length |
+-----------+-------------------+-----------+-------------------+
4| Time Stamp [integer] |
+---------------------------------------------------------------+
5| Time Stamp [fraction] |
+---------------------------------------------------------------+
6| CRC |
+---------------------------------------------------------------+
Common Encapsulation Fields:
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Protocol# IANA-assigned protocol number
identifying the protocol using the
encapsulation. For iFCP the value is
(/TBD/).
Version Encapsulation version
-Protocol# Ones complement of the protocol#
-Version Ones complement of the version
Flags Encapsulation flags (see 6.1.1)
Frame Length Contains the length of the entire FC
Encapsulated frame including the FC
Encapsulation Header and the FC frame
(including SOF and EOF words) in units
of 32-bit words.
-Flags Ones-complement of the Flags field.
-Frame Length Ones-complement of the Frame Length
field.
Time Stamp [integer] Integer component of the frame time
stamp in SNTP format [SNTP].
Time Stamp Fractional component of the time stamp
[fraction] in SNTP format [SNTP].
CRC Header CRC. MUST be valid for iFCP.
The time stamp fields are used to enforce the limit on the
lifetime of a fibre channel frame as described in section
9.2.2.1.
iFCP-specific fields:
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LS_COMMAND For an augmented ELS ACC response, the
LS_COMMAND field SHALL contain bits 31
through 24 of the LS_COMMAND to which
the ACC applies. Otherwise the
LS_COMMAND field shall be set to zero.
IFCP Flags IFCP-specific flags (see below)
SOF Copy of the SOF delimiter encoding
(see section 6.2)
EOF Copy of the EOF delimiter encoding
(see section 6.2)
The iFCP flags word has the following format:
|------------------------Bit----------------------------|
| |
| 23 22 21 20 19 18 17 16 |
+------+------+------+------+------+------+------+------+
| CPL | Reserved | SES | TRN | AUG |
+------+------+------+------+------+------+------+------+
iFCP Flags:
CPL Compliance level:
1 = Encapsulation complies with draft
standard or RFC of iFCP or the
encapsulation specification
0 = Encapsulation complies with
standards track version of iFCP or
the encapsulation specification
SES 1 = Session control frame (TRN and AUG MUST be
0)
TRN 1 = Address transparent mode enabled
0 = Address translation mode enabled
AUG 1 = Augmented frame.
6.1.1 Common Encapsulation Flags
The iFCP usage of the common encapsulation flags is shown
below:
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|------------------------Bit--------------------------|
| |
| 31 30 29 28 27 26 |
+--------------------------------------------+--------+
| Reserved | CRCV |
+--------------------------------------------+--------+
For iFCP, the CRC field MUST be valid and CRCV MUST be set to
one.
6.2 SOF and EOF Delimiter Fields
The format of the delimiter fields is shown below.
W|------------------------------Bit------------------------------|
o| |
r|3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 |
d|1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0|
+---------------+---------------+-------------------------------+
0| SOF | SOF | -SOF | -SOF |
+---------------+---------------+-------------------------------+
1| |
+----- FC frame content -----+
| |
+---------------+---------------+-------------------------------+
n| EOF | EOF | -EOF | -EOF |
+---------------+---------------+-------------------------------+
FC Frame Encapsulation Format
SOF (bits 31-24 and bits 23-16 in word 0): The SOF fields
contain the encoded SOF value selected from the table below.
+-------+----------+
| FC | |
| SOF | SOF Code |
+-------+----------+
| SOFf | 0x28 |
| SOFi2 | 0x2D |
| SOFn2 | 0x35 |
| SOFi3 | 0x2E |
| SOFn3 | 0x36 |
+-------+----------+
Translation of FC SOF
values to SOF field contents
-SOF (bits 15-8 and 7-0 in word 0): The -SOF fields contain
the ones complement of the value in the SOF fields.
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EOF (bits 31-24 and 23-16 in word n): The EOF fields contain
the encoded EOF value selected from the table below.
+-------+----------+
| FC | |
| EOF | EOF Code |
+-------+----------+
| EOFn | 0x41 |
| EOFt | 0x42 |
| EOFni | 0x49 |
| EOFa | 0x50 |
+-------+----------+
Translation of FC EOF values
to EOF field contents
-EOF (bits 15-8 and 7-0 in word n): The -EOF fields contain
the one's complement of the value in the EOF fields.
iFCP implementations shall place a copy of the SOF and EOF
delimiter codes in the appropriate header fields.
6.3 Frame Encapsulation and De-encapsulation
When encapsulating a frame, the frame originator MUST fill in
the header and the SOF and EOF delimiter words as specified
above.
The receiving gateway SHALL perform de-encapsulation as
follows:
Upon receiving the encapsulated frame, the gateway SHALL check
the header CRC. If the CRC is invalid, the gateway SHALL
terminate the N_PORT login session as described in section
5.2.2.2.
If the CRC is valid, any additional header validity checks are
optional. If a header check is unsuccessful, the N_PORT login
session SHALL be terminated as described in section 5.2.2.2.
After header validation, the receiving gateway MAY generate
the FC frame delimiters by:
a) Using the EOF and SOF codes in the encapsulation header or
b) By referencing the SOF and EOF delimiter words.
If the EOF and SOF delimiter words are used, the gateway must
validate the delimiter contents by verifying that the code is
legal and that the delimiter contents conform to the formats
shown above. If an invalid delimiter is detected, the gateway
SHALL terminate the N_PORT login session as specified in
section5.2.2.2.
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If the EOF and SOF in the header are used, the gateway MAY
ignore the contents of the delimiter words. The gateway
SHOULD verify that the SOF and EOF codes in the header are
legal. If an illegal code is detected, the gateway shall
terminate the N_PORT login session as specified in section
5.2.2.2.
After validating the encapsulation, the receiving gateway MAY
verify the frame propagation delay as described in section
9.2.2.1.
7. Link Services
Link services provide a set of functions that allow a port to
send control information or request another port to perform a
specific function.
Each Link Service message (response and reply) is carried by a
Fibre Channel sequence, and can be segmented into multiple
frames.
The iFCP Layer is responsible for transporting Link Service
messages across the IP fabric. This includes mapping Link
Service messages appropriately from the domain of the Fibre
Channel transport to that of the IP network. This process may
involve manipulation of field values as the Link Service
message travels to and from the IP and Fibre Channel fabrics.
It also may also require the inclusion of augmented data by
the iFCP layer.
Each link service or extended link service is processed
according to one of the following rules:
a) Transparent û The link service message and reply MUST be
transported to the receiving N_PORT by the iFCP gateway
without altering the message payload. The link service
message and reply are not processed by the iFCP
implementation.
b) Augmented - Applies to an extended link service reply or
request containing fibre channel addresses in the payload
or requiring other special processing by the iFCP
implementation. The processing for augmented link services
is described in this section.
c) Rejected û When issued by a directly attached N_PORT, the
specified link service request MUST be rejected by the iFCP
implementation. The gateway SHALL respond to a rejected
link service message by returning an LS_RJT response with a
Reason Code of 0x0B (Command Not Supported) and a Reason
Code Explanation of 0x0 (No Additional Explanation).
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This section describes the processing for augmented link
services, including the manner in which augmentation data is
transmitted over the IP network.
Appendix A enumerates all link services and the iFCP
processing policy that applies to each.
7.1 Augmented Link Service Messages
Augmentation applies to extended link service requests that
require the intervention of the iFCP layer. Such intervention
is required in order to:
a) Service any ELS that requires special handling, such as a
PLOGI.
b) In address translation mode only, service any ELS which has
an N_PORT address in the payload.
Such ELS messages are transmitted in a fibre channel frame
having the following format:
Word
31<-bit>24 23<------------------Bit---------------------->0
+----------+------------------------------------------------+
0| R_CTL | D_ID |
| [22] | [Destination of extended link Service request] |
+----------+------------------------------------------------+
1| CS_CTL | S_ID |
| | [Source of extended link service request] |
+----------+------------------------------------------------+
2| TYPE | F_CTL |
+----------+------------------+-----------------------------+
3| SEQ_ID | DF_CTL | SEQ_CNT |
+----------+------------------+-----------------------------+
4| OX_ID | RX_ID |
+-----------------------------+-----------------------------+
5| Parameter |
| [ 00 00 00 00 ] |
+-----------------------------------------------------------+
6| LS_COMMAND |
| [Extended Link Service Command Code] |
+-----------------------------------------------------------+
7| |
.| Additional Service Request Parameters |
.| ( if any ) |
n| |
+-----------------------------------------------------------+
Format of ELS Frame
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7.2 Augmented Link Services Requiring Payload Address
Translation
This section describes the handling for ELS frames containing
N_PORT addresses in the ELS payload. Such addresses SHALL only
be translated when the gateway is operating in address
translation mode. When operating in address transparent mode,
these addresses SHALL NOT be translated and such ELS messages
SHALL not be sent as augmented frames unless other special
processing is required.
Supplemental data includes information required by the
receiving gateway to convert an N_PORT address in the payload
to an N_PORT address in the receiving gatewayÆs address
space. The following rules define the manner in which such
supplemental data is packaged and referenced.
For an N_PORT address field, the gateway originating the frame
MUST set the value in the payload to identify the address
translation type as follows:
0x00 00 00 û The gateway receiving the frame from the IP
network MUST reference the augmentation data to set the
field contents as described below. The augmentation
information is the 64-bit world wide identifier of the
N_PORT as set forth in the fibre channel specification. If
not otherwise part of the ELS, this information MUST be
appended as described below. This translation type SHALL
NOT be used when the address to be converted corresponds
to that of the frame originator or recipient.
0x00 00 01 û The gateway receiving the frame from the IP
network MUST replace the contents of the field with the
N_PORT alias of the frame originator. This translation
type MUST be used when the address to be converted is
that of the source N_PORT.
0x00 00 02 û The gateway receiving the frame from the IP
network MUST replace the contents of the field with the
N_PORT I/D of the destination N_PORT. This translation
type MUST be used when the address to be converted is that
of the destination N_PORT
Since fibre channel addressing rules prohibit the assignment
of fabric addresses with a domain I/D of 0, the above codes
will never correspond to valid N_PORT fabric IDs.
For translation type 0, the receiving gateway SHALL obtain the
information needed to fill in the ELS field by converting the
specified N_PORT world-wide identifier to a gateway IP address
and N_PORT ID. This information MUST be obtained through a
name server query. If the N_PORT is locally attached, the
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gateway MUST fill in the field with the N_PORT ID. If the
N_PORT is remotely attached, the gateway MUST assign and fill
in the field with an N_PORT alias. If an N_PORT alias has
already been assigned, it MUST be reused.
In the event that the sending gateway cannot obtain the world
wide identifier of an N_PORT, or a receiving gateway cannot
obtain the IP address and N_PORT ID, the gateway detecting the
error SHALL terminate the request with an LS_RJT message as
described in [FCS]. The Reason Code SHALL be set to 0x07
(protocol error) and the Reason Explanation SHALL be set to
0x1F (Invalid N_PORT identifier).
[EditorÆs note: Such errors, when detected by the receiving
gateway, may be indicative of a serious problem requiring a
more drastic response. Therefore, this section should be
regarded as tentative.]
Supplemental data is sent with the ELS request or ACC frames
in one of the following ways:
a) By appending the necessary data to the end of the ELS
frame.
b) By extending the sequence through the addition of
additional frames.
In the first case, a new frame SHALL be created whose length
includes the supplemental data. The procedure for extending
the ELS sequence with additional frames is /TBS/.
After applying the supplemental data, the receiving gateway
SHALL forward the resulting ELS to the destination N_PORT with
the supplemental information removed.
When the ACC response must be augmented, the receiving gateway
must act as a proxy for the originator, retaining the state
needed to process the response from the N_PORT to which the
request was directed.
7.3 Augmented Link Services
The following Link Service Messages must receive special
processing or be supplemented with additional control data.
When the iFCP header encapsulates one of these Extended Link
Service messages in the iFCP payload, the AUG bit must be set
to one in the iFCP FLAGS field as specified in section 6.1 and
the supplemental data (if any) must be appended as described
in the following section. An ELS ACC frame that is augmented
must be similarly formatted.
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Link Service Message LS_COMMAND Mnemonic
-------------------- ---------- --------
Abort Exchange 0x06 00 00 00 ABTX
Discover Address 0x52 00 00 00 ADISC
Discover Address Accept 0x02 00 00 00 ADISC ACC
FC Address Resolution Protocol 0x55 00 00 00 FARP-REPLY
Reply
FC Address Resolution Protocol 0x54 00 00 00 FARP-REQ
Request
Logout 0x05 00 00 00 LOGO
Port Login 0x30 00 00 00 PLOGI
Read Exchange Concise 0x13 00 00 00 REC
Read Exchange Concise Accept 0x02 00 00 00 REC ACC
Read Exchange Status Block 0x08 00 00 00 RES
Read Exchange Status Block 0x02 00 00 00 RES ACC
Accept
Read Link Error Status Block 0x0F 00 00 00 RLS
Read Sequence Status Block 0x09 00 00 00 RSS
Reinstate Recovery Qualifier 0x12 00 00 00 RRQ
Request Sequence Initiative 0x0A 00 00 00 RSI
Third Party Process Logout 0x24 00 00 00 TPRLO
The formats of each augmented ELS, including supplemental data
where applicable, are shown in the following sections. Each
ELS diagram shows the basic format, as specified in the
applicable FC standard, followed by supplemental data as shown
below.
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | LS_COMMAND |
+------+------------+------------+-----------+----------+
| 1 | |
| . | |
| . | ELS Payload |
| | |
| n | |
+======+============+============+===========+==========+
| n+1 | |
| . | Supplemental Data |
| . | (if any) |
| n+k | |
+======+================================================+
ELS Diagram (single FC Frame Format)
7.3.1 Abort Exchange (ABTX)
ELS Format:
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+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x6 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | RRQ Status | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID of Tgt exchange | RX_ID of tgt exchange|
+------+------------+------------+-----------+----------+
| 3-10 | Optional association header (32 bytes |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type (see (type 0 only)
------------------- section 7.2) ------------
-----------
Exchange Originator 1, 2 N/A
S_ID
Other Special Processing:
None
7.3.2 Discover Address (ADISC)
Format of ADISC ELS:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x52 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Reserved | Hard address of ELS Originator |
+------+------------+------------+-----------+----------+
| 2-3 | Port Name of Originator |
+------+------------+------------+-----------+----------+
| 4-5 | Node Name of originator |
+------+------------+------------+-----------+----------+
| 6 | Rsvd | N_PORT I/D of ELS Originator |
+======+============+============+===========+==========+
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Fields Requiring Translation Supplemental Data
Address Translation Type (see (type 0 only)
------------------- section 7.2) ------------
-------------
N_PORT I/D of ELS 1 N/A
Originator
Other Special Processing:
The Hard Address of the ELS originator shall be set to 0.
7.3.3 Discover Address Accept (ADISC ACC)
Format of ADISC ACC ELS:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x20 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Reserved | Hard address of ELS Originator |
+------+------------+------------+-----------+----------+
| 2-3 | Port Name of Originator |
+------+------------+------------+-----------+----------+
| 4-5 | Node Name of originator |
+------+------------+------------+-----------+----------+
| 6 | Rsvd | N_PORT I/D of ELS Originator |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type (see (type 0 only)
------------------- section 7.2) ------------
------------
N_PORT I/D of ELS 1 N/A
Originator
Other Special Processing:
The Hard Address of the ELS originator SHALL be set to 0.
7.3.4 FC Address Resolution Protocol Reply (FARP-
REPLY)
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The FARP-REPLY ELS is used in conjunction with the FARP-REQ
ELS (see section 7.3.5) to perform the address resolution
services required by the FC-VI protocol [FC-VI].
Format of FARP-REPLY ELS:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x55 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Match Addr | Requesting N_PORT Identifier |
| | Code Points| |
+------+------------+------------+-----------+----------+
| 2 | Responder | Responding N_PORT Identifier |
| | Action | |
+------+------------+------------+-----------+----------+
| 3-4 | Requesting N_PORT Port_Name |
+------+------------+------------+-----------+----------+
| 5-6 | Requesting N_PORT Node_Name |
+------+------------+------------+-----------+----------+
| 7-8 | Responding N_PORT Port_Name |
+------+------------+------------+-----------+----------+
| 9-10 | Responding N_PORT Node_Name |
+------+------------+------------+-----------+----------+
| 11-14| Requesting N_PORT IP Address |
+------+------------+------------+-----------+----------+
| 15-18| Responding N_PORT IP Address |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type (see (type 0 only)
------------------- section 7.2) -----------------
-------------
Requesting N_PORT 2 N/A
Identifier
Responding N_PORT 1 N/A
identifier
Other Special Processing:
None.
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7.3.5 FC Address Resolution Protocol Request (FARP-
REQ)
The FARP-REQ ELS is used to in conjunction with the FC-VI
protocol [FC-VI] to perform IP and FC address resolution in an
FC fabric. The FARP-REQ ELS is usually directed to the fabric
broadcast server at well-known address 0xFF FF FF for
retransmission to all attached N_PORTs. Section 10.1 describes
the iFCP implementation of FC broadcast server functionality
in an iFCP fabric.
Format of FARP_REQ ELS:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x54 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Match Addr | Requesting N_PORT Identifier |
| | Code Points| |
+------+------------+------------+-----------+----------+
| 2 | Responder | Responding N_PORT Identifier |
| | Action | |
+------+------------+------------+-----------+----------+
| 3-4 | Requesting N_PORT Port_Name |
+------+------------+------------+-----------+----------+
| 5-6 | Requesting N_PORT Node_Name |
+------+------------+------------+-----------+----------+
| 7-8 | Responding N_PORT Port_Name |
+------+------------+------------+-----------+----------+
| 9-10 | Responding N_PORT Node_Name |
+------+------------+------------+-----------+----------+
| 11-14| Requesting N_PORT IP Address |
+------+------------+------------+-----------+----------+
| 15-18| Responding N_PORT IP Address |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type (see (type 0 only)
------------------- section 7.2) -----------------
-----------
Requesting N_PORT 0 Requesting N_PORT
Identifier Port Name
Responding N_PORT 1 N/A
Identifier
Other Special Processing:
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None.
7.3.6 Logout (LOGO)
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x5 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | N_PORT I/D being logged out |
+------+------------+------------+-----------+----------+
| 2-3 | Port name of the LOGO originator (8 bytes) |
+======+============+============+===========+==========+
This ELS shall always be sent as an augmented ELS regardless
of the translation mode in effect.
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) --------------
-----------
N_PORT I/D Being 0, 1 or 2 Port Name of LOGO
Logged Out Originator
Other Special Processing:
See section 5.2.2.1.
7.3.7 Port Login (PLOGI)
PLOGI provides the mechanism for establishing a login session
between two N_PORTs. The PLOGI request carries information
identifying the originating N_PORT, including specification of
its capabilities and limitations. If the destination N_PORT
accepts the login request, it sends an accept (an ACC frame
with PLOGI payload), specifying its capabilities and
limitations. This exchange establishes the operating
environment for the two N_PORTs.
The following figure is duplicated from FC-PH, and shows the
PLOGI message format for both request and accept (ACC)
response. A port will reject a PLOGI request by transmitting
an LS_RJT message, which contains no payload.
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Byte
Offset
+----------------------------------+
0 | LS_COMMAND | 4 Bytes
+----------------------------------+
4 | COMMON SERVICE PARAMETERS | 16 Bytes
+----------------------------------+
20 | PORT NAME | 8 Bytes
+----------------------------------+
28 | NODE NAME | 8 Bytes
+----------------------------------+
36 | CLASS 1 SERVICE PARAMETERS | 16 Bytes
+----------------------------------+
52 | CLASS 2 SERVICE PARAMETERS | 16 Bytes
+----------------------------------+
68 | CLASS 3 SERVICE PARAMETERS | 16 Bytes
+----------------------------------+
86 | CLASS 4 SERVICE PARAMETERS | 16 Bytes
+----------------------------------+
102 | VENDOR VERSION LEVEL | 16 Bytes
+----------------------------------+
Total Length = 116 bytes
Details on the above fields, including common and class-based
service parameters, can be found in [FC-PH]. The above PLOGI
message is transported by the iFCP layer without modification.
[EditorÆs note: The service parameter details that apply to
an iFCP environment are /TBS/.]
7.3.8 Read Exchange Concise
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x13 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID | RX_ID |
+======+============+============+===========+==========+
| 3-4 |Port name of the exchange originator (8 bytes) |
| | (present only for translation type 0) |
+======+============+============+===========+==========+
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Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 0, 1 or 2 Port Name of the
S_ID Exchange
Originator
Other Special Processing:
None.
7.3.9 Read Exchange Concise Accept
Format of ACC Response:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Acc = 0x02 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | OX_ID | RX_ID |
+------+------------+------------+-----------+----------+
| 2 | Rsvd | Exchange Originator N_PORT ID |
+------+------------+------------+-----------+----------+
| 3 | Rsvd | Exchange Responder N_PORT ID |
+------+------------+------------+-----------+----------+
| 4 | Data Transfer Count |
+------+------------+------------+-----------+----------+
| 5 | Exchange Status |
+======+============+============+===========+==========+
| 6-7 |Port name of the Exchange Originator (8 bytes) |
+======+============+============+===========+==========+
| 8-9 |Port name of the Exchange Responder (8 bytes) |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 0, 1 or 2 Port Name of the
N_PORT I/D Exchange Originator
Exchange Responder 0, 1 or 2 Port Name of the
N_PORT I/D Exchange Responder
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When supplemental data is required, the ELS shall be always be
extended by 4 words as shown above. Unused words in the
extended fields SHALL be set to 0.
Other Special Processing:
None.
7.3.10 Read Exchange Status Block (RES)
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x13 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID | RX_ID |
+------+------------+------------+-----------+----------+
| 3-10 | Association header (may be optionally reqÆd) |
+======+============+============+===========+==========+
| 11-18| Port name of the Exchange Originator (8 bytes) |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 0, 1 or 2 Port Name of the
S_ID Exchange Originator
Other Special Processing:
None.
7.3.11 Read Exchange Status Block Accept
Format of ELS Accept Response:
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+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Acc = 0x02 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | OX_ID | RX_ID |
+------+------------+------------+-----------+----------+
| 2 | Rsvd | Exchange Originator N_PORT ID |
+------+------------+------------+-----------+----------+
| 3 | Rsvd | Exchange Responder N_PORT ID |
+------+------------+------------+-----------+----------+
| 4 | Exchange Status Bits |
+------+------------+------------+-----------+----------+
| 5 | Reserved |
+------+------------+------------+-----------+----------+
| 6ûn | Service Parameters and Sequence Statuses |
| | as described in [FCS] |
+======+============+============+===========+==========+
|n+1- | Port name of the Exchange Originator (8 bytes) |
|n+8 | |
+======+============+============+===========+==========+
|n+9- | Port name of the Exchange Responder (8 bytes) |
|n+16 | |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 0, 1 or 2 Port Name of the
N_PORT I/D Exchange Originator
Exchange Responder 0, 1 or 2 Port Name of the
N_PORT I/D Exchange Responder
When supplemental data is required, the ELS SHALL be extended
by 4 words as shown above. Unused words in the extended fields
SHALL be set to 0.
Other Special Processing:
None.
7.3.12 Read Link Error Status (RLS)
ELS Format:
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+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x0F | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | N_PORT Identifier |
+======+============+============+===========+==========+
| 2-9 | Port name of the N_PORT (8 bytes) |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data (type
Address Translation Type(see 0 only)
------------------- section 7.2) ------------------
-----------
N_PORT Identifier 0, 1 or 2 Port Name of the N_PORT
Other Special Processing:
None.
7.3.13 Read Sequence Status Block (RSS)
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x09 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | SEQ_ID | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID | RX_ID |
+======+============+============+===========+==========+
| 3-4 |Port name of the Exchange Originator (8 bytes) |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 0, 1 or 2 Port Name of the
S_ID Exchange Originator
Other Special Processing:
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None.
7.3.14 Reinstate Recovery Qualifier (RRQ)
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x12 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID | RX_ID |
+------+------------+------------+-----------+----------+
| 3-10 | Association header (may be optionally reqÆd) |
+======+============+============+===========+==========+
Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 1 or 2 N/A
S_ID
Other Special Processing:
None.
7.3.15 Request Sequence Initiative (RSI)
ELS Format:
+------+------------+------------+-----------+----------+
| Word | Bits 31û24 | Bits 23û16 | Bits 15û8 | Bits 7-0 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0x0A | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | Rsvd | Exchange Originator S_ID |
+------+------------+------------+-----------+----------+
| 2 | OX_ID | RX_ID |
+------+------------+------------+-----------+----------+
| 3-10 | Association header (may be optionally reqÆd) |
+======+============+============+===========+==========+
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Fields Requiring Translation Supplemental Data
Address Translation Type(see (type 0 only)
------------------- section 7.2) ------------------
-----------
Exchange Originator 1 or 2 N/A
S_ID
Other Special Processing:
None.
7.3.16 Third Party Process Logout (TPRLO)
TPRLO provides a mechanism for an N_PORT (third party) to
remove one or more login sessions that exists between the
destination N_PORT and other N_PORTs specified in the command.
This command includes one or more TPRLO LOGOUT PARAMETER
PAGEs, each of which when combined with the destination N_PORT
identifies a SCSI login session which shall be terminated by
the command.
Byte
Offset
+----------------------------------+
0 | LS_COMMAND | 1 Byte
+----------------------------------+
1 | PAGE LENGTH (0x10) | 1 Byte
+----------------------------------+
2 | PAYLOAD LENGTH (0x14) | 2 Bytes
+----------------------------------+
4 | TPRLO LOGOUT PARAMETER PAGE 1 | 2-4 Bytes
+----------------------------------+
| . . . . | M Bytes
+----------------------------------+
| TPRLO LOGOUT PARAMETER PAGE N | 2-4 Bytes
+----------------------------------+
Total Length = Variable
Each TPRLO LOGOUT PARAMETER PAGE identifies a remote N_PORT
which when combined with the destination N_PORT identifies a
SCSI session to be terminated. The TPRLO LOGOUT PARAMETER
PAGE is of the following format:
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Byte
Offset
+----------------------------------+
0 | TYPE CODE | 1 Byte
+----------------------------------+
1 | TYPE CODE EXTENSION | 1 Byte
+----------------------------------+
2 | TPRLO FLAGS | 2 Bytes
+----------------------------------+
4 | ORIG PROCESS ASSOC (if present) | 4 Bytes
+----------------------------------+
8 | RESP PROCESS ASSOC (if present) | 4 Bytes
+----------------------------------+
12 | RESERVED | 1 Byte
+----------------------------------+
13 | THIRD PARTY ORIGINATOR N_PORT ID | 3 Bytes
+----------------------------------+
When the iFCP header contains a TPRLO message (including the
ACC response), iFCP supplemental data field will contain the
PORT_NAME(s) (WWPN) identifying the N_PORT described by the
equivalent TPRLO LOGOUT PARAMETER PAGE(s). If more than one
TPRLO LOGOUT PARAMETER PAGE is contained in the Link Service
message, the corresponding PORT_NAME shall also be included.
PORT_NAMEs shall be listed in the same order as the equivalent
TPRLO LOGOUT PARAMETER PAGEs in the original Link Service
message.
[The format for passing supplemental data is /TBS/]
Additionally, the THIRD PARTY ORIGINATOR N_PORT ID field in
each TPRLO LOGOUT PARAMETER PAGE shall be cleared when it is
sent by the originating gateway. This applies to both the
original Link Service message and the ACC response.
When the iFCP layer receives a TPRLO message, it shall use the
latter to replace the THIRD PARTY ORIGINATOR N_PORT ID in the
original Link Service message, before forwarding it on to the
upper Fibre Channel layers.
Additional information on TPRLO can be found in [FC-PH-2].
8. TCP Session Control Messages
TCP session control messages are used to create and manage
N_PORT login session.. They are passed between peer FCP
Portals, and are only processed within the iFCP layer. The
response to a TCP session control message (if any) will echo
the original request.
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The message format is based on the extended link service
message template shown below.
Word
31<Bits>24 23<---------------Bits------------------------->0
+----------+------------------------------------------------+
0| R_CTL | D_ID [0x00 00 00] |
|[Req = 22]| [Destination of extended link Service request] |
|[Rep = 23 | |
+----------+------------------------------------------------+
1| CS_CTL | S_ID [0x00 00 00] |
| [0x0] | [Source of extended link service request] |
+----------+------------------------------------------------+
2|TYPE [0x1]| F_CTL [0] |
+----------+------------------+-----------------------------+
3|SEQ_ID | DF_CTL [0x00] | SEQ_CNT [0x00] |
|[0x0] | | |
+----------+------------------+-----------------------------+
4| OX_ID [0x0000] | RX_ID_[0x0000] |
+-----------------------------+-----------------------------+
5| Parameter |
| [ 00 00 00 00 ] |
+-----------------------------------------------------------+
6| LS_COMMAND |
| [Session Control Command Code] |
+-----------------------------------------------------------+
7| |
.| Additional Session Control Parameters |
.| ( if any ) |
n| |
+===========================================================+
n| Fibre Channel CRC |
+| |
1+===========================================================+
Format of Session Control Message
The LS_COMMAND value for the response remains the same as that
used for the request.
The session control ELS frame is terminated with a fibre
channel CRC.
{EditorÆs note: Since these messages are never passed to the
fibre channel device, the use of the FC ELS format is not
required. However, leveraging the format may benefit a
gateway implementation. Depending on the tradeoffs, therefore,
the format may be modified to eliminate use of the ELS as a
message template.]
The encapsulation header for the link Service frame carrying a
TCP ELS message SHALL be set as follows:
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Encapsulation Header Fields:
LS_COMMAND 0
iFCP Flags SES = 1
TRN = 0
AUG = 0
SOF code SOFi3 encoding (0x2E)
EOF code EOFn encoding (0x50)
Time Stamp Integer 0,0
and Fraction fields
The SOF and EOF delimiter words SHALL be set based on the SOF
and EOF codes specified above.
The following lists the TCP Link Service messages and their
corresponding LS_COMMAND values.
Request LS_COMMAND Short Name iFCP Support
------- ---------- ---------- -----------
Control Connection Bind 0xE0 CBIND REQUIRED
Unbind Connection 0xE4 UNBIND REQUIRED
8.1 Connection Bind (CBIND)
The CBIND message binds an N_PORT login session to a specific
TCP connection in preparation for establishing an N_PORT login
session. In the CBIND request message, the source and
destination N_Ports are identified by the N_PORT network
address (iFCP portal address and N_PORT ID).
The following shows the format of the CBIND request.
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+------+------------+------------+-----------+----------+
| Word | Byte 0 | Byte 1 | Byte 2 | Byte 3 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0xE0 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | User Info |
+------+------------+------------+-----------+----------+
| 2 | Interface Speed |
+------+------------+------------+-----------+----------+
| 3 | |
+------+ SOURCE PORT NAME |
| 4 | |
+------+------------------------------------------------+
| 5 | |
+------+ DESTINATION PORT NAME |
| 6 | |
+------+------------------------------------------------+
USER INFO - Contains any data desired by the requester. This
info MUST be echoed by the recipient in the CBIND response
message.
SOURCE PORT NAME - Contains the originating N_PORT's World
Wide Port Name (WWPN).
DESTINATION PORT NAME - Contains the destination N_PORT's
World Wide Port Name (WWPN).
The following shows the format of the CBIND response.
+------+------------+------------+-----------+----------+
| Word | Byte 0 | Byte 1 | Byte 2 | Byte 3 |
+------+------------+------------+-----------+----------+
| 0 | Cmd = 0xE0 | 0x00 | 0x00 | 0x00 |
+------+------------+------------+-----------+----------+
| 1 | User Info |
+------+------------+------------+-----------+----------+
| 2 | |
+------+ SOURCE PORT NAME |
| 3 | |
+------+------------------------------------------------+
| 4 | |
+------+ DESTINATION PORT NAME |
| 5 | |
+------+-------------------------+----------------------+
| 6 | Reserved | CBIND Status |
+------+-------------------------+----------------------+
| 7 | Reserved | CONNECTION HANDLE |
+------+-------------------------+----------------------+
Total Length = 26
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USER INFO - Contains the same value received in the USER INFO
field of the CBIND request message.
DESTINATION PORT NAME - Contains the destination N_PORT's
World Wide Port Name (WWPN).
CBIND STATUS - Indicates success or failure of the CBIND
request. CBIND values are shown below.
Value Description
----- -----------
0 Successful û No other status
1 û 15 Reserved
16 Failed û Unspecified Reason
17 Failed û No such device
18 Failed û N_PORT session already exists
19 Failed û Lack of resources
Others Reserved
CONNECTION HANDLE (CHANDLE) - Contains a value assigned by the
FCP Portal to identify the control connection.
8.2 Unbind Connection (UNBIND)
UNBIND is used to release a bound TCP connection and return it
to the pool of unbound TCP connections. This message is
transmitted in the connection that is to be unbound.
The following is the format of the UNBIND request message.
Byte MSb LSb
Offset 7 6 5 4 3 2 1 0
+----------------------------------+
0 | LS_COMMAND (0xE4000000) | 4 Bytes
+----------------------------------+
4 | USER INFO | 4 Bytes
+----------------------------------+
8 | CONNECTION HANDLE | 4 Bytes
+----------------------------------+
12 | RESERVED | 8 Bytes
+----------------------------------+
Total Length = 20
CONNECTION HANDLE (CHANDLE) - Contains a value assigned by the
FCP Portal to identify the connection
The following shows the format of the UNBIND response message.
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Byte MSb LSb
Offset 7 6 5 4 3 2 1 0
+----------------------------------+
0 | LS_COMMAND (0xE4000000) | 4 Bytes
+----------------------------------+
4 | USER INFO | 4 Bytes
+----------------------------------+
8 | CONNECTION HANDLE | 4 Bytes
+----------------------------------+
16 | RESERVED | 10 Bytes
+----------------------------------+
26 | UNBIND STATUS | 2 Bytes
+----------------------------------+
28 | RESERVED | 2 Bytes
+----------------------------------+
Total Length = 26
UNBIND STATUS - Indicates the success or failure of the UNBIND
request.
Value Description
----- -----------
0 Successful û No other status
1 û 15 Reserved
16 Failed û Unspecified Reason
17 Failed û No such device
18 Failed û Connection ID Invalid
Others Reserved
CONNECTION HANDLE (CHANDLE) - Contains a value assigned by the
FCP Portal to identify the unbound connection.
9. iFCP Error Detection
9.1 Overview
[FCP-2], [FC-PH], and [FC-PH-2] define error detection and
recovery procedures. These Fibre Channel-defined mechanisms
continue to be available in the iFCP environment.
9.2 Timer Definitions and Stale Frame Detection
9.2.1 Error_Detect_Timeout (E_D_TOV)
E_D_TOV is "a reasonable timeout value for detection of a
response to a timed event". The default value specified by
FC-FS of 2 seconds will be also used as the iFCP default
value.
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E_D_TOV is the maximum time allowed between the transmission
of consecutive data frames within a sequence. For Class 2
service, E_D_TOV specifies the maximum time interval between
transmission of a frame, and receipt of the ACK for that
frame.
E_D_TOV MAY be specified individually for each gateway. If a
gateway-specific value is not set, the gateway SHALL obtain
the value from the iSNS name server.
9.2.2 Resource Allocation Timeout (R_A_TOV
R_A_TOV is defined in FC-PH-2 as "the maximum transit time
within a fabric to guarantee that a lost frame will never
emerge from the fabric". A value of 2 x R_A_TOV is the
minimum time that the originator of an ELS request or FC-4 ELS
request shall wait for the response to that request. The fibre
channel default value for R_A_TOV is 10 seconds.
R_A_TOV MAY be specified individually for each gateway. If a
gateway-specific value is not set, the gateway SHALL obtain
the value from the iSNS name server. The iFCP fabric MAY
actively enforce limits on R_A_TOV as described in section
9.2.2.1.
9.2.2.1 Enforcing R_A_TOV Limits
The R_A_TOV limit on frame lifetimes MAY be enforced by means
of the time stamp in the encapsulation header (see section
6.1) as described in this section.
If enforced by a gateway, the propagation delay time limit
(MAX_PROP_DELAY) SHOULD be set well below the value of R_A_TOV
specified for the iFCP fabric and SHOULD be stored in the iSNS
server. A rule of thumb is to set MAX_PROP_DELAY to 50 percent
of R_A_TOV.
The following paragraphs describe the requirements for
synchronizing gateway time bases and the rules for measuring
and enforcing propagation delay limits.
The protocol for synchronizing a gateway time base is SNTP. In
order to insure that all gateways are time-aligned, a gateway
SHOULD obtain the address of an SNTP server via an iSNS query.
If multiple SNTP server addresses are returned by the query,
the servers must be synchronized and the gateway may use any
server in the list. Alternatively, the server may return a
multicast group address in support of operation in Anycast
mode. Implementation of Anycast mode is as specified in RFC
2030, including the precautions defined in that document.
Multicast mode SHOULD NOT be used.
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An SNTP server may use any one of the time reference sources
listed in RFC 2030. The resolution of the time reference MUST
be 125 milliseconds or better.
With regard to the time base, the gateway is in either the
synchronized or unsychronized state. When in the
unsynchronized state, the gateway SHALL:
a) Set the time stamp field to 0,0 for all outgoing frames
b) Ignore the time stamp field for all incoming frames.
When in the synchronized state, the gateway SHALL
a) Set the time stamp field for each outgoing frame in
accordance with the gateway's internal time base
b) Check the time stamp field of each incoming frame.
c) If the incoming frame has a time stamp of 0,0, the
receiving gateway SHALL NOT test the frame to determine if
it is stale.
d) If the incoming frame has a non-zero time stamp, the
receiving gateway shall compute the time in flight and
compare it against the value of MAX_PROP_DELAY specified
for the IP fabric.
e) If the result in step (d) exceeds MAX_PROP_DELAY, the
frame shall be discarded. Otherwise, the frame shall be
accepted.
A gateway SHALL enter the synchronized state upon receiving a
successful response to an SNTP query.
A gateway shall enter the unsynchronized state:
a) Upon power up and before successful completion of an SNTP
query
b) Whenever the gateway looses contact with the SNTP server.
If synchronization is lost, the gateway MAY choose to abort
all N_PORT login sessions with all remote gateways.
10. Fabric Services Supported by an iFCP implementation
An iFCP gateway implementation MUST support the following
fabric services:
N_PORT ID Value Description Section
--------------- ----------- -------
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0xFF FF FE F_PORT Server /TBS/
0xFF FF FD Fabric Controller /TBS/
0xFF FF FC Directory/Name Server /TBS/
In addition, an iFCP gateway MAY support the FC broadcast
server functionality described in section 10.1.
10.1 iFCP Support for the FC Broadcast Service
In Fibre Channel, frames are broadcast by addressing them to
the broadcast server at well-known address 0xff ff ff. The
broadcast server then replicates and delivers the frame to
each attached N_PORT in all zones to which the originating
device belongs. Only class 3 (datagram) service is supported.
In an iFCP/iSNS system, the broadcast functionality MAY be
implemented within each gateway by an iFCP broadcast server.
The broadcast server has an N_PORT I/D of 0xff ff ff.
Outgoing frames to be broadcast are directed to the broadcast
server by locally attached N_PORTs. The broadcast server then
redistributes such frames as follows:
a) One copy is sent to each locally attached N_PORT in the
same zone as the originator.
b) One copy is sent to the broadcast server in each remote
gateway via a UDP datagram, The D_ID field is set to the
well-known address of the broadcast server. The datagram
encapsulation format is identical to the iFCP
encapsulation format described in section 6.
On receiving an iFCP broadcast datagram via UDP, the broadcast
server SHALL:
a) Validate the header as described in section 6.3. If the
header is invalid, the frame SHALL be discarded.
b) Convert the S_ID N_PORT address in the frame to an N_PORT
alias as described in section 3.3.2, if address translation
mode is in effect.
c) If the AUG bit is set in the iFCP flags field, perform any
special processing required by the ELS, including
translation of any addresses in the payload.
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d) Replicate and redistribute the frame to all locally
attached N_PORTs in the discovery domain of the sender.
If no broadcast server is implemented, the receiving gateway
SHALL discard an incoming broadcast frame from a remote
gateway. Frames received from locally attached N_PORTs shall
be processed as specified in [FC-SW].
11. Security
11.1 Overview
As with any other IP-based network, an iFCP storage network
has security issues which must be addressed with the
appropriate security policies and enforcement resources.
There are various levels of security paradigms which when
applied appropriately to an iFCP network can provide
sufficient levels of security, including data integrity,
authentication, and privacy, depending on user needs.
11.2 Physical Security
Most existing SCSI and Fibre Channel interconnections are
deployed in private, physically isolated environments where
hostile entities are not provided access to the SCSI and Fibre
Channel interconnects. This is the most basic security
mechanism, and may be a sufficient model in some cases for an
iFCP network.
11.3 Controlling Access
A second level of security is the use of zoning. Zoning
specifies which devices are allowed to communicate, and is
similar in concept to VLAN (Virtual Local Area Network)
technology. Zoning information is maintained in a Name
Server.
11.4 Authentication and Encryption
Where additional levels of data integrity and privacy are
required for iFCP, existing IPSec specifications can be
applied to iFCP. Because IPSec is a layer-3 technology and
has no knowledge of TCP, UDP, or higher-level protocols such
as iFCP and FCP, it can be applied transparently to iFCP. The
following IETF documents describe the operational framework
and automatic keying mechanisms for IPSec.
RFC2401 Security Architecture for the Internet Protocol
RFC2402 IP Authentication Header
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RFC2406 IP Encapsulating Security Payload
RFC2407 The Internet IP Security Domain of Interpretation for
ISAKMP
RFC2408 Internet Security Association and Key Management
Protocol (ISAKMP)
RFC2409 The Internet Key Exchange (IKE)
11.5 Storage Firewalls
Firewalls are a common and proven methodology for securing
access to IP-based networks, and they can be appropriate for
use in IP-based storage networks as well. A firewall is a
choke point through which all transit traffic must transit in
order to pass between two separate networks. Since all iFCP
traffic uses a well-known IANA-assigned TCP port number, it
can easily be recognized and inspected.
Access to storage resources can be secured by setting up a
single gateway through which all outside non-secured traffic
must pass through in order to access resources in the storage
network. Such a firewall can be a proxy host operating at the
session or application layer, requiring authentication before
allowing traffic to pass. It can also be a stateful
inspection gateway which understands the iFCP protocol, and
can passively inspect and discover security threats as they
transit the gateway. A third option is to use a standard
router access control list to filter authorized traffic based
upon static parameters such as IP addresses and TCP port
numbers.
12. Quality of Service Considerations
12.1 Minimal requirements
Conforming iFCP protocol implementations SHALL correctly
communicate gateway-to-gateway even across one or more
intervening best-effort IP regions. The timings with which
such gateway-to gateway communication is performed, however,
will greatly depend upon BER, packet losses, latency, and
jitter experienced throughout the best-effort IP regions. The
higher these parameters, the higher will be the gap measured
between iFCP observed behaviors and baseline iFCP behaviors
(i.e., as produced by two iFCP gateways directly attached to
one another).
12.2 High-assurance
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It is expected that many iFCP deployments will benefit from a
high degree of assurance on the behaviors of the intervening
IP regions, with resulting high-assurance on the overall end-
to-end path, as directly experienced by Fibre Channel
applications. Such assurance on the IP behaviors stems from
the intervening IP regions supporting standard Quality-of-
Service (QoS) techniques, fully complementary to iFCP, such
as:
a) Congestion avoidance by over-provisioning of the network
b) Integrated Services [IntServ] QoS
c) .Differentiated Services [DiffServ] QoS
d) .Multi-Protocol Label Switching [MPLS]
In the most general definition, two iFCP gateways are
separated by one or more independently managed IP regions,
some of which implement some of the QoS solutions mentioned
above. The IP regions with these QoS solutions are said to
support Service Level Agreements (SLAs). Such agreements
finalize requirements on network parameters such as bandwidth,
loss, latency, jitter, burst length. The requirements may be
expressed in absolute or relative terms, and apply to a
unidirectional flow of packets. Depending on the QoS
techniques available, the dynamic stipulation of a SLA may
require the iFCP gateway to interact with network ancillary
functions such admission control and bandwidth brokers (with
RSVP or other signalling protocols that an IP region may
accept).
Due to the fact that Fibre Channel Class 2 and Class 3 do not
support fractional bandwidth guarantees, and that iFCP is
committed to supporting current Fibre Channel semantics, it is
impossible for an iFCP gateway to autonomously infer bandwidth
requirements from streaming Fibre Channel traffic. Rather, the
requirements on bandwidth or other network parameters need to
be injected out-of-band into a iFCP gateway (or the node that
will actually negotiate the SLA on the gateway's behalf)
through mechanisms outside the scope of this specification
(e.g., through a management interface into the iFCP gateway).
The administrator of a iFCP gateway MAY thus stipulate a
Service Level Agreement with the local IP region for one,
several, or all of an iFCP gateway's TCP sessions used by
iFCP. Alternately, this responsibility may be delegated to a
node downstream. Should an iFCP implementation support
multiple <N_PORT, N_PORT> tuples over the same TCP connection,
and should such a connection be subject to a SLA, then all
these <N_PORT, N_PORT> tuples will share in the same SLA and
the resulting treatment by the network. For finer granularity
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of QoS behaviors, iFCP implementations MAY elect to dedicate a
distinct TCP connection to each active <N_PORT, N_PORT> tuple.
This is the way an individual <N_PORT, N_PORT> tuple can enjoy
a customized SLA.
To render the best emulation of Fibre Channel possible over
IP, it is anticipated that typical SLAs will specify a fixed
amount of bandwidth, null losses, and, to a lesser degree of
relevance, low latency, and low jitter. For example, an IP
region using DiffServ QoS may support SLAs of this nature by
applying EF DSCPs to the iFCP traffic. For the same SLA,
another IP region might as well use a different DSCP or
different QoS techniques alltogether. The way different QoS
techniques are re-mapped at the edge of different intervening
IP regions is beyond the scope of this specification.
[T11/00-603V0] describes a proposal to add fractional
bandwidth guarantees to Class 2 and 3 (migrating it from Class
4). In such proposal, the bandwidth parameters would surface
in the FLOGI request and accept, and PLOGI request and accept.
In this case, it will become possible for an iFCP gateway to
trap this information and autonomously remap it onto the SLA
negotiation mechanism required by the local IP region, without
resorting to out-of-band QoS management. Such an in-band QoS
mechanism would result in true end-to-end provisioning of
network resources. Forthcoming revisions of this iFCP
specification will build upon this new opportunity.
13. References
13.1 Relevant SCSI (T10) Specifications
The following documents are available from: Global
Engineering, 15 Inverness Way East, Englewood, CO 80112-5704.
Telephone (800) 854-7179 or (303) 792-2181, Fax: (303) 792-
2192
[SAM] SCSI-3 Architecture Model (SAM), ANSI X3.270-1996
[SAM-2] SCSI Architecture Model-2 (SAM-2), Project 1157-D,
revision 11
[SPC] SCSI Primary Commands (SPC), ANSI X3.301-1997
[SPC-2] SCSI Primary Commands-2 (SPC-2), Project 1236-D,
revision 16
[FCP] Fibre Channel Protocol for SCSI (FCP), ANSI X3.269-1996
[FCP-2] Fibre Channel Protocol for SCSI, Second Revision (FCP-
2), Project 1144D, revision 04
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10.2 Relevant Fibre Channel (T11) Specifications
The following documents are available from: Global
Engineering, 15 Inverness Way East, Englewood, CO 80112-5704.
Telephone (800) 854-7179 or (303) 792-2181, Fax: (303) 792-
2192
[FC-PH] Fibre Channel Physical and Signaling Interface (FC-PH)
Rev 4.3, ANSI X3.230:1994
[FC-PH-2] Fibre Channel Physical and Signaling Interface (FC-PH-
2) Rev 7.4, ANSI X3.297:1997
[FC-PH-3] Fibre Channel Physical and Signaling Interface (FC-PH-
3) Rev 9.4, ANSI X3.303:1998
[FC-FG] Fibre Channel Generic Requirements (FC-FG) Rev 3.5 ANS
X3.289:1996
[FC-GS-2] Fibre Channel Generic Services (FC-GS-2) Rev 5.2, ANSI
NCITS 288
[FC-AL] Fibre Channel Arbitrated Loop (FC-AL) Rev 4.5, ANSI
X3.272:1996
[FC-AL-2] Fibre Channel Arbitrated Loop (FC-AL-2) Rev 7.0, NCITS
32:1999
[FC-PLDA] Fibre Channel Private Loop SCSI Direct Attachment (FC
LDA), NCITS TR-19:1998
[FC-FLA] Fibre Channel Fabric Loop Attachment (FC-FLA), NCITS
TR-20:1998
[FC-TAPE] Fibre Channel Tape and Tape Medium Changers (FC-TAPE),
NCITS TR-24:1999
10.3 Relevant RFC Documents
[RFC768] User Datagram Protocol
[RFC791] Internet Protocol, DARPA Internet Program Protocol
Specification
[RFC1146] TCP Alternate Checksum Options
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[RFC2401] Security Architecture for Internet Protocol
[RFC2402] IP Authentication Header
[RFC2406] Encapsulating Security Protocol (ESP)
[RFC2407] The Internet IP Security Domain for ISAKMP
[RFC2408] Internet Security Association and Key Management
Protocol (ISAKMP)
[RFC2409] The Internet Key Exchange (IKE)
[RFC2460] Internet Protocol, Version 6 (IPv6) Specification
10.4 Other Reference Documents
Fibre Channel, Gigabit Communications and I/O for Computer
Networks, Alan F. Beener, McGraw-Hill, ISBN 0-07-005669-2
The Fibre Channel Consultant, A Comprehensive Introduction,
Robert W. Kembel, Northwest Learning Associates, ISBN 0-
931836-82-6
The Fibre Channel Consultant, Arbitrated Loop, Rober W.
Kembel, Connectivity Solutions, a division of Northwest
Learning Associates, ISBN 0-931836-84-0
14. Author's Addresses
Charles Monia Franco Travostino
Rod Mullendore Director, Content
Josh Tseng Internetworking Lab,
Nishan Systems Victor Firoiu
3850 North First Street
San Jose, CA 95134 Nortel Networks
Phone: 408-519-3986 3 Federal Street
Email: Billerica, MA 01821
cmonia@nishansystems.com Phone: 978-288-7708
Email:
travos@nortelnetworks.com
David Robinson Wayland Jeong
Sun Microsystems Troika Networks
Senior Staff Engineer Vice President, Hardware
M/S UNWK16-301 Engineering
901 San Antonio Road 2829 Townsgate Road Suite
Palo Alto, CA 94303-4900 200
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Phone: 510-936-2337 Westlake Village, CA 91361
Email: Phone: 805-370-2614
David.Robinson@sun.com Email:
wayland@troikanetworks.com
Rory Bolt Paul Rutherford
Quantum/ATL ADIC
Director, System Design Vice President, Technology &
101 Innovation Drive Software
Irvine, CA 92612 1143 Willows Road N.E.
Phone: 949-856-7760 P.O. Box 97057
Email: rbolt@atlp.com Redmond, WA 98073-9757
Phone: 425-881-8004
Email:
paul.rutherford@adic.com
Mark Edwards
Senior Systems Architect
Eurologic Development, Ltd.
4th Floor, Howard House
Queens Ave, UK. BS8 1SD
Phone: +44 (0)117 930 9600
Email:
medwards@eurologic.com
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Appendix A
A. iFCP Support for Fibre Channel Link Services
For reference purposes, this appendix enumerates all the fibre
channel link services and the manner in which each shall be
processed by an iFCP implementation. The iFCP processing
policies are defined in section 7.
A.1 Basic Link Services
The basic link services are shown in the following table.
Basic Link Services
Name Description iFCP Policy
---- ----------- ----------
ABTS Abort Sequence Transparent
BA_ACC Basic Accept Transparent
BA_RJT Basic Reject Transparent
NOP No Operation Transparent
PRMT Preempted Rejected
(Applies to
Class 1 only)
RMC Remove Connection Rejected
(Applies to
Class 1 only)
A.2 Link Services Processed Transparently
The following link service requests and responses MUST be
processed transparently as defined in section 7.
ELSs Processed Transparently
Name Description
---- -----------
ACC Accept
ADVC Advise Credit
CSR Clock Synchronization Request
CSU Clock Synchronization Update
ECHO Echo
ESTC Estimate Credit
ESTS Establish Streaming
FACT Fabric Activate Alias_ID
FAN Fabric Address Notification
FDACT Fabric Deactivate Alias_ID
FDISC Discover F_Port Service
Parameters
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FLOGI F_Port Login
GAID Get Alias_ID
LCLM Login Control List Management
LINIT Loop Initialize
LIRR Link Incident Record
Registration
LPC Loop Port Control
LS_RJT Link Service Reject
LSTS Loop Status
NACT N_Port Activate Alias_ID
NDACT N_Port Deactivate Alias_ID
PDISC Discover N_Port Service
Parameters
PRLI Process Login
PRLO Process Logout
QoSR Quality of Service Request
RCS Read Connection Status
RLIR Registered Link Incident Report
RNC Report Node Capability
RNFT Report Node FC-4 Types
RNID Request Node Identification
Data
RPL Read Port List
RPS Read Port Status Block
RPSC Report Port Speed Capabilities
RSCN Registered State Change
Notification
RTIN Request Topology Information
RTV Read Timeout Value
RVCS Read Virtual Circuit Status
SBRP Set Bit-error Reporting
Parameters
SCL Scan Remote Loop
SCN State Change Notification
SCR State Change Registration
TEST Test
TPLS Test Process Login State
A.3 Augmented Link Services
The following extended link services are augmented with
additional data and processed by the iFCP implementation as
described in the referenced section listed in the table.
Augmented Link Services
Name Description Section
---- ----------- -------
ABTX Abort Exchange 7.3.1
ADISC Discover Address 7.3.2
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ADISC Discover Address Accept 7.3.3
ACC
FARP- Fibre Channel Address 7.3.4
REPLY Resolution Protocol Reply
FARP-REQ Fibre Channel Address 7.3.5
Resolution Protocol Request
LOGO N_PORT Logout 7.3.6
PLOGI Port Login 7.3.7
REC Read Exchange Concise 7.3.8
REC ACC Read Exchange Concise Accept 7.3.9
RES Read Exchange Status Block 7.3.10
RES ACC Read Exchange Status Block 7.3.11
Accept
RLS Read Link Error Status Block 7.3.12
RRQ Reinstate Recovery Qualifier 7.3.14
RSI Request Sequence Initiative 7.3.15
RSS Read Sequence Status Block 7.3.13
TPRLO Third Party Process Logout 7.3.16
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Appendix B
B. Performance of The Multi-Connection iFCP Session Model
This appendix provides a quantitative analysis of the claim
that N TCP connections carrying the traffic of all the
<N_PORT, N_PORT> sessions active between gateways provide
significantly higher aggregate average throughput than a
single TCP connection carrying the same <N_PORT, N_PORT>
sessions. The analysis shows that the difference is
proportional to the square of the number of TCP sessions, N.
This analyses is based on three fundamental assumptions: (i)
all the available bandwidth in a link is available to iFCP
traffic, (ii) the sender has always data ready to send (as is
most likely the case with a backup application), and (iii) the
maximum window size at the two TCP ends (i.e., the iFCP
gateways) is set to the link nominal capacity multiplied by
the round-trip-time (so as to have the highest chances of
saturating the link yet without unduly raising buffering
requirements at the end nodes). The N^2 factor that emerges
from this analysis is essentially due to the way TCP
congestion control reacts to packet losses.
B.1 Relationship of Throughput to Packet Losses
There are several reasons for packet losses: network
congestion, link errors and network errors. Network congestion
is pervasive in current IP networks, where the only way to
control congestion is through dropping packets. Techniques for
loss prevention, such as traffic engineering, admission
control and bandwidth reservation, are not widely deployed and
hence are not a factor in the behavior of existing networks.
Even in a perfectly engineered network, link errors occur.
Assuming a link error rate equal to that specified for Fibre
Channel (10^-12) and a 10Gb/s link, there is one error every
100 seconds. Network errors also occur with significant
frequency in IP networks. Jonathan Stone and Craig Partridge
recently reported in Sigcomm 2000 that network errors caught
by the TCP checksum occur with significant frequency. Between
one packet in 1100 and 1 in 32000 have errors get past the
link CRC and are detected by the TCP/IP checksum.
TCP throughput is impacted by each packet loss. Following
TCP's congestion control algorithm (supported by the Tahoe,
Reno, New-Reno, and SACK implementations) each packet loss
results in the TCP sender's congestion window being reduced to
half of its current value, and therefore (assuming constant
Round Trip Time), TCP's throughput is halved. After that, the
window increases by roughly one packet every two Round Trip
Times (assuming the widely-used Delayed-Acknowledgement
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algorithm). The temporary decrease in TCP's rate translates
into a missed opportunity to transmit a given amount of data.
As we show in the following Background section, for N storage
connections sharing an IP "pipe" of rate E, the amount of data
missing the opportunity to be transmitted due to a packet loss
is:
D(N) = E^2/(N^2)*RTT^2/(256*M)
where RTT = Round Trip Time, M = packet size.
For example, for a set of N=100 connections totaling E=10Gb/s,
RTT=10ms, M=1500B, the data not transmitted in time due to a
packet loss is D(N)=2.6MB. For the same set transported over
one TCP session, the data not sent in time is D(1)= 26GB, a
10,000 fold increase. The time interval for TCP to recover its
sending rate to its initial value after a packet loss is I(N)=
0.833 seconds in the case N TCP connections, and
I(1)=83.3seconds in the case of a single TCP connection.
Observe that in the latter case, the time to recover its rate,
I(1)=83.3s, is of the same order of magnitude as the time
between two packet losses due exclusively to a link Bit Error
Rate of 10^-12. In other words, a packet loss occurs almost
immediately after TCP has recovered its rate.
This means that a single TCP connection delivers on average
about 3/4 of the required 10Gb/s rate, since 1/4 of the rate
is lost during the time the TCP rate is increasing linearly
from 1/2 to full rate. (More precisely, the effective rate is
8.27Gb/s because 1/4 of the rate is lost during 83.3s, and the
time between two errors is now 120.825s due to a decreased
sending rate). By comparison, N TCP connections deliver
approximately 9.99979Gb/s (i.e., lost 1/4 of one TCP full rate
of 100Mb/s during 0.833s out of a 100s interval).
If the impact of TCP checksum errors is also considered, the
TCP sending rate is limited to an average of
(8M/RTT)sqrt(3/4p), where p is the probability of packet loss
(see [1] for details). For M=1500, RTT=10ms and p=1/32000, TCP
throughput is about 240Mb/s. For p=1/1100, maximum TCP
throughput is 34.4Mb/s. Therefore, to fill a 10Gb/s line,
about 42 simultaneous TCP flows are required (in the case
where p=1/32000) or 291 TCP flows (in the case where
p=1/1100).
Practically, for these reasons the iFCP protocol supports
combinations of M <N_PORT, N_PORT> tuples using N TCP
connections, with M, N >= 1, and with an individual <N_PORT,
N_PORT> tuple using at most one TCP connection (thus M >= N).
B.2 Background.
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For a TCP session to sustain a rate of C bits/second, the
TCP's maximum congestion window W (measured in number of
packets) has to be at least W0=RTT*C/(8*M) where RTT = Round
Trip Time in seconds, M = packet size in Bytes. The following
analyses assumes W=W0. Later, the problems with the
alternative W>W0 are discussed.
The time needed by the TCP sender to recover from a single
packet loss and have its sending rate reach the previous C
value is
I = 2*RTT*W/2 = RTT*W = RTT^2*C/(8*M).
The total amount of data (in Bytes) missing the opportunity to
be transmitted in this time interval I is:
D = C/8*I/4 = C^2*RTT^2/(256*M)
Consider a set of <N_PORT, N_PORT> tuples sharing an IP "pipe"
of rate E to be transported in N TCP sessions. Assuming all
connections are processed equally, each TCP session sends at a
rate of E/N. One packet loss impacts only one TCP session, and
thus, the total amount of data missing the opportunity to be
transmitted due to a packet loss is
D(N) = E^2/(N^2)*RTT^2/(256*M).
On the other hand, if the same set of <N_PORT, N_PORT> tuples
sharing an IP "pipe" of rate E is transported in one TCP
session only, the total amount of data losing the opportunity
to be transmitted due to a packet loss is
D(1) = E^2*RTT^2/(256*M) = D(N)*N^2.
The impact of packet losses on the single-TCP solution can be
reduced by configuring the maximum congestion window to be
larger than the bandwidth*delay product, W>W0. But in this
case, only W0 packets can be in transit on the line, while the
rest (up to the current window size) need to be stored in a
queue at the line's ingress. In order to provide full line
rate utilization assuming periodic losses, the maximum
congestion window should be at least 2*W0, due to TCP's
congestion
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1 Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.
2 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997
Monia Standards Track 67
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