Request for Comments: 4338 Cisco Systems
Obsoletes: 3831, 2625 C. Carlson
Category: Standards Track QLogic Corporation
R. Nixon
Emulex
January 2006
Transmission of IPv6, IPv4, and
Address Resolution Protocol (ARP) Packets over Fibre Channel
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document specifies the way of encapsulating IPv6, IPv4, and
Address Resolution Protocol (ARP) packets over Fibre Channel. This
document also specifies the method of forming IPv6 link-local
addresses and statelessly autoconfigured IPv6 addresses on Fibre
Channel networks, and a mechanism to perform IPv4 address resolution
over Fibre Channel networks.
This document obsoletes RFC 2625 and RFC 3831.
Table of Contents
1. Introduction ....................................................3
2. Summary of Fibre Channel ........................................4
2.1. Overview ...................................................4
2.2. Identifiers and Login ......................................5
2.3. FC Levels and Frame Format .................................5
2.4. Sequences and Exchanges ....................................6
3. IP-capable Nx_Ports .............................................7
4. IPv6, IPv4, and ARP Encapsulation ...............................7
4.1. FC Sequence Format for IPv6 and IPv4 Packets ...............7
4.2. FC Sequence Format for ARP Packets .........................9
4.3. FC Classes of Service .....................................10
4.4. FC Header Code Points .....................................10
4.5. FC Network_Header .........................................11
4.6. LLC/SNAP Header ...........................................12
4.7. Bit and Byte Ordering .....................................12
4.8. Maximum Transfer Unit .....................................12
5. IPv6 Stateless Address Autoconfiguration .......................13
5.1. IPv6 Interface Identifier and Address Prefix ..............13
5.2. Generating an Interface ID from a Format 1 N_Port_Name ....14
5.3. Generating an Interface ID from a Format 2 N_Port_Name ....15
5.4. Generating an Interface ID from a Format 5 N_Port_Name ....16
5.5. Generating an Interface ID from an EUI-64 Mapped
N_Port_Name ...............................................17
6. Link-local Addresses ...........................................18
7. ARP Packet Format ..............................................18
8. Link-layer Address/Hardware Address ............................20
9. Address Mapping for Unicast ....................................20
9.1. Overview ..................................................20
9.2. IPv6 Address Mapping ......................................20
9.3. IPv4 Address Mapping ......................................21
10. Address Mapping for Multicast .................................22
11. Sequence Management ...........................................23
12. Exchange Management ...........................................23
13. Interoperability with RFC 2625 ................................24
14. Security Considerations .......................................25
15. IANA Considerations ...........................................25
16. Acknowledgements ..............................................25
17. Normative References ..........................................26
18. Informative References ........................................26
A. Transmission of a Broadcast FC Sequence over FC Topologies
(Informative) ..................................................28
B. Validation of the <N_Port_Name, N_Port_ID> Mapping
(Informative) ..................................................29
C. Fibre Channel Bit and Byte Numbering Guidance ..................30
D. Changes from RFC 2625 ..........................................31
E. Changes from RFC 3831 ..........................................31
1. Introduction
Fibre Channel (FC) is a high-speed serial interface technology that
supports several Upper Layer Protocols including Small Computer
System Interface (SCSI), IPv6 [IPv6], and IPv4 [IPv4].
[RFC-2625] defined how to encapsulate IPv4 and Address Resolution
Protocol (ARP) packets over Fibre Channel for a subset of Fibre
Channel devices. This specification enables the support of IPv4 for
a broader category of Fibre Channel devices. In addition, this
specification simplifies [RFC-2625] by removing unused options and
clarifying current implementations. This document obsoletes
[RFC-2625].
Specific [RFC-2625] limitations that this document aims to resolve
are the following:
- N_Port_Name format restriction. [RFC-2625] restricts the use of
IPv4 to Fibre Channel devices having the format 0x1 N_Port_Name,
but many current implementations use other N_Port_Name formats.
- Use of Fibre Channel Address Resolution Protocol (FARP).
[RFC-2625] requires the support of FARP to map N_Port_Names to
N_Port_IDs, but many current implementations use other methods,
such as the Fibre Channel Name Server.
- Missing support for IPv4 multicast. [RFC-2625] does not specify
how to transmit IPv4 packets with a multicast destination address
over Fibre Channel.
[RFC-3831] defines how to encapsulate IPv6 over Fibre Channel and a
method of forming IPv6 link-local addresses [AARCH] and statelessly
autoconfigured IPv6 addresses on Fibre Channel networks. [RFC-3831]
also describes the content of the Source/Target Link-layer Address
option used in Neighbor Discovery [DISC] when the messages are
transmitted on a Fibre Channel network. This document obsoletes
[RFC-3831].
Warning to readers familiar with Fibre Channel: both Fibre Channel
and IETF standards use the same byte transmission order. However,
the bit numbering is different. See Appendix C for guidance.
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 [KEYWORDS].
2. Summary of Fibre Channel
2.1. Overview
Fibre Channel (FC) is a gigabit-speed network technology primarily
used for storage networking. Fibre Channel is standardized in the
T11 Technical Committee of the InterNational Committee for
Information Technology Standards (INCITS), an American National
Standard Institute (ANSI) accredited standards committee.
Fibre Channel devices are called Nodes. Each Node has one or more
Ports that connect to Ports of other devices. Fibre Channel may be
implemented using any combination of the following three topologies:
- a point-to-point link between two Ports;
- a set of Ports interconnected by a switching network called a
Fabric, as defined in [FC-FS];
- a set of Ports interconnected with a loop topology, as defined in
[FC-AL-2].
A Node Port that does not operate in a loop topology is called an
N_Port. A Node Port that operates in a loop topology using the
loop-specific protocols is designated as an NL_Port. The term
Nx_Port is used to indicate a Node Port that is capable of operating
in either mode.
A Fabric Port that does not operate in a loop topology is called an
F_Port. A Fabric Port that operates in a loop topology using the
loop-specific protocols is designated as an FL_Port. The term
Fx_Port is used to indicate a Fabric Port that is capable of
operating in either mode.
A Fibre Channel network, built with any combination of the FC
topologies described above, is a multiaccess network with broadcast
capabilities.
From an IPv6 point of view, a Fibre Channel network is an IPv6 Link
[IPv6]. IP-capable Nx_Ports are what [IPv6] calls Interfaces.
From an IPv4 point of view, a Fibre Channel network is an IPv4 Local
Network [IPv4]. IP-capable Nx_Ports are what [IPv4] calls Local
Network Interfaces.
2.2. Identifiers and Login
Fibre Channel entities are identified by non-volatile 64-bit
Name_Identifiers. [FC-FS] defines several formats of
Name_Identifiers. The value of the most significant 4 bits defines
the format of a Name_Identifier. These Name_Identifiers are referred
to in a more concise manner as follows:
- an Nx_Port’s Name_Identifier is called N_Port_Name;
- an Fx_Port’s Name_Identifier is called F_Port_Name;
- a Node’s Name_Identifier is called Node_Name;
- a Fabric’s Name_Identifier is called Fabric_Name.
An Nx_Port connected to a Fibre Channel network is associated with
two identifiers, its non-volatile N_Port_Name and a volatile 24-bit
address called N_Port_ID. The N_Port_Name is used to identify the
Nx_Port, and the N_Port_ID is used for communications among Nx_Ports.
Each Nx_Port acquires an N_Port_ID from the Fabric by performing a
process called Fabric Login, or FLOGI. The FLOGI process is used
also to negotiate several communications parameters between the
Nx_Port and the Fabric, such as the receive data field size, which
determines the maximum size of the Fibre Channel frames that may be
transferred between the Nx_Port and the Fabric.
Before effective communication may take place between two Nx_Ports,
they must complete a process called Port Login, or PLOGI. The PLOGI
process provides each Nx_Port with the other Nx_Port’s N_Port_Name,
and negotiates several communication parameters, such as the receive
data field size, which determines the maximum size of the Fibre
Channel frames that may be transferred between the two Nx_Ports.
Both Fabric Login and Port Login may be explicit (i.e., performed
using specific FC control messages called Extended Link Services, or
ELSes) or implicit (i.e., in which the parameters are specified by
configuration or other methods).
2.3. FC Levels and Frame Format
[FC-FS] describes the Fibre Channel protocol using 5 different
levels. The FC-2 and FC-4 levels are relevant for this
specification. The FC-2 level defines the FC frame format, the
transport services, and the control functions necessary for
information transfer. The FC-4 level supports Upper Level Protocols,
such as IPv6, IPv4, and SCSI. The Fibre Channel frame format is
shown in figure 1.
+-----+-----------+-----------+--------//-------+-----+-----+
| | | Data Field | | |
| SOF | FC Header |<--------------------------->| CRC | EOF |
| | | Optional | Frame | | |
| | | Header(s) | Payload | | |
+-----+-----------+-----------+--------//-------+-----+-----+
Figure 1: Fibre Channel Frame Format
The Start of Frame (SOF) and End of Frame (EOF) are special FC
transmission words that act as frame delimiters. The Cyclic
Redundancy Check (CRC) is 4 octets long and is used to verify the
integrity of a frame.
The FC Header is 24 octets long and contains several fields
associated with the identification and control of the Data Field.
The Data Field is of variable size, ranging from 0 to 2112 octets,
and includes the user data in the Frame Payload field and Optional
Headers. The currently defined Optional Headers are the following:
- ESP_Header;
- Network_Header;
- Association_Header;
- Device_Header.
The value of the SOF field determines the FC Class of service
associated with the frame. Five Classes of service are specified in
[FC-FS]. They are distinguished primarily by the method of flow
control between the communicating Nx_Ports and by the level of data
integrity provided. A given Fabric or Nx_Port may support one or
more of the following Classes of service:
- Class 1: Dedicated physical connection with delivery confirmation;
- Class 2: Frame multiplexed service with delivery confirmation;
- Class 3: Datagram service;
- Class 4: Fractional bandwidth;
- Class 6: Reliable multicast via dedicated connections.
Classes 3 and 2 are commonly used for storage networking
applications; Classes 1 and 6 are typically used for specialized
applications in avionics. Class 3 is recommended for IPv6, IPv4, and
ARP (see section 4.3).
2.4. Sequences and Exchanges
An application-level payload such as an IPv6 or IPv4 packet is called
an Information Unit at the FC-4 level of Fibre Channel. Each FC-4
Information Unit is mapped to an FC Sequence by the FC-2 level. An
FC Sequence consists of one or more FC frames related by the value of
the Sequence_ID (SEQ_ID) field of the FC Header.
The architectural maximum data that may be carried by an FC frame is
2112 octets. The maximum usable frame size depends on the Fabric and
Nx_Port implementations and is negotiated during the Login process.
Whenever an Information Unit to be transmitted exceeds this value,
the FC-2 level segments it into multiple FC frames, sent as a single
Sequence. The receiving Nx_Port reassembles the Sequence of frames
and delivers a reassembled Information Unit to the FC-4 level. The
Sequence Count (SEQ_CNT) field of the FC Header may be used to ensure
frame ordering.
Multiple Sequences may be grouped together as belonging to the same
FC Exchange. The Exchange is a mechanism used by two Nx_Ports to
identify and manage an operation between them. The Exchange is
opened when the operation is started between the two Nx_Ports, and
closed when the operation ends. FC frames belonging to the same
Exchange are related by the value of the Exchange_ID fields in the FC
Header. An Originator Exchange_ID (OX_ID) and a Responder
Exchange_ID (RX_ID) uniquely identify the Exchange between a pair of
Nx_Ports.
3. IP-capable Nx_Ports
This specification requires an IP-capable Nx_Port to have the
following properties:
- The format of its N_Port_Name MUST be one of 0x1, 0x2, 0x5, 0xC,
0xD, 0xE, 0xF (see section 5.1);
- It MUST support Class 3;
- It MUST support continuously increasing SEQ_CNT [FC-FS];
- It MUST be able to transmit and receive an FC-4 Information Unit
at least 1304 octets long (see section 4.1);
- It SHOULD support a receive data field size for Device_Data FC
frames of at least 1024 octets (see section 10).
4. IPv6, IPv4, and ARP Encapsulation
4.1. FC Sequence Format for IPv6 and IPv4 Packets
An IPv6 or IPv4 packet is mapped to an Information Unit at the FC-4
level of Fibre Channel, which in turn is mapped to an FC Sequence by
the FC-2 level [FC-FS]. An FC Information Unit containing an IP
packet MUST carry the FC Network_Header [FC-FS] and the Logical Link
Control/SubNetwork Access Protocol (LLC/SNAP) header [IEEE-LLC],
resulting in the FC Information Unit format shown in figure 2.
+---------------+---------------+---------------+---------------+
| |
+- -+
| Network_Header |
+- (16 octets) -+
| |
+- -+
| |
+---------------+---------------+---------------+---------------+
| LLC/SNAP header |
+- (8 octets) -+
| |
+---------------+---------------+---------------+---------------+
| |
+- -+
/ IPv6 or IPv4 Packet /
/ /
+- -+
| |
+---------------+---------------+---------------+---------------+
Figure 2: FC Information Unit Mapping an IP Packet
In order to support the minimum IPv6 MTU (i.e., 1280 octets), an
Nx_Port supporting IP MUST be able to transmit and receive an FC-4
Information Unit at least 1304 octets long (i.e., 1280 + 8 + 16).
The FC ESP_Header [FC-FS] MAY be used to secure the FC frames
composing an IP FC Sequence. Other FC Optional Headers MUST NOT be
used in an IP FC Sequence.
An IP FC Sequence often consists of more than one frame, all frames
having the same TYPE (see section 4.4). The first frame of the
Sequence MUST include the FC Network_Header and the LLC/SNAP header.
The other frames MUST NOT include them, as shown in figure 3.
First Frame of an IP FC Sequence
+-----------+-------------------+-----------------+-------//--------+
| FC Header | FC Network_Header | LLC/SNAP header | First chunk of |
| | | | the IP Packet |
+-----------+-------------------+-----------------+-------//--------+
Subsequent Frames of an IP FC Sequence
+-----------+-----------------//--------------------+
| FC Header | Additional chunk of the IP Packet |
+-----------+----------------//---------------------+
Figure 3: Optional Headers in an IP FC Sequence
4.2. FC Sequence Format for ARP Packets
An ARP packet is mapped to an Information Unit at the FC-4 level of
Fibre Channel, which in turn is mapped to an FC Sequence by the FC-2
level. An FC Information Unit containing an ARP packet MUST carry
the FC Network_Header [FC-FS] and the LLC/SNAP header [IEEE-LLC],
resulting in the FC Information Unit format shown in figure 4.
+---------------+---------------+---------------+---------------+
| |
+- -+
| Network_Header |
+- (16 octets) -+
| |
+- -+
| |
+---------------+---------------+---------------+---------------+
| LLC/SNAP header |
+- (8 octets) -+
| |
+---------------+---------------+---------------+---------------+
| |
+- -+
/ ARP Packet /
/ /
+- -+
| |
+---------------+---------------+---------------+---------------+
Figure 4: FC Information Unit Mapping an ARP Packet
Given the limited size of an ARP packet (see section 7), an FC