INTERNET DRAFT Vivek Kashyap
<draft-ietf-ipoib-ip-over-infiniband-01.txt> IBM
Expiration Date: November 20, 2002
H.K. Jerry Chu
Sun Microsystems
May 20, 2002
IP encapsulation and address resolution over InfiniBand networks
Status of this memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC 2026.
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This document specifies the frame format for transmission of
IP and ARP packets over InfiniBand networks. Unless explicitly
specified, the term 'IP' refers to both IPv4 and IPv6. The
term 'ARP' refers to all the ARP protocols/op-codes such as
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ARP/RARP. This document also describes the method of forming
IPv6 link-local addresses, and the content of the
source/target link layer address option used in Neighbour
solicitation and advertisement, router advertisement, router
redirect and router solicitation on IPv6 over InfiniBand.
Table of Contents
1.0 Introduction
2.0 InfiniBand Datalink
2.1 IP Support on IPoIB Link
3.0 Frame Format
4.0 Maximum Transmission Unit
5.0 IPv6 Stateless Autoconfiguration
5.1 IPv6 Link Local Address
6.0 Address Mapping - Unicast
6.1 Link-Information
6.1.1 Link Layer Address/Hardware Address
6.1.2 Auxiliary Link Information
6.2 Address Resolution in IPv4 Subnets
6.3 Address Resolution in IPv6 Subnets
7.0 IANA Considerations
8.0 Security Considerations
9.0 Acknowledgements
10.0 References
11.0 Authors' Addresses
1.0 Introduction
The InfiniBand specification[IB_ARCH] can be found at
www.infinibandta.org. The document [IPoIB_ARCH] provides a
short overview of InfiniBand architecture along with
considerations for specifying IP over InfiniBand networks. The
document [IPoIB_MCAST] defines the configuration of IPoIB
links and the support of IP multicast over InfiniBand
networks.
The InfiniBand architecture(IBA) defines multiple modes of
transport over which IP may be implemented. The unreliable
datagram(UD) transport method best matches the needs of IP and
the need for universality in general as described
in [IPoIB_ARCH].
This document specifies IPoIB over IB's unreliable
datagram(UD) mode. A separate document will describe the
implementation of IP subnets over IB's other transport
mechanisms.
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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.
2.0 InfiniBand Datalink
The document [IPoIB_MCAST] defines the IPoIB link, its setup,
and IP multicast over InfiniBand in detail. The following
discussion gives a short overview.
An IB subnet is formed by a network of IB nodes interconnected
either directly or via IB switches. IB subnets may be
connected using IB routers to form a fabric made of multiple
IB subnets. Multiple IP subnets may be overlaid over this IB
cloud. The boundary of this IP subnet is arbitrary and not
associated with a physical demarcation. The IPoIB nodes that
are members of this subnet are interconnected by an abstract
'link'. The link is defined by its members and common
characteristics such as the P_Key, link MTU and Q_Key that are
defined per 'link'.
IPv4 defines a limited-broadcast address over the link. All
IPv4 hosts that are members of the IPv4 subnet are members of
this address. IPv6 defines a multicast address referred to as
the all-IP hosts address. IPoIB associates a multicast GID
with these addresses [IPoIB_MCAST]. This multicast GID will
henceforth be referred to as the broadcast-GID. The
broadcast-GID is required to be setup for an IPoIB subnet to
be formed.
Every IPoIB interface MUST join the InfiniBand multicast group
defined by the broadcast-GID. This operation returns the MTU
and the Q_Key associated with the IPoIB link. Thus the IPoIB
subnet (and the link) is formed by the IPoIB nodes joining the
broadcast GID.
The P_Key is a configuration parameter that must be known
before the broadcast-GID can be formed[IPoIB_MCAST].
2.1 IP Support on IPoIB Link
The unreliable datagram (UD) mode of communication is
supported by all IB elements be they IB routers, HCAs or TCAs.
In addition to being the only universal transmission method it
supports multicasting, partitioning and a 32-bit
CRC [IB_ARCH]. Though multicasting support is optional in IB
fabrics, IPoIB architecture requires the participating
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components to support it [IPoIB_MCAST].
All IPoIB implementations MUST support IP over the unreliable
datagram (UD) transport mode of IBA.
3.0 Frame Format
All IP and ARP datagrams transported over InfiniBand are
prefixed by a 4-byte encapsulation header as illustrated
below.
+--------+--------+--------+--------+
| | |
| 16-bits | 16 bits |
| type[15-0] | Reserved |
+-----------------+-----------------+
Figure 1
The type field SHALL indicate the encapsulated protocol as per
the following table.
+----------+-------------+
| Type | Protocol |
|------------------------|
| 0x800 | IPv4 |
|------------------------|
| 0x806 | ARP |
|------------------------|
| 0x8035 | RARP |
|------------------------|
| 0x86DD | IPv6 |
+------------------------+
Table 1
These values are taken from the 'ETHER TYPE' numbers assigned
by [IANA]. Other network protocols, identified by different
values of 'ETHER TYPE', may use the encapsulation format
defined herein but such use is outside of the scope of this
document.
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|<------ IB Frame headers -------->|<- Payload ->|<- IB trailers ->|
+-------+------+---------+---------+-------------+---------+-------+
|Local | |Base |Datagram | | | |
|Routing| GRH* |Transport|Extended |4-byte header|Invariant|Variant|
|Header |Header|Header |Transport| + | CRC | CRC |
| | | |Header | IP/ARP | | |
+-------+------+---------+---------+-------------+---------+-------+
Figure 2
Figure 2 depicts the IB frame encapsulating an IP/ARP
datagram. The InfiniBand specification requires the use of
Global Routing Header (GRH) [IPoIB_ARCH] when multicasting or
when an InfiniBand packet traverses from one IB subnet to
another through an IB router. Its use is optional when used
for unicast transmission between nodes within an IB subnet.
The IPoIB implementation MUST be able to handle packets
received with or without the use of GRH.
4.0 Maximum Transmission Unit
Every IP/ARP datagram includes a 4 byte encapsulation header
as defined above. Therefore the IP MTU can be found by
subtracting 4 from the IPoIB link MTU.
To illustrate the calculation of IP MTU the following table
lists some likely values :
IPoIB Link MTU IP MTU
4096 4092
2048 2044
1504 1500
1284 1280
The IPv4 MTU MUST NOT be set below 1500 bytes. The minimum
IPv6 MTU is 1280 bytes [RFC2373].
IB links, switches and CAs support multiple MTUs (IB_MTU):
256, 512, 1024, 2048, 4096 bytes. The above conditions on IP
MTU require that IB components used in IPoIB subnets support a
minimum of 2048 byte MTUs. The IPoIB link MTU is set to the
MTU associated with the IB multicast group defined by the
broadcast-GID [IPoIB_MCAST].
In IPv6 subnets the MTU may be reduced by a Router
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Advertisement [RFC2461] containing an MTU option which
specifies a smaller MTU, or by manual configuration of each
node. If a Router Advertisement received on an IPoIB interface
has an MTU option specifying an MTU larger than the link MTU
or larger than a manually configured value, that MTU option
may be logged to system management but must be otherwise
ignored.
Similarly, the IPv4 MTU may also be reduced by manual
configuration of each node.
For purposes of this document, information received from DHCP
is considered "manually configured".
5.0 IPv6 Stateless Autoconfiguration
IB architecture associates an EUI-64 identifier termed the
GUID (Globally Unique Identifier) [IPoIB_ARCH, IB_ARCH] with
each port. The LID (16 bits) is unique within an IB subnet
only.
The interface identifier may be chosen from:
1) The EUI-64 compliant Globally unique
identifier(GUID) assigned by the manufacturer.
2) If the IPoIB subnet is fully contained within an IB
subnet any of the unique 16-bit LIDs of the port
associated with the IPoIB interface.
The LID values of a port may change after a
reboot/power-cycle of the IB node. Therefore, if a
persistent value is desired, it would be prudent to
not use the LID to form the interface identifier.
On the other hand, the LID provides an identifier
that can be used to create a more anonymous IPv6
address since the LID is not globally unique and is
subject to change over time.
It is RECOMMENDED that the link-local address be constructed
from the port's EUI-64 identifier as per the rules specified
in [RFC2373].
The interface identifier may also be chosen as per the
guidelines specified in [RFC3041].
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5.1 IPv6 Link Local Address
The IPv6 link local address for an IPoIB interface is formed
in accordance with the guidelines in [RFC2373]. The link local
address is of the format:
10 bits 54 bits 64 bits
+----------+-----------------------+----------------------------+
|1111111010| (zeros) | Interface Identifier |
+----------+-----------------------+----------------------------+
Figure 2
6.0 Address Mapping - Unicast
Address resolution in IPv4 subnets is accomplished through
Address Resolution protocol (ARP)[RFC826]. It is accomplished
in IPv6 subnets using the Neighbor discovery
protocol[RFC2461].
6.1 Link Information
An InfiniBand packet over the UD mode includes multiple
headers such as the LRH(local route header), GRH(global route
header), BTH(base transport header), DETH(datagram extended
header) as depicted in Figure 1 and specified in the
InfiniBand architecture[IB_ARCH]. All these headers comprise
the link-layer in an IPoIB link.
The parameters needed in these IBA headers constitute the
link-layer information that needs to be determined before an
IP packet may be transmitted across the IPoIB link.
The parameters that need to be determined are:
a) LID (local identifier)
The LID is always needed. A packet always includes the
LRH that is targeted at the remote node's LID, or an
IB router's LID to get to the remote node in another
IB subnet.
b) GID (global identifier)
The GID is not needed when exchanging information
within an IB subnet though it may be included in any
packet. It is an absolute necessity when transmitting
across the IB subnet since the IB routers use the GID
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to correctly forward the packets. The source and
destination GIDs are fields included in the GRH.
The GID, if formed using the GUID, can be used to
unambiguously identify an endpoint.
c) QPN (queue pair number)
Every unicast UD communication is always directed to a
particular queue pair(QP) at the peer.
d) Q_Key
A Q_Key is associated with each unreliable datagram
QPN. The received packets must contain a Q_Key that
matches the QP's Q_Key to be accepted.
e) P_Key
A successful communication between two IB nodes using
UD mode can occur only if the two nodes have
compatible P_Keys. This is referred to as being in the
same partition[IB_ARCH]. P_Keys are checked at the
receiving channel adapter and may be optionally
checked at intermediate switches/IB routers. If the
P_Key in the packet does not match the expected P_Key
the packet is dropped.
f) SL (service level)
Every IBA packet contains an SL value. A path in IBA
is defined by the three-tuple (source LID, destination
LID, SL). The SL in turns is mapped to a virtual
lane(VL) at every xCA, switch that sends/forwards the
packet [IPoIB_ARCH]. Multiple SLs may be used between
two endpoints to provide for load-balancing, SLs may
be used for providing a QoS infrastructure, or may be
used to avoid deadlocks in the IBA fabric.
Another auxiliary piece of information, not included in the
IBA headers, is :
g) Path rate
The InfiniBand architecture defines multiple link
speeds. A higher speed transmitter can swamp
switches/xCAs. To avoid such congestion every source
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transmitting at greater than 1x speeds is required to
determine the 'path rate' before the data may be
transmitted [IB_ARCH].
6.1.1 Link Layer Address/Hardware Address
Though the list of information required for a successful
transmittal of an IPoIB packet is large not all the
information need be determined during the IP address
resolution process.
The IPoIB link-layer address used in the source/target
link-layer address option in IPv6 and the 'hardware address'
in IPv4/ARP has the same format.
The format is as described below:
+--------+--------+--------+--------+
|Reserved| QPN[23-0] |
+--------+--------+--------+--------+
| GID[127-96] |
+ +
| GID[95-64] |
+ +
| GID[63-32] |
+ +
| GID[31-0] |
+--------+--------+--------+--------+
Figure 3
a) Reserved Flags
These 8 bits are reserved for future use. These bits
MUST be set to zero on send and ignored on receive
unless specified differently in a future document.
b) Queue Pair Number (QPN)
Every unicast communication in IB architecture is
directed to a specific queue pair(QP)[IB_ARCH]. This
QP number is included in the link description. All IP
communication to the relevant IPoIB interface MUST be
directed to this QPN. In the case of IPv4 subnets the
address resolution protocol(ARP) reply packets are
also directed to the same QPN.
The choice of the QPN for IP/ARP communication is up
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to the implementation.
c) Global Identifier (GID)
This is one of the Global Identifiers(GIDs)[IB_ARCH]
of the port associated with the IPoIB interface. IB
associates multiple GIDs with a port. It is
RECOMMENDED that the GID formed by the combination of
the IB subnet prefix and the port's GUID be included
in the link-layer/hardware address.
6.1.2 Auxiliary Link Information
The rest of the parameters are determined as follows:
a) Local Identifier(LID)
The method of determining the peer's LID is not
defined in this document. It is up to the
implementation to use any of the IBA approved methods
to determine the destination LID. One such method is
to use the GID determined during the address
resolution, to retrieve the associated LID from the IB
routing infrastructure or the SA.
It is the responsibility of the administrator to
ensure that the IB subnet(s) have unicast connectivity
between the IPoIB nodes. The GID exchanged between two
endpoints in a multicast message(ARP/ND) does not
guarantee the existence of a unicast path between the
two. This has to be ensured by the fabric
administrator.
There may be multiple LIDs, and hence paths, between
the endpoints. The criteria for selection of the LIDs
are beyond the scope of this document.
b) Q_Key
The Q_Key received on joining the broadcast-GID MUST
be used for all IPoIB communication over the
particular IPoIB link.
c) P_Key
The network administrator is required to setup an
IPoIB link by setting up an IB partition and assigning
it a unique P_Key[IPoIB_MCAST].
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Thus the P_Key to be used in the IP subnet is not
discovered but is a configuration parameter.
d) Service Level(SL)
The method of determining the SL is not defined in
this document. The SL is determined by any of the IBA
approved methods.
e) Path rate
The implementation must leverage IB methods to
determine the path rate as required.
6.2 Address Resolution in IPv4 Subnets
The ARP packet header is as defined in [RFC826]. The hardware
type is set to 32(decimal) as specified by Internet Assigned
Numbers Authority(IANA). The rest of the fields are used as
per RFC826.
16 bits: hardware type
16 bits: protocol
8 bits: length of hardware address
8 bits: length of protocol address
16 bits: ARP operation
The remaining fields in the packet hold the sender/target
hardware and protocol addresses.
[ sender hardware address ]
[ sender protocol address ]
[ target hardware address ]
[ target protocol address ]
The hardware address included in the ARP packet will be as
specified in section 6.1.1 and depicted in Figure 3.
The length of the hardware address used in ARP packet header
therefore is 20.
6.3 Address Resolution in IPv6 Subnets
The Source/Target Link-layer address option is used in Router
Solicit, Router advertisements, Redirect, Neighbour
Solicitation and Neighbour Advertisement messages when such
messages are transmitted on InfiniBand networks.
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The source/target address option is specified as follows:
Type:
Source Link-layer address 1
Target Link-layer address 2
Length: 3
Link-layer address:
The link-layer address is as specified in section
6.1.1 and depicted in Figure 3.
7.0 IANA Considerations
To support ARP over InfiniBand a value for the Address
Resolution Parameter 'Number Hardware Type (hrd)' is required.
IANA has assigned the number '32' to indicate
InfiniBand[IANA_ARP].
8.0 Security Considerations
This document specifies IP transmission over a multicast
network. Any network of this kind is vulnerable to a sender
claiming another's identity and forge traffic or eavesdrop. It
is the responsibility of the higher layers or applications to
implement suitable counter-measures if this is a problem.
9.0 Acknowledgements
The authors would like to thank Bruce Beukema, David Brean,
Dan Cassiday, Yaron Haviv, Thomas Narten, Erik Nordmark, Greg
Pfister, Jim Pinkerton, Renato Recio, Kevin Reilly, Madhu
Talluri and Satya Sharma for their suggestions and many
clarifications on the IBA specification.
10.0 References
[IB_ARCH] InfiniBand Architecture Specification, Volume 1.0a
www.infinibandta.org
[IPoIB_ARCH] draft-ietf-ipoib-architecture-01.txt
[IPoIB_MCAST] draft-ietf-ipoib-link-multicast-00.txt
[RFC2373] IP Version 6 Addressing Architecture
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[RFC2375] IPv6 Multicast Address Assignments
[RFC826] An Ethernet Address Resolution Protocol
[RFC1700] Assigned Numbers.
[RFC2434] Guidelines for Writing an IANA Considerations Section in RFCs
[RFC2461] Neighbor Discovery for IP version 6 (IPv6)
[RFC3041] Extensions to IPv6 Address Autoconfiguration
[IANA] Internet assigned numbers authority, www.iana.org
[IANA_ARP] www.iana.org/assignments/arp-parameters
11.0 Authors' Address
Vivek Kashyap
15450, SW Koll Parkway
Beaverton, OR 97006
USA
Phone: +1 503 578 3422
Email: vivk@us.ibm.com
H.K. Jerry Chu
17 Network Circle, UMPK17-201
Menlo Park, CA 94025
USA
Phone: +1 650 786-5146
Email: jerry.chu@sun.com
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