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Versions: 00 01 02 03 04 05 06 07 08 09 rfc4391                         
INTERNET DRAFT                                                    Vivek Kashyap
<draft-ietf-ipoib-ip-over-infiniband-00.txt>                                IBM
Expiration Date: August 6, 2002                                  H.K. Jerry Chu
                                                               Sun Microsystems

                                                               February 6, 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.

        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

        The list of Internet-Draft Shadow Directories can be accessed
        at http://www.ietf.org/shadow.html

        This memo provides information for the Internet community.
        This memo does not specify an Internet standard of any kind.
        Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.


        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
        ARP/RARP. This document also describes the method of forming

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        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     Maximum Transmission Unit
        4.0     Frame Format
        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     Link-Layer Address in IPv6
        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

        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

        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

        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL

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        "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 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 components to support
        it [IPoIB_MCAST].

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        All IPoIB implementations MUST support IP over the unreliable
        datagram(UD) transport mode of IBA.

Note to WG: There is an ongoing discussion in the WG with respect to
            packet encapsulation. A consensus call by the chair on the
            'ethertype' discussion is awaited. The final draft of this
            document will reflect the consensus.

            The decision on 'ethertype' may effect the following two

            3.0 Maximum Transmission Unit
            4.0 Frame Format

3.0 Maximum Transmission Unit

        The IB architecture supports multiple MTU values: 256, 512,
        1024, 2048, 4096 bytes. An implementation determines the IPoIB
        link MTU from the MTU listed in the MCGroupRecord of the
        broadcast GID[IPoIB_MCAST]. The IPoIB link does not have a
        default MTU.

        It is RECOMMENDED that the IP MTU be set equal to that of the
        IPoIB link MTU.

        In IPv6 subnets the IP MTU derived from the IPoIB link MTU may
        be reduced by a Router 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 from the link MTU
        value by manual configuration of each node.

        For purposes of this document, information received from DHCP
        is considered "manually configured".

        Ethernet LANs, which are very common, support an MTU of 1500
        bytes. The IPv6 specification further requires a minimum MTU
        of 1280 bytes. Therefore it is very appropriate to set the IP
        MTU to these values depending on the networking needs. It must
        however be ensured that the IPoIB link MTU is at least 2048
        bytes. IBA MTUs of smaller values are not optimal for

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        internetworking to other IP subnets.

4.0 Frame Format

        The IP and ARP datagrams are directly encapsulated in IB's
        Unreliable Datagrams payload.

        |<------ IB Frame headers -------->|Payload|<-IB trailers -->|
        |Local  |      |Base     |Datagram |       |Invariant|Variant|
        |Routing| GRH* |Transport|Extended |IPv4/v6| CRC     | CRC   |
        |Header |Header|Header   |Transport|  /ARP |         |       |
        |       |      |         |Header   |       |         |       |
                                Figure 1

        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.

        The IP/ARP datagrams SHALL be encapsulated in IB unreliable
        datagrams in the payload. The QPs advertised for IP
        communication MUST NOT be used for other protocols.

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

        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.

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                   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].

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

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.

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        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
                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

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                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
                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

        |Reserved|         QPN[23-0]        |
        |           GID[127-96]             |
        +                                   +
        |           GID[95-64]              |
        +                                   +
        |           GID[63-32]              |
        +                                   +
        |           GID[31-0]               |

                        Figure 3

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        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
                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

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                two. This has to be ensured by the fabric

                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].

                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

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        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 Link-Layer Address in IPv6

        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.

        The source/target address option is specified as follows:

                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

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

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        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

[IPoIB_ARCH]    draft-ietf-ipoib-architecture-01.txt

[IPoIB_MCAST]   draft-ietf-ipoib-link-multicast-00.txt

[RFC2373]       IP Version 6 Addressing Architecture

[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

Phone: +1 503 578 3422
Email: vivk@us.ibm.com

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H.K. Jerry Chu

901 San Antonio Road, UMPK17-201
Palo Alto, CA 94303-4900

Phone: +1 650 786-5146
Email: jerry.chu@sun.com

Full Copyright Statement

        Copyright (C) The Internet Society (2001). All Rights Reserved.

        This document and translations of it may be copied and
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        part, without restriction of any kind, provided that the above
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        The limited permissions granted above are perpetual and will
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        This document and the information contained herein is provided

Kashyap, Chu                                                   [Page 13]

Vivek Kashyap
Linux Technology Center, IBM
503 578 3422 (o)