GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc4755

Network Working Group V. Kashyap Request for Comments: 4755 IBM Category: Standards Track December 2006

                 IP over InfiniBand: Connected Mode

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 IETF Trust (2006).

Abstract

 This document specifies transmission of IPv4/IPv6 packets and address
 resolution over the connected modes of InfiniBand.

Kashyap Standards Track [Page 1] RFC 4755 Connected Mode IPoIB December 2006

Table of Contents

 1. Introduction ....................................................2
 2. IPoIB-connected Mode ............................................3
    2.1. Multicasting ...............................................3
    2.2. Outline of Address Resolution ..............................4
    2.3. Outline of Connection Setup ................................4
 3. Address Resolution ..............................................4
    3.1. Link-layer Address .........................................4
    3.2. IB Connection Setup ........................................6
    3.3. Simultaneous IB Connections ................................6
    3.4. IPoIB-CM IB Connection Teardown ............................7
    3.5. Service-ID .................................................7
 4. Frame Format ....................................................8
 5. Maximum Transmission Unit .......................................8
    5.1. Per-Connection MTU .........................................9
 6. Private-Data Format .............................................9
 7. IPoIB-CM Considerations ........................................10
    7.1. A Cautionary Note on IPoIB-RC .............................10
    7.2. IPoIB-CM Per-Destination MTU ..............................10
 8. Security Considerations ........................................11
 9. IANA Considerations ............................................11
 10. Acknowledgements ..............................................11
 11. Normative References ..........................................11
 12. Informative References ........................................11

1. Introduction

 The InfiniBand specification [IB_ARCH] can be found at
 www.infinibandta.org.  The document [RFC4392] provides a short
 overview of InfiniBand architecture along with consideration for
 specifying IP over InfiniBand networks.
 The InfiniBand Architecture (IBA) defines multiple modes of
 transports.  Of these the unreliable datagram (UD) transport method
 best matches the needs of IP.  IP over InfiniBand (IPoIB) over UD is
 described in [RFC4391].  This document describes IP transmission over
 the connected modes of IBA.
 IBA defines two connected modes:
    1.  Reliable Connected (RC)
    2.  Unreliable Connected (UC)
 As is evident from the nomenclature, the two modes differ mainly in
 providing reliability of data delivery across the connection.  This
 document applies equally to both the connected modes.  IPoIB over
 these two modes is referred to as IPoIB-CM (connected mode) in this

Kashyap Standards Track [Page 2] RFC 4755 Connected Mode IPoIB December 2006

 document.  For clarity, IPoIB over the unreliable datagram mode as
 described in [RFC4391] is referred to as IPoIB-UD.
 IBA requires that all Host Channel Adapters (HCAs) support the
 reliable and unreliable connected modes [IB_ARCH].  It is optional
 for Target Channel Adapters (TCAs) to support the connected modes.
 The connected modes offer link MTUs of up to 2^31 octets in length.
 Thus, the use of connected modes can offer significant benefits by
 supporting reasonably large MTUs.  The datagram modes of InfiniBand
 Architecture (IBA) are limited to 4096 octets.
 Reliability is also enhanced if the underlying feature of "automatic
 path migration" supported by the connected modes is utilized.
 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 [RFC2119].

2. IPoIB-connected Mode

 IPoIB over connected mode is an OPTIONAL extension to IPoIB-UD.
 Every IPoIB implementation MUST support [RFC4391] and MAY support the
 extensions described in this document.
 Therefore, IP encapsulation, default MTU, link-layer address format,
 and the IPv6 stateless autoconfiguration mechanism apply to IPoIB-CM
 exactly as described in [RFC4391].

2.1. Multicasting

 The connected modes of IBA define a non-broadcast, multiple-access
 network.  The connected modes of IBA do not support multicasting
 though every node can communicate with every other node if desired.
 This requires that multicasting be emulated in some form by the
 network.  However, in the case of an InfiniBand network, instead of
 an emulation, an unreliable datagram (UD) queue pair (QP) can be used
 to support multicasting while the connected mode QP is used for
 unicast traffic.  Since every IPoIB implementation is required to
 support the UD mode, every implementation supporting IPoIB-CM will be
 able to utilize the pre-existing IPoIB-UD QP for all
 broadcast/multicast communications.  Multicast mapping, transmission,
 and reception of multicast packets and multicast routing MUST use the
 UD QP associated with the IPoIB interface.

Kashyap Standards Track [Page 3] RFC 4755 Connected Mode IPoIB December 2006

2.2. Outline of Address Resolution

 Every IPoIB-CM interface MUST have two sets of QPs associated with
 it:
    1) One unreliable datagram QP
    2) One or more connected mode QPs
 [RFC4391] describes the address resolution method to determine the
 link address of the peer.  This response is received on the UD QP
 associated with the IPoIB interface.

2.3. Outline of Connection Setup

 Once the link address of the remote node is known, an IB connection
 must be set up between the nodes before any IP communication may
 occur.
 To make a connection, the sender must know the service-ID to use in
 the request to make a connection [IB_ARCH].  It must also supply the
 "connection mode" queue pair to the remote node.  The peer replies
 with its queue pair.  Each IB connection is peer to peer and uses one
 connected mode QP at each end.
 Though the address resolution occurs at an individual IP address
 level, the connection between the nodes is at the IB layer.
 Therefore, every individual address resolution does not imply a new
 connection between the peers.

3. Address Resolution

 Address resolution queries are sent out on the "broadcast-GID"
 (Broadcast-Group Identifier) over the UD QP associated with the IPoIB
 interface [RFC4391].  A unicast reply is received on the UD QP.

3.1. Link-layer Address

 IPoIB encapsulation [RFC4391] describes the link-layer address as
 follows:
    <1 octet reserved>:QP: GID
 This document extends the link-layer address as follows:
    <Flags>:QPN:GID

Kashyap Standards Track [Page 4] RFC 4755 Connected Mode IPoIB December 2006

 Flags:
    This is a single-octet field.  The bits indicate the connected
    modes supported by the interface.
    Bit 0 specifies the support for the "reliable connected" (RC)
    mode.  Bit 1 indicates the support for the "unreliable connected"
    (UC) mode.  All other bits in the octet are reserved and MUST be
    set to 0 on transmits and ignored on receives.  The format of the
    flags is as follows:
              +--+--+--+--+--+--+--+--+
              |RC|UC| 0| 0| 0| 0| 0| 0|
              +--+--+--+--+--+--+--+--+
    Both the RC and UC MAY be set at the same time if the interface
    supports both the modes.  Since the IPoIB-UD mode is always
    supported, there are no flags to indicate IPoIB-UD support.
    If IPoIB-CM is not supported, i.e., if the implementation only
    supports IPoIB-UD, then the implementation MUST ignore the <Flags>
    on reception.  It MUST set the <Flags> octet to all zeros on
    transmission as specified in [RFC4391].
 QPN:
    The queue-pair number (QPN) on which the unicast address
    resolution replies will be received [RFC4391].  An IPoIB interface
    has only one UD QP associated with it whether or not it supports
    this extension.
    The QPN also serves another purpose.  It is used to form the
    Service-ID that is used to set up the IB connection.
 On receiving the multicast/broadcast address resolution request, the
 receiver replies with its own link address, including the associated
 UD QPN and the appropriate flags.
 The receiver's reply is unicast back to the sender after the receiver
 has, as in the case of IPoIB-UD, resolved the GID to the Local
 Identifier (LID), and determined other required parameters [RFC4391].
 Once the address resolution is completed, the underlying IB
 connection on the supported connection modes can be set up.  An
 implementation is NOT REQUIRED to set up a connection merely because
 the peer indicates the capability.  The decision to make such a
 connection is left to the implementation.

Kashyap Standards Track [Page 5] RFC 4755 Connected Mode IPoIB December 2006

3.2. IB Connection Setup

 Once the address resolution is complete, the IB connection can be set
 up by either of the peers.  To set up a connection, IB Management
 Datagrams (MADs) are directed to the peer's communication manager
 (CM).  The connection request always contains a Service-ID for the
 peer to associate the request with the appropriate service.  If the
 request is accepted, the peer returns the relevant connected mode QPN
 in the response MAD.  The format of the CM connection messages and
 the IB connection setup process is described in [IB_ARCH].  The
 overall handshake is of the form:
           REQ ---->
                <---- REP [or REJ(reject)]
           RTA ---->
           [or REJ(reject)]
 The CM messages include, among other parameters, the Service-ID,
 Local connection-mode QPN, and the payload size to use over the
 connection.
 Note: The IB connection is set up using the Service-ID as defined in
       Section 3.5 below.  The node MUST keep a record of IB
       connections it is participating in.  The node MAY attempt
       another connection to the remote peer using the same Service-ID
       as used for an existing IB connection.  Similarly, the receiver
       of such a connection MAY drop the request with a suitable error
       indication in the CM response.  The decision to accept or
       initiate multiple connections from or to an IPoIB interface is
       left to the implementation.
 The node that initiated the connection is aware of the target node's
 IP address as described above.  The node receiving the IB connection
 request, however, cannot determine the initiating node's link
 address.  To enable this determination, every CM message exchanged in
 setting up the IB connection MUST include the sender's IPoIB-UD QPN
 in the "private data" [IB_ARCH] field.  The IPoIB-UD QPN MUST be
 included in all "REJ" [IB_ARCH] messages too.

3.3. Simultaneous IB Connections

 To ensure that two IB connections are not set up between the peers
 due to REQ crossing, the following rules MUST be followed:
    The receiver forms the remote node's link-layer address using the
    UD QPN received in the "private data" field of the "REQ" message
    and the GID of the sender included in the "REQ" message.  The
    link-layer address is used to determine if there is already an

Kashyap Standards Track [Page 6] RFC 4755 Connected Mode IPoIB December 2006

    outstanding connection request "REQ" sent by the local interface
    to the given received link-layer address.  If such an outstanding
    request is determined, then the two link-layer addresses (local
    and remote) are numerically compared.  If the local link-layer
    address is numerically smaller, then the connection is accepted,
    otherwise rejected.  The error code in "REJ" MAD is set to
    "Consumer Reject" [IB_ARCH].
    Note: The link-layer addresses formed for comparison zero out the
          connection mode flags specified in Section 3.1.  The
          comparison is performed from the most significant octet to
          the least significant octet of the link-layer address.
    The above holds even if the receiver supports multiple IB
    connections from the same peer.  This is to ensure that only one
    more connection is set up when the "REQ" messages cross.

3.4. IPoIB-CM IB Connection Teardown

 IB connections created through IPoIB-CM are considered part of an
 IPoIB interface.  As such, they SHOULD be torn down when the IPoIB
 interfaces they are associated with are torn down.
 Furthermore, the IB connection between two peers MAY be torn down by
 either peer whenever the address resolution entry expires.  An
 implementation is free to implement alternative policies for tearing
 down of IB connections between peers.

3.5. Service-ID

 The InfiniBand specification defines a block of Service-IDs for IETF
 use.  The InfiniBand specification has left the definition and
 management of this block to the IETF [IB_ARCH].  The 64-bit block is
 as follows:
+--------+--------+--------+--------+-------+--------+--------+------+
|00000001|<-------------------IETF use------------------------------>|
+--------+--------+--------+--------+-------+--------+--------+------+

Kashyap Standards Track [Page 7] RFC 4755 Connected Mode IPoIB December 2006

 The Service-IDs used by IPoIB will be in the following format:
+--------+--------+--------+--------+-------+-------+--------+-------+
|00000001|  Type  |         Reserved        |        QPN             |
+--------+--------+--------+--------+-------+-------+--------+-------+
       The "Type" field MUST be set to 0.
       The "Reserved" field MUST be set to zeros.
       The QPN MUST be the UD QP exchanged during address resolution.

4. Frame Format

 All IP datagrams transported over InfiniBand are prefixed by a
 4-octet encapsulation header as described in [RFC4391].
   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |                               |
   |         Type                  |       Reserved                |
   |                               |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       The type field SHALL indicate the encapsulated protocol as per
       the following table.
                       +----------+-------------+
                       | Type     |    Protocol |
                       |------------------------|
                       | 0x800    |    IPv4     |
                       |------------------------|
                       | 0x86DD   |    IPv6     |
                       +------------------------+
 These values are taken from the "ETHER TYPE" numbers assigned by
 Internet Assigned Numbers Authority (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.

5. Maximum Transmission Unit

 The IB connection setup might be used for both IPv4 and IPv6 or it
 could be used for only one of them while a different connection is
 used for the other.  The link MTU MUST be able to support the minimum
 MTU required by the protocols.

Kashyap Standards Track [Page 8] RFC 4755 Connected Mode IPoIB December 2006

 The default MTU of the IPoIB-CM interface is 2044 octets, i.e.,
 2048-octet IPoIB-link MTU minus the 4-octet encapsulation header.
 However, connected modes of InfiniBand allow message sizes up to 2^31
 octets.  Therefore, IPoIB-CM can use a much larger MTU for unicast
 communication between any two endpoints.  The maximum and/or optimal
 payload that can be received or sent over an InfiniBand connection is
 dependent on the implementation, IB Channel Adapter, and the
 resources configured.
 An implementation MAY utilize the following mechanism to exchange the
 optimal message size across the IB connection.

5.1. Per-Connection MTU

 Every IB connection setup message includes a "private data" field
 [IB_ARCH].  The "private data" field in the connection setup message
 (CM REQ) MUST include the "Receive MTU".  This indicates the maximum
 packet size the requester can accept.  The requester MUST be able to
 accept smaller MTU sizes as well.
 It is up to the implementation to utilize this mechanism for setting
 the per-IB connection MTU.  To calculate the resultant IPoIB MTU over
 the connection the smaller of the two IB "Receive MTU" values is used
 by both the peers.  The IPoIB interface must also account for the 4-
 octet encapsulation header and so the IPoIB MTU over the connection
 will be further reduced by that amount.

6. Private-Data Format

 The "private data" field in every CM message for connection
 establishment must include the following values:
    1.  UD QPN of the sender
    2.  Receive MTU supported by the sender
 The format of the "private data" field MUST be as follows:
          0        7       15       23       31
          +--------+--------+--------+--------+
          |Reserved|         UD QPN           |
          +--------+--------+--------+--------+
          |            Receive MTU            |
          +--------+--------+--------+--------+
 The Reserved value MUST be set to zero on transmit and ignored on
 receive.

Kashyap Standards Track [Page 9] RFC 4755 Connected Mode IPoIB December 2006

7. IPoIB-CM Considerations

 Every IPoIB interface supports IPoIB-UD.  It may additionally support
 one or both of the IPoIB-CM modes.  Therefore, there can be multiple
 methods of communicating between any two peers.  This implies that an
 interface MAY transmit/receive a packet over any of the RC, UC, or UD
 modes depending on the modes supported between it and the peer.  It
 further follows that every IPoIB implementation compliant with this
 document MUST accept all IP unicast transmissions over any of the
 IPoIB modes it supports.  Multicast and broadcast packets by their
 nature will always be transmitted and received over the IPoIB-UD QP.
 Additionally, all address resolution responses (ARP or Neighbor
 Discovery) MUST always be encapsulated in a UD mode packet.

7.1. A Cautionary Note on IPoIB-RC

 The RC mode of InfiniBand guarantees in-order delivery of packets.
 Every message transmitted over the RC connection is broken into
 physical MTU-sized packets by the RC connection.  If any packet is
 lost, it is retransmitted until the complete message is exchanged.
 Therefore, there is a possibility of an upper transport layer
 experiencing a timeout, while the RC layer is still in the process of
 transferring the complete message.  TCP will view the timeout as an
 indicator of congestion and enter slow-start thereby affecting
 throughput drastically [RFC2581].  Other upper-layer protocols might
 insert retransmissions into the fabric, adding to the already
 existing congestion.
 The applicability of Infiniband reliability is on a fabric with short
 latencies (not wide area).  Therefore, the RC timer values should be
 short compared with the starting minimum time values used by the
 upper end-to-end transports.  In addition, because the RC mode does
 not have measurement-based reliable transmission, its use over
 fabrics with long latency or very dynamic latency may be a concern
 for congestion-aware traffic traversing those fabrics.

7.2. IPoIB-CM Per-Destination MTU

 As described above, interfaces on the same subnet may support
 different link MTUs based on the negotiated value or due to the link
 type (UD or connected mode).  Therefore, an implementation might
 choose to define a large IP MTU, which is reduced based on the MTU to
 the destination.  The relevant MTU may be stored in a suitable per-
 destination object, such as a route cache or a neighbor cache.  The
 per-destination MTU is known to the IPoIB-CM interface as described
 in Section 5.

Kashyap Standards Track [Page 10] RFC 4755 Connected Mode IPoIB December 2006

 Implementations might choose not to support differing MTU values and
 always support an MTU equal to the IPoIB-UD MTU determined from the
 broadcast GID.

8. Security Considerations

 An impostor may return a false set of flags to an IPOIB interface.
 This may cause unnecessary attempts and some delay/disruption in
 IPoIB communication.  The same is the case if wrong/spurious QPN
 values are provided during address resolution broadcast/multicast.

9. IANA Considerations

 Future uses of the reserved bits and octets in the link-layer address
 (Section 3.1), Service-ID (Section 3.5), and "Private-Data Format"
 (Section 6) MUST be published as RFCs.  This document requires that
 the reserved bits be set to zero on sends.

10. Acknowledgements

 The author thanks the IPoIB Working Group for the various comments
 and suggestions.  A special thanks to Bernie King-Smith and Dror
 Goldenberg for the detailed review and suggestions.

11. Normative References

 [IB_ARCH]    InfiniBand Architecture Specification, version 1.2
              www.infinibandta.org
 [RFC4392]    Kashyap, V., "IP over InfiniBand (IPoIB) Architecture",
              RFC 4392, April 2006.
 [RFC4391]    Chu, J. and V. Kashyap, "Transmission of IP over
              InfiniBand (IPoIB)", RFC 4391, April 2006.
 [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

12. Informative References

 [RFC2581]    Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
              Control ", RFC 2581, April 1999.

Kashyap Standards Track [Page 11] RFC 4755 Connected Mode IPoIB December 2006

Author's Address

 Vivek Kashyap
 15350, SW Koll Parkway
 Beaverton
 OR 97006
 Phone: +1 503 578 3422
 EMail: vivk@us.ibm.com

Kashyap Standards Track [Page 12] RFC 4755 Connected Mode IPoIB December 2006

Full Copyright Statement

 Copyright (C) The IETF Trust (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST,
 AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
 IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
 PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Kashyap Standards Track [Page 13]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4755.txt · Last modified: 2006/12/08 23:57 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki