Subject: [Ipoverib] IPoIB -- connected mode update

From: Vivek Kashyap <[email-masked]>
Date: Wed, 3 Aug 2005 23:50:59 -0700 (PDT)

Attached is an udpated draft (will be posting to internet drafts after the
current ietf ends) for ipoib-connected mode based on the discussions on
ipoib wg, openib (IB on Linux), and other communications. Two threads
that saw good discussion are given below. I believe the attached updated
draft captures all the discussions. Please comment.

http://openib.org/pipermail/openib-general/2005-May/006751.html
http://www1.ietf.org/mail-archive/web/ipoverib/current/msg01212.html

thanks,

 	Vivek

--------------------------------

                    IP over InfiniBand: Connected Mode

Abstract

         This document specifies a method for transmitting IPv4/IPv6
         packets and address resolution over the connected modes of
         InfiniBand.

         Table of Contents

         1.0       Introduction
         2.0       IPoIB-connected mode
         2.1       Multicasting
         2.2       Outline of Address Resolution
         2.3       Outline of Connection Setup
         3.0       Address Resolution
         3.1       Link-layer Address
         3.2       IB Connection Setup
         3.3       Service-ID
         4.0       Frame Format
         5.0       Maximum Transmission Unit
         5.1       Per-Connection MTU
         6.0       IPoIB-CM Considerations
         6.1       A Cautionary Note on IPoIB-RC
         7.0       Security Considerations
         8.0       IANA Considerations
         9.0       References

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
         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 [IPoIB_UD]. 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 document.  For clarity IPoIB over the unreliable
         datagram mode, as described in [IPoIB_UD] 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.

2.0 IPoIB-connected mode

         Every IPoIB implementation MUST support IPoIB-UD. The IPoIB-CM
         support is OPTIONAL.

         This document extensively refers to [IPoIB_UD] and extends IPoIB
         description given in [IPoIB_UD] to IPoIB-CM. Therefore, only
         additional requirements or enhancements needed to enable IPoIB-
         CM are described.

         The IP encapsulation, default MTU, link layer address format and
         the IPv6 stateless autoconfiguration mechanism apply to IPoIB-CM
         exactly as described in [IPoIB_UD].

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 coexisting
         IPoIB-UD QP for all broadcast/multicast communications.

         Multicast mapping, transmission and reception of multicast
         packets and multicast routing MUST use the IPoIB-UD QP
         associated with the IPoIB-CM interface.

2.2 Outline of Address Resolution

         Every IPoIB-CM interface MUST have two QPs associated with it:

                 1) A connected mode QP
                 2) An unreliable datagram mode QP

         [IPoIB_UD] proposes that the address resolution query is
         multicast over an IB multicast address that is joined by every
         member of the IPoIB subnet. This IB multicast address is
         referred to as the "broadcast-GID" [IPoIB_UD]. The "broadcsat-
         GID" is "FullMember" joined by every IPoIB-UD implementation on
         the associated QP [IPoIB-UD].

         A broadcast-GID is formed with the knowledge of the scope bits,
         IP version, the partition key (P_Key) associated with the
         subnet. Thus these three parameters must be known to the node
         before an IPoIB interface can be brought up. The exact format
         and rules to setup the broadcast-GID are defined in [IPoIB_UD].

         In response to the query the response is received on the IPoIB-
         UD QP [IPoIB_UD].

2.3 Outline of Connection setup

         Once the link address of the remote node is known an IB
         connection must be setup 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.

3.0 Address Resolution

         Address resolution queries are sent out on the "broadcast-GID"
         over the IPoIB-UD QP associated with the IPoIB-CM interface. A
         unicast reply is received on the UD QP.

3.1 Link-layer Address

         IPoIB encapsulation [IPoIB_UD] describes the link-layer address
         as follows:

             <1 octet reserved>:QP: GID

         This document extends the link-layer address as follows:

             <Flags>:QPN:GID

             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:

                     +--+--+--+--+--+--+--+--+
                     |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 zeroes on transmission as specified in
                 [IPoIB_UD].

             QPN:

                 The queue-pair number (QPN) on which the unicast address
                 resolution reply will be received. This allows the
                 IPoIB-UD address resolution code and method to be used
                 for IPoIB-CM address resolution.

                 The QPN also serves another purpose. It is used to form
                 the Service-ID that is used to setup 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 LID and determined other required parameters [IPoIB_UD].

         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 setup a connection merely
         because the peer indicates the capability. The decision to make
         such a connection is left to the implementation.

3.2 IB Connection Setup

         The IB reliable/unreliable mode connection may be setup by any
         of the peers though it is more likely that the one that
         initiated the address resolution phase, probably as a result of
         the need to send IP data, will initiate the connection setup.
         IBA allows passive-active and active-active connection setup
         [IB_ARCH].

         To setup 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 entity. 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 CM messages include, among other parameters, the Service-ID,
         Local QPN, and the payload size to use over the connection.

         Note:
               The IB connection is setup using the Service-ID as defined
               above. 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.

3.3 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:

   +--------+--------+--------+--------+-------+--------+--------+------+
   |00000001|<-------------------IETF use------------------------------>|
   +--------+--------+--------+--------+-------+--------+--------+------+

         The Service-IDs used by IPoIB will be in the format:

   +--------+--------+--------+--------+-------+-------+--------+-------+
   |00000001|  Type  |         Reserved        |        QPN             |
   +--------+--------+--------+--------+-------+-------+--------+-------+

         The Reserved fields MUST be transmitted as zeroes. They are
         ignored on reception.

         The QPN MUST be the UD QP exchanged during address resolution.

         The Type MUST be set to 0.

4.0 Frame Format

         All IP and ARP datagrams transported over InfiniBand are
         prefixed  by a 4-octet encapsulation header as described in
         [IPoIB_UD].

     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     |
                         |------------------------|
                         | 0x806    |    ARP      |
                         |------------------------|
                         | 0x8035   |    RARP     |
                         |------------------------|
                         | 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.

5.0 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.

         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, HCA
         and the resources configured.

         An implementation MAY utilise 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 MUST carry the following
         information:

                         0               15
                         +----------------+
                         | Receive   MTU  |
                         +----------------+

         The connection setup message (CM REQ) MUST insert the requested
         MTU in the "Receive MTU" field. 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. The IPoIB interface must
         account for the 4-octet encapsulation header and so the IPoIB
         MTU over the connection will be smaller by that amount.

         This mechanism allows for different MTU values per peer, however
         to enable implmentations to work with a single "connection" MTU,
         a configuration parameter called "IPoIB-CM MTU multiplier" is
         introduced.  The default value of "IPoIB-CM MTU multiplier" is
         1. The "Receive MTU" MUST NOT be set less than "IPoIB-CM MTU
         multiplier" times 2048.

6.0 IPoIB-CM Considerations

         Every IPoIB interface supports IPoIB-UD. It may additionally
         support one or both of 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
         unicast transmissions over any fo the IPoIB modes it supports.
         Multicast and broadcast packets by their nature will always be
         transmitted and received over the IPoIB-UD QP.

6.1 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 a
         reliable transport layer, such as TCP, retransmitting due to a
         shorter timeout while the RC layer is still in the process of
         transferring the complete message. A retransmission at the upper
         layer will add to the already existing congestion.

         Therefore, the RC timers as well as the maximum message size
         supported at the IPoIB-RC connection must be set judiciously.

7.0 Security Considerations

         A node may be returned a false set of flags by an impostor. 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.

8.0 IANA Considerations

         This document requires that the reserved bits and octets be set
         to zero on sends and ignored on receives.  Proposed uses of the
         reserved bits MUST be published as RFCs.

9.0 References

Normative

         [IB_ARCH]      InfiniBand Architecture Specification, version 1.1
                        www.infinibandta.org

         [IPoIB_ARCH]   draft-ietf-ipoib-architecture-04.txt, V. Kashyap

         [IPoIB_UD]     draft-ietf-ipoib-ip-over-infiniband-9.txt,
                        H.K. Jerry Chu, V. Kashyap

Author's Address

         Vivek Kashyap

         15350, SW Koll Parkway Beaverton, OR 97006

         Phone: +1 503 578 3422 Email: [email-masked]

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