INTERNET-DRAFT                                            H.K. Jerry Chu
<draft-ietf-ipoib-link-multicast-02.txt>                Sun Microsystems
                                                           Vivek Kashyap
Expires: October, December, 2002                                     April,                                       June, 2002

             IP link and multicast 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 RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   Copyright (C) The Internet Society (date).  All Rights Reserved.


   This document specifies a method for setting up IP subnets and
   multicast services over InfiniBand(TM) networks. Discussions in this
   document are applicable to both IPv4 and IPv6, unless explicitly
   specified. A separate document will cover unicast and encapsulation
   of IP datagrams over InfiniBand networks.

Table of Contents
   1.0     Introduction
   2.0     Terminology
   3.0     Basic IPoIB Transport - Unreliable Datagram
   4.0     IB Multicast Architecture
   5.0     IB Links vs IPoIB Links
   6.0     Setting up an IPoIB Link
   6.1     Maximum Transmission Unit
   6.2     IPoIB Link Q_Key
   6.3     Other Link Attributes
   7.0     The IPoIB All-Node Multicast and Broadcast Group
   8.0     Mapping for other Multicast Groups
   9.0     Sending and Receiving IP Multicast Packets
   10.0    Support for IP Multicast Routing
   11.0    Security Considerations
   11.0    Acknowledgments
   12.0    References
   13.0    Author's Address
   14.0    Full Copyright Statement

1.0 Introduction

   InfiniBand Architecture (IBA) defines four layers of network services
   corresponding to layer one through layer four of the OSI reference
   model.  For the purpose of running IP over an InfiniBand (IB)
   network, the IB link, network, and transport layers collectively
   constitute the data link layer to the IP stack. One can find a
   general overview of IB architecture related to IP networks in

   This document will focus on the necessary steps required in order to lay out
   an IP network on top of an IB network. It will describe all the
   elements of an IP over InfiniBand (IPoIB) link consists of, link, how to configure its
   associated link attributes, and how to set up basic broadcast and
   multicast services on an IPoIB link. for it. IPoIB link is the building block
   for upon
   which an IP network to be decomposed into multiple consisting of many IP subnets connected by
   IP routers.
   routers can be built.  Subnetting allows the containment of broadcast
   traffic within a single subnet. link. It also provides certain degree of
   isolation for administration purpose between nodes on different
   subnets. The latter may be an important
   consideration for administration purpose.

2.0 Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.0 Basic IPoIB Transport - Unreliable Datagram

   InfiniBand defines four types of transport services [IBTA]. They are
   reliable connection, unreliable connection, reliable datagram,
   unreliable datagram. IBA also defines a special raw datagram service
   for encapsulation purpose. Both unreliable datagram and raw datagram
   define support for multicast. They provide the basic transport
   mechanism that best matches the IP datagram paradigm.

   IB unreliable datagram provides many additional transport features such as the
   partition key (P_Key) protection, multiple queue pairs (QPs), and
   Q_Key protection. Moreover, it requires a 32-bit invariant CRC
   checksum, which provides a much stronger protection against data
   corruption, compared with the 16-bit CRC that a raw datagram carries.

   For these reasons, IB unreliable datagram is considered to be a much
   better choice as the basic IPoIB transport than the raw datagram, and
   is chosen as the default IPoIB transport mechanism ([IPoIB_ARCH],

4.0 IB Multicast Architecture

   The following discussion gives a short overview of the multicast
   architecture in InfiniBand. For a more complete description, the
   reader is referred to [IBTA] and [IPoIB_ARCH].

   IBA defines two layers of multicast services. Its link layer uses
   multicast LIDs (MLIDs), which are allocated by the Subnet Manager
   (SM) and fall in the range between 0xC0000 to 0xFFFE (approximately
   16k). MLIDs are used by IB switches to program their multicast
   forwarding tables. An IB switch implementation may support much fewer
   MLIDs in its forwarding table though.

   IB network layer uses multicast GIDs (MGIDs), which closely resemble
   IPv6 multicast addresses [AARCH] shown below.

   |   8    |  4 |  4 |                  112 bits                   |
   +------ -+----+----+---------------------------------------------+
   |11111111|flgs|scop|                  group ID                   |

                                 Figure 1

   [IPoIB_ARCH] describes each field in more details.

   Since every IB multicast packet is required to carry both LRH and
   GRH, a valid MGID and a valid MLID are both needed before a valid IB
   multicast packet can be constructed.

   An IB multicast group is uniquely identified by a valid MGID. Before
   a MGID can be used within an IB subnet, either as a destination
   address of a multicast packet, or representing a multicast group that
   an IB node can join, a "MCGroupRecord" an IB multicast group corresponding to the MGID
   must be created through the Subnet Administrator (SA). Besides the
   MGID, the creator must supply values of the path MTU, Q_Key, TClass,
   FlowLabel, HopLimit that are appropriate for all the potential
   clients of the multicast group to use. In return, SA will allocate a
   MLID to be used by switches in the local IB subnet.

   Unreliable multicast is defined by IBA as an optional functionality
   for channel adaptors (CAs) and switches. In today's IP technology,
   link multicast has become an indispensable function for better
   supporting a modern IP network. For this reason, it is required that
   an IPoIB fabric supports multicast. This includes all the CAs and
   switches that make up are part of an IP network.

5.0 IB Links vs IPoIB Links

   A link segment on top of which an IP subnet can be configured is
   defined in [IPV6] as a communication facility or medium over which
   nodes can communicate at the "link" layer.  For most types of
   communication media, the boundary between different data link
   segments follows the physical topology of the network connectivity,
   and is pretty obvious. network. E.g. an
   Ethernet network connected by switches, hubs, or bridges usually
   forms a single link segment and broadcast/multicast domain. Different
   Ethernet segments can be connected together by IP routers at the
   network layer.

   InfiniBand defines its own link-layer and subnets consisting of nodes
   connected by IB switches. However, the IPoIB link boundary need not
   follow the IB link boundary. Nodes residing on different IB subnets
   can still communicate directly with one another through IB routers at
   the InfiniBand network layer. This communication at the network layer
   applies to both unicast as well as multicast.

   The ultimate requirement for two nodes in the same IB fabric to
   communicate at the IB level, besides the physical connectivity, is a
   common P_Key.

   Partitioning in IB provides an isolation mechanism among nodes in an
   IB fabric, much like VLANs in an the Ethernet network.  Each HCA (Host
   Channel Adaptor) port of an endnode contains a P_Key table of holding
   all the valid P_Keys the port is allowed to use. The P_Key table is
   set up by the SM of the local IB subnet. Each QP is programmed with a
   P_Key from the local P_Key table. This P_Key is carried in all the
   outgoing packets from the QP, and is used to compare against the
   P_Key of the incoming packets to the QP. Reception of Any packet with an invalid P_Key causes the packet to
   will be discarded. discarded by the QP and trigger a P_Key violation trap.  IB
   switches may optionally enforce partition checking too.

   Therefore P_Key and

   Following the above, IB partition partitions are the natural choice for
   defining IPoIB link boundary. It also affords provides much needed
   flexibility to the for a network
   administrators when multiple links are set up administrator to group nodes logically into
   different subnets in a large network.

6.0 Setting up an IPoIB Link

   A network administrator defines an IPoIB link by setting up an IB
   partition and assigning it a unique P_Key. An IB partition may or may
   not span multiple IB subnets, subnets; and whether it does or not is mostly
   transparent to IPoIB.

   Each node attached to the IB partition MUST have one of its HCAs
   assigned the P_Key to use. Note that the P_key table of a an HCA port
   may contain many P_Keys. It is up to an the implementation to define the
   method by which the P_Key relevant to a particular IPoIB subnet is
   determined and conveyed to the IPoIB stack. E.g. implementations can
   resort to a manual configuration to choose the P_key or a set of
   P_Keys for IPoIB use, and rely on DHCP [DHCP] on each IPoIB link to assign an IP subnet number.
   number to each IPoIB link.

   Once an IB partition is established for IPoIB use, the link MTU and
   Q_Key are two other important attributes that must be chosen before the IPoIB
   link can be configured.

6.1 Maximum Transmission Unit

   IB defines five permissible maximum payload sizes. sizes (MTUs). They are
   256, 512, 1024, 2048 and 4096 bytes. [IPV6] requires a link MTU of
   1280 bytes or greater. To be better compatible with Ethernet, the
   dominant network media in both the LAN and WAN environment, the IPoIB
   link MTU SHALL be 1500 bytes or greater. This leaves only 2048 and
   4096 bytes as the two acceptable maximum payload sizes MTUs for IPoIB. Channel adaptors
   supporting a maximum payload size MTU less than the minimal requirement can still expose
   an acceptable link MTU to IP through an adaptation layer that fragments
   larger messages into smaller IB packets, and reassembles them on the
   receiving end. But this must be done in a way that is totally transparent to
   the IP stack.

   It is up to the network administrator to select a link MTU to use
   when configuring an IPoIB link. The link MTU SHALL not be greater
   than the maximum payload size MTU of any IB component that is part of device on the IPoIB link minus "EtherType" the size of the
   "Type" field encapsulated in the payload [IPoIB_ENCAP]. This includes Here the IB
   devices include IB switches, CAs, or routers.

   In general, a full maximal link MTU should be employed whenever possible
   to attain better throughput performance. One caveat is that once a
   link MTU is chosen for a given IPoIB link, nodes connected by CAs of
   a smaller maximum payload size MTU won't be able to join the link unless the whole link
   and all the devices attached to it are reconfigured to use a smaller

   The flexibility of configuring a smaller than the full link MTU size
   does make it easier for one to bridge an IPoIB link with an Ethernet
   link, by setting the IPoIB link MTU of all the connecting nodes to 1500 bytes. For IPv4, this may
   require a manual configuration of a MTU different
   from the default, link MTU size on than the
   maximum that all the nodes belonging to an
   IPoIB link. support. (See 7.0 below.)  For IPv6, one
   can use the link MTU option of the router advertisement [DISC] to announce
   a smaller MTU to all the nodes.

   In case an IPoIB link spans more than one IB subnet, the IPoIB link
   MTU MUST not exceed the path MTU of any path connecting two nodes in
   the same IB partition. It is up to the network administrator to
   determine the appropriate path MTU value that will work for any node
   in the same IPoIB link.

6.2 IPoIB Link Q_Key

   A Q_Key is programmed by the source QP in every IB datagram, and is
   verified by the destination QP
   compared against the Q_Key it has been
   assigned. of the destination QP.  A Q_Key violation
   will cause the offending datagram to be dropped, and a Q_Key
   violation trap to be raised.

   A Q_Key must be selected to be used by all the QPs attached to an
   IPoIB link. It is recommended that a controlled Q_Key be used with
   the high order bit set. This is to prevent non-privileged software
   from fabricating and sending out bogus IP datagrams. All QPs
   configured to use be used on a given IPoIB link SHALL be assigned the
   same per-link Q_Key.

6.3 Other Link Attributes

   TClass, FlowLabel, and HopLimit are three other attributes that are
   required for if an IPoIB link covering covers more than a single IB subnet.  The
   selection of these values are implementation dependent. But it must
   take into account the topology of IB subnets comprising the IPoIB
   link in order to ensure allow successful communication between any two nodes
   in the same IPoIB link.

7.0 The IPoIB All-Node Multicast and Broadcast Group

   Once an IB partition is created with link attributes identified for
   an IPoIB link, the network administrator must create a special IB
   all-node multicast group for (henceforth referred to as the broadcast
   group) with these link attributes that every node on the IPoIB link to
   can join. This is
   achieved through the creation of "MCGroupRecord" in each IB subnet
   that the IB partition encompasses, as described in section 4 above.

   The MGID of the broadcast group will have embed in it the P_Key of the IB
   partition that defines the IPoIB link embedded in it. link. A special signature is also
   embedded to identify the MGID for IPoIB use only. For IPv4 over IB,
   the signature will be "0x401B". For IPv6 over IB, the signature will
   be "0x601B".

   For an IPv4 subnet, the MGID for this special IB multicast group
   SHALL have the following format:

   |   8    |  4 |  4 |     16 bits    | 16 bits | 48 bits  | 32 bits |
   |11111111|0001|scop|<IPoIB signature>|<
   |11111111|0001|scop|0100000000011011|< P_Key >|00.......0|<all 1's>|

                                 Figure 2

   For an IPv6 subnet, the format of the MGID SHALL look like this:

   |   8    |  4 |  4 |     16 bits    | 16 bits |       80 bits      |
   |11111111|0001|scop|<IPoIB signature>|<
   |11111111|0001|scop|0110000000011011|< P_Key >|000.............0001|

                                 Figure 3

   As for the scop bits, if the IPoIB link is fully contained within a
   single IB subnet, the scop bits SHALL be set to 2 (link-local).
   Otherwise the scope will be set higher.

   A MCGroupRecord

   The broadcast group for IPv4 will be created with all the IPoIB link attributes
   described before. serve to provide a broadcast
   service for protocol like ARP to use.

   When a node is attached to brought up on an IPoIB link identified by a P_Key, it
   must look for a special, all-node multicast/broadcast the right broadcast group to join. This is done by
   constructing the MGID with the link P_Key and the IPoIB signature.
   The node SHOULD always look for a MGID of a link-local scope first
   before attempting one with a greater scope.

   Once the right MGID and MCGroupRecord broadcast group are identified, the local
   node SHOULD use the link MTU recorded in associated with the MCGroupRecord. broadcast group.  In case
   link MTU of the broadcast group is greater than the maximum payload size that what the local HCA can
   support, the node can not join the IPoIB link and operate as an IP
   node. Otherwise the local node must join the special all-node
   multicast/broadcast broadcast group by calling the SA to create a
   MCMemberRecord corresponding to the MGID. The SA will return all and use
   the rest of link attributes for associated with the local node to use. The node MUST use these
   attributes in group for all future multicast operations
   communication to the local IPoIB link.  The broadcast group for IPv4 will serve to provide a broadcast
   service for protocol like ARP to use.

   In addition to the special all-node multicast/broadcast group, multicast group for broadcast
   purpose, an all-router multicast group SHOULD be created at link
   configuration time if an IP router will be attached to the link. This
   is to facilitate IP multicast operations described later. A MCGroupRecord An IB
   multicast group for the all-
   router all-router MGID must be created in cover every IB subnet
   that the IPoIB link encompasses.  The format of the all-router MGID
   will be covered in next section.

8.0 Mapping for other Multicast Groups

   The support of general IP multicast [IPMULT] over IB is similar to
   the case of the special all-node multicast/broadcast broadcast group discussed above. An
   algorithmic mapping is used so that given an IP multicast address,
   individual host can compute the corresponding IB multicast address
   (MGID) all by itself without having to consult an external entity.
   This also removes the need for an externally maintained IP to IB
   multicast mapping table.

   The IPoIB multicast mapping is defined as follows. depicted in Figure 4. The same mapping
   function is used for both IPv4 and IPv6 except the IPoIB signature

   |   8    |  4 |  4 |     16 bits     | 16 bits |      80 bits       |
   +------ -+----+----+-----------------+---------+--------------------+
   |11111111|0001|scop|<IPoIB signature>|< P_Key >|      group ID      |

                                 Figure 4

   Since a MGID allocated for transporting IP multicast datagrams is
   considered only a transient link-layer multicast address, all IB
   MGIDs allocated for IPoIB purpose SHOULD have T = 1. The scope bits
   SHALL be the same as that of the all-node MGID for the same IPoIB


   The IP multicast address is used together with a given IPoIB link
   P_Key to form the MGID of the IB multicast group. For IPv6 the lower
   80-bit of the group ID is used directly in the lower 80-bit of the
   MGID. For IPv4, the group ID is only 28-bit long and the rest of the
   80 bits are filled with 0.

   The rest of the bits are the same as those of the all-node broadcast MGID.
   E.g. on an IPoIB link that is fully contained within a single IB
   subnet with a P_Key of 8, the MGIDs for the all-router multicast
   group with group ID 2 [AARCH, IGMP2] are:



   for IPv4 in a compressed format, and




   for IPv6 in a compressed format.

   A special case exists for the IPv4 limited broadcast address
   "" [HOSTS]. The address SHALL be mapped to the
   broadcast MGID for IPv4 networks as described in section 7 above.
   Also the IPv6 all-node multicast address "FF0X::1" [AARCH] will be
   mapped maps
   naturally to the the special all-node broadcast MGID for IPv6 networks.

9.0 Sending and Receiving IP Multicast Packets

   In order

   For any MGID the equivalent IB multicast group must be created first
   before use. The implication for a sender is that to send a packet
   destined for an IP multicast address, a
   node it must first check for the
   existence of MCGroupRecord the IB multicast group corresponding to the MGID of on the
   outbound link. If one already exists, the MLID allocated by the SM for associated with the MCGroupRecord
   multicast group is used as the DLID for the packet. Otherwise, it means
   implies no member exists on the local link. The packet should be
   forwarded to the all-router
   multicast group locally connected routers. This is to ensure the correct delivery of allow local
   routers to forward the packet to multicast listeners on remote
   networks. (See section 10 below.) If an  The specific mechanism for a sender to forward packets to
   routers are left to implementations. One can use, for example, the
   broadcast group, or the all-router multicast group doesn't already exist, it implies no
   router presence on for this purpose.

   A sender of multicast packets should cache information regarding the local subnet. The packet can then be safely

   Note that
   the local node MUST MLID and other attributes of the target IB multicast group in
   order to avoid expensive SA calls on every outgoing multicast packet.
   The cache may need to be notified when an validated periodically. E.g., if SA supports
   multicast group create/delete traps, the sender should register to
   monitor the status of the target IB multicast group
   corresponding through event
   notification. If multicast packets were sent to the MGID ever comes into existence later. This
   signifies that an interested party just showed all-router
   multicast group because no local listener existed, the sender must be
   notified by SA when listeners show up later on the local link
   and therefore must be copied. link. This
   allows the sender to change the forwarding to the right multicast

   For a node to join an IP multicast group to receive IP multicast
   packets, group, it must first construct a
   MGID corresponding to the IP
   multicast group, for it, using the rule described above. Note that it must
   remember the scope bits from the all-node MGID, and use the same
   scope in all the MGIDs it constructs.

   The local node then checks with calls SA to see if a MCGroupRecord join the IB multicast group
   corresponding to the MGID already exists. MGID. If not, the group doesn't already exist, one
   must be
   created.  The MCGroupRecord MUST be created first with the IPoIB link MTU. For the rest of the
   attributes, it is recommended that it uses the same values from the all-node
   multicast/broadcast group corresponding
   to the link.

   Note that for an IPoIB link that spans more than one IB subnet
   connected by IB routers, adequate multicast forwarding support at the
   IB level is required for multicast packets to be forwarded properly
   to members in remote IB subnets. The specific mechanism for this will be covered in [IBTA], and is out of scope of this document.

   Once the IB multicast group is identified, the node must join the
   group, unless it is a member already, by calling the SA to create a
   MCMemberRecord corresponding to the MGID. used.

   The join call enables SM to program local IB switches and routers
   with the new multicast information. Specifically it causes an IB
   switch to add the LID of the caller to its forwarding table entry
   corresponding to the MLID allocated for the group. It also causes an
   IB router to attach itself to the IB multicast tree corresponding to
   the MGID.

   In case any of the above IB operations fails, a node MAY choose to
   simply join the all-router multicast group. This will ensure it
   receives a copy of every multicast packet on the local link. Nodes
   doing so MUST filter out those multicast packets that are of no
   interest to the local node.

   When a node leaves an IP multicast group, it SHOULD delete the
   MCMemberRecord from the SA. This allows notify the SA to free up in
   order for all the related
   resources. resources to be freed up. This gives SM should an
   opportunity to delete MCGroupRecords an IB multicast group that are is no longer in use,
   and free up the MLIDs MLID allocated for them. it. The specific algorithm is
   implementation-dependent, and therefore is out of the scope of this document.

10.0 Support

   Note that for IP Multicast Routing

   IP multicast routing requires a router to receive a copy of every an IPoIB link multicast packet on a locally that spans more than one IB subnet
   connected link [IPMULT, IP6MLD].
   For Ethernet this is usually done by turning on promiscuous IB routers, an adequate multicast
   mode on a locally connected Ethernet interface.

   Unfortunately IBA does not forwarding support promiscuous multicast mode.
   Therefore the IPoIB driver should forward a copy of every outbound
   multicast datagram to the MGID corresponding to at
   the all-router
   multicast group.  This IB level is to ensure required for multicast packets be properly
   forwarded to reach listeners on
   remote IP networks, IB subnets. The specific mechanism for this will be covered in
   [IBTA], and applies to IP hosts as well as
   multicast routers.

11.0 is beyond the scope of IPoIB.

10.0 Security Considerations

   All the operations for creating and configuring an IPoIB link
   described in this document, including assigning P_Keys to CAs,
   creating MCGroupRecords and MCMemberRecords IB multicast groups in SA, creating and attaching QPs to IB
   multicast groups,... etc are privileged operations, and MUST be
   protected by the underlying operating system. This is to prevent
   malicious, non- privileged software from hijacking important
   resources and configurations.  E.g. A bogus all-node IPoIB
   multicast broadcast group may
   prevent a proper one from being created when the network
   administrator tries to set up a link.

   Controlled Q_Keys SHOULD be used in IB multicast groups in order IPoIB links. This is to prevent
   non-privileged software from fabricating IP datagrams to send, as
   mentioned in section 6.2.


11.0 Acknowledgments

   The authors would like to thank Bruce Beukema, David Brean, Dan
   Cassiday, Aditya Dube, Yaron Haviv, Michael Krause, Thomas Narten,
   Erik Nordmark, Greg Pfister, Renato Recio, Satya Sharma, and David L.
   Stevens, and Madhu Talluri
   Stevens for their suggestions and many clarifications on the IBA


12.0 References

   [AARCH]   Hinden, R. and S. Deering "IP Version 6 Addressing
             Architecture", RFC 2373, July 1998.

   [DHCP]    R. Droms "Dynamic Host Configuration Protocol", RFC 2131,
             March 1997.

   [DISC]    Narten, T., Nordmark, E. and W. Simpson, "Neighbor
             Discovery for IP Version 6 (IPv6)", RFC 2461, December

   [HOSTS]   Braden R., "Requirements for Internet Hosts --
             Communication Layers", RFC 1122, October 1989

   [IBTA]    InfiniBand Architecture Specification, Release 1.0.a by
             InfiniBand Trade Association at

   [IGMP2]   Fenner W., "Internet Group Management Protocol, Version 2",
             RFC 2236, November 1997.

   [IPMULT]  Deering S., "Host Extensions for IP Multicasting", RFC
             1112, August 1989.

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

   [IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-00.txt draft-ietf-ipoib-ip-over-infiniband-01.txt

   [IPV6]    Deering, S. and R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", RFC 2460, December 1998.

   [IP6MLD]  Deering S., Fenner W., Haberman B., "Multicast Listener
             Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.


13.0 Author's Address

   H.K. Jerry Chu
   901 San Antonio Road,
   17 Network Circle, UMPK17-201
   Palo Alto,
   Menlo Park, CA 94303-4900 94025

   Phone: +1 650 786-5146

   Vivek Kashyap
   15450, SW Koll Parkway
   Beaverton, OR 97006

   Phone: 503 578 3422


14.0 Full Copyright Statement

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