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RFC 4391

Transmission of IP over InfiniBand (IPoIB)

Pages: 21
Proposed Standard
Updated by:  8064

Top   ToC   RFC4391 - Page 1
Network Working Group                                             J. Chu
Request for Comments: 4391                              Sun Microsystems
Category: Standards Track                                     V. Kashyap
                                                                     IBM
                                                              April 2006


               Transmission of IP over InfiniBand (IPoIB)


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 Internet Society (2006).

Abstract

This document specifies a method for encapsulating and transmitting IPv4/IPv6 and Address Resolution Protocol (ARP) packets over InfiniBand (IB). It describes the link-layer address to be used when resolving the IP addresses in IP over InfiniBand (IPoIB) subnets. The document also describes the mapping from IP multicast addresses to InfiniBand multicast addresses. In addition, this document defines the setup and configuration of IPoIB links.

Table of Contents

1. Introduction ....................................................2 2. IP over UD Mode .................................................2 3. InfiniBand Datalink .............................................3 4. Multicast Mapping ...............................................3 4.1. Broadcast-GID Parameters ...................................5 5. Setting Up an IPoIB Link ........................................6 6. Frame Format ....................................................6 7. Maximum Transmission Unit .......................................8 8. IPv6 Stateless Autoconfiguration ................................8 8.1. IPv6 Link-Local Address ....................................9 9. Address Mapping - Unicast .......................................9 9.1. Link Information ...........................................9 9.1.1. Link-Layer Address/Hardware Address ................11 9.1.2. Auxiliary Link Information .........................12
Top   ToC   RFC4391 - Page 2
      9.2. Address Resolution in IPv4 Subnets ........................13
      9.3. Address Resolution in IPv6 Subnets ........................14
      9.4. Cautionary Note on QPN Caching ............................14
   10. Sending and Receiving IP Multicast Packets ....................14
   11. IP Multicast Routing ..........................................16
   12. New Types of Vulnerability in IB Multicast ....................17
   13. Security Considerations .......................................17
   14. IANA Considerations ...........................................18
   15. Acknowledgements ..............................................18
   16. References ....................................................18
      16.1. Normative References .....................................18
      16.2. Informative References ...................................19

1. Introduction

The InfiniBand specification [IBTA] can be found at http://www.infinibandta.org. The document [RFC4392] provides a short overview of InfiniBand architecture (IBA) along with considerations for specifying IP over InfiniBand networks. IBA defines multiple modes of transport over which IP may be implemented. The Unreliable Datagram (UD) transport mode best matches the needs of IP and the need for universality as described in [RFC4392]. This document specifies IPoIB over IB's UD mode. The implementation of IP subnets over IB's other transport mechanisms is out of scope of this document. This document describes the necessary steps required in order to lay out an IP network on top of an IB network. It describes all the elements of an IPoIB link, how to configure its associated attributes, and how to set up basic broadcast and multicast services for it. It further describes IP address resolution and the encapsulation of IP and Address Resolution Protocol (ARP) packets in InfiniBand frame. 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. IP over UD Mode

The unreliable datagram mode of communication is supported by all IB elements be they IB routers, Host Channel Adapters (HCAs), or Target Channel Adapters (TCAs). In addition to being the only universal transmission method, it supports multicasting, partitioning, and a
Top   ToC   RFC4391 - Page 3
   32-bit Cyclic Redundancy Check (CRC) [IBTA].  Though multicasting
   support is optional in IB fabrics, IPoIB architecture requires the
   participating components to support it.

   All IPoIB implementations MUST support IP over the UD transport mode
   of IBA.

3. InfiniBand Datalink

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. Nodes residing in different IB subnets can communicate directly with one another through IB routers at the IB network layer. Multiple IP subnets may be overlaid over this IB network. An IP subnet is configured over a communication facility or medium over which nodes can communicate at the "link" layer [IPV6]. For example, an ethernet segment is a link formed by interconnected switches/hubs/bridges. The segment is therefore defined by the physical topology of the network. This is not the case with IPoIB. IPoIB subnets are built over an abstract "link". The link is defined by its members and common characteristics such as the P_Key, link MTU, and the Q_Key. Any two ports using UD communication mode in an IB fabric can communicate only if they are in the same partition (i.e., have the same P_Key and the same Q_Key) [RFC4392]. The link MTU provides a limit to the size of the payload that may be used. The packet transmission and routing within the IB fabric are also affected by additional parameters such as the traffic class (TClass), hop limit (HopLimit), service level (SL), and the flow label (FlowLabel) [RFC4392]. The determination and use of these values for IPoIB communication are described in the following sections.

4. Multicast Mapping

IB identifies multicast groups by the Multicast Global Identifiers (MGIDs), which follow the same rules as IPv6 multicast addresses. Hence the MGIDs follow the same rules regarding the transient addresses and scope bits albeit in the context of the IB fabric. The resultant address therefore resembles IPv6 multicast addresses. The documents [IBTA, RFC4392] give a detailed description of IB multicast. The IPoIB multicast mapping is depicted in figure 1. The same mapping function is used for both IPv4 and IPv6 except for the IPoIB signature field.
Top   ToC   RFC4391 - Page 4
   Unless explicitly stated, all addresses and fields in the protocol
   headers in this document are stored in the network byte order.

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

                                 Figure 1

   Since an MGID allocated for transporting IP multicast datagrams is
   considered only a transient link-layer multicast address [RFC4392],
   all IB MGIDs allocated for IPoIB purpose MUST set T-flag to 1 [IBTA].

   A special signature is embedded to identify the MGID for IPoIB use
   only.  For IPv4 over IB, the signature MUST be "0x401B".  For IPv6
   over IB, the signature MUST be "0x601B".

   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 is placed
   directly in the lower 28 bits of the MGID.  The rest of the group ID
   bits in the MGID are filled with 0.

   E.g., on an IPoIB link that is fully contained within a single IB
   subnet with a P_Key of 0x8000, the MGIDs for the all-router multicast
   group with group ID 2 [AARCH, IGMP3] are:

       FF12:401B:8000::2,  for IPv4 in compressed format, and
       FF12:601B:8000::2,  for IPv6 in compressed format.

   A special case exists for the IPv4 limited broadcast address
   "255.255.255.255" [HOSTS].  The address SHALL be mapped to the
   "broadcast-GID", which is defined as follows:

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

                                 Figure 2

   All MGIDs used in the IPoIB subnet MUST use the same scop bits as in
   the corresponding broadcast-GID.
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4.1. Broadcast-GID Parameters

The broadcast-GID is set up with the following attributes: 1. P_Key A "Full Membership" P_Key (high-order bit is set to 1) MUST be used so that all members may communicate with one another. 2. Q_Key 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. 3. IB MTU The value assigned to the broadcast-GID must not be greater than any physical link MTU spanned by the IPoIB subnet. The following attributes are required in multicast transmissions and also in unicast transmissions if an IPoIB link covers more than a single IB subnet. 4. Other parameters The selection of TClass, FlowLabel, and HopLimit values is implementation dependent. But it must take into account the topology of IB subnets comprising the IPoIB link in order to allow successful communication between any two nodes in the same IPoIB link. An SL also needs to be assigned to the broadcast-GID. This SL is used in all multicast communication in the subnet. The broadcast-GID's scope bits need to be set based on whether the IPoIB link is confined within an IB subnet or the IPoIB link spans multiple IB subnets. A default of local-subnet scope (i.e., 0x2) is RECOMMENDED. A node might determine the scope bits to use by interactively searching for a broadcast- GID of ever greater scope by first starting with the local- scope. Or, an implementation might include the scope bits as a configuration parameter.
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5. Setting Up an IPoIB Link

The broadcast-GID, as defined in the previous section, MUST be set up for an IPoIB subnet to be formed. Every IPoIB interface MUST "FullMember" join the IB multicast group defined by the broadcast- GID. This multicast group will henceforth be referred to as the broadcast group. The join operation returns the MTU, the Q_Key, and other parameters associated with the broadcast group. The node then associates the parameters received as a result of the join operation with its IPoIB interface. The broadcast group also serves to provide a link-layer broadcast service for protocols like ARP, net-directed, subnet-directed, and all-subnets-directed broadcasts in IPv4 over IB networks. The join operation is successful only if the Subnet Manager (SM) determines that the joining node can support the MTU registered with the broadcast group [RFC4392] ensuring support for a common link MTU. The SM also ensures that all the nodes joining the broadcast-GID have paths to one another and can therefore send and receive unicast packets. It further ensures that all the nodes do indeed form a multicast tree that allows packets sent from any member to be replicated to every other member. Thus, the IPoIB link is formed by the IPoIB nodes joining the broadcast group. There is no physical demarcation of the IPoIB link other than that determined by the broadcast group membership. The P_Key is a configuration parameter that must be known before the broadcast-GID can be formed. For a node to join a partition, one of its ports must be assigned the relevant P_Key by the SM [RFC4392]. The method of creation of the broadcast group and the assignment/choice of its parameters are up to the implementation and/or the administrator of the IPoIB subnet. The broadcast group may be created by the first IPoIB node to be initialized, or it can be created administratively before the IPoIB subnet is set up. It is RECOMMENDED that the creation and deletion of the broadcast group be under administrative control. InfiniBand multicast management, which includes the creation, joining, and leaving of IB multicast groups by IB nodes, is described in [RFC4392].

6. Frame Format

All IP and ARP datagrams transported over InfiniBand are prefixed by a 4-octet encapsulation header as illustrated below.
Top   ToC   RFC4391 - Page 7
   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                |
   |                               |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 3

   The "Reserved" field MUST be set to zero on send and ignored on
   receive unless specified differently in a future document.

   The "Type" field SHALL indicate the encapsulated protocol as per the
   following table.

                      +----------+-------------+
                      | Type     |    Protocol |
                      |------------------------|
                      | 0x800    |    IPv4     |
                      |------------------------|
                      | 0x806    |    ARP      |
                      |------------------------|
                      | 0x8035   |    RARP     |
                      |------------------------|
                      | 0x86DD   |    IPv6     |
                      +------------------------+

                                 Table 1

   These values are taken from the "ETHER TYPE" numbers assigned by
   Internet Assigned Numbers Authority (IANA) [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.

   |<------ IB Frame headers -------->|<- Payload ->|<- IB trailers ->|
   +-------+------+---------+---------+-------------+---------+-------+
   |Local  |      |Base     |Datagram |   4-octet   |         |       |
   |Routing| GRH* |Transport|Extended |   header    |Invariant|Variant|
   |Header |Header|Header   |Transport|      +      |  CRC    |  CRC  |
   |       |      |         |Header   |   IP/ARP    |         |       |
   +-------+------+---------+---------+-------------+---------+-------+

                                 Figure 4

   Figure 4 depicts the IB frame encapsulating an IP/ARP datagram.  The
   InfiniBand specification requires the use of Global Routing Header
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   (GRH) [RFC4392] 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.

7. Maximum Transmission Unit

IB MTU: The IB components, that is, IB links, switches, Channel Adapters (CAs), and IB routers, may support maximum payloads of 256, 512, 1024, 2048, or 4096 octets. The maximum IB payload supported by the IB components in any IB path is the IB MTU for the path. IPoIB-Link MTU: The IPoIB-link MTU is the MTU value associated with the broadcast group. The IPoIB-link MTU can be set to any value up to the smallest IB MTU supported by the IB components comprising the IPoIB link. In order to reduce problems with fragmentation and path-MTU discovery, this document requires that all IPoIB implementations support an MTU of 2044 octets, that is, a 2048-octet IPoIB-link MTU minus the 4-octet encapsulation overhead. Larger and smaller MTUs MAY be supported subject to other existing MTU requirements [IPV6], but the default configuration must support an MTU of 2044 octets.

8. IPv6 Stateless Autoconfiguration

IB architecture associates an EUI-64 identifier termed the Globally Unique Identifier (GUID) [RFC4392, IBTA] with each port. The Local Identifier (LID) is unique within an IB subnet only. The interface identifier may be chosen from the following: 1) The EUI-64-compliant 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 not to use the LID to form the interface identifier. On the other hand, the LID provides an identifier that can be used to create a more anonymous IPv6 address since the LID is not globally unique and is subject to change over time.
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   It is RECOMMENDED that the link-local address be constructed from the
   port's EUI-64 identifier as given below.

   [AARCH] requires that the interface identifier be created in the
   "Modified EUI-64" format when derived from an EUI-64 identifier.
   [IBTA] is unclear if the GUID should use IEEE EUI-64 format or the
   "Modified EUI-64" format.  Therefore, when creating an interface
   identifier from the GUID, an implementation MUST do the following:

      => Determine if the GUID is a modified EUI-64 identifier ("u" bit
      is toggled) as defined by [AARCH]

      => If the GUID is a modified EUI-64 identifier, then the "u" bit
      MUST NOT be toggled when creating the interface identifier

      => If the GUID is an unmodified EUI-64 identifier, then the "u"
      bit MUST be toggled in compliance with [AARCH]

8.1. IPv6 Link-Local Address

The IPv6 link-local address for an IPoIB interface is formed as described in [AARCH] using the interface identifier as described in the previous section.

9. Address Mapping - Unicast

Address resolution in IPv4 subnets is accomplished through Address Resolution Protocol (ARP) [ARP]. It is accomplished in IPv6 subnets using the Neighbor Discovery protocol [DISC].

9.1. 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 transport header) as depicted in figure 4 and specified in the InfiniBand architecture [IBTA]. 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 as follows:

      a) LID

         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) Global Identifier (GID)

         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) Queue Pair Number (QPN)

         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 [IBTA].

      f) SL

         Every IBA packet contains an SL value.  A path in IBA is
         defined by the three-tuple (source LID, destination LID, SL).
         The SL in turns is mapped to a virtual lane (VL) at every CA,
         switch that sends/forwards the packet [RFC4392].  Multiple SLs
         may be used between two endpoints to provide for load
         balancing.  SLs may be used for providing a Quality of Service
         (QoS) infrastructure, or may be used to avoid deadlocks in the
         IBA fabric.
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   Another auxiliary piece of information, not included in the IBA
   headers, is the following:

      g) Path rate

         IBA defines multiple link speeds.  A higher-speed transmitter
         can swamp switches and the CAs.  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
         [IBTA].

9.1.1. 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 20-octet IPoIB link-layer address used in the source/target link-layer address option in IPv6 and the "hardware address" in IPv4/ARP has the same format. The format is as described below: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Queue Pair Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + GID + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5 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.
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      b) QPN

         Every unicast communication in IB architecture is directed to a
         specific QP [IBTA].  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) GID

         This is one of the GIDs of the port associated with the IPoIB
         interface [IBTA].  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 "Port GUID" [IBTA] be included in
         the link-layer/hardware address.

9.1.2. Auxiliary Link Information

The rest of the parameters are determined as follows: a) 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 Subnet Administrator (SA). It is the responsibility of the administrator to ensure that the IB subnet(s) have unicast connectivity between the IPoIB nodes. The GID exchanged between two endpoints in a multicast message (ARP/ND) does not guarantee the existence of a unicast path between the two. 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.
Top   ToC   RFC4391 - Page 13
      b) Q_Key

         The Q_Key received on joining the broadcast group MUST be used
         for all IPoIB communication over the particular IPoIB link.

      c) P_Key

         The P_Key to be used in the IP subnet is not discovered but is
         a configuration parameter.

      d) 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.

9.2. Address Resolution in IPv4 Subnets

The ARP packet header is as defined in [ARP]. The hardware type is set to 32 (decimal) as specified by IANA [IANA]. The rest of the fields are used as per [ARP]. 16 bits: hardware type 16 bits: protocol 8 bits: length of hardware address 8 bits: length of protocol address 16 bits: ARP operation The remaining fields in the packet hold the sender/target hardware and protocol addresses. [ sender hardware address ] [ sender protocol address ] [ target hardware address ] [ target protocol address ] The hardware address included in the ARP packet will be as specified in section 9.1.1 and depicted in figure 5. The length of the hardware address used in ARP packet header therefore is 20.
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9.3. Address Resolution in IPv6 Subnets

The Source/Target Link-layer address option is used in Router Solicit, Router advertisements, Redirect, Neighbor Solicitation, and Neighbor Advertisement messages when such messages are transmitted on InfiniBand networks. The source/target address option is specified as follows: Type: Source Link-layer address 1 Target Link-layer address 2 Length: 3 Link-layer address: The link-layer address is as specified in section 9.1.1 and depicted in figure 5. [DISC] specifies the length of source/target option in number of 8-octets as indicated by a length of '3' above. Since the IPoIB link-layer address is only 20 octets long, two octets of zero MUST be prepended to fill the total option length of 24 octets.

9.4. Cautionary Note on QPN Caching

The link-layer address for IPoIB includes the QPN, which might not be constant across reboots or even across network interface resets. Cached QPN entries, such as in static ARP entries or in Reverse Address Resolution Protocol (RARP) servers, will only work if the implementation(s) using these options ensure that the QPN associated with an interface is invariant across reboots/network resets. It is RECOMMENDED that implementations revalidate ARP caches periodically due to the aforementioned QPN-induced volatility of IPoIB link-layer addresses.

10. Sending and Receiving IP Multicast Packets

Multicast in InfiniBand differs in a number of ways from multicast in ethernet. This adds some complexity to an IPoIB implementation when supporting IP multicast over IB. A) An IB multicast group must be explicitly created through the SA before it can be used.
Top   ToC   RFC4391 - Page 15
         This implies that in order to send a packet destined for an IP
         multicast address, the IPoIB implementation must check with the
         SA on the outbound link first for a "MCMemberRecord" that
         matches the MGID.  If one does exist, the Multicast Local
         Identifier (MLID) associated with the multicast group is used
         as the Destination Local Identifier (DLID) for the packet.
         Otherwise, it implies no member exists on the local link.  If
         the scope of the IP multicast group is beyond link-local, the
         packet must be sent to the on-link routers through the use of
         the all-router multicast group or the broadcast group.  This is
         to allow local routers to forward the packet to multicast
         listeners on remote networks.  The all-router multicast group
         is preferred over the broadcast group for better efficiency.
         If the all-router multicast group does not exist, the sender
         can assume that there are no routers on the local link; hence
         the packet can be safely dropped.

      B) A multicast sender must join the target multicast group before
         outgoing multicast messages from it can be successfully routed.
         The "SendOnlyNonMember" join is different from the regular
         "FullMember" join in two aspects.  First, both types of joins
         enable multicast packets to be routed FROM the local port, but
         only the "FullMember" join causes multicast packets to be
         routed TO the port.  Second, the sender port of a
         "SendOnlyNonMember" join will not be counted as a member of the
         multicast group for purposes of group creation and deletion.

   The following code snippet demonstrates the steps in a typical
   implementation when processing an egress multicast packet.

   if the egress port is already a "SendOnlyNonMember", or a
   "FullMember"
       => send the packet

   else if the target multicast group exists
       => do "SendOnlyNonMember" join
       => send the packet

   else if scope > link-local AND the all-router multicast group exists
       => send the packet to all routers

   else
       => drop the packet

   Implementations should cache the information about the existence of
   an IB multicast group, its MLID and other attributes.  This is to
   avoid expensive SA calls on every outgoing multicast packet.  Senders
   MUST subscribe to the multicast group create and delete traps in
Top   ToC   RFC4391 - Page 16
   order to monitor the status of specific IB multicast groups.  For
   example, multicast packets directed to the all-router multicast group
   due to a lack of listener on the local subnet must be forwarded to
   the right multicast group if the group is created later.  This
   happens when a listener shows up on the local subnet.

   A node joining an IP multicast group must first construct an MGID
   according to the rule described in section 4 above.  Once the correct
   MGID is calculated, the node must call the SA of the outbound link to
   attempt a "FullMember" join of the IB multicast group corresponding
   to the MGID.  If the IB multicast group does not already exist, one
   must be created first with the IPoIB link MTU.  The MGID MUST use the
   same P_Key, Q_Key, SL, MTU, and HopLimit as those used in the
   broadcast-GID.  The rest of attributes SHOULD follow the values used
   in the broadcast-GID as well.

   The join request will cause the local port to be added to the
   multicast group.  It also enables the SM to program IB switches and
   routers with the new multicast information to ensure the correct
   forwarding of multicast packets for the group.

   When a node leaves an IP multicast group, it SHOULD make a
   "FullMember" leave request to the SA.  This gives the SM an
   opportunity to update relevant forwarding information, to delete an
   IB multicast group if the local port is the last FullMember to leave,
   and to free up the MLID allocated for it.  The specific algorithm is
   implementation-dependent and is out of the scope of this document.

   Note that for an IPoIB link that spans more than one IB subnet
   connected by IB routers, an adequate multicast forwarding support at
   the IB level is required for multicast packets to reach listeners on
   a remote IB subnet.  The specific mechanism for this is beyond the
   scope of IPoIB.

11. IP Multicast Routing

IP multicast routing requires each interface over which the router is operating to be configured to listen to all link-layer multicast addresses generated by IP [IPMULT, IP6MLD]. For an Ethernet interface, this is often achieved by turning on the promiscuous multicast mode on the interface. IBA does not provide any hardware support for promiscuous multicast mode. Fortunately, a promiscuous multicast mode can be emulated in the software running on a router through the following steps: A) Obtain a list of all active IB multicast groups from the local SA.
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      B) Make a "NonMember" join request to the SA for every group that
         has a signature in its MGID matching the one for either IPv4 or
         IPv6.

      C) Subscribe to the IB multicast group creation events using a
         wildcarded MGID so that the router can "NonMember" join all IB
         multicast groups created subsequently for IPv4 or IPv6.

   The "NonMember" join has the same effect as a "FullMember" join
   except that the former will not be counted as a member of the
   multicast group for purposes of group creation or deletion.  That is,
   when the last "FullMember" leaves a multicast group, the group can be
   safely deleted by the SA without concerning any "NonMember" routers.

12. New Types of Vulnerability in IB Multicast

Many IB multicast functions are subject to failures due to a number of possible resource constraints. These include the creation of IB multicast groups, the join calls ("SendOnlyNonMember", "FullMember", and "NonMember"), and the attaching of a QP to a multicast group. In general, the occurrence of these failure conditions is highly implementation-dependent, and is believed to be rare. Usually, a failed multicast operation at the IB level can be propagated back to the IP level, causing the original operation to fail and the initiator of the operation to be notified. But some IB multicast functions are not tied to any foreground operation, making their failures hard to detect. For example, if an IP multicast router attempts to "NonMember" join a newly created multicast group in the local subnet, but the join call fails, packet forwarding for that particular multicast group will likely fail silently, that is, without the attention of local multicast senders. This type of problem can add more vulnerability to the already unreliable IP multicast operations. Implementations SHOULD log error messages upon any failure from an IB multicast operation. Network administrators should be aware of this vulnerability, and preserve enough multicast resources at the points where IP multicast will be used heavily. For example, HCAs with ample multicast resources should be used at any IP multicast router.

13. 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 forging traffic or eavesdropping. It is the responsibility of the higher layers or applications to implement suitable countermeasures if this is a problem.
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   Successful transmission of IP packets depends on the correct setup of
   the IPoIB link, creation of the broadcast-GID, creation of the QP and
   its attachment to the broadcast-GID, and the correct determination of
   various link parameters such as the LID, service level, and path
   rate.  These operations, many of which involve interactions with the
   SM/SA, MUST be protected by the underlying operating system.  This is
   to prevent malicious, non-privileged software from hijacking
   important resources and configurations.

   Controlled Q_Keys SHOULD be used in all transmissions.  This is to
   prevent non-privileged software from fabricating IP datagrams.

14. IANA Considerations

To support ARP over InfiniBand, a value for the Address Resolution Parameter "Number Hardware Type (hrd)" is required. IANA has assigned the number "32" to indicate InfiniBand [IANA_ARP]. Future uses of the reserved bits in the frame format (Figure 3) and link-layer address (Figure 5) MUST be published as RFCs. This document requires that the reserved bits be set to zero on send and ignored on receive.

15. Acknowledgements

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

16. References

16.1. Normative References

[AARCH] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003. [ARP] Plummer, David C., "Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware ", STD 37, RFC 826, November 1982. [DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.
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   [IANA]       Internet Assigned Numbers Authority, URL
                http://www.iana.org

   [IANA_ARP]   URL http://www.iana.org/assignments/arp-parameters

   [IBTA]       InfiniBand Architecture Specification, URL
                http://www.infinibandta.org/specs

   [RFC4392]    Kashyap, V., "IP over InfiniBand (IPoIB) Architecture",
                RFC 4392, April 2006.

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

16.2. Informative References

[HOSTS] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [IGMP3] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. Thyagarajan, "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [IP6MLD] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener Discovery (MLD) for IPv6", RFC 2710, October 1999. [IPMULT] Deering, S., "Host extensions for IP multicasting", STD 5, RFC 1112, August 1989. [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.
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Authors' Addresses

H.K. Jerry Chu 17 Network Circle, UMPK17-201 Menlo Park, CA 94025 USA Phone: +1 650 786 5146 EMail: jerry.chu@sun.com Vivek Kashyap 15350, SW Koll Parkway Beaverton, OR 97006 USA Phone: +1 503 578 3422 EMail: vivk@us.ibm.com
Top   ToC   RFC4391 - Page 21
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