draft-ietf-ipoib-link-multicast-01.txt   draft-ietf-ipoib-link-multicast-02.txt 
INTERNET-DRAFT H.K. Jerry Chu INTERNET-DRAFT H.K. Jerry Chu
<draft-ietf-ipoib-link-multicast-01.txt> Sun Microsystems <draft-ietf-ipoib-link-multicast-02.txt> Sun Microsystems
Vivek Kashyap Vivek Kashyap
IBM IBM
Expires: October, 2002 April, 2002 Expires: December, 2002 June, 2002
IP link and multicast over InfiniBand networks IP link and multicast over InfiniBand networks
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
skipping to change at page 2, line 8 skipping to change at page 2, line 8
Table of Contents Table of Contents
1.0 Introduction 1.0 Introduction
2.0 Terminology 2.0 Terminology
3.0 Basic IPoIB Transport - Unreliable Datagram 3.0 Basic IPoIB Transport - Unreliable Datagram
4.0 IB Multicast Architecture 4.0 IB Multicast Architecture
5.0 IB Links vs IPoIB Links 5.0 IB Links vs IPoIB Links
6.0 Setting up an IPoIB Link 6.0 Setting up an IPoIB Link
6.1 Maximum Transmission Unit 6.1 Maximum Transmission Unit
6.2 IPoIB Link Q_Key 6.2 IPoIB Link Q_Key
6.3 Other Link Attributes 6.3 Other Link Attributes
7.0 The IPoIB All-Node Multicast and Broadcast Group 7.0 The IPoIB Broadcast Group
8.0 Mapping for other Multicast Groups 8.0 Mapping for other Multicast Groups
9.0 Sending and Receiving IP Multicast Packets 9.0 Sending and Receiving IP Multicast Packets
10.0 Support for IP Multicast Routing 10.0 Security Considerations
11.0 Security Considerations 11.0 Acknowledgments
12.0 Acknowledgments 12.0 References
13.0 References 13.0 Author's Address
14.0 Author's Address 14.0 Full Copyright Statement
15.0 Full Copyright Statement
1.0 Introduction 1.0 Introduction
InfiniBand Architecture (IBA) defines four layers of network services InfiniBand Architecture (IBA) defines four layers of network services
corresponding to layer one through layer four of the OSI reference corresponding to layer one through layer four of the OSI reference
model. For the purpose of running IP over an InfiniBand (IB) model. For the purpose of running IP over an InfiniBand (IB)
network, the IB link, network, and transport layers collectively network, the IB link, network, and transport layers collectively
constitute the data link layer to the IP stack. One can find a constitute the data link layer to the IP stack. One can find a
general overview of IB architecture related to IP networks in general overview of IB architecture related to IP networks in
[IPoIB_ARCH]. [IPoIB_ARCH].
This document will focus on the steps required to lay out an IP This document will focus on the necessary steps in order to lay out
network on top of an IB network. It will describe all the elements an an IP network on top of an IB network. It will describe all the
IP over InfiniBand (IPoIB) link consists of, how to configure its elements of an IP over InfiniBand (IPoIB) link, how to configure its
associated link attributes, and how to set up basic broadcast and associated attributes, and how to set up basic broadcast and
multicast services on an IPoIB link. IPoIB link is the building block multicast services for it. IPoIB link is the building block upon
for an IP network to be decomposed into multiple subnets connected by which an IP network consisting of many IP subnets connected by
IP routers. Subnetting allows the containment of broadcast traffic routers can be built. Subnetting allows the containment of broadcast
within a single subnet. It also provides certain degree of isolation traffic within a single link. It also provides certain degree of
between nodes on different subnets. The latter may be an important isolation for administration purpose between nodes on different
consideration for administration purpose. subnets.
2.0 Terminology 2.0 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3.0 Basic IPoIB Transport - Unreliable Datagram 3.0 Basic IPoIB Transport - Unreliable Datagram
InfiniBand defines four types of transport services [IBTA]. They are InfiniBand defines four types of transport services [IBTA]. They are
reliable connection, unreliable connection, reliable datagram, reliable connection, unreliable connection, reliable datagram,
unreliable datagram. IBA also defines a special raw datagram service unreliable datagram. IBA also defines a special raw datagram service
for encapsulation purpose. Both unreliable datagram and raw datagram for encapsulation purpose. Both unreliable datagram and raw datagram
define support for multicast. They provide the basic transport define support for multicast. They provide the basic transport
mechanism that best matches the IP datagram paradigm. mechanism that best matches the IP datagram paradigm.
IB unreliable datagram provides many additional transport features IB unreliable datagram provides many additional features such as the
such as the partition key (P_Key) protection, multiple queue pairs partition key (P_Key) protection, multiple queue pairs (QPs), and
(QPs), and Q_Key protection. Moreover, it requires a 32-bit invariant Q_Key protection. Moreover, it requires a 32-bit invariant CRC
CRC checksum, which provides a much stronger protection against data checksum, which provides a much stronger protection against data
corruption, compared with the 16-bit CRC that a raw datagram carries. corruption, compared with the 16-bit CRC that a raw datagram carries.
For these reasons, IB unreliable datagram is considered to be a much For these reasons, IB unreliable datagram is considered to be a much
better choice as the basic IPoIB transport than the raw datagram, and better choice as the basic IPoIB transport than the raw datagram, and
is chosen as the default IPoIB transport mechanism ([IPoIB_ARCH], is chosen as the default IPoIB transport mechanism ([IPoIB_ARCH],
[IPoIB_ENCAP]). [IPoIB_ENCAP]).
4.0 IB Multicast Architecture 4.0 IB Multicast Architecture
The following discussion gives a short overview of the multicast The following discussion gives a short overview of the multicast
skipping to change at page 3, line 39 skipping to change at page 3, line 38
MLIDs in its forwarding table though. MLIDs in its forwarding table though.
IB network layer uses multicast GIDs (MGIDs), which closely resemble IB network layer uses multicast GIDs (MGIDs), which closely resemble
IPv6 multicast addresses [AARCH] shown below. IPv6 multicast addresses [AARCH] shown below.
| 8 | 4 | 4 | 112 bits | | 8 | 4 | 4 | 112 bits |
+------ -+----+----+---------------------------------------------+ +------ -+----+----+---------------------------------------------+
|11111111|flgs|scop| group ID | |11111111|flgs|scop| group ID |
+--------+----+----+---------------------------------------------+ +--------+----+----+---------------------------------------------+
Figure 1
[IPoIB_ARCH] describes each field in more details. [IPoIB_ARCH] describes each field in more details.
Since every IB multicast packet is required to carry both LRH and 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 GRH, a valid MGID and a valid MLID are both needed before a valid IB
multicast packet can be constructed. multicast packet can be constructed.
An IB multicast group is uniquely identified by a valid MGID. Before 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 a MGID can be used within an IB subnet, either as a destination
address of a multicast packet, or representing a multicast group that address of a multicast packet, or representing a multicast group that
an IB node can join, a "MCGroupRecord" corresponding to the MGID must an IB node can join, an IB multicast group corresponding to the MGID
be created through the Subnet Administrator (SA). Besides the MGID, must be created through the Subnet Administrator (SA). Besides the
the creator must supply values of the path MTU, Q_Key, TClass, MGID, the creator must supply values of the path MTU, Q_Key, TClass,
FlowLabel, HopLimit that are appropriate for all the potential FlowLabel, HopLimit that are appropriate for all the potential
clients of the multicast group to use. In return, SA will allocate a clients of the multicast group to use. In return, SA will allocate a
MLID to be used by switches in the local IB subnet. MLID to be used by switches in the local IB subnet.
Unreliable multicast is defined by IBA as an optional functionality Unreliable multicast is defined by IBA as an optional functionality
for channel adaptors (CAs) and switches. In today's IP technology, for channel adaptors (CAs) and switches. In today's IP technology,
link multicast has become an indispensable function for better link multicast has become an indispensable function for better
supporting a modern IP network. For this reason, it is required that supporting a modern IP network. For this reason, it is required that
an IPoIB fabric supports multicast. This includes all the CAs and an IPoIB fabric supports multicast. This includes all the CAs and
switches that make up an IP network. switches that are part of an IP network.
5.0 IB Links vs IPoIB Links 5.0 IB Links vs IPoIB Links
A link segment on top of which an IP subnet can be configured is 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 defined in [IPV6] as a communication facility or medium over which
nodes can communicate at the "link" layer. For most types of nodes can communicate at the "link" layer. For most types of
communication media, the boundary between different data link communication media, the boundary between different data link
segments follows the physical topology of the network connectivity, segments follows the physical topology of the network. E.g. an
and is pretty obvious. E.g. an Ethernet network connected by Ethernet network connected by switches, hubs, or bridges usually
switches, hubs, or bridges usually forms a single link segment and forms a single link segment and broadcast/multicast domain. Different
broadcast/multicast domain. Different Ethernet segments can be Ethernet segments can be connected together by IP routers at the
connected by IP routers at the network layer. network layer.
InfiniBand defines its own link-layer and subnets consisting of nodes InfiniBand defines its own link-layer and subnets consisting of nodes
connected by IB switches. However, the IPoIB link boundary need not connected by IB switches. However, the IPoIB link boundary need not
follow the IB link boundary. Nodes residing on different IB subnets follow the IB link boundary. Nodes residing on different IB subnets
can still communicate directly with one another through IB routers at can still communicate directly with one another through IB routers at
the InfiniBand network layer. This communication at the network layer the InfiniBand network layer. This communication at the network layer
applies to both unicast as well as multicast. applies to unicast as well as multicast.
The ultimate requirement for two nodes in the same IB fabric to The ultimate requirement for two nodes in the same IB fabric to
communicate at the IB level, besides the physical connectivity, is a communicate at the IB level, besides physical connectivity, is a
common P_Key. common P_Key.
Partitioning in IB provides an isolation mechanism among nodes in an Partitioning in IB provides an isolation mechanism among nodes in an
IB fabric, much like VLANs in an Ethernet network. Each HCA (Host IB fabric, much like VLANs in the Ethernet network. Each HCA (Host
Channel Adaptor) port of an endnode contains a P_Key table of all the Channel Adaptor) port of an endnode contains a P_Key table holding
valid P_Keys the port is allowed to use. The P_Key table is set up by all the valid P_Keys the port is allowed to use. The P_Key table is
the SM of the local IB subnet. Each QP is programmed with a P_Key set up by the SM of the local IB subnet. Each QP is programmed with a
from the local P_Key table. This P_Key is carried in all the 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 outgoing packets from the QP, and is used to compare against the
P_Key of the incoming packets to the QP. Reception of an invalid P_Key of incoming packets to the QP. Any packet with an invalid P_Key
P_Key causes the packet to be discarded. IB switches may optionally will be discarded by the QP and trigger a P_Key violation trap. IB
enforce partition checking too. switches may optionally enforce partition checking too.
Therefore P_Key and IB partition are the natural choice for defining Following the above, IB partitions are the natural choice for
IPoIB link boundary. It also affords much flexibility to the network defining IPoIB link boundary. It also provides much needed
administrators when multiple links are set up in a large network. flexibility for a network administrator to group nodes logically into
different subnets in a large network.
6.0 Setting up an IPoIB Link 6.0 Setting up an IPoIB Link
A network administrator defines an IPoIB link by setting up an IB 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 partition and assigning it a unique P_Key. An IB partition may or may
not span multiple IB subnets, and whether it does or not is mostly not span multiple IB subnets; and whether it does or not is mostly
transparent to IPoIB. transparent to IPoIB.
Each node attached to the IB partition MUST have one of its HCAs 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 HCA port assigned the P_Key to use. Note that the P_key table of an HCA port
may contain many P_Keys. It is up to an implementation to define the may contain many P_Keys. It is up to the implementation to define the
method by which the P_Key relevant to a particular IPoIB subnet is method by which the P_Key relevant to a particular IPoIB subnet is
determined and conveyed to the IPoIB stack. E.g. implementations can 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 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 P_Keys for IPoIB use, and rely on DHCP [DHCP] to assign an IP subnet
assign an IP subnet number. number to each IPoIB link.
Once an IB partition is established for IPoIB use, the link MTU and 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 Q_Key are two other attributes that must be chosen before the IPoIB
the IPoIB link can be configured. link can be configured.
6.1 Maximum Transmission Unit 6.1 Maximum Transmission Unit
IB defines five permissible maximum payload sizes. They are 256, 512, IB defines five permissible maximum payload sizes (MTUs). They are
1024, 2048 and 4096 bytes. [IPV6] requires a link MTU of 1280 bytes 256, 512, 1024, 2048 and 4096 bytes. [IPV6] requires a link MTU of
or greater. To be better compatible with Ethernet, the dominant 1280 bytes or greater. To be better compatible with Ethernet, the
network media in both the LAN and WAN environment, the IPoIB link MTU dominant network media in both the LAN and WAN environment, the IPoIB
SHALL be 1500 bytes or greater. This leaves only 2048 and 4096 bytes link MTU SHALL be 1500 bytes or greater. This leaves only 2048 and
as two acceptable maximum payload sizes for IPoIB. Channel adaptors 4096 bytes as the two acceptable MTUs for IPoIB. Channel adaptors
supporting a maximum payload size less than the minimal requirement supporting a MTU less than the minimal requirement can still expose
can still expose an acceptable link MTU to IP through an adaptation an acceptable MTU to IP through an adaptation layer that fragments
layer that fragments larger messages into smaller IB packets, and larger messages into smaller IB packets, and reassembles them on the
reassembles them on the receiving end. But this must be done in a way receiving end. But this must be done in a way that is transparent to
that is totally transparent to the IP stack. the IP stack.
It is up to the network administrator to select a link MTU to use 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 when configuring an IPoIB link. The link MTU SHALL not be greater
than the maximum payload size of any IB component that is part of the than the MTU of any IB device on the IPoIB link minus the size of the
IPoIB link minus "EtherType" [IPoIB_ENCAP]. This includes IB "Type" field encapsulated in the payload [IPoIB_ENCAP]. Here the IB
switches, CAs, or routers. devices include IB switches, CAs, or routers.
In general, a full link MTU should be employed whenever possible to In general, a maximal link MTU should be employed whenever possible
attain better throughput performance. One caveat is that once a link to attain better throughput performance. One caveat is that once a
MTU is chosen for a given IPoIB link, nodes connected by CAs of a link MTU is chosen for a given IPoIB link, nodes connected by CAs of
smaller maximum payload size won't be able to join the link unless a smaller MTU won't be able to join the link unless the whole link
the whole link and all the devices attached to it are reconfigured to and all the devices attached to it are reconfigured to use a smaller
use a smaller MTU. MTU.
The flexibility of configuring a smaller than the full link MTU size 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 does make it easier for one to bridge an IPoIB link with an Ethernet
link, by setting the MTU of all the connecting nodes to 1500 bytes. link, by setting the IPoIB link MTU to 1500 bytes. For IPv4, this may
For IPv4, this may require a manual configuration of a MTU different require a manual configuration of a different link MTU than the
from the default, link MTU size on all the nodes belonging to an maximum that all the nodes support. (See 7.0 below.) For IPv6, one
IPoIB link. For IPv6, one can use the link MTU option of the router can use the MTU option of the router advertisement [DISC] to announce
advertisement [DISC] to announce a smaller MTU to all the nodes. a smaller MTU to all the nodes.
In case an IPoIB link spans more than one IB subnet, the IPoIB link 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 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 the same IB partition. It is up to the network administrator to
determine the appropriate path MTU value that will work for any node determine the appropriate path MTU value that will work for any node
in the same IPoIB link. in the same IPoIB link.
6.2 IPoIB Link Q_Key 6.2 IPoIB Link Q_Key
A Q_Key is programmed by the source QP in every IB datagram, and is A Q_Key is programmed by the source QP in every IB datagram, and is
verified by the destination QP against the Q_Key it has been compared against the Q_Key of the destination QP. A Q_Key violation
assigned. A Q_Key violation will cause the offending datagram to be will cause the offending datagram to be dropped, and a Q_Key
dropped, and a Q_Key violation trap to be raised. violation trap to be raised.
A Q_Key must be selected to be used by all the QPs attached to an 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 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 the high order bit set. This is to prevent non-privileged software
from fabricating and sending out bogus IP datagrams. All QPs from fabricating and sending out bogus IP datagrams. All QPs
configured to use on a given IPoIB link SHALL be assigned the same configured to be used on a given IPoIB link SHALL be assigned the
per-link Q_Key. same per-link Q_Key.
6.3 Other Link Attributes 6.3 Other Link Attributes
TClass, FlowLabel, and HopLimit are three other attributes that are TClass, FlowLabel, and HopLimit are three other attributes that are
required for an IPoIB link covering more than a single IB subnet. required if an IPoIB link covers more than a single IB subnet. The
The selection of these values are implementation dependent. But it selection of these values are implementation dependent. But it must
must take into account the topology of IB subnets comprising the take into account the topology of IB subnets comprising the IPoIB
IPoIB link to ensure successful communication between any two nodes link in order to allow successful communication between any two nodes
in the same IPoIB link. in the same IPoIB link.
7.0 The IPoIB All-Node Multicast and Broadcast Group 7.0 The IPoIB Broadcast Group
Once an IB partition is created with link attributes identified for Once an IB partition is created with link attributes identified for
an IPoIB link, the network administrator must create a special IB an IPoIB link, the network administrator must create a special IB
multicast group for every node on the IPoIB link to join. This is all-node multicast group (henceforth referred to as the broadcast
achieved through the creation of "MCGroupRecord" in each IB subnet group) with these link attributes that every node on the IPoIB link
that the IB partition encompasses, as described in section 4 above. can join.
The MGID will have the P_Key of the IB partition that defines the The MGID of the broadcast group will embed in it the P_Key of the IB
IPoIB link embedded in it. A special signature is also embedded to partition that defines the IPoIB link. A special signature is also
identify the MGID for IPoIB use only. For IPv4 over IB, the signature embedded to identify the MGID for IPoIB use only. For IPv4 over IB,
will be "0x401B". For IPv6 over IB, the signature will be "0x601B". 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 For an IPv4 subnet, the MGID for this special IB multicast group
SHALL have the following format: SHALL have the following format:
| 8 | 4 | 4 | 16 bits | 16 bits | 48 bits | 32 bits | | 8 | 4 | 4 | 16 bits | 16 bits | 48 bits | 32 bits |
+--------+----+----+-----------------+---------+----------+---------+ +--------+----+----+----------------+---------+----------+---------+
|11111111|0001|scop|<IPoIB signature>|< P_Key >|00.......0|<all 1's>| |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: For an IPv6 subnet, the format of the MGID SHALL look like this:
| 8 | 4 | 4 | 16 bits | 16 bits | 80 bits | | 8 | 4 | 4 | 16 bits | 16 bits | 80 bits |
+--------+----+----+-----------------+---------+--------------------+ +--------+----+----+----------------+---------+--------------------+
|11111111|0001|scop|<IPoIB signature>|< P_Key >|000.............0001| |11111111|0001|scop|0110000000011011|< P_Key >|000.............0001|
+--------+----+----+-----------------+---------+--------------------+ +--------+----+----+----------------+---------+--------------------+
Figure 3
As for the scop bits, if the IPoIB link is fully contained within a 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). single IB subnet, the scop bits SHALL be set to 2 (link-local).
Otherwise the scope will be set higher. Otherwise the scope will be set higher.
A MCGroupRecord will be created with all the IPoIB link attributes The broadcast group for IPv4 will serve to provide a broadcast
described before. When a node is attached to an IPoIB link identified
by a P_Key, it must look for a special, all-node multicast/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 are identified, the local node
SHOULD use the link MTU recorded in the MCGroupRecord. In case the
link MTU is greater than the maximum payload size that 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 group by calling the SA to create a
MCMemberRecord corresponding to the MGID. The SA will return all the
link attributes for the local node to use. The node MUST use these
attributes in all future multicast operations to the local IPoIB
link. The broadcast group for IPv4 will serve to provide a broadcast
service for protocol like ARP to use. service for protocol like ARP to use.
In addition to the all-node multicast/broadcast group, an all-router When a node is brought up on an IPoIB link identified by a P_Key, it
multicast group SHOULD be created at link configuration time if an IP must look for the right broadcast group to join. This is done by
router will be attached to the link. This is to facilitate IP constructing the MGID with the link P_Key and the IPoIB signature.
multicast operations described later. A MCGroupRecord for the all- The node SHOULD always look for a MGID of a link-local scope first
router MGID must be created in every IB subnet that the IPoIB link before attempting one with a greater scope.
encompasses. The format of the all-router MGID will be covered in
next section. Once the right MGID and broadcast group are identified, the local
node SHOULD use the MTU associated with the broadcast group. In case
the MTU of the broadcast group is greater than 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 broadcast group and use
the rest of link attributes associated with the group for all future
communication to the link.
In addition to the special all-node 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. An IB
multicast group for the all-router MGID must 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 8.0 Mapping for other Multicast Groups
The support of general IP multicast [IPMULT] over IB is similar to The support of general IP multicast [IPMULT] over IB is similar to
the case of the special all-node multicast/broadcast group discussed the case of the special broadcast group discussed above. An
above. An algorithmic mapping is used so that given an IP multicast algorithmic mapping is used so that given an IP multicast address,
address, individual host can compute the corresponding IB multicast individual host can compute the corresponding IB multicast address
address (MGID) all by itself without having to consult an external (MGID) all by itself without having to consult an external entity.
entity. This also removes the need for an externally maintained IP to This also removes the need for an externally maintained IP to IB
IB multicast mapping table. multicast mapping table.
The IPoIB multicast mapping is defined as follows. The same mapping The IPoIB multicast mapping is depicted in Figure 4. The same mapping
function is used for both IPv4 and IPv6 except the IPoIB signature function is used for both IPv4 and IPv6 except the IPoIB signature
field. field.
| 8 | 4 | 4 | 16 bits | 16 bits | 80 bits | | 8 | 4 | 4 | 16 bits | 16 bits | 80 bits |
+------ -+----+----+-----------------+---------+--------------------+ +------ -+----+----+-----------------+---------+--------------------+
|11111111|0001|scop|<IPoIB signature>|< P_Key >| group ID | |11111111|0001|scop|<IPoIB signature>|< P_Key >| group ID |
+--------+----+----+-----------------+---------+--------------------+ +--------+----+----+-----------------+---------+--------------------+
Figure 4
Since a MGID allocated for transporting IP multicast datagrams is Since a MGID allocated for transporting IP multicast datagrams is
considered only a transient link-layer multicast address, all IB considered only a transient link-layer multicast address, all IB
MGIDs allocated for IPoIB purpose SHOULD have T = 1. The scope bits 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 SHALL be the same as that of the all-node MGID for the same IPoIB
link. link.
An IP multicast address is used together with a given IPoIB link 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 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 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 MGID. For IPv4, the group ID is only 28-bit long and the rest of the
80 bits are filled with 0. 80 bits are filled with 0.
The rest of the bits are the same as those of the all-node MGID. The rest of the bits are the same as those of the broadcast MGID.
E.g. on an IPoIB link that is fully contained within a single IB 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 subnet with a P_Key of 8, the MGIDs for the all-router multicast
group with group ID 2 [AARCH, IGMP2] are: group with group ID 2 [AARCH, IGMP2] are:
FF12:401B:8:0:0:0:0:2 FF12:401B:8:0:0:0:0:2
or or
FF12:401B:8::2 FF12:401B:8::2
for IPv4 in a compressed format, and for IPv4 in a compressed format, and
FF12:601B:8:0:0:0:0:2 FF12:601B:8:0:0:0:0:2
or or
FF12:601B:8::2 FF12:601B:8::2
for IPv6 in a compressed format. for IPv6 in a compressed format.
A special case exists for the IPv4 limited broadcast address A special case exists for the IPv4 limited broadcast address
"255.255.255.255" [HOSTS]. The address SHALL be mapped to the "255.255.255.255" [HOSTS]. The address SHALL be mapped to the
broadcast MGID for IPv4 networks as described in section 7 above. broadcast MGID for IPv4 networks as described in section 7 above.
Also the IPv6 all-node multicast address "FF0X::1" [AARCH] will be Also the IPv6 all-node multicast address "FF0X::1" [AARCH] maps
mapped to the the special all-node MGID for IPv6 networks. naturally to the the special broadcast MGID for IPv6 networks.
9.0 Sending and Receiving IP Multicast Packets 9.0 Sending and Receiving IP Multicast Packets
In order to send a packet destined for an IP multicast address, a For any MGID the equivalent IB multicast group must be created first
node must first check for the existence of MCGroupRecord before use. The implication for a sender is that to send a packet
corresponding to the MGID of the outbound link. If one already destined for an IP multicast address, it must first check for the
exists, the MLID allocated by the SM for the MCGroupRecord is used as existence of the IB multicast group corresponding to the MGID on the
the DLID for the packet. Otherwise, it means no member exists on the outbound link. If one already exists, the MLID associated with the
local link. The packet should be forwarded to the all-router multicast group is used as the DLID for the packet. Otherwise, it
multicast group to ensure the correct delivery of the packet to implies no member exists on the local link. The packet should be
multicast listeners on remote networks. (See section 10 below.) If an forwarded to locally connected routers. This is to allow local
all-router multicast group doesn't already exist, it implies no routers to forward the packet to multicast listeners on remote
router presence on the local subnet. The packet can then be safely networks. The specific mechanism for a sender to forward packets to
dropped. routers are left to implementations. One can use, for example, the
broadcast group, or the all-router multicast group for this purpose.
Note that the local node MUST be notified when an IB multicast group A sender of multicast packets should cache information regarding the
corresponding to the MGID ever comes into existence later. This the MLID and other attributes of the target IB multicast group in
signifies that an interested party just showed up on the local link order to avoid expensive SA calls on every outgoing multicast packet.
and therefore must be copied. The cache may need to be 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 through event
notification. If multicast packets were sent to the 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. This
allows the sender to change the forwarding to the right multicast
group.
For a node to join an IP multicast group to receive IP multicast For a node to join an IP multicast group, it must first construct a
packets, it must first construct a MGID corresponding to the IP MGID for it, using the rule described above. Note that it must
multicast group, using the rule described above. Note that it must
remember the scope bits from the all-node MGID, and use the same remember the scope bits from the all-node MGID, and use the same
scope in all the MGIDs it constructs. scope in all the MGIDs it constructs.
The local node then checks with SA to see if a MCGroupRecord The local node then calls SA to join the IB multicast group
corresponding to the MGID already exists. If not, one must be corresponding to the MGID. If the group doesn't already exist, one
created. The MCGroupRecord MUST be created with the IPoIB link MTU. must be created first with the IPoIB link MTU. For the rest of
For the rest of the attributes, it is recommended that it uses the attributes, it is recommended the same values from the all-node
same values from the all-node multicast/broadcast group corresponding multicast/broadcast group be used.
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. 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 the SA to free up related
resources. SM should delete MCGroupRecords that are no longer in use,
and free up the MLIDs allocated for them. The specific algorithm is
implementation-dependent, and therefore is out of scope of this
document.
10.0 Support for IP Multicast Routing 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.
IP multicast routing requires a router to receive a copy of every When a node leaves an IP multicast group, it SHOULD notify the SA in
link multicast packet on a locally connected link [IPMULT, IP6MLD]. order for all the related resources to be freed up. This gives SM an
For Ethernet this is usually done by turning on promiscuous multicast opportunity to delete an IB multicast group that is no longer in use,
mode on a locally connected Ethernet interface. and free up the MLID allocated for it. The specific algorithm is
implementation-dependent, and is out of the scope of this document.
Unfortunately IBA does not support promiscuous multicast mode. Note that for an IPoIB link that spans more than one IB subnet
Therefore the IPoIB driver should forward a copy of every outbound connected by IB routers, an adequate multicast forwarding support at
multicast datagram to the MGID corresponding to the all-router the IB level is required for multicast packets to reach listeners on
multicast group. This is to ensure multicast packets be properly remote IB subnets. The specific mechanism for this will be covered in
forwarded to remote IP networks, and applies to IP hosts as well as [IBTA], and is beyond the scope of IPoIB.
multicast routers.
11.0 Security Considerations 10.0 Security Considerations
All the operations for creating and configuring an IPoIB link All the operations for creating and configuring an IPoIB link
described in this document, including assigning P_Keys to CAs, described in this document, including assigning P_Keys to CAs,
creating MCGroupRecords and MCMemberRecords in SA, creating and creating IB multicast groups in SA, creating and attaching QPs to IB
attaching QPs to IB multicast groups,... etc are privileged multicast groups,... etc are privileged operations, and MUST be
operations, and MUST be protected by the underlying operating system. protected by the underlying operating system. This is to prevent
This is to prevent malicious, non- privileged software from hijacking malicious, non- privileged software from hijacking important
important resources and configurations. E.g. A bogus all-node IPoIB resources and configurations. E.g. A bogus IPoIB broadcast group may
multicast group may prevent a proper one from being created when the prevent a proper one from being created when the network
network administrator tries to set up a link. administrator tries to set up a link.
Controlled Q_Keys SHOULD be used in IB multicast groups in order to Controlled Q_Keys SHOULD be used in IPoIB links. This is to prevent
prevent non-privileged software from fabricating IP datagrams to non-privileged software from fabricating IP datagrams to send, as
send, as mentioned in section 6.2. mentioned in section 6.2.
12.0 Acknowledgments 11.0 Acknowledgments
The authors would like to thank Bruce Beukema, David Brean, Dan The authors would like to thank Bruce Beukema, David Brean, Dan
Cassiday, Aditya Dube, Yaron Haviv, Michael Krause, Thomas Narten, Cassiday, Aditya Dube, Yaron Haviv, Michael Krause, Thomas Narten,
Erik Nordmark, Greg Pfister, Renato Recio, Satya Sharma, David L. Erik Nordmark, Greg Pfister, Renato Recio, Satya Sharma, and David L.
Stevens, and Madhu Talluri for their suggestions and many Stevens for their suggestions and many clarifications on the IBA
clarifications on the IBA specification. specification.
13.0 References 12.0 References
[AARCH] Hinden, R. and S. Deering "IP Version 6 Addressing [AARCH] Hinden, R. and S. Deering "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
[DHCP] R. Droms "Dynamic Host Configuration Protocol", RFC 2131, [DHCP] R. Droms "Dynamic Host Configuration Protocol", RFC 2131,
March 1997. March 1997.
[DISC] Narten, T., Nordmark, E. and W. Simpson, "Neighbor [DISC] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998. 1998.
skipping to change at page 11, line 40 skipping to change at page 11, line 31
InfiniBand Trade Association at www.infinibandta.org InfiniBand Trade Association at www.infinibandta.org
[IGMP2] Fenner W., "Internet Group Management Protocol, Version 2", [IGMP2] Fenner W., "Internet Group Management Protocol, Version 2",
RFC 2236, November 1997. RFC 2236, November 1997.
[IPMULT] Deering S., "Host Extensions for IP Multicasting", RFC [IPMULT] Deering S., "Host Extensions for IP Multicasting", RFC
1112, August 1989. 1112, August 1989.
[IPoIB_ARCH] draft-ietf-ipoib-architecture-01.txt [IPoIB_ARCH] draft-ietf-ipoib-architecture-01.txt
[IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-00.txt [IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-01.txt
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (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 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
14.0 Author's Address 13.0 Author's Address
H.K. Jerry Chu H.K. Jerry Chu
901 San Antonio Road, UMPK17-201 17 Network Circle, UMPK17-201
Palo Alto, CA 94303-4900 Menlo Park, CA 94025
USA USA
Phone: +1 650 786-5146 Phone: +1 650 786-5146
EMail: jerry.chu@sun.com EMail: jerry.chu@sun.com
Vivek Kashyap Vivek Kashyap
IBM IBM
15450, SW Koll Parkway 15450, SW Koll Parkway
Beaverton, OR 97006 Beaverton, OR 97006
Phone: 503 578 3422 Phone: 503 578 3422
EMail: vivk@us.ibm.com EMail: vivk@us.ibm.com
15.0 Full Copyright Statement 14.0 Full Copyright Statement
Copyright (C) The Internet Society (2001>. All Rights Reserved. Copyright (C) The Internet Society (2002>. All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
 End of changes. 

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