INTERNET-DRAFT H.K. Jerry Chu <draft-ietf-ipoib-link-multicast-02.txt> Sun Microsystems Vivek Kashyap IBM Expires: December, 2002 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 groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright (C) The Internet Society (date). All Rights Reserved. Abstract 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 Chu & Kashyap [Page 1]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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 Broadcast Group 8.0 Mapping for other Multicast Groups 9.0 Sending and Receiving IP Multicast Packets 10.0 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 [IPoIB_ARCH]. This document will focus on the necessary steps 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, how to configure its associated attributes, and how to set up basic broadcast and multicast services for it. IPoIB link is the building block upon which an IP network consisting of many IP subnets connected by routers can be built. Subnetting allows the containment of broadcast traffic within a single link. It also provides certain degree of isolation for administration purpose between nodes on different subnets. 2.0 Terminology 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 [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 Chu & Kashyap [Page 2]
draft-ietf-ipoib-link-multicast-02.txt June 2002 mechanism that best matches the IP datagram paradigm. IB unreliable datagram provides many additional 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], [IPoIB_ENCAP]). 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, 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, Chu & Kashyap [Page 3]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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 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. 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 unicast as well as multicast. The ultimate requirement for two nodes in the same IB fabric to communicate at the IB level, besides physical connectivity, is a common P_Key. Partitioning in IB provides an isolation mechanism among nodes in an IB fabric, much like VLANs in the Ethernet network. Each HCA (Host Channel Adaptor) port of an endnode contains a P_Key table 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 incoming packets to the QP. Any packet with an invalid P_Key will be discarded by the QP and trigger a P_Key violation trap. IB switches may optionally enforce partition checking too. Following the above, IB partitions are the natural choice for defining IPoIB link boundary. It also provides much needed flexibility for a network administrator to group nodes logically into Chu & Kashyap [Page 4]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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; 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 an HCA port 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 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] to assign an IP subnet number to each IPoIB link. Once an IB partition is established for IPoIB use, the link MTU and Q_Key are two other attributes that must be chosen before the IPoIB link can be configured. 6.1 Maximum Transmission Unit IB defines five permissible maximum payload 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 MTUs for IPoIB. Channel adaptors supporting a MTU less than the minimal requirement can still expose an acceptable 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 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 MTU of any IB device on the IPoIB link minus the size of the "Type" field encapsulated in the payload [IPoIB_ENCAP]. Here the IB devices include IB switches, CAs, or routers. In general, a 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 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 MTU. Chu & Kashyap [Page 5]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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 to 1500 bytes. For IPv4, this may require a manual configuration of a different link MTU than the maximum that all the nodes support. (See 7.0 below.) For IPv6, one can use the 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 compared against the Q_Key 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 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 if an IPoIB link 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 allow successful communication between any two nodes in the same IPoIB link. 7.0 The IPoIB 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 (henceforth referred to as the broadcast group) with these link attributes that every node on the IPoIB link can join. The MGID of the broadcast group will embed in it the P_Key of the IB partition that defines the IPoIB link. A special signature is also embedded to identify the MGID for IPoIB use only. For IPv4 over IB, Chu & Kashyap [Page 6]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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|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|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. The broadcast group for IPv4 will serve to provide a broadcast service for protocol like ARP to use. When a node is brought up on an IPoIB link identified by a P_Key, it must look for 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 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 Chu & Kashyap [Page 7]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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 The support of general IP multicast [IPMULT] over IB is similar to the case of the special 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 depicted in Figure 4. The same mapping function is used for both IPv4 and IPv6 except the IPoIB signature field. | 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 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 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 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: FF12:401B:8:0:0:0:0:2 or FF12:401B:8::2 Chu & Kashyap [Page 8]
draft-ietf-ipoib-link-multicast-02.txt June 2002 for IPv4 in a compressed format, and FF12:601B:8:0:0:0:0:2 or FF12:601B:8::2 for IPv6 in a 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 MGID for IPv4 networks as described in section 7 above. Also the IPv6 all-node multicast address "FF0X::1" [AARCH] maps naturally to the the special broadcast MGID for IPv6 networks. 9.0 Sending and Receiving IP Multicast Packets 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, it must first check for the existence of the IB multicast group corresponding to the MGID on the outbound link. If one already exists, the MLID associated with the multicast group is used as the DLID for the packet. Otherwise, it implies no member exists on the local link. The packet should be forwarded to locally connected routers. This is to allow local routers to forward the packet to multicast listeners on remote networks. 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 for this purpose. A sender of multicast packets should cache information regarding the the 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 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, it must first construct a MGID 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. Chu & Kashyap [Page 9]
draft-ietf-ipoib-link-multicast-02.txt June 2002 The local node then calls SA to join the IB multicast group corresponding to the MGID. If the group doesn't already exist, one must be created first with the IPoIB link MTU. For the rest of attributes, it is recommended the same values from the all-node multicast/broadcast group be 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. When a node leaves an IP multicast group, it SHOULD notify the SA in order for all the related resources to be freed up. This gives SM an opportunity to delete an IB multicast group that is no longer in use, and 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 remote IB subnets. The specific mechanism for this will be covered in [IBTA], and 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 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 IPoIB 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 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 for their suggestions and many clarifications on the IBA specification. Chu & Kashyap [Page 10]
draft-ietf-ipoib-link-multicast-02.txt June 2002 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 1998. [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 www.infinibandta.org [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-01.txt [IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [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 17 Network Circle, UMPK17-201 Menlo Park, CA 94025 USA Phone: +1 650 786-5146 EMail: jerry.chu@sun.com Vivek Kashyap IBM Chu & Kashyap [Page 11]
draft-ietf-ipoib-link-multicast-02.txt June 2002 15450, SW Koll Parkway Beaverton, OR 97006 Phone: 503 578 3422 EMail: vivk@us.ibm.com 14.0 Full Copyright Statement Copyright (C) The Internet Society (2002>. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Chu & Kashyap [Page 12]
