INTERNET DRAFT V. Kashyap IBM Expiration Date: April 2006 October 2005 IP over InfiniBand: Connected Mode Status of this memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 Notice Copyright (C) The Internet Society (2005). All Rights Reserved. Abstract This document specifies a method for transmitting IPv4/IPv6 packets and address resolution over the connected modes of InfiniBand. Kashyap [Page 1] INTERNET-DRAFT Connected mode IPoIB October 2005 Table of Contents 1.0 Introduction 2.0 IPoIB-connected mode 2.1 Multicasting 2.2 Outline of Address Resolution 2.3 Outline of Connection Setup 3.0 Address Resolution 3.1 Link-layer Address 3.2 IB Connection Setup 3.3 Simultaneous IB Connections 3.4 IPoIB-CM IB Connection Teardown 3.5 Service-ID 4.0 Frame Format 5.0 Maximum Transmission Unit 5.1 Per-Connection MTU 6.0 Private-Data Format 7.0 IPoIB-CM Considerations 7.1 A Cautionary Note on IPoIB-RC 7.2 IPoIB-CM Per-Destination MTU 8.0 Security Considerations 9.0 IANA Considerations 10.0 Acknowledgements 11.0 References 12.0 Authorどﾖs Address 1.0 Introduction The InfiniBand specification [IB_ARCH] can be found at www.infinibandta.org. The document [IPoIB_ARCH] provides a short overview of InfiniBand architecture along with consideration for specifying IP over InfiniBand networks. The InfiniBand architecture (IBA) defines multiple modes of transports. Of these the unreliable datagram (UD) transport method best matches the needs of IP. IP over InfiniBand (IPoIB) over UD is described in [IPoIB_UD]. This document describes IP transmission over the connected modes of IBA. IBA defines two connected modes: 1. Reliable Connected (RC) 2. Unreliable Connected (UC) As is evident from the nomenclature, the two modes differ mainly in providing reliability of data delivery across the connection. This document applies equally to both the connected modes. IPoIB over these two modes is referred to as IPoIB-CM (connected Kashyap [Page 2] INTERNET-DRAFT Connected mode IPoIB October 2005 mode) in this document. For clarity, IPoIB over the unreliable datagram mode as described in [IPoIB_UD], is referred to as IPoIB-UD. IBA requires that all Host Channel Adapters (HCAs) support the reliable and unreliable connected modes [IB_ARCH]. It is optional for Target Channel Adapters (TCAs) to support the connected modes. The connected modes offer link MTUs of up to 2^31 octets in length. Thus, the use of connected modes can offer significant benefits by supporting reasonably large MTUs. The datagram modes of InfiniBand Architecture (IBA) are limited to 4096 octets. Reliability is also enhanced if the underlying feature of "automatic path migration" supported by the connected modes is utilized. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. 2.0 IPoIB-connected mode Every IPoIB implementation MUST support IPoIB-UD. The support of IPoIB-CM is OPTIONAL. This document extensively refers to [IPoIB_UD] and extends IPoIB description given in [IPoIB_UD] to IPoIB-CM. Therefore, only additional requirements or enhancements needed to enable IPoIB- CM are described. The IP encapsulation, default MTU, link layer address format and the IPv6 stateless autoconfiguration mechanism apply to IPoIB-CM exactly as described in [IPoIB_UD]. 2.1 Multicasting The connected modes of IBA define a non-broadcast, multiple access network. The connected modes of IBA do not support multicasting though every node can communicate with every other node if desired. This requires that multicasting be emulated in some form by the network. However, in the case of an InfiniBand network, instead of an emulation, an unreliable datagram (UD) queue pair (QP) can be used to support multicasting while the connected mode QP Kashyap [Page 3] INTERNET-DRAFT Connected mode IPoIB October 2005 is used for unicast traffic. Since every IPoIB implementation is required to support the UD mode, every implementation supporting IPoIB-CM will be able to utilize the coexisting IPoIB-UD QP for all broadcast/multicast communications. Multicast mapping, transmission and reception of multicast packets and multicast routing MUST use the IPoIB-UD QP associated with the IPoIB-CM interface. 2.2 Outline of Address Resolution Every IPoIB-CM interface MUST have two QPs associated with it: 1) A connected mode QP 2) An unreliable datagram mode QP [IPoIB_UD] proposes that the address resolution query is multicast over an IB multicast address that is joined by every member of the IPoIB subnet. This IB multicast address is referred to as the "broadcast-GID" [IPoIB_UD]. The "broadcast- GID" is "FullMember" joined by every IPoIB-UD implementation on the associated QP [IPoIB-UD]. A broadcast-GID is formed with the knowledge of the scope bits, IP version, the partition key (P_Key) associated with the subnet. Thus, these three parameters must be known to the node before an IPoIB interface can be brought up. The exact format and rules to setup the broadcast-GID are defined in [IPoIB_UD]. In response to the query the response is received on the IPoIB- UD QP [IPoIB_UD]. 2.3 Outline of Connection setup Once the link address of the remote node is known, an IB connection must be setup between the nodes before any IP communication may occur. To make a connection, the sender must know the service-ID to use in the request to make a connection [IB_ARCH]. It must also supply the "connection mode" queue pair to the remote node. The peer replies with its queue pair. Each IB connection is peer to peer and uses one connected mode QP at each end. Though the address resolution occurs at an individual IP address level, the connection between the nodes is at the IB layer. Therefore, every individual address resolution does not imply a new connection between the peers. Kashyap [Page 4] INTERNET-DRAFT Connected mode IPoIB October 2005 3.0 Address Resolution Address resolution queries are sent out on the "broadcast-GID" over the IPoIB-UD QP associated with the IPoIB-CM interface. A unicast reply is received on the UD QP. 3.1 Link-layer Address IPoIB encapsulation [IPoIB_UD] describes the link-layer address as follows: <1 octet reserved>:QP: GID This document extends the link-layer address as follows: :QPN:GID Flags: This is a single octet field. The bits indicate the connected modes supported by the interface. Bit 0 specifies the support for the "reliable connected" (RC) mode. Bit 1 indicates the support for the "unreliable connected" (UC) mode. All other bits in the octet are reserved and MUST be set to 0 on transmits and ignored on receives. The format of the flags is: +--+--+--+--+--+--+--+--+ |RC|UC| 0| 0| 0| 0| 0| 0| +--+--+--+--+--+--+--+--+ Both the RC and UC MAY be set at the same time if the interface supports both the modes. Since the IPoIB-UD mode is always supported there are no flags to indicate IPoIB-UD support. If IPoIB-CM is not supported i.e. if the implementation only supports IPoIB-UD, then the implementation MUST ignore the on reception. It MUST set the octet to all zeroes on transmission as specified in [IPoIB_UD]. QPN: The queue-pair number (QPN) on which the unicast address resolution reply will be received. This allows the IPoIB-UD address resolution code and method to be used Kashyap [Page 5] INTERNET-DRAFT Connected mode IPoIB October 2005 for IPoIB-CM address resolution. The QPN also serves another purpose. It is used to form the Service-ID that is used to setup the IB connection. On receiving the multicast/broadcast address resolution request, the receiver replies with its own link-address, including the associated UD QPN and the appropriate flags. The receiverどﾖs reply is unicast back to the sender after the receiver has, as in the case of IPoIB-UD, resolved the GID to the LID, and determined other required parameters [IPoIB_UD]. Once the address resolution is completed the underlying IB connection on the supported connection modes can be set up. An implementation is NOT REQUIRED to setup a connection merely because the peer indicates the capability. The decision to make such a connection is left to the implementation. 3.2 IB Connection Setup Once the address resolution is complete the IB connection can be setup by either of the peers. To setup a connection IB Management Datagrams (MADs) are directed to the peerどﾖs communication manager (CM). The connection request always contains a Service-ID for the peer to associate the request with the appropriate service. If the request is accepted, the peer returns the relevant connected mode QPN in the response MAD. The format of the CM connection messages and the IB connection setup process is described in [IB_ARCH]. The overall handshake is of the form: REQ ----> <---- REP [or REJ(reject)] RTA ----> [or REJ(reject)] The CM messages include, among other parameters, the Service-ID, Local connection-mode QPN, and the payload size to use over the connection. Note: The IB connection is setup using the Service-ID as defined above. The node MUST keep a record of IB connections it is participating in. The node MAY attempt another connection to the remote peer using the same Service-ID as used for an existing IB connection. Similarly, the receiver of such a connection MAY drop the request with a suitable error Kashyap [Page 6] INTERNET-DRAFT Connected mode IPoIB October 2005 indication in the CM response. The decision to accept or initiate multiple connections from or to an IPoIB interface is left to the implementation. The node that initiated the connection is aware of the target nodeどﾖs IP address as described above. The node receiving the IB connection request, however cannot determine the initiating nodeどﾖs IP address. To enable this determination, every CM message exchanged in setting up the IB connection, MUST include the senderどﾖs IPoIB-UD QP in the "private data" [IB_ARCH] field . The IPoIB-UD QP MUST be included in all "REJ" [IB_ARCH] messages too. 3.3 Simultaneous IB Connections To ensure that two IB connections are not setup between the peers, the following rules MUST be followed: The receiver forms the remote nodeどﾖs link-layer address using the UD QPN received in the "private data" field of the "REQ" message and the GID of the sender included in the "REQ" message. The link-layer address is used to determine if there is already an outstanding connection request "REQ" sent by the local interface to the given received link-layer address. If such an outstanding request is determined, then the two link-layer addresses (local and remote) are numerically compared. If the local link-layer address is numerically smaller, then the connection is accepted, otherwise rejected. The error code in "REJ" MAD is set to "Consumer Reject" [IB_ARCH]. Note: The link-layer addresses formed for comparison do not include the connection mode flags specified in section 3.1. The comparison is made using the link-layer address formed using the QPN and GID only. The above holds even if the receiver supports multiple IB connections from the same peer. This is to ensure that only one more connection is setup when the "REQ" messages cross. 3.4 IPoIB-CM IB Connection Teardown The IB connection between two peers MAY be torn down by either peer whenever the address resolution entry expires. An implementation is free to implement alternative policies for tearing down of IB connections between peers. Kashyap [Page 7] INTERNET-DRAFT Connected mode IPoIB October 2005 3.5 Service-ID The InfiniBand specification defines a block of service IDs for IETF use. The InfiniBand specification has left the definition and management of this block to the IETF [IB_ARCH]. The 64-bit block is: +--------+--------+--------+--------+-------+--------+--------+------+ |00000001|<-------------------IETF use------------------------------>| +--------+--------+--------+--------+-------+--------+--------+------+ The Service-IDs used by IPoIB will be in the format: +--------+--------+--------+--------+-------+-------+--------+-------+ |00000001| Type | Reserved | QPN | +--------+--------+--------+--------+-------+-------+--------+-------+ The Reserved fields MUST be transmitted as zeroes. It is dependent on the CM to ignore or check for zeroes in the Reserved fields. This is because some implementations of CMs require all ServiceIDs to be explicitly specified and cannot listen to a range of values. The QPN MUST be the UD QP exchanged during address resolution. The Type MUST be set to 0. 4.0 Frame Format All IP and ARP datagrams transported over InfiniBand are prefixed by a 4-octet encapsulation header as described in [IPoIB_UD]. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Type | Reserved | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Kashyap [Page 8] INTERNET-DRAFT Connected mode IPoIB October 2005 The type field SHALL indicate the encapsulated protocol as per the following table. +----------+-------------+ | Type | Protocol | |------------------------| | 0x800 | IPv4 | |------------------------| | 0x806 | ARP | |------------------------| | 0x8035 | RARP | |------------------------| | 0x86DD | IPv6 | +------------------------+ These values are taken from the "ETHER TYPE" numbers assigned by Internet Assigned Numbers Authority (IANA). Other network protocols, identified by different values of "ETHER TYPE", may use the encapsulation format defined herein, but such use is outside of the scope of this document. 5.0 Maximum Transmission Unit The IB connection setup might be used for both IPv4 and IPv6 or it could be used for only one of them while a different connection is used for the other. The link MTU MUST be able to support the minimum MTU required by the protocols. The default MTU of the IPoIB-CM interface is 2044 octets i.e. 2048 octet IPoIB-link MTU minus the 4 octet encapsulation header. However, connected modes of InfiniBand allow message sizes up to 2^31 octets. Therefore, IPoIB-CM can use a much larger MTU for unicast communication between any two endpoints. The maximum and/or optimal payload that can be received or sent over an InfiniBand connection is dependent on the implementation, HCA and the resources configured. An implementation MAY utilise the following mechanism to exchange the optimal message size across the IB connection. 5.1 Per-Connection MTU Every IB connection setup message includes a "private data" field [IB_ARCH]. The "private data" field in the connection setup message (CM REQ) MUST include the "Receive MTU". This indicates the maximum packet size the requester can accept. The Kashyap [Page 9] INTERNET-DRAFT Connected mode IPoIB October 2005 requester MUST be able to accept smaller MTU sizes as well. It is up to the implementation to utilize this mechanism for setting the per IB connection MTU. The IPoIB interface must account for the 4-octet encapsulation header and so the IPoIB MTU over the connection will be smaller by that amount. 6.0 Private-Data Format The "private data" field in every CM message for connection establishment must include the following values: 1. UD QPN of the sender 2. Receive MTU supported by the sender The format of "private data" field MUST be: 0 7 15 23 31 +--------+--------+--------+--------+ |Reserved| UD QPN | +--------+--------+--------+--------+ | Receive MTU | +--------+--------+--------+--------+ The Reserved value MUST be set to zero on transmit and ignored on receive. 7.0 IPoIB-CM Considerations Every IPoIB interface supports IPoIB-UD. It may additionally support one or both of IPoIB-CM modes. Therefore, there can be multiple methods of communicating between any two peers. This implies that an interface MAY transmit/receive a packet over any of the RC, UC or UD modes depending on the modes supported between it and the peer. It further follows that every IPoIB implementation compliant with this document MUST accept all unicast transmissions over any of the IPoIB modes it supports. Multicast and broadcast packets by their nature will always be transmitted and received over the IPoIB-UD QP. 7.1 A Cautionary Note on IPoIB-RC The RC mode of InfiniBand guarantees in-order delivery of packets. Every message transmitted over the RC connection is broken into physical MTU sized packets by the RC connection. If any packet is lost, it is retransmitted until the complete Kashyap [Page 10] INTERNET-DRAFT Connected mode IPoIB October 2005 message is exchanged. Therefore, there is a possibility of a reliable transport layer, such as TCP, retransmitting due to a shorter timeout, while the RC layer is still in the process of transferring the complete message. A retransmission at the upper layer will add to the already existing congestion. Therefore, the RC timers as well as the maximum message size supported at the IPoIB-RC connection must be set judiciously. 7.2 IPoIB-CM Per-Destination MTU As described above, interfaces on the same subnet may support different link MTUs based on the negotiated value or due to the link type (UD or connected mode). Therefore, an implementation might choose to define a large IP MTU which is reduced based on the MTU to the destination. The relevant MTU may be stored in a suitable per-destination object, such as a route cache or a neighbour cache. The per-destination MTU is known to the IPoIB- CM interface as described in section 5.0. Implementations might choose not to support differing MTU values and always support an MTU equal to the IPoIB-UD MTU determined from the broadcast GID. 8.0 Security Considerations A node may be returned a false set of flags by an impostor. This may cause unnecessary attempts and some delay/disruption in IPoIB communication. The same is the case if wrong/spurious QPN values are provided during address resolution broadcast/multicast. 9.0 IANA Considerations This document requires that the reserved bits and octets be set to zero on sends. Proposed uses of the reserved bits MUST be published as RFCs. 10.0 Acknowledgements The author thanks the IPoIB WG for the various comments and suggestions. A special thanks to Bernie King-Smith and Dror Goldenberg for the detailed review and suggestions. Kashyap [Page 11] INTERNET-DRAFT Connected mode IPoIB October 2005 11.0 References Normative [IB_ARCH] InfiniBand Architecture Specification, version 1.1 www.infinibandta.org [IPoIB_ARCH] draft-ietf-ipoib-architecture-04.txt, V. Kashyap [IPoIB_UD] draft-ietf-ipoib-ip-over-infiniband-9.txt, H.K. Jerry Chu, V. Kashyap 12.0 Authorどﾖs Address Vivek Kashyap 15350, SW Koll Parkway Beaverton OR 97006 Phone: +1 503 578 3422 Email: vivk@us.ibm.com Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any Kashyap [Page 12] INTERNET-DRAFT Connected mode IPoIB October 2005 license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Kashyap [Page 13]