INTERNET DRAFT Vivek Kashyap IBM Expiration Date: February 2003 August 2002 DHCP over InfiniBand Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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 This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved. Abstract An InfiniBand network uses a link-layer addressing scheme that is 20-bytes long. This is larger than the 16-bytes reserved for the hardware address in DHCP/BOOTP message. The above inequality imposes restrictions on the use of the DHCP message fields when used over an IP over InfiniBand(IPoIB) network. This document describes the use of DHCP message fields when implementing DHCP over IPoIB. Kashyap [Page 1] INTERNET-DRAFT DHCP over InfiniBand April 2002 1. Introduction The Dynamic Host Configuration Protocol(DHCP) provides a framework for passing configuration information to hosts on a TCP/IP network [RFC2131]. DHCP is based on the Bootstrap Protocol (BOOTP) [RFC951] adding the capability of automatic allocation of reusable network addresses and additional configuration options [RFC2131,RFC2132]. The DHCP server receives a broadcast request from the DHCP client. The DHCP server uses the client interface's hardware-address to unicast a reply back when the client doesn't yet have an IP address assigned to it. The 'chaddr' field in the DHCP message carries the client's hardware address. The 'chaddr' field is 16-bytes in length. The IPoIB link-layer address is 20-bytes in length. Therefore the IPoIB link-layer address will not fit in the 'chaddr' field making it impossible for the DHCP server to unicast a reply back to the client. To ensure interoperability the usage of the fields and the method for DHCP interaction must be clarified. This document describes the IPoIB specific usage of some fields of DHCP. See [RFC2131] for the mechanism of DHCP and the explanations of each field. 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. The DHCP over IPoIB mechanism As noted above, because of the link-layer address length being larger than the 'chaddr' field length, the link-layer address is unavailable to the DHCP server. Therefore, a DHCP client MUST request that the server sends a broadcast reply by setting the BROADCAST flag when IPoIB ARP is not possible, i.e. in situations where the client does not know its IP address. RFC1542 notes that the use of a broadcast reply is discouraged. But in the case of IPoIB this is a necessity. There is no option but to broadcast back to the client since it is not possible to reply the client's unicast address. To desynchronise broadcasts at subnet startup, the RFC2131 Kashyap [Page 2] INTERNET-DRAFT DHCP over InfiniBand April 2002 suggests that a client wait a random time (1 to 10 seconds) before initiating server discovery. The same timeout will equally spread out the DHCP server broadcast responses generated due to the use of the use of the BROADCAST bit. The client hardware address, 'chaddr', is unique in the subnet and hence can be used to identify the client interface. But in the absence of a unique chaddr the client-identifier must be used. The DHCP protocol states that the 'client identifier' option may be used as the unique identifying value for the client. This value must be unique within the subnet the client is a member of. The client identifier option includes a type and identifier pair. The identifier included in the client-identifier option may consist of a hardware address or any other unique value such as the DNS name of the client. When a hardware address is used, the type field should be one of the ARP hardware types listed in [ARPPARAM]. The client-identifier itself SHOULD not be interpreted by the server. [RFC2132] 2.1 IPoIB specific usage of DHCP message fields A DHCP client, when working over an IPoIB interface, MUST follow the following rules: 'htype' (hardware address type) MUST be 32 [ARPPARAM] 'hlen' (hardware address length) MUST be 0. 'chaddr' (client hardware address) field MUST be zeroed. 'client identifier' option MUST be used in DHCP messages. According to RFC2132 the 'client identifier' option MAY consist of any data, but IPoIB clients SHOULD use the following format for the client-identifier option: Code Len Type Client-Identifier +-----+-----+-----+-----+-----+-----+-----+-------------------....----+ | 61 | 21 | 32 |Interface-id (4 bytes) | GID (16 bytes) | +-----+-----+-----+-----+-----+-----+-----+-------------------....----+ Every IPoIB interface is associated with an identifier Kashyap [Page 3] INTERNET-DRAFT DHCP over InfiniBand April 2002 referred to as the GID [IPoIB_ARCH]. The GID is unique in the InfiniBand fabric. An invariant GID is formed by appending the port's EUI-64 identifier to the InfiniBand subnet prefix. The GID is associated with a particular hardware port. The GID and a QPN define an IPoIB interface at the port. Therefore an implementation may associate multiple IPoIB interfaces on the same port. It is up to the implementation to ensure a unique client-identifier when multiple IPoIB interfaces are defined over the same port and same GID. A unique, invariant 'interface-id' value MUST be included in addition to the GID to achieve this. Note: a port may be associated with multiple GIDs. Therefore, multiple IPoIB interfaces may exist on the same port while using a different GID from among the GIDs associated with the port. A unique interface-id may be formed by including the QPN associated with the relevant IPoIB interface if the implementation is designed to keep this association constant across boots. A timestamp or some other value unique to the implementation may also be used for the same purpose. If there is only one IPoIB interface associated with a particular GID, then use of the GID is sufficient. By default, an implementation zeroes out the interface-id field in the client identifier described above. This document does not preclude the use of other 'client identifier' type, such as fully qualified domain name(FQDN) or the EUI-64 value associated with the interface. 2.2 Use of the BROADCAST flag A DHCP client on IPoIB SHOULD set a BROADCAST flag in DHCPDISCOVER and DHCPREQUEST messages (and set 'ciaddr' to zero) to ensure that the server (or the relay agent) broadcasts its reply to the client. Note: As described in [RFC2131], 'ciaddr' MUST be filled in with client's IP address during BOUND, RENEWING or REBINDING state, therefore, the BROADCAST flag MUST NOT be set. In these cases, the DHCP server unicasts DHCPACK message to the address in 'ciaddr'. The link address will be resolved by IPoIB ARP. Kashyap [Page 4] INTERNET-DRAFT DHCP over InfiniBand April 2002 3. Security Considerations DHCP currently provides no authentication or security mechanisms. Potential exposures to attack are discussed in section 7 of the DHCP protocol specification [RFC2131]. A malicious client can falsify the client-identifier, thus masquerading as another client. 4. Acknowledgement This document borrows extensively from [RFC 2855]. Roy Larsen pointed out the length discrepancy between the IPoIB link address and DHCP's chaddr field. References [RFC2119] Key words for use in RFCs to Indicate Requirement Levels S. Bradner [RFC2131] Dynamic Host Configuration Protocol, R. Droms [RFC2132] DHCP Options and BOOTP Vendor Extensions, S. Alexander, R. Droms [RFC951] Bootstrap Protocol, B. Croft, J. Gilmore [RFC1542] Clarifications and Extensions for the Bootstrap Protocol W. Wimer [ARPPARAM] http://www.iana.org/numbers.html [RFC2855] DHCP for IEEE 1394, K. Fujisawa [IPoIB_ARCH] draft-ietf-ipoib-architecture-01.txt, V. Kashyap [IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-01.txt, V. Kashyap, H.K. Jerry Chu Kashyap [Page 5] INTERNET-DRAFT DHCP over InfiniBand April 2002 Author's Address Vivek Kashyap IBM 15450, SW Koll Parkway Beaverton OR 97006 Phone: +1 503 578 3422 EMail: vivk@us.ibm.com Full Copyright Statement Copyright (C) The Internet Society (2000). 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. Kashyap [Page 6]