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Network Working Group                                      Vivek KashyapRequest for Comments: 4390                                           IBMCategory: Standards Track                                     April 2006Dynamic Host Configuration Protocol (DHCP) over InfiniBandStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   IP over Infiniband (IPoIB) link-layer address is 20 octets long.   This is larger than the 16 octets reserved for the hardware address   in a Dynamic Host Configuration Protocol/Bootstrap Protocol   (DHCP/BOOTP) message.  The above inequality imposes restrictions on   the use of the DHCP message fields when used over an IPoIB network.   This document describes the use of DHCP message fields when   implementing DHCP over IPoIB.Table of Contents1. Introduction ....................................................22. The DHCP over IPoIB Mechanism ...................................22.1. IPoIB-specific Usage of DHCP Message Fields ................32.2. Use of the BROADCAST flag ..................................33. Security Considerations .........................................34. Acknowledgement .................................................45. References ......................................................45.1. Normative References .......................................45.2. Informative References .....................................4Kashyap                     Standards Track                     [Page 1]

RFC 4390                  DHCP Over Infiniband                April 20061.  Introduction   The Dynamic Host Configuration Protocol (DHCP) provides a framework   for passing configuration information to hosts on an 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 a client.  The DHCP   server uses the client interface's hardware address to unicast a   reply when the client does not 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 octets in length.  The IPoIB link-layer   address is 20 octets in length [RFC4391].  Therefore, the IPoIB   link-layer address will not fit in the "chaddr" field making it   impossible for the DHCP server to unicast a reply 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 [RFC2119].2.  The DHCP over IPoIB Mechanism   As described above, the link-layer address is unavailable to the DHCP   server because the link-layer address is larger than the "chaddr"   field length.  As a result, the server cannot unicast its reply to   the client.  Therefore, a DHCP client MUST request that the server   send a broadcast reply by setting the BROADCAST flag when IPoIB   Address Resolution Protocol (ARP) is not possible, i.e., in   situations where the client does not know its IP address.   [RFC1542] discourages the use of a broadcast reply.  But in the case   of IPoIB, this is a necessity because the server does not receive the   link-layer address.  To desynchronise broadcasts at subnet startup,   [RFC2131] suggests that a client wait a random time (1 to 10 seconds)   before initiating server discovery.  The same timeout will spread out   the DHCP server broadcast responses generated due to the use of the   BROADCAST bit.Kashyap                     Standards Track                     [Page 2]

RFC 4390                  DHCP Over Infiniband                April 2006   The client hardware address, "chaddr", is unique in the subnet and   hence can be used to identify a client interface.  But in the absence   of a unique "chaddr", another unique 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 [RFC2132].  This   value must be unique within the client's subnet.   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].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.   The "client identifier" used in DHCP messages MUST conform to   [RFC4361].2.2.  Use of the BROADCAST flag   A DHCP client on IPoIB MUST set the 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 the         client's IP address during BOUND, RENEWING or REBINDING states;         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 ARP.3.  Security Considerations   [RFC2131] describes the security considerations relevant to DHCP.   This document does not introduce any new issues.Kashyap                     Standards Track                     [Page 3]

RFC 4390                  DHCP Over Infiniband                April 20064.  Acknowledgement   This document borrows extensively from [RFC2855].  Roy Larsen pointed   out the length discrepancy between the IPoIB link address and DHCP's   "chaddr" field.5.  References5.1.  Normative References   [RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate                   Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2131]       Droms, R., "Dynamic Host Configuration Protocol",RFC2131, March 1997.   [RFC2132]       Alexander, S. and R. Droms, "DHCP Options and BOOTP                   Vendor Extensions",RFC 2132, March 1997.   [RFC951]        Housley, R., Horting, T., and P. Yee, "TELNET                   Authentication Using KEA and SKIPJACK",RFC 2951,                   September 2000.   [RFC4391]       Chu, J. and V. Kashyap "Transmission of IP over                   InfiniBand (IPoIB)",RFC 4391, April 2006.   [ARPPARAM]http://www.iana.org/numbers.html   [RFC4361]       Lemon, T. and B. Sommerfeld, "Node-specific Client                   Identifiers for Dynamic Host Configuration Protocol                   Version Four (DHCPv4)",RFC 4361, February 2006.5.2.  Informative References   [RFC2855]       Fujisawa, K., "DHCP for IEEE 1394",RFC 2855, June                   2000.   [RFC1542]       Wimer, W., "Clarifications and Extensions for the                   Bootstrap Protocol",RFC 1542, October 1993.Kashyap                     Standards Track                     [Page 4]

RFC 4390                  DHCP Over Infiniband                April 2006Author's Address   Vivek Kashyap   15350, SW Koll Parkway   Beaverton, OR 97006   USA   Phone: +1 503 578 3422   EMail: vivk@us.ibm.comKashyap                     Standards Track                     [Page 5]

RFC 4390                  DHCP Over Infiniband                April 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 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   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 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 inBCP 78 andBCP 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 athttp://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 provided by the IETF   Administrative Support Activity (IASA).Kashyap                     Standards Track                     [Page 6]