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rfc:rfc4390

Network Working Group Vivek Kashyap Request for Comments: 4390 IBM Category: Standards Track April 2006

     Dynamic Host Configuration Protocol (DHCP) over InfiniBand

Status 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 Contents

 1. Introduction ....................................................2
 2. The DHCP over IPoIB Mechanism ...................................2
    2.1. IPoIB-specific Usage of DHCP Message Fields ................3
    2.2. Use of the BROADCAST flag ..................................3
 3. Security Considerations .........................................3
 4. Acknowledgement .................................................4
 5. References ......................................................4
    5.1. Normative References .......................................4
    5.2. Informative References .....................................4

Kashyap Standards Track [Page 1] RFC 4390 DHCP Over Infiniband April 2006

1. 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 2006

4. 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. References

5.1. 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", RFC
                 2131, 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 2006

Author's Address

 Vivek Kashyap
 15350, SW Koll Parkway
 Beaverton, OR 97006
 USA
 Phone: +1 503 578 3422
 EMail: vivk@us.ibm.com

Kashyap Standards Track [Page 5] RFC 4390 DHCP Over Infiniband April 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 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.

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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Kashyap Standards Track [Page 6]

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