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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET DRAFT Vivek Kashyap 3 IBM 4 Expiration Date: February 2003 August 2002 6 DHCP over InfiniBand 8 Status of this memo 10 This document is an Internet-Draft and is in full conformance 11 with all provisions of Section 10 of RFC 2026. 13 Internet-Drafts are working documents of the Internet 14 Engineering Task Force (IETF), its areas, and its working 15 groups. Note that other groups may also distribute working 16 documents as Internet- Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six 19 months and may be updated, replaced, or obsoleted by other 20 documents at any time. It is inappropriate to use 21 Internet-Drafts as Reference material or to cite them other 22 than as ``work in progress''. 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt 27 The list of Internet-Draft Shadow Directories can be accessed 28 at http://www.ietf.org/shadow.html 30 This memo provides information for the Internet community. 31 This memo does not specify an Internet standard of any kind. 32 Distribution of this memo is unlimited. 34 Copyright Notice 36 Copyright (C) The Internet Society (2001). All Rights Reserved. 38 Abstract 40 An InfiniBand network uses a link-layer addressing scheme that 41 is 20-bytes long. This is larger than the 16-bytes reserved for 42 the hardware address in DHCP/BOOTP message. The above 43 inequality imposes restrictions on the use of the DHCP message 44 fields when used over an IP over InfiniBand(IPoIB) network. 45 This document describes the use of DHCP message fields when 46 implementing DHCP over IPoIB. 48 1. Introduction 50 The Dynamic Host Configuration Protocol(DHCP) provides a 51 framework for passing configuration information to hosts on a 52 TCP/IP network [RFC2131]. DHCP is based on the Bootstrap 53 Protocol (BOOTP) [RFC951] adding the capability of automatic 54 allocation of reusable network addresses and additional 55 configuration options [RFC2131,RFC2132]. 57 The DHCP server receives a broadcast request from the DHCP 58 client. The DHCP server uses the client interface's 59 hardware-address to unicast a reply back when the client 60 doesn't yet have an IP address assigned to it. The 'chaddr' 61 field in the DHCP message carries the client's hardware 62 address. 64 The 'chaddr' field is 16-bytes in length. The IPoIB link-layer 65 address is 20-bytes in length. Therefore the IPoIB link-layer 66 address will not fit in the 'chaddr' field making it 67 impossible for the DHCP server to unicast a reply back to the 68 client. 70 To ensure interoperability the usage of the fields and the 71 method for DHCP interaction must be clarified. This document 72 describes the IPoIB specific usage of some fields of DHCP. See 73 [RFC2131] for the mechanism of DHCP and the explanations of 74 each field. 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 77 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and 78 "OPTIONAL" in this document are to be interpreted as described 79 in RFC 2119 [RFC2119]. 81 2. The DHCP over IPoIB mechanism 83 As noted above, because of the link-layer address length being 84 larger than the 'chaddr' field length, the link-layer address 85 is unavailable to the DHCP server. Therefore, a DHCP client 86 MUST request that the server sends a broadcast reply by 87 setting the BROADCAST flag when IPoIB ARP is not possible, 88 i.e. in situations where the client does not know its IP 89 address. 91 RFC1542 notes that the use of a broadcast reply is 92 discouraged. But in the case of IPoIB this is a necessity. 93 There is no option but to broadcast back to the client since 94 it is not possible to reply the client's unicast address. To 95 desynchronise broadcasts at subnet startup, the RFC2131 96 suggests that a client wait a random time (1 to 10 seconds) 97 before initiating server discovery. The same timeout will 98 equally spread out the DHCP server broadcast responses 99 generated due to the use of the use of the BROADCAST bit. 101 The client hardware address, 'chaddr', is unique in the subnet 102 and hence can be used to identify the client interface. But in 103 the absence of a unique chaddr the client-identifier must be 104 used. 106 The DHCP protocol states that the 'client identifier' option 107 may be used as the unique identifying value for the client. 108 This value must be unique within the subnet the client is a 109 member of. 111 The client identifier option includes a type and identifier 112 pair. The identifier included in the client-identifier option 113 may consist of a hardware address or any other unique value 114 such as the DNS name of the client. When a hardware address is 115 used, the type field should be one of the ARP hardware types 116 listed in [ARPPARAM]. 118 The client-identifier itself SHOULD not be interpreted by the 119 server. [RFC2132] 121 2.1 IPoIB specific usage of DHCP message fields 123 A DHCP client, when working over an IPoIB interface, MUST 124 follow the following rules: 126 'htype' (hardware address type) MUST be 32 [ARPPARAM] 128 'hlen' (hardware address length) MUST be 0. 130 'chaddr' (client hardware address) field MUST be zeroed. 132 'client identifier' option MUST be used in DHCP messages. 134 According to RFC2132 the 'client identifier' option MAY 135 consist of any data, but IPoIB clients SHOULD use the 136 following format for the client-identifier option: 138 Code Len Type Client-Identifier 139 +-----+-----+-----+-----+-----+-----+-----+-------------------....----+ 140 | 61 | 21 | 32 |Interface-id (4 bytes) | GID (16 bytes) | 141 +-----+-----+-----+-----+-----+-----+-----+-------------------....----+ 143 Every IPoIB interface is associated with an identifier 144 referred to as the GID [IPoIB_ARCH]. The GID is unique in the 145 InfiniBand fabric. An invariant GID is formed by appending the 146 port's EUI-64 identifier to the InfiniBand subnet prefix. 148 The GID is associated with a particular hardware port. The GID 149 and a QPN define an IPoIB interface at the port. Therefore an 150 implementation may associate multiple IPoIB interfaces on the 151 same port. It is up to the implementation to ensure a unique 152 client-identifier when multiple IPoIB interfaces are defined 153 over the same port and same GID. A unique, invariant 154 'interface-id' value MUST be included in addition to the GID 155 to achieve this. 157 Note: a port may be associated with multiple GIDs. Therefore, 158 multiple IPoIB interfaces may exist on the same port while 159 using a different GID from among the GIDs associated with the 160 port. 162 A unique interface-id may be formed by including the QPN 163 associated with the relevant IPoIB interface if the 164 implementation is designed to keep this association constant 165 across boots. A timestamp or some other value unique to the 166 implementation may also be used for the same purpose. 168 If there is only one IPoIB interface associated with a 169 particular GID, then use of the GID is sufficient. By default, 170 an implementation zeroes out the interface-id field in the 171 client identifier described above. 173 This document does not preclude the use of other 'client 174 identifier' type, such as fully qualified domain name(FQDN) or 175 the EUI-64 value associated with the interface. 177 2.2 Use of the BROADCAST flag 179 A DHCP client on IPoIB SHOULD set a BROADCAST flag in 180 DHCPDISCOVER and DHCPREQUEST messages (and set 'ciaddr' to 181 zero) to ensure that the server (or the relay agent) 182 broadcasts its reply to the client. 184 Note: As described in [RFC2131], 'ciaddr' MUST be filled in 185 with client's IP address during BOUND, RENEWING or REBINDING 186 state, therefore, the BROADCAST flag MUST NOT be set. In these 187 cases, the DHCP server unicasts DHCPACK message to the address 188 in 'ciaddr'. The link address will be resolved by IPoIB ARP. 190 3. Security Considerations 192 DHCP currently provides no authentication or security 193 mechanisms. Potential exposures to attack are discussed 194 in section 7 of the DHCP protocol specification [RFC2131]. 196 A malicious client can falsify the client-identifier, 197 thus masquerading as another client. 199 4. Acknowledgement 201 This document borrows extensively from [RFC 2855]. Roy Larsen 202 pointed out the length discrepancy between the IPoIB link 203 address and DHCP's chaddr field. 205 References 207 [RFC2119] Key words for use in RFCs to Indicate Requirement Levels 208 S. Bradner 210 [RFC2131] Dynamic Host Configuration Protocol, R. Droms 212 [RFC2132] DHCP Options and BOOTP Vendor Extensions, 213 S. Alexander, R. Droms 215 [RFC951] Bootstrap Protocol, B. Croft, J. Gilmore 217 [RFC1542] Clarifications and Extensions for the Bootstrap Protocol 218 W. Wimer 220 [ARPPARAM] http://www.iana.org/numbers.html 222 [RFC2855] DHCP for IEEE 1394, K. Fujisawa 224 [IPoIB_ARCH] draft-ietf-ipoib-architecture-01.txt, V. Kashyap 226 [IPoIB_ENCAP] draft-ietf-ipoib-ip-over-infiniband-01.txt, 227 V. Kashyap, H.K. Jerry Chu 229 Author's Address 231 Vivek Kashyap 233 IBM 234 15450, SW Koll Parkway 235 Beaverton 236 OR 97006 238 Phone: +1 503 578 3422 239 EMail: vivk@us.ibm.com 241 Full Copyright Statement 243 Copyright (C) The Internet Society (2000). All Rights Reserved. 245 This document and translations of it may be copied and furnished to 246 others, and derivative works that comment on or otherwise explain it 247 or assist in its implementation may be prepared, copied, published 248 and distributed, in whole or in part, without restriction of any 249 kind, provided that the above copyright notice and this paragraph are 250 included on all such copies and derivative works. However, this 251 document itself may not be modified in any way, such as by removing 252 the copyright notice or references to the Internet Society or other 253 Internet organizations, except as needed for the purpose of 254 developing Internet standards in which case the procedures for 255 copyrights defined in the Internet Standards process must be 256 followed, or as required to translate it into languages other than 257 English. 259 The limited permissions granted above are perpetual and will not be 260 revoked by the Internet Society or its successors or assigns. 262 This document and the information contained herein is provided on an 263 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 264 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 265 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 266 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 267 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.