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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Historic RFC: RFC 1058 (ref. '5') ** Downref: Normative reference to an Historic RFC: RFC 1878 (ref. '9') Summary: 9 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Ted Lemon 2 Internet Draft Nominum, Inc. 3 Obsoletes: draft-ietf-dhc-csr-00.txt January, 2000 4 Expires July 2000 6 The Classless Static Route Option for DHCP 7 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 This document is an Internet-Draft. Internet-Drafts are working 15 documents of the Internet Engineering Task Force (IETF), its areas, 16 and its working groups. Note that other groups may also distribute 17 working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other 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 at 28 http://www.ietf.org/shadow.html. 30 Abstract 32 This document defines a new DHCP option which is passed from the 33 DHCP Server to the DHCP Client to configure a list of static routes 34 in the client. This option supersedes the Static Route option 35 (option 33) defined in [2]. 37 Introduction 39 The IP protocol [4] uses routers to transmit packets from hosts 40 connected to one IP subnet to hosts connected to a different IP 41 subnet. When an IP host (the source host) wishes to transmit a 42 packet to another IP host (the destination), it first checks to see 43 if the IP address of the destination host to see if it is on a 44 subnet to which the source host is connected. If the destination 45 host's IP address is not on a subnet to which the source host is 46 connected, then the source host consults its routing table to 47 determine the IP address of the router that should be used to 48 forward the packet to the destination host. 50 The routing table on an IP host can be maintained in a variety of 51 ways - using a routing information protocol such as RIP [5], ICMP 52 router discovery [6,7] or using the DHCP Router option, defined in 53 [2]. 55 In a network that already provides DHCP service, using DHCP to 56 update the routing table on a DHCP client has several virtues. It 57 is efficient, since it makes use of messages that would have been 58 sent anyway. It is convenient - the DHCP server configuration 59 is already being maintained, so maintaining routing information, at 60 least on a relatively stable network, requires little extra work. 61 If DHCP service is already in use, no additional infrastructure 62 need be deployed. 64 The DHCP protocol as defined in [1] and the options defined in [2] 65 only provide a mechanism for installing a default route or 66 installing a table of classed routes. Classed routes are routes 67 whose subnet mask is implicit in the subnet number - see section 68 3.2 of [4] for details on classed routing. 70 Classed routing is no longer in common use, so the DHCP Static 71 Route option is no longer useful. Currently, classless routing, 72 described in [8] and [9], is the most commonly-deployed form of 73 routing on the Internet. In classless routing, IP addresses 74 consist of a network number (the combination of the network number 75 and subnet number described in [8]) and a host number. 77 In classed IP, the network number and host number are derived from 78 the IP address using a bitmask whose value is determined by the first 79 few bits of the IP address. In classless IP, the network number 80 and host number are derived from the IP address using a seperate 81 quantity, the subnet mask. In order to determine the network to 82 which a given route applies, an IP host must know both the network 83 number AND the subnet mask for that network. 85 The Static Routes option does not provide a subnet mask for each 86 route - it is assumed that the subnet mask is implicit in whatever 87 network number is specified in each route entry. The Classless 88 Static Routes option does provide a subnet mask for each entry, so 89 that the subnet mask can be other than what would be determined 90 using the algorithm specified in [4] and [8]. 92 Definitions 94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this 96 document are to be interpreted as described in RFC 2119 [3]. 98 This document also uses the following terms: 100 "DHCP client" 102 DHCP client or "client" is an Internet host using DHCP to 103 obtain configuration parameters such as a network address. 105 "DHCP server" 107 A DHCP server or "server" is an Internet host that returns 108 configuration parameters to DHCP clients. 110 Classless Route Option Format 112 The code for this option is TBD, and its minimum length is 12 bytes. 113 This option can contain one or more static routes, each of which 114 consists of a destination network number, a destination subnet mask 115 and the IP address of the router that should be used to reach that 116 destination. 118 Code Len Destination 1 Subnet Mask 1 Router 1 119 +----+---+----+----+----+----+----+----+----+----+----+----+----+----+ 120 | 33 | n | d1 | d2 | d3 | d4 | m1 | m2 | m3 | m4 | r1 | r2 | r3 | r4 | 121 +----+---+----+----+----+----+----+----+----+----+----+----+----+----+ 123 Destination 2 Subnet Mask 2 Router 2 124 +----+----+----+----+----+----+----+----+----+----+----+----+ 125 | d1 | d2 | d3 | d4 | m1 | m2 | m3 | m4 | r1 | r2 | r3 | r4 | 126 +----+----+----+----+----+----+----+----+----+----+----+----+ 128 In the above example, two static routes are specified. 130 DHCP Client Behavior 132 The DHCP client MAY use this option to install a set of static 133 routes in its routing table. A DHCP client that implements this 134 option SHOULD use this option in preference to the Static routes 135 option if both are present in a reply from the DHCP server. 137 Security Considerations 139 DHCP currently provides no authentication or security mechanisms. 140 Potential exposures to attack are discussed in section 7 of the DHCP 141 protocol specification [1]. The Classless Static Routes option can 142 be used to misdirect network traffic by providing incorrect IP 143 addresses for routers. 145 References 147 [1] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, 148 Bucknell University, March 1997. 149 [2] Alexander, S. and Droms, R., "DHCP Options and BOOTP Vendor 150 Extensions", RFC 2132, Silicon Graphics, Inc., Bucknell 151 University, March 1997. 152 [3] Bradner, S., "Key words for use in RFCs to indicate requirement 153 levels", RFC 2119, Harvard University, March 1997. 154 [4] Postel, J., "Internet Protocol", RFC 791, USC/Information 155 Sciences Institute, September 1981. 156 [5] Hedrick, C.L., "Routing Information Protocol", RFC 1058, 157 Rutgers University, June 1, 1988. 158 [6] Deering, S., "ICMP Router Discovery Messages", RFC 1256, 159 Xerox PARC, September 1991. 160 [7] Postel, J., "Internet Control Message Protocol", RFC 792, 161 USC/Information Sciences Institute, September 1981. 162 [8] Mogul, J., Postel, J., "Internet Standard Subnetting 163 Procedure", RFC950, Stanford University, USC/Information 164 Sciences Institute, August 1985. 165 [9] Pummill, T., Manning, B., "Variable Length Subnet Table For 166 IPv4", RFC1878, Alantec, USC/Information Sciences Institute, 167 December, 1995 169 Author Information 171 Ted Lemon 172 Nominum, Inc. 173 950 Charter Street 174 Redwood City, CA 94043 175 email: Ted.Lemon@nominum.com 177 Expiration 179 This document will expire on July 31, 2000. 181 Full Copyright Statement 183 Copyright (C) The Internet Society (2000). All Rights Reserved. 185 This document and translations of it may be copied and furnished to 186 others, and derivative works that comment on or otherwise explain it 187 or assist in its implementation may be prepared, copied, published 188 and distributed, in whole or in part, without restriction of any 189 kind, provided that the above copyright notice and this paragraph are 190 included on all such copies and derivative works. However, this 191 document itself may not be modified in any way, such as by removing 192 the copyright notice or references to the Internet Society or other 193 Internet organizations, except as needed for the purpose of 194 developing Internet standards in which case the procedures for 195 copyrights defined in the Internet Standards process must be 196 followed, or as required to translate it into languages other than 197 English. 199 The limited permissions granted above are perpetual and will not be 200 revoked by the Internet Society or its successors or assigns. 202 This document and the information contained herein is provided on an 203 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 204 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 205 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 206 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 207 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.