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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IDR E. Chen 3 Internet-Draft Palo Alto Networks 4 Updates: 4271 (if approved) J. Scudder 5 Intended status: Standards Track Juniper Networks 6 Expires: October 24, 2021 April 22, 2021 8 Extended Optional Parameters Length for BGP OPEN Message 9 draft-ietf-idr-ext-opt-param-13 11 Abstract 13 The Optional Parameters in the BGP OPEN message as defined in the 14 base BGP specification are limited to 255 octets due to a one-octet 15 length field. BGP Capabilities are carried in this field and may 16 foreseeably exceed 255 octets in the future, leading to concern about 17 this limitation. 19 This document updates RFC 4271 by extending, in a backward-compatible 20 manner, the length of the Optional Parameters in the BGP OPEN. The 21 Parameter Length field of individual Optional Parameters is also 22 extended. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on October 24, 2021. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 1. Introduction 58 The Optional Parameters Length field in the BGP OPEN message is 59 defined in the base BGP specification [RFC4271] as one octet, thus 60 limiting the Optional Parameters field in the OPEN message to 255 61 octets. Since BGP Capabilities [RFC5492] are carried in the Optional 62 Parameters field, and new BGP capabilities continue to be introduced, 63 the limitation is a concern for BGP development. 65 This document updates [RFC4271] by extending, in a backward- 66 compatible manner, the length of the Optional Parameters in BGP OPEN. 67 This is done by using Optional Parameter Type 255 as a distinguished 68 value, that indicates an extended Optional Parameters Length field 69 follows and that the parsing of the BGP OPEN should be modified 70 according to these procedures. In this case the Parameter Length 71 field of the individual Optional Parameters in the BGP OPEN message 72 is also extended. 74 1.1. Requirements Language 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 77 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 78 "OPTIONAL" in this document are to be interpreted as described in BCP 79 14 [RFC2119] [RFC8174] when, and only when, they appear in all 80 capitals, as shown here. 82 2. Update to RFC 4271 84 This document reserves Optional Parameter Type code 255 as the 85 "Extended Length" type code. 87 In the event that the length of Optional Parameters in the BGP OPEN 88 message does not exceed 255, the encodings of the base BGP 89 specification [RFC4271] SHOULD be used without alteration. 90 Configuration MAY override this to force the extended format to be 91 used in all cases; this might be used, for example to test that a 92 peer supports this specification. (In any case, an implementation 93 MUST accept an OPEN message that uses the encoding of this 94 specification even if the length of Optional Parameters is 255 or 95 less.) 96 However, if the length of Optional Parameters in the BGP OPEN message 97 does exceed 255, the OPEN message MUST be encoded according to the 98 procedure below. 100 0 1 2 3 101 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 102 +-+-+-+-+-+-+-+-+ 103 | Version | 104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 105 | My Autonomous System | 106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 107 | Hold Time | 108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 109 | BGP Identifier | 110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 111 |Non-Ext OP Len.|Non-Ext OP Type| Extended Opt. Parm. Length | 112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 113 | | 114 | Optional Parameters (variable) | 115 | | 116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 Figure 1: Extended Encoding OPEN Format 120 The Non-Extended Optional Parameters Length field (Non-Ext OP Len) 121 SHOULD be set to 255 on transmission and in any event MUST NOT be set 122 to 0, and MUST be ignored on receipt once the use of the extended 123 format is determined positively by inspection of the Non-Extended 124 Optional Parameters Type (Non-Ext OP Type) field. 126 The subsequent one-octet field (that would be the first Optional 127 Parameter Type field in the non-extended format, and is called "Non- 128 Ext OP Type" in the figure above) MUST be set to 255 on transmission. 129 On receipt, a value of 255 for this field is the indication that the 130 extended format is in use. 132 In this extended encoding, the subsequent two-octet field, termed the 133 Extended Optional Parameters Length field, is an unsigned integer 134 indicating the total length of the Optional Parameters field in 135 octets. If the value of this field is zero, no Optional Parameters 136 are present. 138 Likewise, in that situation the Optional Parameters encoding is 139 modified to be the following: 141 0 1 2 142 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 | Parm. Type | Parameter Length | 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 ~ Parameter Value (variable) ~ 147 | | 148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 Figure 2: Extended Parameters Format 152 The rules for encoding Optional Parameters are unchanged with respect 153 to those given in [RFC4271] other than the extension of the Parameter 154 Length field to be a two-octet unsigned integer. 156 In parsing an OPEN message, if the one-octet "Optional Parameters 157 Length" field (labeled "Non-Ext OP Len." in Figure 1) is non-zero, a 158 BGP speaker MUST use the value of the octet following the one-octet 159 "Optional Parameters Length" field (labeled "Non-Ext OP Type" in 160 Figure 1) to determine both the encoding of the Optional Parameters 161 length and the size of the "Parameter Length" field of individual 162 Optional Parameters. If the value of the "Non-Ext OP Type" field is 163 255, then the encoding described above is used for the Optional 164 Parameters length. Otherwise the encoding defined in [RFC4271] is 165 used. 167 3. Backward Compatibility 169 If a BGP speaker supporting this specification (a "new speaker") is 170 peering with one which does not (an "old speaker") no 171 interoperability issues arise unless the new speaker needs to encode 172 Optional Parameters whose length exceeds 255. In that case, it will 173 transmit an OPEN message which the old speaker will interpret as 174 containing an Optional Parameter with type code 255. Since by 175 definition the old speaker will not recognize that type code, the old 176 speaker is expected to close the connection with a NOTIFICATION with 177 an Error Code of OPEN Message Error and an Error Subcode of 178 Unsupported Optional Parameters, according to Section 6.2 of 179 [RFC4271]. 181 Although the Optional Parameter Type code 255 is used in this 182 specification as the indication that the extended encoding is in use, 183 it is not a bona fide Optional Parameter Type in the usual sense, and 184 MUST NOT be used other than as described above. If encountered in 185 any position other than the first Optional Parameter Type, it MUST be 186 treated as an unrecognized Optional Parameter and handled according 187 to [RFC4271] Section 6.2. 189 It is not considered an error to receive an OPEN message whose 190 Extended Optional Parameters Length value is less than or equal to 191 255. It is not considered a fatal error to receive an OPEN message 192 whose (non-extended) Optional Parameters Length value is not 255, and 193 whose first Optional Parameter type code is 255 -- in this case the 194 encoding of this specification MUST be used for decoding the message. 196 4. IANA Considerations 198 IANA is requested to designate type code 255 in the BGP OPEN Optional 199 Parameter Types registry as the Extended Length type code. 201 5. Security Considerations 203 This extension to BGP does not change the underlying security or 204 confidentiality issues inherent in the existing BGP [RFC4272]. 206 6. Acknowledgements 208 The authors would like to thank Yakov Rekhter and Srihari Sangli for 209 discussing various options to enlarge the Optional Parameters field. 210 We would also like to thank Matthew Bocci, Bruno Decraene, John 211 Heasley, Jakob Heitz, Christer Holmberg, Pradosh Mohapatra, Keyur 212 Patel and Hannes Gredler for their valuable comments. 214 7. References 216 7.1. Normative References 218 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 219 Requirement Levels", BCP 14, RFC 2119, 220 DOI 10.17487/RFC2119, March 1997, 221 . 223 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 224 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 225 DOI 10.17487/RFC4271, January 2006, 226 . 228 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 229 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 230 May 2017, . 232 7.2. Informative References 234 [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", 235 RFC 4272, DOI 10.17487/RFC4272, January 2006, 236 . 238 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 239 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 240 2009, . 242 Authors' Addresses 244 Enke Chen 245 Palo Alto Networks 247 Email: enchen@paloaltonetworks.com 249 John Scudder 250 Juniper Networks 252 Email: jgs@juniper.net