[Idr] AD Review of draft-ietf-idr-ext-opt-param-09
Alvaro Retana <aretana.ietf@gmail.com> Thu, 18 March 2021 21:54 UTC
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From: Alvaro Retana <aretana.ietf@gmail.com>
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To: draft-ietf-idr-ext-opt-param@ietf.org
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Subject: [Idr] AD Review of draft-ietf-idr-ext-opt-param-09
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Enke/John: Hi! Thank you for your persistence in getting this work done! I have several comments inline below. I believe that all of them should be easy to address. Thanks! Alvaro. [Line numbers from idnits.] ... 11 Abstract ... 19 In this document we update RFC 4271 by extending, in a backward- 20 compatible manner, the length of the Optional Parameters in the BGP 21 OPEN. The Parameter Length field of individual Optional Parameters 22 is also extended. [style nit] s/In this document we update/This document updates/g ... 72 1.1. Requirements Language 74 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 75 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 76 document are to be interpreted as described in RFC 2119 [RFC2119]. [major] Use the template from rfc8174. 78 2. Protocol Extensions ... 83 In the event that the length of Optional Parameters in the BGP OPEN 84 message does not exceed 255, the encodings of the base BGP 85 specification [RFC4271] MUST be used without alteration. However, an 86 implementation MUST be prepared to accept an OPEN message that uses 87 the encoding of this specification for Optional Parameters of any 88 length. [major] "MUST be prepared to accept an OPEN message...of any length." The OPEN message is not covered by rfc8654, so the length is still limited to 4k...which means that the full Extended OP length/Parameter Length cannot be used. Besides clarifying that, I think that new OPEN Message Error subcodes are needed for the cases where the length is invalid. This type of error is possible in the non-extended version of the OPEN too -- I guess rfc4271 just assumed that this error would never happen. 90 If the length of Optional Parameters is greater than 255, the 91 extended encoding defined here MUST be used. The (non-extended) 92 length field MUST be set to 255. The subsequent octet (which would 93 be the first Optional Parameter Type in the non-extended format) MUST 94 be set to 255 as well. The subsequent two octets carry the actual 95 length. In addition, the "Parameter Length" field of each Optional 96 Parameter is enlarged to two octets. Other than the larger sizes of 97 the given fields, there is no change to the BGP OPEN message defined 98 in [RFC4271]. [minor] This paragraph references the modified OPEN message, but it hasn't been introduced yet. Please refer to the figures or move them (and the description of the fields) to the beginning of this section. Also, please be consistent with the field names from the figure. ... 111 0 1 2 3 112 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 1 113 +-+-+-+-+-+-+-+-+ 114 | Version | 115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 116 | My Autonomous System | 117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 | Hold Time | 119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 120 | BGP Identifier | 121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 122 |Non-Ext OP Len.|Non-Ext OP Type| Extended Opt. Parm. Length | 123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 124 | | 125 | Optional Parameters (variable) | 126 | | 127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [] Please add a figure number and title. 129 The non-extended Optional Parameters Length field MUST be set to 255 130 on transmission, and MUST be ignored on receipt once the use of the 131 extended format is determined positively by inspection of the (non- 132 extended) Optional Parameters Type field. [major] "non-extended Optional Parameters Length" Please refer to the names of the fields in the figure. s/.../non-extended Optional Parameters Length (Non-Ext OP Len.) ... 148 0 1 2 149 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 151 | Parm. Type | Parameter Length | 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 ~ Parameter Value (variable) ~ 154 | | 155 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ [] Please add a figure number and title. ... 178 The choice to mandate that when the extended encoding is in use, the 179 (non-extended) Optional Parameters Length field must be 255 was made 180 for backward compatibility with implementations of earlier versions 181 of this specification. When the extended encoding is in use, the 182 value 0 MUST NOT be used in that field since the presence of that 183 value could have the effect of causing a message parser to never 184 inspect the following octet. [] I don't think it's a good idea to justify anything based on pre-standard implementations. s/MUST be set to 255 on transmission/SHOULD be set to 255 on transmission will cover both cases without the justification. [major] "0 MUST NOT be used" Move this part to where the field is described. 186 3. Errors 188 If a BGP speaker supporting this specification (a "new speaker") is 189 peering with one which does not (an "old speaker") no 190 interoperability issues arise unless the new speaker needs to encode 191 Optional Parameters whose length exceeds 255. In that case, it will 192 transmit an OPEN message which the old speaker will interpret as 193 containing an Optional Parameter with type code 255. Since by 194 definition the old speaker will not recognize that type code, the old 195 speaker may be expected to close the connection with a NOTIFICATION 196 with an Error Code of OPEN Message Error and an Error Subcode of 197 Unsupported Optional Parameters, according to Section 6.2 of 198 [RFC4271]. [minor] s/may be expected/is expected 200 Although the above is the most likely error to be sent, it is not 201 impossible that the old speaker might detect some other error first, 202 such as a length error, depending on the details of the 203 implementation. In no case would the peering be expected to 204 establish successfully; the only question is which NOTIFICATION would 205 be generated. [] No need to speculate about implementations. The text above points at rfc4271 anyway. 207 We note that in any case, such a peering could not succeed, since by 208 definition the extended length encoding would not be used by the new 209 speaker unless the basic encoding was insufficient. [] I don't understand what you mean here. It sounds as if the new speaker shouldn't have used the encoding anyway... ?? ... 219 It is not considered an error to receive an OPEN message whose 220 Extended Optional Parameters Length value is less than or equal to 221 255, any value SHOULD be silently accepted. It is not considered a 222 fatal error to receive an OPEN message whose (non-extended) Optional 223 Parameters Length value is not 255, and whose first Optional 224 Parameter type code is 255 -- in this case the encoding of this 225 specification MUST be used for decoding the message. A warning MAY 226 be logged. [major] "any value SHOULD be silently accepted" When is it ok to not (silently) accept the message? IOW, why is this recommended and not required? In any case, I don't think that the last part of the sentence is needed because the first part already says this is not an error. [End of Review]
- [Idr] AD Review of draft-ietf-idr-ext-opt-param-09 Alvaro Retana
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Jeffrey Haas
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Alvaro Retana
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Jeffrey Haas
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… John Scudder
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… John Scudder
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Alvaro Retana
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Jeffrey Haas
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… John Scudder
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Alvaro Retana
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… John Scudder
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Alvaro Retana
- Re: [Idr] AD Review of draft-ietf-idr-ext-opt-par… Enke Chen