Re: [Idr] Robert Wilton's Discuss on draft-ietf-idr-rfc5575bis-23: (with DISCUSS and COMMENT)
"Rob Wilton (rwilton)" <rwilton@cisco.com> Fri, 24 April 2020 13:43 UTC
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From: "Rob Wilton (rwilton)" <rwilton@cisco.com>
To: Susan Hares <shares@ndzh.com>, 'The IESG' <iesg@ietf.org>, "aretana.ietf@gmail.com" <aretana.ietf@gmail.com>
CC: "draft-ietf-idr-rfc5575bis@ietf.org" <draft-ietf-idr-rfc5575bis@ietf.org>, "idr-chairs@ietf.org" <idr-chairs@ietf.org>, "idr@ietf.org" <idr@ietf.org>, 'Jie Dong' <jie.dong@huawei.com>
Thread-Topic: Robert Wilton's Discuss on draft-ietf-idr-rfc5575bis-23: (with DISCUSS and COMMENT)
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Date: Fri, 24 Apr 2020 13:43:36 +0000
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Subject: Re: [Idr] Robert Wilton's Discuss on draft-ietf-idr-rfc5575bis-23: (with DISCUSS and COMMENT)
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Hi Susan, Thanks for the quick response and explanation. Please see inline ... > -----Original Message----- > From: Susan Hares <shares@ndzh.com> > Sent: 24 April 2020 13:01 > To: Rob Wilton (rwilton) <rwilton@cisco.com>; 'The IESG' <iesg@ietf.org> > Cc: draft-ietf-idr-rfc5575bis@ietf.org; idr-chairs@ietf.org; idr@ietf.org; > 'Jie Dong' <jie.dong@huawei.com>; aretana.ietf@gmail.com > Subject: RE: Robert Wilton's Discuss on draft-ietf-idr-rfc5575bis-23: > (with DISCUSS and COMMENT) > > Robert: > > Thank you for your question. I'm pulling the DISCUSS to the front. > > The Discuss in the phrases: > > "SHOULD be set to 0 on encoding, and MUST be ignored during decoding." > > is actually language used in many past routing drafts for expansion > purposes. [RW] Yes. I appreciate that historical precedent holds a lot of weight. Prior to my discuss I had tried to quickly find examples of this, but was looking in the wrong documents. ;-) > > The difficultly in deploying new code is in the partial deployments. > The "must be ignored" clause allows the transmitter to change > to something besides zero. [RW] Yes, it is the partial deployments that is concerning me. But I don't understand why that means the sender is a "SHOULD be 0" not a "MUST be 0"? In the interop case either sender or receiver could be upgraded, so why the asymmetry? My understanding is that these fields should be set to 0 unless there is a new specification that gives them meaning which affects both sender and receiver. > > This is a RFC5575bis document based past history of these > statements in routing code. [RW] I agree, and I have no intention of unduly holding up a document, but just want to check that this is being expressed in the most correct and understandable way. > > I've taken the remainder of your comments as editorial comments. > Our authoring team loads these comments into github, and you are welcome > to > Contribute to the resolutions. [RW] That sounds fine, thank you. Regards, Rob > > Susan Hares > > -----Original Message----- > From: Robert Wilton via Datatracker [mailto:noreply@ietf.org] > Sent: Friday, April 24, 2020 5:49 AM > To: The IESG > Cc: draft-ietf-idr-rfc5575bis@ietf.org; idr-chairs@ietf.org; idr@ietf.org; > Jie Dong; aretana.ietf@gmail.com; jie.dong@huawei.com > Subject: Robert Wilton's Discuss on draft-ietf-idr-rfc5575bis-23: (with > DISCUSS and COMMENT) > > Robert Wilton has entered the following ballot position for > draft-ietf-idr-rfc5575bis-23: Discuss > > When responding, please keep the subject line intact and reply to all > email addresses included in the To and CC lines. (Feel free to cut this > introductory paragraph, however.) > > > Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html > for more information about IESG DISCUSS and COMMENT positions. > > > The document, along with other ballot positions, can be found here: > https://datatracker.ietf.org/doc/draft-ietf-idr-rfc5575bis/ > > > > ---------------------------------------------------------------------- > DISCUSS: > ---------------------------------------------------------------------- > > I don't know if this is a valid discuss point, so happy to be educated > that it is always written this way and I'll remove my discuss ... > > I note that in 5 places this document has text that states the equivalent > to "SHOULD be set to 0 on encoding, and MUST be ignored during decoding." > (example given below). > > Doesn't this make extending this in future more risky because if new > meaning are given to these bits then there could be senders already > transmitting non 0 values which a receiver might then misinterpret? > > Hence, I was surprised that the constraints did not also include a MUST on > the encoding side (i.e. be strict in what you send ...), i.e. "MUST be set > to 0 on encoding, and MUST be ignored during decoding." > > Example: > The extended is encoded as follows: > > 0 1 2 3 > 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 > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | reserved | reserved | reserved | reserved | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > | reserved | r.| DSCP | > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ > > Figure 6: Traffic Marking Extended Community Encoding > > o DSCP: new DSCP value for the transiting IP packet. > > o reserved, r.: SHOULD be set to 0 on encoding, and MUST be ignored > during decoding. > > > ---------------------------------------------------------------------- > COMMENT: > ---------------------------------------------------------------------- > > Hi, > > I also had a few minor comments on this document: > > 4.1. Length Encoding > > o If the NLRI length is smaller than 240 (0xf0 hex) octets, the > length field can be encoded as a single octet. > > o Otherwise, it is encoded as an extended-length 2-octet value in > which the most significant nibble of the first octet is all ones. > > This describes the first nibble in binary, and then later it is shown in > hex. > It might be more clear to write ... in which the most significant nibble > has the hex value 0xf. > > In Figure 1 above, values less-than 240 are encoded using two hex > digits (0xnn). Values above 239 are encoded using 3 hex digits > (0xfnnn). The highest value that can be represented with this > encoding is 4095. For example the length value of 239 is encoded as > 0xef (single octet) while 240 is encoded as 0xf0f0 (2-octet). > > 4.2. NLRI Value Encoding > > Components MUST follow strict type ordering by increasing numerical > order. A given component type may (exactly once) or may not be > present in the Flow Specification. If present, it MUST precede any > component of higher numeric type value. > > I wasn't sure, but wondering whether "may (exactly once) or may not be" > should be "MAY (exactly once) be"? > > Sue: (treating as a "editorial) > > Does this work for you? > Old/A given component type may (exactly once) or may not be > present in the flow Specification/ > > New/Each given component type may or may not be present in the > Flow Specification. If a type is present, it may be present only once./ > > > 5.1. Ordering of Flow Specifications > > For all other component types, unless otherwise specified, the > comparison is performed by comparing the component data as a binary > string using the memcmp() function as defined by [ISO_IEC_9899]. For > strings with equal lengths the lowest string (memcmp) has higher > precedence. For strings of different lengths, the common prefix is > compared. If the common prefix is not equal the string with the > lowest prefix has higher precedence. If the common prefix is equal, > the longest string is considered to have higher precedence than the > shorter one. > > I think that the intended comparison here is clear, but I was wondering > whether this text should flag endian concerns at all. E.g. if the > component data has been stored in memory and any numeric values have had > endian conversion performed on them then a naive memcmp() could give a > different answer. > > [Sue]: (treating as a "editorial) > If you have a suggestion on endian statements, please let us know. > We provide links to from other BGP specifications for the types. > Appendix A was intended to provide an example of the flow rule comparison. > Do you think this helps? > > The example encodings in section 4 were intended to provide examples > for implementers. > > >
- [Idr] Robert Wilton's Discuss on draft-ietf-idr-r… Robert Wilton via Datatracker
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Susan Hares
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Rob Wilton (rwilton)
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Susan Hares
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Rob Wilton (rwilton)
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Alvaro Retana
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Susan Hares
- Re: [Idr] Robert Wilton's Discuss on draft-ietf-i… Alvaro Retana