Re: [Idr] draft-ietf-idr-ext-opt-param-06.txt - 2 Week WG LC (7/30 to 8/13/2019)

John Scudder <jgs@juniper.net> Fri, 02 August 2019 01:27 UTC

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From: John Scudder <jgs@juniper.net>
To: "bruno.decraene@orange.com" <bruno.decraene@orange.com>
CC: Hares Susan <shares@ndzh.com>, "idr@ietf.org" <idr@ietf.org>
Thread-Topic: [Idr] draft-ietf-idr-ext-opt-param-06.txt - 2 Week WG LC (7/30 to 8/13/2019)
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Subject: Re: [Idr] draft-ietf-idr-ext-opt-param-06.txt - 2 Week WG LC (7/30 to 8/13/2019)
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Hi Bruno,

Thanks for your comments. I’ve just posted version -07 that I believe addresses them; more in-line below.

—John

On Jul 31, 2019, at 5:17 AM, bruno.decraene@orange.com<mailto:bruno.decraene@orange.com> wrote:

Hi Sue,

Fully support.
I’m also fine with the _current_ version of the document.

Nevertheless, I’ll try some comments, possibly useless but at minimum to show to the shepherd/AD that I’ve read and reviewed the doc.

1.  Introduction
[…]
The Parameter Length field of individual Optional Parameters is similarly extended.

I would rather remove ‘similarly’ or change it to ‘also’. As although the technical specification is crystal clear, I fear that the sentence could be interpreted as the length field for individual optional parameters been extended the same way (length 255, followed by extended length) while this is not the case.

Done.


---

The (non-extended) length field is set to

   255, as is the subsequent octet that in the non-extended format would

   be the first Optional Parameter Type.  The subsequent two octets

   carry the actual length.


This works so let it be so.
One could have argued that this encoding is borderline as per RFC 4271. May be an encoding  more in line with 4271 could have been Type: 255, Length: 2, Value: actual/extended length. (i.e. adding/keeping the ‘length’ field of the Optional Parameter type 255). That would also have been more friendly for protocol parser (e.g. wireshark) especially since there is a chance that network operator get surprised the first time that the BGP session get rejected and may want to have a look at the open message).
Note that I understand that my comment is way too late … and also a matter of opinion.

This comment led Enke and me to consider why it’s necessary to mandate any particular value for the length field; as you say the length could be 2, and for that matter it could indeed be any nonzero value. In the end we chose to leave it as 255 because there are implementations of -06 that do expect to see 255 as a magic value, but to make the spec more permissive as to what values may be received. We didn’t choose to mandate the TLV version you describe, first and most important for backward-compatibility reasons, but second because it’s actually not a TLV — it’s (candidly) a hack that (ab)uses the first two bytes of what would otherwise be a TLV, to indicate use of a different encoding. But whether you find the latter argument convincing or not, probably the former is sufficiently compelling.

I do want to draw your (and the WG’s) attention to the fact we made this change though, which is normative although entirely backward-compatible with -06.

---

   In the event that the length of Optional Parameters in the BGP OPEN

   message does not exceed 255, the encodings of the base BGP

   specification [RFC4271<https://urldefense.proofpoint.com/v2/url?u=https-3A__tools.ietf.org_html_rfc4271&d=DwMFAg&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=hLt5iDJpw7ukqICc0hoT7A&m=ex0u_LhOZGOAxeHCrhS7eMnFmWvTlJhesBv2w33xhT0&s=rURYD2UMPN8kYVYuMNnoqQHElix3WSXZYAx23CLspb0&e=>;] MUST be used without alteration.


Could the document define the error handling if this MUST is not followed? I believe any option (notification or silently ignore) works, but in general I have a preference for error handling to be covered by the spec.

That may also be the opportunity to remove the following sentence “If the value of this field is zero, no Optional Parameters are present (this would never be expected to happen with the extended encoding, however). » which is both not general enough (does not cover length 1-254) and appears in the general specification/behavior while it’s about error handling.

Done and done.


---
As of 2019, I feel that this extension may have been an opportunity to also enable the use of BGP extended message length for the BGP OPEN message. (if the “BGP Extended Message” capability was also exchanged.). Alternatively, the burden of defining this could also been in draft-ietf-idr-bgp-extended-messages. But probably too late for both documents so let’s move forward.

Yes, a pity but as you say let’s move forward.


Thanks,
Regards,
--Bruno


From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of Susan Hares
Sent: Tuesday, July 30, 2019 6:06 PM
To: idr@ietf.org<mailto:idr@ietf.org>
Subject: [Idr] draft-ietf-idr-ext-opt-param-06.txt - 2 Week WG LC (7/30 to 8/13/2019)

This begins a 2 week working group last call on draft-ietf-idr-ext-opt-param-06.txt from 7/30 to 8/13/2019.

You can access the draft at:

https://datatracker.ietf.org/doc/draft-ietf-idr-ext-opt-param/<https://urldefense.proofpoint.com/v2/url?u=https-3A__datatracker.ietf.org_doc_draft-2Dietf-2Didr-2Dext-2Dopt-2Dparam_&d=DwMFAg&c=HAkYuh63rsuhr6Scbfh0UjBXeMK-ndb3voDTXcWzoCI&r=hLt5iDJpw7ukqICc0hoT7A&m=ex0u_LhOZGOAxeHCrhS7eMnFmWvTlJhesBv2w33xhT0&s=oZuwj43Z5yf5dr7GxgFV6J9yoJ5j79MwHWFOih-yW8E&e=>

John and Enke – I am counting on you gather information on the 2 implementations and post this on the IDR Wiki during these 2 weeks.

For the WG, consider if:

1)      The technology is ready for publication or if there are flaws that prevent its publication,
2)      Is this technology useful to BGP deployments?
3)      Are there any minor editorial errors the authors should address before publication.


Cheerily, Sue Hares




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