Re: [Gen-art] Review of draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-05

Roni Even <> Wed, 01 February 2017 07:03 UTC

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From: Roni Even <>
To: tianxiang li <>, Roni Even <>
Thread-Topic: [Gen-art] Review of draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-05
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Subject: Re: [Gen-art] Review of draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-05
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See inline

From: Gen-art [] On Behalf Of tianxiang li
Sent: יום ג 31 ינואר 2017 17:59
To: Roni Even
Cc: dhcwg;;;
Subject: Re: [Gen-art] Review of draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-05

Dear Roni,

Thank you for providing a thorough review of this document.

I have a few questions regarding the comments, please see inline.

Best regards,

2017-01-29 17:02 GMT+08:00 Roni Even <<>>:
Reviewer: Roni Even
Review result: Almost Ready

I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
like any other last call comments.

For more information, please see the FAQ at


Document: draft-ietf-dhc-dhcpv6-prefix-length-hint-issue-05
Reviewer: Roni Even
Review Date: 2017-01-29
IETF LC End Date: 2017-02-09
IESG Telechat date: 2017-02-16

Summary: This draft is almost ready for publication as a standard
track RFC.

Major issues:

Minor issues:

1.      I think that this document updates RFC3633 and it should be
mentioned in the title and abstract

[Tianxiang] This document does not change any of the text in RFC 3633, but specifies the client and server behavior when using the "prefix-length hint", which was not explained in RFC3633. Would it be suitable to state "this document updates RFC3633"?
[Roni Even] Yes, this is what I meant and it needs to be written in  the title and abstract, it will also point people looking at RFC3633 to this document

2.      In section 3.1 reference RFC3315 for solicit message and 3.3 for
advertise messge

[Tianxiang] Okay, we'll add reference to RFC3315 in section 3.1 and 3.3 when mentioning Solicit and Advertise messgae.
[Roni Even] OK

3.      In section 3.1 solution last paragraph is the order of the two
IAPREFIX options important?

[Tianxiang] There is no strict requirement for the order of the two options. Would you prefer if we added a sentence to specify this?
[Roni Even] I assumed this was the case but it will better to clarify

4.      In section 3.2 solution why are you suing SHOULD and not MUST in
all recommendations?

[Tianxiang] In this document, we used "MUST" for some of the client behaviors, as they are mandatory to avoid client failure and necessary if the client wanted to express its prefix-length requirement.

For server behavior, we used "SHOULD" because this document specifies the desired server behavior if the server wants to consider the prefix-length hint, but the server could have its own behavioral policy (e.g. neglect the prefix-length hint).
[Roni Even] This make sense, but it will be good to clarify why it is a SHOULD using your explanation

5.      In section 3.2 solution, what should the server do if cannot
provide any of the requests

[Tianxiang] If the server could not provide the requested prefix or prefix-length, it should provide a prefix closest to the prefix-length hint, as stated in the last sentence of section 3.2.

Are you referring to what the sever should do of it simply could not provide ANY prefixes to the client? In that case, we could add a sentence at the end of the section 3.2:

"If the server will not assign any prefixes to any IA_PDs in a subsequent Request from the client, the server MUST send an Advertise message to the client as described in section 11.2 of RFC 3633."
[Roni Even] This sentence is what I was looking for.

6.      In section 3.2 solution last paragraph “SHOULD try to provide” and
in the first paragraph “SHOULD provide” should be the same in both.

[Tianxiang] Thanks for pointing that out, we'll change it to "SHOULD provide".

[Roni Even] OK

7.      In section 3.4 “If the client decided to use  the prefix provided
by the server despite being longer than the  prefix-length hint” yet I
did not see in section 3.2 that the server can provide a longer

[Tianxiang] This was mentioned in the last sentence of section 3.2:

"If the requested prefix is not available in the server's prefix pool, and the client also included a prefix-length hint in the same IA_PD option, then the server SHOULD try to provide a prefix matching the prefix-length value, or the prefix with the shortest length possible which is closest to the prefix-length hint value."
[Roni Even] I understood from 3.2 that it should provide a shorter length prefix  closer to the request maybe “or the prefix with the closest possible length to the prefix-length hint value”

8.      In section 3.5 solution the document use “as close as possible” and
section 3.2 only talk about smaller.

[Tianxiang] This was mentioned in the last sentence of section 3.2.
[Roni Even] See above to point 7

9.     In section 3.5 solution why offer options 3 and 4. The draft
says that option 3 will break client connections and 4 talks about “a
short non-zero valid-lifetime” which may cause the  client to lose
connection if "too short for the client" since “short” is not an exact

[Tianxiang] The idea was to list all the options, and discuss their consequences. And the server could decide which option to use depending on its policy.

Option 3 avoids the complexity of handling multiple delegated prefixes, despite of breaking up all connections. Option 4 allows to server to configure a valid-lifetime for the old prefix depending on actual requirements, rather than let the old prefix expire on its own.
[Roni Even] OK, still option 4 may have similar result to 3 since “a short non-zero” may be too short. Why not add a recommended value?

Nits/editorial comments: