Subject: [RTG-DIR] RtgDir review: draft-ietf-ospf-ospfv3-segment-routing-extensions-17.txt

From: Tomonori Takeda <[email-masked]>
Date: Wed, 14 Nov 2018 20:49:19 +0900

Hello,

I have been selected as the Routing Directorate reviewer for this draft. 
The Routing Directorate seeks to review all routing or routing-related 
drafts as they pass through IETF last call and IESG review, and 
sometimes on special request. The purpose of the review is to provide 
assistance to the Routing ADs. For more information about the Routing 
Directorate, please see 
​http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir

Although these comments are primarily for the use of the Routing ADs, it 
would be helpful if you could consider them along with any other IETF 
Last Call comments that you receive, and strive to resolve them through 
discussion or by updating the draft.

  Document: draft-ietf-ospf-ospfv3-segment-routing-extensions-17.txt
  Reviewer: Tomonori Takeda
  Review Date: Nov 14th, 2018
  IETF LC End Date: Nov 16th, 2018
  Intended Status: Proposed Standard

o Summary:
This document is basically ready for publication, but has nits that 
should be considered prior to publication.

o Comments:
This document defines OSPFv3 extensions for Segment Routing with MPLS 
data plane.

This document is mostly ready, but further clarification would be good 
for better understanding of the protocol definitions (see below).

This document is well aligned with a related document 
draft-ietf-ospf-segment-routing-extensions.

o Major Issues:
None

o Minor Issues:
1) Flooding Scope of SR-Algorithm TLV
In Section 4.1, it says:

   "If the SR-Algorithm TLV appears in
    multiple OSPFv3 Router Information Opaque LSAs that have different
    flooding scopes, the SR-Algorithm TLV in the OSPFv3 Router
    Information Opaque LSA with the area-scoped flooding scope MUST be
    used."

At the same time, it say:

   "For the purpose of SR-Algorithm TLV advertisement, area-
    scoped flooding is REQUIRED."

So, does it mean a) a router MUST use area-scoped flooding for sending, 
and b) a router MUST support different flooding scopes for receiving?

2) LSA Type for OSPFv3 Extended Prefix Range TLV
In Section 5, it defines IA-Flag. It is not clear how this relates to 
LSA type. Do we simply ignore LSA type being used to carry OSPFv3 
Extended Prefix Range TLV?

3) Meaning of SID/Index/Label in Prefix SID Sub-TLV
In Section 6, it says:

      "SID/Index/Label: According to the V and L flags, it contains
       either:

          A 32-bit index defining the offset in the SID/Label space
          advertised by this router.

          A 24-bit label where the 20 rightmost bits are used for
          encoding the label value."

I understand how V Flag relates to this selection, but it is not clear 
how L flag relates to this selection.

o Nits
None

Thanks,
Tomonori Takeda

---

From: Peter Psenak <[email-masked]>
Date: Wed, 14 Nov 2018 14:13:37 +0100

Hi Tomonori,

please see inline:

On 14/11/18 12:49 , Tomonori Takeda wrote:
> Directorate, please see ​
> http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir
>
> and

no. It says that that for the purpose of the SR-Algorithm TLV area scope 
is required. That means it cannot be link-scope, but it can be 
autonomous-system scope, because that is also covering the area-scope.

b) a router MUST support different flooding scopes for receiving?

SR-Algorithm TLV is sub-TLV of  Router Information Opaque LSA, which can 
be flooded in various flooding scopes - link, area, autonomous system. 
The flooding scope is not specific to SR-Algorithm TLV, it is generic 
one applicable to Router Information Opaque LSA.

> Extended Prefix Range TLV?

I think we can remove this bit, given that we know the route type from 
the LSA type itself. This was taken from the OSPFv2, where the Extended 
Prefix LSA does not carry the type.

Will remove.

> how L flag relates to this selection.

L flag is not relevant, I will remove the reference to it.

Please let me know if you are fine with my responses.

thanks,
Peter

> .

---

From: Erik Auerswald <[email-masked]>
Date: Wed, 14 Nov 2018 14:24:16 +0100

Hi Peter,

please see inline (I have kept just the relevant part):

On Wed, Nov 14, 2018 at 02:13:37PM +0100, Peter Psenak wrote:
> > [...]
> no. It says that that for the purpose of the SR-Algorithm TLV area scope is
> required. That means it cannot be link-scope, but it can be

May I suggest to add the words "at least" to make the wording more
explicit?

    "For the purpose of SR-Algorithm TLV advertisement, at least
     area-scoped flooding is REQUIRED."

Thanks,
Erik

---

From: Peter Psenak <[email-masked]>
Date: Wed, 14 Nov 2018 14:59:46 +0100

Hi Erik,

>       area-scoped flooding is REQUIRED."

sure, will do that.

thanks,
Peter

---

From: Tomonori Takeda <[email-masked]>
Date: Thu, 15 Nov 2018 08:59:17 +0900

Hi Peter, Eric,

Thanks.
Proposed changes look good to me.

Tomonori

-- 
Tomonori Takeda
NTT Network Service Systems Labs.
+81-422-59-7092