Re: [Gen-art] Gen-ART Last Call review of draft-ietf-ospf-two-part-metric-05

"Acee Lindem (acee)" <> Mon, 08 August 2016 17:47 UTC

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From: "Acee Lindem (acee)" <>
To: Brian E Carpenter <>, "" <>, General Area Review Team <>
Thread-Topic: Gen-ART Last Call review of draft-ietf-ospf-two-part-metric-05
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Subject: Re: [Gen-art] Gen-ART Last Call review of draft-ietf-ospf-two-part-metric-05
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Hi Brian, 

Thanks much for the thorough review. Jeffrey and I discussed your comments
this morning. See responses to your major/minor comments below. We will
incorporate all the nits.

On 8/6/16, 9:38 PM, "Brian E Carpenter" <>

>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-ospf-two-part-metric-05.txt
>Reviewer: Brian Carpenter
>Review Date: 2016-08-07
>IETF LC End Date: 2016-08-15
>IESG Telechat date:
>Summary: Almost ready
>Major issues:
>> Updates: 2328, 5340 (if approved)
>If that is so, the text needs to explain what is changed in those two
>RFCs. Since
>this draft describes an "optional extension" to OSPF, it does not
>obviously update
>them. Is any text in those two RFCs made invalid by this draft?

This has been an ongoing debate as to whether an RFC the augments an
existing draft updates it or whether it must actually change the existing
behavior. In this case, the SPF calculation is modified as specified in
section 3.6 but only when the new Network-to-Router metric is advertised.
In RFC 2328 and RFC 5340, this cost is always zero (i.e., cost to reach
all routers connected to the network is solely the outgoing metric metric
or Router-to-Network metric).

I, for one, would be very happy to have consensus of precisely what
constitutes update to an existing RFC. If we don’t update the existing
RFCs, we would avoid the pre-2008 IPR language.

>> 3.6.  SPF Calculation
>>   During the first stage of shortest-path tree calculation for an area,
>>   when a vertex V corresponding to a Network-LSA is added to the
>>   shortest-path tree and its adjacent vertex W (joined by a link in V's
>>   corresponding Network LSA), the cost from V to W, which is W's
>>   network-to-router cost, is determined as follows:
>I can't parse that sentence. If we delete the subordinate clauses, we get
>  When a vertex V is added to the shortest-path tree and its adjacent
>vertex W,
>  the cost from V to W is determined as follows:
>What does that mean? What does "its" refer to? Is W adjacent to V, or is
>W adjacent
>to the existing tree? Is W added to the tree before V, or is V added
>before W?
>If I was coding this, I'd have no idea what to do.

You really do have to look at RFC 2328 to understand it. Does this
modified text parse better?

    The first stage of the shortest-path tree calculation is described
    in section 16.1 of [RFC 2328] and modified for OSPFv3 as described in
    section 4.8.1 of [RFC 5340]. When a vertex V corresponding to a
    has just been added to the Shortest Path Tree (SPT) and an adjacent
vertex W 
    (joined by a link in V’s corresponding Network-LSA) is being added to
    the SPT, the cost from V to W (W’s network-to-router cost) is
    as follows:

>> 3.7.  Backward Compatibility
>This calls for a Router Functional Capability Bit assignment under RFC
>The bit number should be given as (say) TBD1 not as 0.
>> 4.  IANA Considerations
>The IANA considerations ask for four assignments. These should be
>specified as TBD1,
>TBD2, TBD3, TBD4 and the TBDs elsewhere in the text should be updated
>Also, please reference the relevant RFCs (7770 and whatever defines the
>Sub-TLV registries.)

3.7 and 4 are both fixed in -06 based on comments from Alia.

>Finally, to put this on the standards track, I would really expect to see
>an Implementation Status section (RFC 7942). Has this been tested?

The implementation of this stalled. However, it is viewed by the WG as
straight-forward enough to advance.

>Minor issues:
>Please check the three occurrences of lower-case "must" in Section 3.
>Should they be "MUST"?
>> 5.  Security Considerations
>>   This document does not introduce new security risks.
>That's easy to say but hard to prove. Shouldn't you at least refer to the
>considerations of OSPFv2 and OSPFv3?

We will add the reference.

>Also, does section 3.7 introduce a new risk whereby a rogue router could
>flap its
>Two-Part Metric bit on and off, causing all its OSPF peers to continually
>their routes?

This is no more of a risk than other intra-area metric change.

Jeffrey and Acee 

>> Requirements Language
>It's unusual to put this at the front. The normal place is after the
>>  This document may contain material from IETF Documents or IETF
>>  Contributions published or made publicly available before November
>>  10, 2008. ...
>Why is this needed? What did you copy from an old document?
>> 0 OSPF Two-part Metric [TPM]
>The abbreviation TPM is defined but not used, so why bother? Also,
>s/[TPM]/(TPM)/ to
>avoid confusion with a reference.
>> routes w/o considering any network-to-router costs.
>Just say "without".