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From: Hannes Gredler <hannes@rtbrick.com>
In-Reply-To: <5909F4C0.2010306@cisco.com>
Date: Wed, 3 May 2017 17:40:13 +0200
Cc: Stig Venaas <stig@venaas.com>, rtg-dir@ietf.org, ospf@ietf.org,
 ospf-chairs@ietf.org,
 draft-ietf-ospf-segment-routing-extensions.all@ietf.org
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References: <CAHANBt+ZdrU_=CquJSzisV1ore_=_QmPcxDfM=MBGYDj0GKZbg@mail.gmail.com>
 <5909F4C0.2010306@cisco.com>
To: Peter Psenak <ppsenak@cisco.com>
Archived-At: <https://mailarchive.ietf.org/arch/msg/ospf/hi4zYOIIY3juOTHAS5-npL7xv6o>
Subject: Re: [OSPF] RtgDir QA review:
 draft-ietf-ospf-segment-routing-extensions-12
Precedence: list

not sure where the ordering requirements have come in. no need from my POV.
feel free to drop it.
/hannes

> On 3 May 2017, at 17:18, Peter Psenak <ppsenak@cisco.com> wrote:
>=20
> Hi Stig,
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> please see inline:
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>> On 27/04/17 00:08 , Stig Venaas wrote:
>> Hello,
>>=20
>> I have been selected as the Routing Directorate reviewer for this
>> draft. This is just an early QA review.
>>=20
>> The draft is in good shape, but I did find some minor issues and nits.
>> It is fairly readable, but it could be improved in a few places.
>>=20
>>=20
>> Minor issues:
>>=20
>> In 3.1:
>> The SR-Algorithm TLV is some places called a Sub-TLV. It might be
>> good to be consistent.
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> fixed.
>=20
>>=20
>> This is not clear in 3.1:
>>    The SR-Algorithm Sub-TLV is optional. It MAY only be advertised once
>>    in the Router Information Opaque LSA.
>> Is this trying to say that it MUST NOT be advertised more than
>> once? With the current wording this is not obviously that strict.
>=20
> yes, I changed the text to: "It MUST only be advertised once in the Router=
 Information Opaque LSA". Hope that is clear enough.
>=20
>=20
>>=20
>> I see some text regarding multiple SR-Algorithm sub-TLVs, but it also
>> looks like one can have multiple algorithms in one sub-TLV. At least
>> from the diagram.
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> yes, multiple algorithms in the same SR-Algorithm TLV is fine.
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>> But I don't see any discussion about this. Is it OK
>> to add multiple? When can it be done, what does it mean? What if
>> routers don't support the exact same set of algorithms?
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> router advertise all algorithms it supports. Each router may support diffe=
rent set.
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>>=20
>> The term "lowest flooding scope" is used a couple of places. I think I
>> know what it means, but it might be good to point it out. Also, I'm
>> used to seeing the term "smallest" rather than "lowest". I'm assuming
>> they mean the same.
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> I changed all places to "narrowest flooding scope".
>=20
>>=20
>> In 3.2 there is this bullet point:
>>    The receiving router must adhere to the order in which the ranges
>>    are advertised when calculating a SID/label from a SID index.
>>=20
>> You probably should use MUST here.
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> fixed.
>=20
>>=20
>> Section 4:
>> In section 4 there is a range for advertising a range of prefixes.
>> But it looks like it contains a single prefix length and it says
>> the length is the length of the prefix. While it says range size
>> is the number of prefixes. I don't understand from the text what
>> really prefix length and range size means and how this should be
>> used.
>=20
> 10.0.1.0/24 - 10.0.100.0/24 represents a range of 100 /24 prefixes, where:=

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> (starting) prefix - 10.0.1.0
> length of the prefix is 24
> range size is 100
>=20
>>=20
>> I understand this is IPv4 only since OSPFv2, but rather than just
>> saying IPv4 is 0, maybe refer to an IANA AF registry? This might
>> be helpful if you want to use the same sub-TLV in OSPFv3 and
>> use the same code for parsing etc. IANA has 1 for IPv4 though.
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> this is equivalent to section 2.1 of RFC7684. I have updated the text to m=
atch RFC7684.
>=20
>>=20
>> Section 5:
>> Is it intentional that the flags start in position 1 rather than
>> 0?
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> yes. Originally we had N-flag (Node Flag) defined at position 0, but we mo=
ved that to the OSPFv2 Extended Prefix TLV (section 2.1 of RFC7684). Due to a=
n existing implementations, we did not shift all other bits after that.
>=20
>>=20
>> I see that the NP flag should be ignored when M is set. Then I
>> see this text:
>>    As the Mapping Server does not specify the originator of a prefix
>>    advertisement, it is not possible to determine PHP behavior solely
>>    based on the Mapping Server advertisement.  However, PHP behavior may
>>    safely be done in following cases:
>> This seems not very precise. Could you say exactly what the behavior
>> should be, rather than saying "behavior may be done"?
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> would changing  "may safely be done" to "SHOULD be done" be sufficient?
>=20
>>=20
>> Section 6:
>> It might be good to make clear that other flag positions are
>> reserved, set to 0 and ignored... Perhaps also point out that
>> weight is in the range 0-255
>=20
> fixed both.
>=20
>>=20
>> I see this sentence:
>>       If the SID/Label Sub-TLV appears in the SID/Label Binding Sub-TLV
>>       more than once, instances other than the first will be ignored and
>>=20
>> Should it say MUST be ignored?
>=20
> changed to SHOULD as the previous text says "SHOULD only appear once".
>=20
>>=20
>> Section 6.2 it says:
>>    All ERO Sub-TLVs must immediately follow the SID/Label Sub-TLV.
>>    All Backup ERO Sub-TLVs must immediately follow the last ERO Sub-TLV.
>>=20
>> Should these be normative MUSTs?
>=20
> Changed both to MUST.
> I'm also going to clarify this with Hannes, whether that is still required=
, because I do not see equivalent text in ISIS draft.
>=20
>>=20
>> In 6.2.1:
>> It would be good for all of these to specify that other flags are
>> reserved.
>=20
> done.
>=20
>=20
>>=20
>>=20
>> Nits:
>> The intro should perhaps mention LAN adjacency and binding SIDs?
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> LAN Adjacency SID is a sub-type of the Adjacency SID. I have added sentenc=
e about binding/other SID types.
>=20
>>=20
>> 2nd paragraph of section 2 is confusing. It sounds like
>> the Opaque LSAs in 7684 were defined for SID in particular,
>> but it is a generic mechanism. Perhaps SID was the
>> motivation though?
>=20
> this part is a left-over from the original draft before we split to RFC768=
4 and this draft.
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> I replaced the whole paragraph with:
>=20
> "Extended Prefix/Link Opaque LSAs defined in <xref target=3D"RFC7684"/> ar=
e used for advertisements of the various SID types."
>=20
>>=20
>> Section 6.1:
>> It says:
>>    The ERO Metric Sub-TLV advertises the cost of an ERO path.  It is
>>    used to compare the cost of a given source/destination path.  A
>>    router SHOULD advertise the ERO Metric Sub-TLV in an advertised ERO
>>    TLV.
>>=20
>> Is the ERO TLV the ERO Sub-TLVs defined in 6.2? It would be good to
>> point that out.
>=20
> ERO Metric Sub-TLV as well as all the other ERO sub-TLVs in sectin 6.2 are=
 at the same level - they are all sub-TLVs of the Binding TLV. I added some t=
ext to 6.2 to make that clear.
>=20
>>=20
>> In 8.4.2:
>>    Broadcast, NBMA or or hybrid
>> Extra "or".
>=20
> fixed.
>=20
>>=20
>> Section 9:
>> There are no new registries and most of the TLVs are already
>> allocated? It seems there are a few new ones where it should
>> probably say TBD, or say something about being suggested values.
>> That was done in earlier sections. I see in some places it says
>> "are allocated" here, while it says "suggested" in the definition
>> of the TLV.
>=20
> section 9 lists all the updates to the four different registries. Values a=
re explicitly mentioned in section 9 for every single code point.
>=20
>>=20
>> Section 10:
>> It says there are responses from 2 implementers, but I see 3.
>=20
> fixed
>=20
>>=20
>> Section 11:
>> Are these really all the potential security issues?
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> I'm not aware of any others. Feel free to suggest more if required.
>=20
>>=20
>> I'm on vacation the next 2 weeks, so I may not reply to any
>> emails during that period.
>=20
> I will post the new version after closing on the ERO part with Hannes and o=
thers.
>=20
> thanks,
> Peter
>=20
>>=20
>> Regards,
>> Stig
>> .
>>=20
>=20