Re: [Lsr] Working Group Last Call for draft-ietf-lsr-ip-flexalgo-04 - "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks"

[Ketan Talaulikar <[e-mail]>]

Thanks Peter and the changes look good to me.

Thanks,
Ketan


On Mon, May 16, 2022 at 3:25 PM Peter Psenak <[e-mail]> wrote:

> Hi Ketan,
>
>
> On 13/05/2022 15:32, Ketan Talaulikar wrote:
> > Hi Peter,
> >
> > Thanks for your updates to the draft and your responses below.
> >
> > I would like to point out a few remaining points to be fixed/addressed.
> >
> > a) There is a discrepancy regarding the size of the Metric field for the
> > OSPFv2 IP Algo Reachability sub-TLV between the figure and the text
> > description. The text needs to be fixed to reflect 4 octets size.
>
> fixed
>
> >
> > b) For the OSPFv3 IP Algo Prefix Reachability sub-TLV the Type should be
> > 2 octets and the discrepancy in the sub-TLV name in the Figure needs to
> > be corrected. Length should now become 8.
>
> fixed.
>
> >
> > c) The references to the sections of draft-lsr-flex-algo in this
> > document need corrections in Sec 7 ? In general, I think the references
> > to the base draft sections 11, 12, and 13 (except that M-flag is always
> > used) would be helpful.
>
> I removed the references to any particular sections and kept only the
> references to the draft itself. This is better as the sections tends to
> change and the result is that the references to sections are incorrect.
>
> thanks,
> Peter
>
>
> >
> > Thanks,
> > Ketan
> >
> > On Wed, May 11, 2022 at 3:20 PM Peter Psenak <[e-mail]
> > <mailto:[e-mail]>> wrote:
> >
> >     Hi Ketan,
> >
> >
> >     please see inline (##PP):
> >
> >     On 11/04/2022 08:25, Ketan Talaulikar wrote:
> >      > Hello All,
> >      >
> >      > Following are some comments on this draft:
> >      >
> >      > 1) Is this draft about opening the use of all IGP Algorithms for
> IP
> >      > (Algo) Routing or intended to be specific to Flexible Algorithms
> >     (i.e.
> >      > algo 128-255) alone. I think it is important to specify the scope
> >      > unambiguously. Perhaps it makes sense to restrict the usage in
> this
> >      > particular document to FlexAlgorithms alone. If not, the draft
> >     probably
> >      > needs an update and we need to also cover algo 1 (Strict SPF)
> >      > applicability and update the text to refer more generically to
> >      > algo-specific IP routing.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      > 2) The relationship between the algo usage for IP FlexAlgo and
> other
> >      > data planes (e.g. FlexAlgo with SR) is not very clear. There arise
> >      > complications when the algo usage for IP FlexAlgo overlap with
> other
> >      > (say SR) data planes since the FAD is shared but the node
> >     participation
> >      > is not shared. While Sec 9 suggests that we can work through these
> >      > complications, I question the need for such complexity. The
> FlexAlgo
> >      > space is large enough to allow it to be shared between various
> data
> >      > planes without overlap. My suggestion would be to neither carve
> out
> >      > parallel algo spaces within IGPs for various types of FlexAlgo
> data
> >      > planes nor allow the same algo to be used by both IP and SR data
> >     planes.
> >      > So that we have a single topology computation in the IGP for a
> given
> >      > algo based on its FAD and data plane participation and then when
> it
> >      > comes to prefix calculation, the results could involve
> >     programming of
> >      > entries in respective forwarding planes based on the signaling of
> >     the
> >      > respective prefix reachabilities. The coverage of these aspects
> in a
> >      > dedicated section upfront will help.
> >
> >     ##PP
> >     this has been discussed previously in this thread.
> >
> >
> >      >
> >      > 3) This draft makes assertions that IGP FlexAlgo cannot be
> deployed
> >      > without SR. This is not true since the base IGP FlexAlgo spec
> >     explicitly
> >      > opens it up for usage outside of the SR forwarding plane. We
> already
> >      > have BIER and MLDP forwarding planes as users of the IGP
> >     FlexAlgo. My
> >      > suggestion is to remove such assertions from the document. It is
> >      > sufficient to just say that the document enables the use of IGP
> >     FlexAlgo
> >      > for IP prefixes with native IP forwarding.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      > 4) The draft is mixing up "address" and "prefix" in some places.
> IGP
> >      > path computation is for prefixes and not addresses. There are a
> few
> >      > instances where "address" should be replaced by "prefix".
> >     References to
> >      > RFC791 and RFC8200 seem unnecessary.
> >
> >
> >     ##PP
> >     Done
> >
> >      >
> >      > 5) The draft does not cover the actual deployment use-case or
> >      > applicability of IP FlexAlgo. The text in Sec 3 is not clear and
> >      > insufficient. What is the point/use of sending traffic to a
> >     loopback of
> >      > the egress router? Perhaps it makes sense in a deployment where
> >     IP-in-IP
> >      > encapsulation is used for delivering an overlay service? If so,
> >     would be
> >      > better to clarify this. The other deployment scenario is where
> >      > "external" or "host/leaf prefixes" are associated with a FlexAlgo
> to
> >      > provide them a different/appropriate routing path through the
> >     network.
> >      > Yet another is the use of IP FlexAlgo along with LDP. Sec 9 does
> not
> >      > address the topic well enough. I would suggest expanding and
> >     clarifying
> >      > this and perhaps other such deployment use cases (or
> >     applicability) in
> >      > the document in one of the earlier sections to provide a better
> >     context
> >      > to the reader.
> >
> >
> >     ##PP
> >     Done
> >
> >
> >      >
> >      > 6) It would be better to move the common (i.e. not protocol
> >     specific)
> >      > text from 5.1 and 5.2 under 5. This might also apply to some
> >     extent to
> >      > the contents of sec 6.
> >
> >
> >     ##PP
> >     Done. For section 6, I would prefer to keep it in the protocol
> specific
> >     sections.
> >
> >      >
> >      > 7) Most of the text with MUSTs in sec 5 doesn't really make sense
> in
> >      > repeating - this is covered in the base FlexAlgo spec already.
> >     The only
> >      > key/important MUST is the one related to using separate algo for
> IP
> >      > FlexAlgo over SR data planes. See my previous comment (2) above.
> >
> >     ##PP
> >     I prefer to keep the MUSTs there
> >
> >      >
> >      > 8) Sec 5.1, the SHOULD needs to be MUST in the text below.
> >      >
> >      >     A router receiving multiple IP Algorithm
> >      >     sub-TLVs from the same originator SHOULD select the first
> >      >     advertisement in the lowest-numbered LSP and subsequent
> >     instances of
> >      >     the IP Algorithm Sub-TLV MUST be ignored.
> >
> >     ##PP
> >     Done.
> >
> >      >
> >      >
> >      > 9) Sec 5.1, I would suggest changing the following text as
> >     indicated.
> >      > Also, perhaps add that the algo 0 MUST NOT be advertised and a
> >     receiver
> >      > MUST ignore if it receives algo 0.
> >      > OLD
> >      >
> >      >     The IP Algorithm Sub-TLV could be used to advertise
> >      >     support for non-zero standard algorithms, but that is outside
> the
> >      >     scope of this document.
> >      >
> >      > NEW
> >      >
> >      >     The use of IP Algorithm Sub-TLV to advertise support for
> >     algorithms
> >      >
> >      >     outside the flex-algorithm range is outside the
> >      >     scope of this document.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 10) Sec 5.1, the SHOULD needs to be MUST in the text below
> >      >
> >      >     The IP Algorithm TLV is optional.  It SHOULD only be
> >     advertised once
> >      >     in the Router Information Opaque LSA.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 11) Sec 6. The following text is better moved into the respective
> >      > protocol sub-sections. OSPFv3 is not covered anyway by it.
> >      >
> >      >     Two new top-level TLVs are defined in ISIS [ISO10589
> >     <
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#ref-ISO10589
> >     <
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#ref-ISO10589
> >>]
> >     to advertise
> >      >     prefix reachability associated with a Flex-Algorithm.
> >      >
> >      >     *  The IPv4 Algorithm Prefix Reachability TLV
> >      >
> >      >     *  The IPv6 Algorithm Prefix Reachability TLV
> >      >
> >      >     New top-level TLV of OSPFv2 Extended Prefix Opaque LSA
> >     [RFC7684  <https://datatracker.ietf.org/doc/html/rfc7684
> >     <https://datatracker.ietf.org/doc/html/rfc7684>>] is
> >      >     defined to advertise prefix reachability associated with a
> Flex-
> >      >     Algorithm in OSPFv2.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      > 12) Sec 6.1 & 6.2. There is no discussion regd the use of the
> Prefix
> >      > Attribute Flags sub-TLV with the new top-level TLVs.
> >      >
> >      > I think their usage MUST (or at least SHOULD) be included as it
> >     helps
> >      > determine the route type and prefix attributes that
> >      >
> >      > have proven to be quite useful for various use cases and
> deployments.
> >
> >     ##PP
> >
> >     Why? We have a text that says:
> >
> >     "This new TLV shares the sub-TLV space defined for TLVs 135, 235, 236
> >     and 237."
> >
> >     Why do we need to describe the usage of the specific sub-TLV?
> >
> >      >
> >      >
> >      > 13) Sec 6.2 what happens when the same prefix is advertised as
> SRv6
> >      > Locator as well as IPv6 Algo Prefix (same or conflicting algos).
> >     Perhaps
> >      > both must be ignored?
> >      >
> >      > The same applies for OSPFv3 as well.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 14) Sec 6.3, OSPFv2 MT-ID reference should be RFC4915. Perhaps
> >     the range
> >      > of MT should be mentioned since it is a 8 bit field here.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 15) Sec 6.4, the metric field in the sub-TLV has to be 32-bit.
> While
> >      > 24-bit is ok when the FAD uses IGP metric, it will not suffice
> >     for other
> >      > IGP metric types.
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 16) Sec 6.3 & 6.4, the conflict checking with base algo 0 prefix
> >      > reachability cannot be limited only to the OSPFv2/3 Extended LSAs
> >     but
> >      > should also cover the base fixed form >
> >      > OSPFv2/v3 LSAs. We could use a more generic term like "normal
> prefix
> >      > reachability" advertisements perhaps to cover the different LSAs?
> >
> >     ##PP
> >     Done
> >
> >
> >      >
> >      >
> >      > 17) Sec 7 and 8, suggest to not use the term "application" to
> avoid
> >      > confusion with ASLA. My understanding is that there is a single
> >     FlexAlgo
> >      > application when it comes to ASLA.
> >      >
> >      > Perhaps the intention here is "data plane" ?
> >
> >     ##PP
> >     Done
> >
> >      >
> >      >
> >      > 18) The relationship between the BIER IPA and this draft needs
> some
> >      > clarifications - should the BIER WG be notified if they want to
> >     update
> >      > draft-ietf-bier-bar-ipa?
> >      >
> >      > This (in some way) goes back to my comment (2) above.
> >
> >     ##PP
> >     I don't see the relationship to BIER IPA here.
> >
> >      >
> >      >
> >      > 19) Sec 8, what prevents the use of IP FlexAlgo paths programmed
> >     by LDP
> >      > as well. Or if the intention is to use them strictly for IP
> >     forwarding only
> >      >
> >      > then this needs to be clarified.
> >
> >     ##PP
> >     nothing prevents someone to advertise LDP label for the IP
> algo-prefix
> >     and use it with the labeled forwarding. I don't see a problem. But
> this
> >     specification does not specify any of it.
> >
> >      >
> >      >
> >      > 20) The following text in Sec 9 is about using the same FlexAlgo
> >     (with a
> >      > common definition) for multiple data-planes at the same time. The
> >     key is
> >      > that we only are able to use
> >      >
> >      > prefix in one algo/data-plane? I am wondering if we can improve
> this
> >      > text to bring this out in a better way. Or altogether remove this
> >     if we
> >      > agree to not allow sharing of algo
> >      >
> >      > between different data planes to keep things simple.
> >      >
> >      >     Multiple application can use the same Flex-Algorithm value at
> the
> >      >
> >      >     same time and and as such share the FAD for it.  For example
> >     SR-MPLS
> >      >     and IP can both use such common Flex-Algorithm.  Traffic for
> >     SR-MPLS
> >      >     will be forwarded based on Flex-algorithm specific SR SIDs.
> >     Traffic
> >      >     for IP Flex-Algorithm will be forwarded based on
> Flex-Algorithm
> >      >     specific prefix reachability announcements.
> >
> >     ##PP
> >     Done.
> >
> >     thanks,
> >     Peter
> >      >
> >      >
> >      > Thanks,
> >      >
> >      > Ketan
> >      >
> >      >
> >      >
> >      > On Fri, Apr 8, 2022 at 12:38 AM Acee Lindem (acee)
> >      > <acee=[e-mail]
> >     <mailto:[e-mail]>
> >     <mailto:[e-mail]
> >     <mailto:[e-mail]>>> wrote:
> >      >
> >      >     This begins a WG last call for
> >     draft-ietf-lsr-ip-flexalgo-04.  The
> >      >     draft had a lot of support and discussion initially and has
> been
> >      >     stable for some time. Please review and send your comments,
> >     support,
> >      >     or objection to this list before 12 AM UTC on April 22^nd ,
> >     2022.____
> >      >
> >      >     __ __
> >      >
> >      >     Thanks,
> >      >     Acee____
> >      >
> >      >     _______________________________________________
> >      >     Lsr mailing list
> >      > [e-mail] <mailto:[e-mail]> <mailto:[e-mail]
> >     <mailto:[e-mail]>>
> >      > https://www.ietf.org/mailman/listinfo/lsr
> >     <https://www.ietf.org/mailman/listinfo/lsr>
> >      >     <https://www.ietf.org/mailman/listinfo/lsr
> >     <https://www.ietf.org/mailman/listinfo/lsr>>
> >      >
> >
>
>