Hi Acee Fixing a typo
On Fri, Apr 15, 2022 at 10:34 PM Gyan Mishra <[email protected]> wrote: > > Hi Acee > > My question cane up from the list of questions posed by Ketan and Peter’s > response to question #3. > > See excerpt below. > > I am confused by what Ketan stated in his question below and also Peter’s > response which is why I am asking the question again. > > I believe the goal of the draft is for Flex Ago to be deployed > independently of SR filling the gap of IGP Flex Algo providing that > solution. So based on what Ketan stated in his question that IGP Flex Algo > is data plane agnostic and can be used with IP data plane then there is no > gap to be filled by this draft. > > Maybe I am misreading Ketan’s question. > > So this is a very important point made by Ketan that if IGP Flex Algo is > open to usage “outside of SR”, then it is very important to restate the > goal of this draft, removing assertions in the draft that this draft is for > non SR IP data planes, as that can be accomplished today by IGP Flex Algo, > and the gap or new solution being filled by this draft is for IP prefix > based Flex Algo with Native IP Forwarding. > > This as well is quite confusing to me as if IGP Flex Algo can be used > outside of SR then can do everything that this draft is supposed to > accomplish. > > So what then is the purpose of this draft? > > In Peter’s response is stated that each Flex Algo data plane / app can be > deployed independently meaning this draft and IGP flex Algo can act as 2 > ships in the night. Also confusing. > > 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 > where do you see such assertion? Each flex-algo data-plane/app can be > deployed independently. > > > > On Fri, Apr 15, 2022 at 7:51 PM Acee Lindem (acee) <[email protected]> wrote: > >> Gyan, >> >> >> >> What is your point here? Is this a trick question? >> >> >> >> Thanks, >> >> Acee >> >> >> >> *From: *Gyan Mishra <[email protected]> >> *Date: *Friday, April 15, 2022 at 5:31 PM >> *To: *"Peter Psenak (ppsenak)" <[email protected]> >> *Cc: *Acee Lindem <[email protected]>, Ketan Talaulikar < >> [email protected]>, "[email protected]" < >> [email protected]>, "[email protected]" <[email protected]> >> *Subject: *Re: [Lsr] Working Group Last Call for >> draft-ietf-lsr-ip-flexalgo-04 - "IGP Flexible Algorithms (Flex-Algorithm) >> In IP Networks" >> >> >> >> >> >> Hi Peter >> >> >> >> My understanding is that the main goal of this draft is to be able to use >> flex algo over IPv4 or IPv6 data plane as that is not possible with >> existing Flex Algo which can only be used on SR data plane. >> >> >> >> Is that correct or am I missing something? >> >> >> >> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo >> >> >> >> >> >> Abstract >> >> >> >> An IGP Flexible Algorithm (Flex-Algorithm) allows IGP to compute >> >> constraint-based paths. As currently defined, IGP Flex-Algorithm is >> >> used with Segment Routing (SR) data planes - SR MPLS and SRv6. >> >> Therefore, Flex-Algorithm cannot be deployed in the absence of SR. >> >> >> >> This document extends IGP Flex-Algorithm, so that it can be used for >> >> regular IPv4 and IPv6 prefixes. This allows Flex-Algorithm to be >> >> deployed in any IP network, even in the absence of SR. >> >> >> >> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-flex-algo-19 >> >> >> >> Abstract >> >> >> >> IGP protocols traditionally compute best paths over the network based >> >> on the IGP metric assigned to the links. Many network deployments >> >> use RSVP-TE based or Segment Routing based Traffic Engineering to >> >> steer traffic over a path that is computed using different metrics or >> >> constraints than the shortest IGP path. This document proposes a >> >> solution that allows IGPs themselves to compute constraint-based >> >> paths over the network. This document also specifies a way of using >> >> Segment Routing (SR) Prefix-SIDs and SRv6 locators to steer packets >> >> along the constraint-based paths. >> >> >> >> Kind Regards >> >> >> >> Gyan >> >> >> >> >> >> On Mon, Apr 11, 2022 at 3:37 AM Peter Psenak <ppsenak= >> [email protected]> wrote: >> >> Hi Ketan, >> >> please responses to some of your comments 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 >> the intent is to use FlexAlgorithms only. >> >> > >> > 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 >> I strongly disagree. >> >> FAD is data-pane/app independent. Participation is data-plane/app >> dependent. Base flex-algo specification is very clear about that. That >> has advantages and we do not want to modify that part. >> >> Topology calculation for algo/data-plane needs to take both FAD and >> participation into account. You need independent calculation for each >> data-plane/app in the same algo. >> >> The fact that the same FAD is shareable between all apps has it >> advantages and use cases - e.g. if the participation for algo X is the >> same in SR and IP data-planes, one can use SR to protect IP in that algo. >> >> >> > >> > 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 >> where do you see such assertion? Each flex-algo data-plane/app can be >> deployed independently. >> >> > >> > 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. >> > >> > 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. >> > >> > 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. >> > >> > 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. >> > >> > 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. >> > >> > >> > 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. >> > >> > >> > 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. >> > >> > >> > 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>] >> 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>] is >> > defined to advertise prefix reachability associated with a Flex- >> > Algorithm in OSPFv2. >> > >> > 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. >> > >> > >> > 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. >> > >> > >> > 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. >> > >> > >> > 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. >> > >> > >> > 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? >> > >> > >> > 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" ? >> > >> > >> > 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? >> >> ##PP >> what is the relationship? I see none. >> >> >> > >> > This (in some way) goes back to my comment (2) above. >> > >> > >> > 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. >> > >> > >> > 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 >> above text does not talk about the same prefix. It talks in general how >> forwarding works in presence of multiple data-planes/apps using the same >> algo. >> >> thanks, >> Peter >> >> > >> > >> > Thanks, >> > >> > Ketan >> > >> > >> > >> > On Fri, Apr 8, 2022 at 12:38 AM Acee Lindem (acee) >> > <[email protected] <mailto:[email protected]>> >> 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 >> > [email protected] <mailto:[email protected]> >> > https://www.ietf.org/mailman/listinfo/lsr >> > <https://www.ietf.org/mailman/listinfo/lsr> >> > >> >> _______________________________________________ >> Lsr mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/lsr >> >> -- >> >> [image: Image removed by sender.] <http://www.verizon.com/> >> >> *Gyan Mishra* >> >> *Network Solutions Architect * >> >> *Email [email protected] <[email protected]>* >> >> *M 301 502-1347* >> >> >> > -- > > <http://www.verizon.com/> > > *Gyan Mishra* > > *Network Solutions A**rchitect * > > *Email [email protected] <[email protected]>* > > > > *M 301 502-1347* > > -- <http://www.verizon.com/> *Gyan Mishra* *Network Solutions A**rchitect * *Email [email protected] <[email protected]>* *M 301 502-1347*
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