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. 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. 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. Thanks, Ketan On Wed, May 11, 2022 at 3:20 PM Peter Psenak <[email protected]> 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>] > 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. > > ##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) > > <[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> > > > >
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