On Sat, Aug 21, 2021 at 11:51 AM Robert Raszuk <[email protected]> wrote:
> Tony > > > I see a value in the "A" bit from multiple angles (which I do not read > as "all applications" but "any application". > > Spot on ! Yes we did mean "any app" not "all apps". Even title says "any" > :) Each app can still cherry pick what it uses in FAD. > ok, yepp, as I said, I did not scan the draft yet and if all that has been abundantly clear no damage in spelling it out again. > > > (I didn't read the 'a' draft yet so it may be taken care of) is whether > SABM length is 1 with all 0s or > > length is 0 on A bit presence and if 0 will the current implementations > hold up to that ;-) > > I am not following this one ... > > SABM length in octets describes length of the actual application bit > octets. A-bit or R,S,F,X are part of it. > > So for A-bit length must be at least 1 or more. > > But now comes Les and says: > > *> (For the purposes of this discussion it does not matter whether I use > the existing 0 length * > *> ABM format or the proposed new “A-bit” format)* > > That to me is ambiguous as it sort of means that 0 length ABM flags may be > defined as any application. > it's not a good suggestion AFAIS, a natural semantics for 0 length ABM is realy "_no_ application" > > If that would be the case (which I believe is not today) then indeed no > need to define A-bit. > > Cheers, > R. > > > On Sat, Aug 21, 2021 at 9:05 AM Tony Przygienda <[email protected]> > wrote: > >> My quick take: >> >> 1. yes, A bit will necessitate being either deployed in a well understood >> part of the network (because as Les says old nodes will basically see _no_ >> application [which seems desirable, they basically take themselves out]) or >> forklifting. Not that different from flex-algo being same kind of forklift >> AFAIS. >> 2. any application introduced after that will precondition implementation >> of A bit if we don't want to get into the rathole of "do not encode using >> A, encode using repetition per application if you have old routers". >> >> I see a value in the "A" bit from multiple angles (which I do not read as >> "all applications" but "any application". The distinction is subtle but >> important) >> >> a) it fits what flex-algo needs in ASLA architecture. E'one wins AFAIS. >> b) if we want to replace A with X|Y|Z we need to know on a router about >> _all_ applications on all routers and that may be non-trivial and on every >> change may force re-adverts (unless we set all bits 1 on a 8 bytes ASLA >> mask [as in _all_ applications]. That does not seem like a good idea given >> the encoding sizes). A as "any" basically means "any application on this >> router uses this metric" and avoids both problems. Significantly simpler >> AFAIS. >> >> A very, very subtle point (I didn't read the 'a' draft yet so it may be >> taken care of) is whether SABM length is 1 with all 0s or length is 0 on A >> bit presence and if 0 will the current implementations hold up to that ;-) >> >> Les, correct me if I'm off somewhere, I was watching lots of that just >> from the corner of my eye ;-) >> >> -- tony >> >> >> >> On Sat, Aug 21, 2021 at 2:06 AM Les Ginsberg (ginsberg) <ginsberg= >> [email protected]> wrote: >> >>> Robert - >>> >>> >>> >>> *From:* Robert Raszuk <[email protected]> >>> *Sent:* Friday, August 20, 2021 5:01 PM >>> *To:* Les Ginsberg (ginsberg) <[email protected]> >>> *Cc:* Ron Bonica <[email protected]>; [email protected] >>> *Subject:* Re: [Lsr] New Version Notification for >>> draft-hegde-lsr-asla-any-app-00.txt >>> >>> >>> >>> Hi Les, >>> >>> >>> >>> *The point being is that “A-bit” is no different than introducing any >>> other new application bit. Until all routers in the network understand it >>> you cannot safely use it.* >>> >>> >>> >>> That is true. >>> >>> >>> >>> But the entire point of A-bit is that you are doing this exercise to >>> make sure your routers understand A-bit only one time. >>> >>> *[LES:] This does not mean that you can introduce support for a new >>> application (call it “bit N”) w/o upgrading your routers simply because you >>> already have A-bit support. I hope that is obvious. **😊* >>> >>> >>> >>> *My original point was simply that the statement about “backwards >>> compatibility” regarding A-bit isn’t accurate. Good that we now agree on >>> that.* >>> >>> >>> >>> * Les* >>> >>> >>> >>> Otherwise you need to do it each time you invent a new bit. >>> >>> >>> >>> Thx, >>> >>> R. >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> On Sat, Aug 21, 2021 at 1:34 AM Les Ginsberg (ginsberg) < >>> [email protected]> wrote: >>> >>> Robert – >>> >>> >>> >>> Inline. >>> >>> >>> >>> *From:* Robert Raszuk <[email protected]> >>> *Sent:* Friday, August 20, 2021 1:29 PM >>> *To:* Les Ginsberg (ginsberg) <[email protected]> >>> *Cc:* Ron Bonica <[email protected]>; [email protected] >>> *Subject:* Re: [Lsr] New Version Notification for >>> draft-hegde-lsr-asla-any-app-00.txt >>> >>> >>> >>> Hi Les, >>> >>> >>> >>> Please see below. >>> >>> >>> >>> It is not just that a new application wants to use the same link >>> attribute value that allows you to use the "all applications" encoding. It >>> is also necessary for the set of links used by the new application to be >>> identical to the set of links used by the existing applications. >>> >>> >>> >>> Not really. You can use subset of links when you apply affinity bits to >>> it. >>> >>> *[LES:] This isn’t relevant.* >>> >>> *Let me try explaining this a different way.* >>> >>> >>> >>> *Suppose I have 1000 links in my network. * >>> >>> *On 500 of those links I have Attribute #1 advertised using “all >>> applications”. (For the purposes of this discussion it does not matter >>> whether I use the existing 0 length ABM format or the proposed new “A-bit” >>> format)* >>> >>> *There are currently two applications, X and Y, deployed in the network >>> and they are both using the same value of attribute #1 on the same set of >>> 500 links.* >>> >>> *All is well.* >>> >>> *Now, I want to enable application Z. If I do so and make no changes to >>> the existing link attribute advertisements, application Z will think it can >>> use Attribute #1 on all 500 of the links on which the “all” form of the >>> ASLA sub-TLV is being advertised.* >>> >>> *If application Z is intended to use all of those 500 links all is well. >>> But if application Z is NOT meant to use one or more of the links on which >>> the ALL ASLA sub-TLVs are being advertised then I have to make changes to >>> at least some of the existing advertisements.* >>> >>> >>> >>> *This is why, in RFC 8919/8920, we advise caution in using the “all” >>> form – and why we do not allow both the “all” form and the “app-specific” >>> form to be used by a given application. It is too easy for mistakes to >>> occur, especially when enabling a new application.* >>> >>> >>> >>> *Implementations that I am aware of do not send the “ALL” form for this >>> reason i.e., it introduces dependencies between applications which are hard >>> to validate.* >>> >>> >>> >>> Likewise as Peter confirmed you also need to use affinities to select >>> subset of links carrying given flex-algo metric to be used only by some >>> selective flex-algo topologies. >>> >>> >>> >>> >>> >>> " The solution described in this document is backward compatible with >>> [RFC8919] and [RFC8920]." >>> >>> This is FALSE. >>> >>> >>> >>> Well I am not sure what Shraddha wanted to express by this sentence or >>> what "backwards" means here. But if you delete "backwards" the rest of the >>> sentence seems just fine. >>> >>> >>> >>> Let's observe that even if you define a new application and define new >>> bit participating nodes need to support it. That means that you must keep >>> upgrading your OS on all participating nodes each time new new bit is >>> invented. >>> >>> >>> >>> *[LES:] Again, a simple example should suffice.* >>> >>> *All routers in my network support application X and application Y.* >>> >>> *Some of the routers support the proposed A-bit, some do not.* >>> >>> *For the set of links on which applications X and Y are using the same >>> attribute we will then have some links using A-bit ASLA, some not using >>> A-bit ASLA.* >>> >>> *For those routers which support the A-bit, they will see links with >>> both styles of ASLA advertisements as usable by applications X and Y.* >>> >>> *For those routers which do NOT support A-bit, they will see only the >>> links w/0 A-bit ASLA as usable by applications X and Y.* >>> >>> >>> >>> *The point being is that “A-bit” is no different than introducing any >>> other new application bit. Until all routers in the network understand it >>> you cannot safely use it.* >>> >>> >>> >>> * Les* >>> >>> >>> >>> >>> >>> Don't you think this is pretty bad ? >>> >>> >>> >>> How often do you think operators upgrade their core routers ? >>> >>> >>> >>> With A-bit and affinities at least your OS is ready to support any >>> application based on already defined metrics without keep inventing new >>> bits. >>> >>> >>> >>> Of course if we assume velocity of inventing new applications is near >>> zero then this is not a problem. But then the usefulness of ASLA also can >>> be challenged. >>> >>> >>> >>> Thx, >>> R. >>> >>> >>> >>> _______________________________________________ >>> Lsr mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/lsr >>> >>
_______________________________________________ Lsr mailing list [email protected] https://www.ietf.org/mailman/listinfo/lsr
