Robert,

On 30/09/2020 16:28, Robert Raszuk wrote:
Peter,

Let's see if we are talking about the same thing ...

Take SRv6 as example ... You can run flex algorithm only on selected segment endpoints as you do encap and dst rewrite. So rest of the network (P/transit routers) do not need to have a clue about any flex-algo other then plain old SPF.

if all transit nodes do not participate/understand flex-algo, you will not be able to route the traffic between the segment endpoints based on the flex-algo, in other words algo specific locators will not be reachable.


Now in Ron's case where there is no encap and you are applying flex-algo to naked packets don't you think there is a difference and a bit of deployment difficulty to make it work ?

it is the same as with SRv6 locator - prefix associated with algorithm, with some additional SRv6 data. From the flex-algo calculation and forwarding perspective there is no difference.


So assume one P node will not support it. This is native IP switching so BGP advertises routes with new flex-algo next hop. If that next hop is unreachable as signalling to that flex algo loopback was not understood by P (new signalling extension) packets will be dropped.

such P node would never ever be in the flex-algo forwarding path for prefix associated with flex-algo. We are talking underlay here, not BGP. BGP service allocates the SRV6 SID from the algo specific locator in case of SRv6. It can pick the NH as algo specific prefix I assume and the rest is the same.


But what if that next hop would happen to be covered by some aggregate route not subject perhaps to intended IP TE ?

aggregation needs to be algo aware for it to work.

thanks,
Peter



Cheers,
R.



On Wed, Sep 30, 2020 at 2:11 PM Peter Psenak <ppse...@cisco.com <mailto:ppse...@cisco.com>> wrote:

    Hi Robert,

    On 30/09/2020 09:28, Robert Raszuk wrote:
     > Hi,
     >
     >  > It uses the HBH option
     >
     > Currently Ron's proposal seems to work well for both IPv4 and IPv6
     > addresses. I hope this discussion will not try to derail it to
    IPv6 only
     > track.
     >
     > I see no issue with loopback to flexible algorithm mapping in 1:1
    fashion.
     >
     > I do however see some issues in deploying such technology as it will
     > only work well if *all* nodes in the network support this new
     > functionality. In contrast in SR world or control plane based TE I
     > proposed or any encapsulation based proposal only anchor nodes
    need to
     > support the new functionality while rest of the network does not
    need to
     > be even aware about it.

    above is not really true.

    Algo participation needs to be signaled, one way or the other. It's
    done
    for SR as well. There is no need for all routers to understand
    flex-algo, as only those that participate (and as a result also
    understand it) will be used during the flex-algo path computation and
    consequently flex-algo specific forwarding. This applies to
    flex-algo in
    general, regardless of the data plane being used.

    thanks,
    Peter


     >
     > Many thx,
     > R.
     >
     >
     > On Wed, Sep 30, 2020 at 6:10 AM Huzhibo <huzh...@huawei.com
    <mailto:huzh...@huawei.com>
     > <mailto:huzh...@huawei.com <mailto:huzh...@huawei.com>>> wrote:
     >
     >     Hi Joel:
     >
     >          For details about the method defined in RFC 6550. It
    uses the
     >     HBH option to carry the RPLInstaceID. The RPLInstaceID and
     >     FlexAlgoID are similar.
     >
     >     Thanks
     >
     >     Zhibo
     >
     >     -----Original Message-----
     >     From: Lsr [mailto:lsr-boun...@ietf.org
    <mailto:lsr-boun...@ietf.org>
     >     <mailto:lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>>]
    On Behalf Of Joel M. Halpern
     >     Sent: Wednesday, September 30, 2020 12:05 PM
     >     Cc: lsr@ietf.org <mailto:lsr@ietf.org> <mailto:lsr@ietf.org
    <mailto:lsr@ietf.org>>
     >     Subject: Re: [Lsr] New Version Notification for
     >     draft-bonica-lsr-ip-flexalgo-00.txt
     >
     >     I am missing something in this discussion of multiple algorithms.
     >
     >     My understanding of flex-algo whether for MPLS, SRv6, SRH, or
    IPv6,
     >     is that you need to associated a forwarding label (e.g. MPLS
    label
     >     or IPv6
     >     address) with a specific algorithm so that you can compute
    the next
>     hope for the forwarding label using the proper algorithm. Then when
     >     a packet arrives, it is simply forwarded according to the
    forwarding
     >     table (e.g.
     >     FIB, LIB, ..)
     >
     >     If that is so, then I do not understand how a given prefix can be
     >     safely associated with more than one algorithm.  I could imagine
     >     doing several calculations according to different
    algorithms.  But
     >     how do you decide which one applies to the packet?  As far as I
     >     know, flex-algo does not look at the QoS/CoS/ToS bits.
     >
     >     Yours,
     >     Joel
     >
     >     PS: I will admit that it took until  an operator described some
     >     "interesting" constraints before I understood why one would
    even do
     >     this.
     >
     >     On 9/29/2020 11:50 PM, Huzhibo wrote:
     >      > Hi.
     >      >
     >      > Associating multiple algorithms with a given prefix is an
     >     interesting topic, and I think this can simplify the
    complexity of
     >     FlexAlgo. I wonder if the author would consider using cases with
     >     multiple algorithms with a given prefix.
     >      >
     >      > Thanks
     >      >
     >      > ZHibo
     >      >
     >      > -----Original Message-----
     >      > From: Lsr [mailto:lsr-boun...@ietf.org
    <mailto:lsr-boun...@ietf.org>
     >     <mailto:lsr-boun...@ietf.org <mailto:lsr-boun...@ietf.org>>]
    On Behalf Of tony...@tony.li <mailto:tony...@tony.li>
     >     <mailto:tony...@tony.li <mailto:tony...@tony.li>>
     >      > Sent: Tuesday, September 29, 2020 10:05 PM
     >      > To: Ron Bonica <rbonica=40juniper....@dmarc.ietf.org
    <mailto:40juniper....@dmarc.ietf.org>
     >     <mailto:40juniper....@dmarc.ietf.org
    <mailto:40juniper....@dmarc.ietf.org>>>
     >      > Cc: lsr@ietf.org <mailto:lsr@ietf.org>
    <mailto:lsr@ietf.org <mailto:lsr@ietf.org>>
     >      > Subject: Re: [Lsr] New Version Notification for
     >      > draft-bonica-lsr-ip-flexalgo-00.txt
     >      >
     >      >
     >      > Ron,
     >      >
     >      > This is nice. It makes it clear that constraint based path
     >     computation need not have MPLS overhead for those that don’t
    want it.
     >      >
     >      > One thing that you don’t talk about is how this gets used, tho
     >     that may be blindingly obvious: you’ll need all nodes placing
    their
     >     prefixes in the RIB/FIB, where it will need to be selected over
     >     other path computation for the same prefixes.  This somewhat
     >     precludes the possibility of a given prefix being useful in
    multiple
     >     flex-algos.
     >      >
     >      > More text on application would be most welcome, just to ensure
     >     that we’re on the same page.
     >      >
     >      > Tony
     >      >
     >      >
     >      >> On Sep 29, 2020, at 6:37 AM, Ron Bonica
     >     <rbonica=40juniper....@dmarc.ietf.org
    <mailto:40juniper....@dmarc.ietf.org>
     >     <mailto:40juniper....@dmarc.ietf.org
    <mailto:40juniper....@dmarc.ietf.org>>> wrote:
     >      >>
     >      >>
     >      >> Please review and comment
     >      >>
     >      >>                                        Ron
     >      >>
     >      >>
     >      >>
     >      >> Juniper Business Use Only
     >      >>
     >      >>> -----Original Message-----
     >      >>> From: internet-dra...@ietf.org
    <mailto:internet-dra...@ietf.org>
     >     <mailto:internet-dra...@ietf.org
    <mailto:internet-dra...@ietf.org>> <internet-dra...@ietf.org
    <mailto:internet-dra...@ietf.org>
     >     <mailto:internet-dra...@ietf.org
    <mailto:internet-dra...@ietf.org>>>
     >      >>> Sent: Tuesday, September 29, 2020 9:36 AM
     >      >>> To: Parag Kaneriya <pkane...@juniper.net
    <mailto:pkane...@juniper.net>
     >     <mailto:pkane...@juniper.net <mailto:pkane...@juniper.net>>>;
    Shraddha Hegde
     >      >>> <shrad...@juniper.net <mailto:shrad...@juniper.net>
    <mailto:shrad...@juniper.net <mailto:shrad...@juniper.net>>>; Ron
     >     Bonica <rbon...@juniper.net <mailto:rbon...@juniper.net>
    <mailto:rbon...@juniper.net <mailto:rbon...@juniper.net>>>; Rajesh M
     >      >>> <mraj...@juniper.net <mailto:mraj...@juniper.net>
    <mailto:mraj...@juniper.net <mailto:mraj...@juniper.net>>>; William
     >     Britto A J <bwill...@juniper.net
    <mailto:bwill...@juniper.net> <mailto:bwill...@juniper.net
    <mailto:bwill...@juniper.net>>>
     >      >>> Subject: New Version Notification for
     >      >>> draft-bonica-lsr-ip-flexalgo-00.txt
     >      >>>
     >      >>> [External Email. Be cautious of content]
     >      >>>
     >      >>>
     >      >>> A new version of I-D, draft-bonica-lsr-ip-flexalgo-00.txt
     >      >>> has been successfully submitted by Ron Bonica and posted
    to the
     >     IETF
     >      >>> repository.
     >      >>>
     >      >>> Name:           draft-bonica-lsr-ip-flexalgo
     >      >>> Revision:       00
     >      >>> Title:          IGP Flexible Algorithms (Flexalgo) In IP
    Networks
     >      >>> Document date:  2020-09-29
     >      >>> Group:          Individual Submission
     >      >>> Pages:          14
     >      >>> URL:
     > https://urldefense.com/v3/__https://www.ietf.org/id/draft-bonica-
     >      >>> lsr-ip-flexalgo-00.txt__;!!NEt6yMaO-gk!X7PVDP-
     >      >>> FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck80Zbjoij$
     >      >>> Status:
     >      >>>
     > https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-b
     >      >>> o
     >      >>> nica-lsr-
     >      >>> ip-flexalgo/__;!!NEt6yMaO-gk!X7PVDP-
     >      >>> FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck8x7e5ZqI$
     >      >>> Htmlized:
     >      >>>
     > https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/dr
     >      >>> a
     >      >>> ft-
     >      >>> bonica-lsr-ip-flexalgo__;!!NEt6yMaO-gk!X7PVDP-
     >      >>> FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck82w_6CyU$
     >      >>> Htmlized:
     > https://urldefense.com/v3/__https://tools.ietf.org/html/draft-
     >      >>> bonica-lsr-ip-flexalgo-00__;!!NEt6yMaO-gk!X7PVDP-
     >      >>> FnUA0oCcZMw3Qde6in0C72hu_9hOZ53kPspIarR8fNDyU9Vck81_QrJ_p$
     >      >>>
     >      >>>
     >      >>> Abstract:
     >      >>>    An IGP Flexible Algorithm computes a constraint-based
    path
     >     and maps
     >      >>>    that path to an identifier.  As currently defined,
    Flexalgo
     >     can only
     >      >>>    map the paths that it computes to Segment Routing (SR)
     >     identifiers.
     >      >>>    Therefore, Flexalgo cannot be deployed in the absence
    of SR.
     >      >>>
     >      >>>    This document extends Flexalgo, so that it can map
    the paths
     >     that it
     >      >>>    computes to IP addresses.  This allows Flexalgo to be
     >     deployed in any
     >      >>>    IP network, even in the absence of SR.
     >      >>>
     >      >>>
     >      >>>
     >      >>>
     >      >>> Please note that it may take a couple of minutes from
    the time of
     >      >>> submission until the htmlized version and diff are
    available at
     > tools.ietf.org <http://tools.ietf.org> <http://tools.ietf.org>.
     >      >>>
     >      >>> The IETF Secretariat
     >      >>>
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