Re: [Lsr] New Version Notification for draft-bonica-lsr-ip-flexalgo-00.txt

[Peter Psenak <[e-mail]>]

Robert,

On 30/09/2020 19:30, Robert Raszuk wrote:
> Peter,
> 
> Granted - you can do this with MPLS encapsulation.
> 
> But if you are doing native IP forwarding or SRv6 I am still unclear.
> 
> Imagine you get allocated by RIR say IPv4 /16 or IPv6  /32.
> 
> So you take some part of that block and use it for flex algo next hops 
> .. flood it via IGP and have flex algo F1 running/enabled on some nodes. 
> So far so good.
> 
> But what prevents the non enabled nodes to still use for those next hops 
> less specific say /8 from someone else in the Internet ?

we are talking IGPs here. A node send FA(X) route and inside the area 
all routers see it and can only route to it via nodes that are 
participating in FA(X). The only place where routes can get modified is 
at the inter-area or inter-domain boundary. That needs to be FA(X) aware 
if you want end-to-end FA(X) path.

The case you are describing is that a BGP speaker that is not FA(X) 
aware outside of the originating AS will pick the NH that is advertised 
in a summary that is not associated with any FA. Traffic will get 
directed to the right AS, and inside that AS, the first FA(X) aware 
router will switch to FA(X) aware path.

thanks,
Peter



> 
> Sure in some implementations (we both are a bit familiar with) we have a 
> way to track that next hop is declared unreachable if it was learned 
> from prefix shorter then /X. But this constrain seems to be not 
> documented anywhere in respect to flex algo. At min I think IP flex algo 
> use should make it clear and make it also a MUST.
> 
> So my point is that for SRv6 or Ron's proposal next hop MUST be only 
> learned via local IGP or be of no less then /X to be used for BGP next 
> hop resolution.
> 
> Many thx,
> R,
> 
> 
> 
> 
> 
> 
> 
> On Wed, Sep 30, 2020 at 5:18 PM Peter Psenak <[e-mail] 
> <mailto:[e-mail]>> wrote:
> 
>     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 <[e-mail]
>     <mailto:[e-mail]>
>      > <mailto:[e-mail] <mailto:[e-mail]>>> 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
>     <[e-mail] <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>
>      >      > <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>> 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:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]> <mailto:[e-mail]
>     <mailto:[e-mail]>>>]
>      >     On Behalf Of Joel M. Halpern
>      >      >     Sent: Wednesday, September 30, 2020 12:05 PM
>      >      >     Cc: [e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>> <mailto:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>>
>      >      >     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:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]> <mailto:[e-mail]
>     <mailto:[e-mail]>>>]
>      >     On Behalf Of [e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>
>      >      >      > Sent: Tuesday, September 29, 2020 10:05 PM
>      >      >      > To: Ron Bonica
>     <rbonica=[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>>>
>      >      >      > Cc: [e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>
>      >     <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>
>      >      >      > 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=[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>>> wrote:
>      >      >      >>
>      >      >      >>
>      >      >      >> Please review and comment
>      >      >      >>
>      >      >      >>                                        Ron
>      >      >      >>
>      >      >      >>
>      >      >      >>
>      >      >      >> Juniper Business Use Only
>      >      >      >>
>      >      >      >>> -----Original Message-----
>      >      >      >>> From: [e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>> <[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail]
>     <mailto:[e-mail]>>>>
>      >      >      >>> Sent: Tuesday, September 29, 2020 9:36 AM
>      >      >      >>> To: Parag Kaneriya <[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>
>      >      >     <mailto:[e-mail]
>     <mailto:[e-mail]> <mailto:[e-mail]
>     <mailto:[e-mail]>>>>;
>      >     Shraddha Hegde
>      >      >      >>> <[e-mail]
>     <mailto:[e-mail]> <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >     <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>>; Ron
>      >      >     Bonica <[e-mail]
>     <mailto:[e-mail]> <mailto:[e-mail]
>     <mailto:[e-mail]>>
>      >     <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>>; Rajesh M
>      >      >      >>> <[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>
>      >     <mailto:[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>>; William
>      >      >     Britto A J <[e-mail]
>     <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>
>     <mailto:[e-mail] <mailto:[e-mail]>
>      >     <mailto:[e-mail] <mailto:[e-mail]>>>>
>      >      >      >>> 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> <http://tools.ietf.org>.
>      >      >      >>>
>      >      >      >>> The IETF Secretariat
>      >      >      >>>
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