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

[Gyan Mishra <[e-mail]>]

Thanks Peter for the responses to help clear up my flex algo understanding!!

On Sat, Oct 3, 2020 at 5:45 AM Peter Psenak <[e-mail]> wrote:

> Gyan,
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>
>
> On 03/10/2020 02:14, Gyan Mishra wrote:
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> >
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> > Hi  Jeff
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> >
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> >  From a domain perspective where you have a group of nodes and
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> > associated IP addressed and SID are part of a discrete underlay instance
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> > flex algo topology.  On those same set of nodes you could have another
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> > topology and associated address and SIDs for a different flex algo.
>
>
>
> above is right.
>

   Gyan>  So per my response to Robert, what  I was thinking is that as the
algo 0 strict spf would be used as the base algo to provide reachability to
all nodes within the domain and all neighbors are formed between all nodes
in the domain to populate IGP rib providing base connectivity
reachability.  So then underneath of that you can have any subset of nodes
out of the superset all top layer domain nodes level  that can run any
other algo desired. Basically creating algo layers under the top domain
wide layer.

>
>
>
> > How
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> > this would work is that the topologies would have to be segregated from
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> > each other as different MT instances or routing process instances.  Is
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> > that correct?
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>
>
> no MT at all. You can think of each flex-algo as a set of constraints
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> that is used to calculate the path over the common topology. You can
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> have many such felx-algos running on a common topology.
>
>
    Gyan> Is it safe to say that we can think of it as RSVP TE “like” cSPF
constraints that we are build via traffic engineering PCALC algorithms to
run for dynamic LSP dyamic ERO that is built based on IGP constraints from
TEDs database of TE link attributes and TE or IGP weights metric
constraints to create the dynamic LSP path.  So we could think of in TE
framework analogy to flex algo In the per VRF TE next hop vpn coloring use
case with different loopback next hop rewrite per VRF that normal IGP non
TE BAU VPNs traffic would be like the flex algo base strict algo 0 and the
non zero discrete algo would be like the per VRF next hop loopback rewrite
where each per VRF te loopback rewrite would be a different steering non
zero discrete flex algo all running in parallel as ships in the night with
the base algo 0.   Sorry for the complex analogy but I think I am getting
it!!😃

Does a flex algo use case draft exist and if not I would not mind using the
analogy I said above and build out a use case draft.  Cheers! 😊

>
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> >
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> > Can two nodes that run two different flex algo become ospf or isis
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> > neighbors?
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> absolutely.
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>
>
> Peter
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>
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> >
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> > Kind Regards
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> >
>
> > Gyan
>
> >
>
> > On Fri, Oct 2, 2020 at 6:25 PM Jeff Tantsura <[e-mail]
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> > <mailto:[e-mail]>> wrote:
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> >
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> >     Hi Yingzhen,
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> >
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> >
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> >
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> >
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> >
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> >     Yes, that’s the case.  The most important property of an algo
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> >     computed path is that is has to be consecutive, as either SID or IP
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> >     address associated with a particular topology is only known within
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> >     that topology.
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> >
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> >
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> >     Looking specifically at Ron’s draft (MPLS could be more complex due
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> >     to potential hierarchy) - the prefix itself defines the
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> >     context(topology) and must be globally unique, since IPv4 header
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> >     can’t have any additional meta-data attached.
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> >
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> >
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> >     Cheers,
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> >
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> >     Jeff
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> >
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> >
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> >
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> >
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> >
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> >     On Oct 2, 2020, 1:15 PM -0700, Yingzhen Qu
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> >     <[e-mail] <mailto:[e-mail]>>,
> wrote:
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> >
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> >
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> >>     Hi Peter,
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     My understanding of flex-algo is that for traffic destined to a
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> >>     prefix on a particular algo, it can only be routed on routers
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> >>     belong to that algo, which also means only routers in that algo
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> >>     calculates how to reach that prefix and install it into the
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> >>     routing table. It seems to me that using flex-algo (section 12 of
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> >>     the draft) it's possible to have a loopback address associated
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> >>     with only one algo, please correct me if I'm missing or
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> >>     misunderstood something.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     Thanks,
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> >>
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> >>
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> >>     Yingzhen
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     On 10/2/20, 9:43 AM, "Lsr on behalf of Peter Psenak"
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> >>     <[e-mail] <mailto:[e-mail]> on behalf of
>
> >>     ppsenak=[e-mail]
>
> >>     <mailto:[e-mail]>> wrote:
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     Gyan,
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     On 02/10/2020 18:30, Gyan Mishra wrote:
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> >>
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> >>
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> >>>     All,
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> >>>
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> >>>
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> >>>
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> >>>
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> >>>
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> >>>     With SRv6 and IP based flex algo a generic question as it applies
> to
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> >>>
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> >>>
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> >>>     both. Is it possible to have within a single IGP domain different
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> >>>     sets
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> >>>
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> >>>
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> >>>     of nodes or segments of the network running different algorithms.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     absolutely.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>>     From
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> >>>
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> >>>
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> >>>     both drafts it sounds like all nodes have to agree on same
> algorithm
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> >>>
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> >>>
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> >>>     similar to concept of metric and reference bandwidth all have to
> have
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> >>>
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> >>>
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> >>>     the same style metric and play to the same sheet of music.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     all participating nodes need to agree on the definition of the
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> >>     flex-algo
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> >>
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> >>
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> >>     and advertise the participation. That's it.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>>     If there was
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> >>>
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> >>>
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> >>>     a way to use multiple algorithms simultaneously based on SFC or
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> >>>     services
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> >>>
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> >>>
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> >>>     and instantiation of specific algorithm based on service to be
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> >>>
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> >>>
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> >>>     rendered. Doing so without causing a routing loop or sub optimal
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> >>>
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> >>>
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> >>>     routing.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     you can certainly use multiple algorithms simultaneously and use
> algo
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> >>
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> >>
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> >>     specific paths to forward specific traffic over it. How that is done
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> >>
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> >>
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> >>     from the forwarding perspective depends in which forwarding plane
> you
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> >>
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> >>
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> >>     use. Flex-algo control plane is independent of the forwarding plane.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>>     I thought with flex algo that there exists a feature that on
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> >>>
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> >>>
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> >>>     each hop there is a way to specify which algo to use hop by hop
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> >>>     similar
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> >>>
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> >>>
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> >>>     to a hop by hop policy based routing.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     no, there is no hop-by-hop classification, that is problematic and
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> >>     does
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> >>
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> >>
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> >>     not scale for high speeds. Classification is done at the ingress
> only.
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>     thanks,
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> >>
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> >>
>
> >>     Peter
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> >>
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> >>
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> >>
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> >>
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> >>
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> >>>
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> >>
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> >>
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> >>
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> >>
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> >>
>
> >>     _______________________________________________
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> >>
>
> >>
>
> >>     Lsr mailing list
>
> >>
>
> >>
>
> >>     [e-mail] <mailto:[e-mail]>
>
> >>
>
> >>
>
> >>
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> >>
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> >>
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> >>
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> >
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> > --
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> >
>
> > <http://www.verizon.com/>
>
> >
>
> > *Gyan Mishra*
>
> >
>
> > /Network Solutions A//rchitect /
>
> >
>
> > /M 301 502-1347
>
> > 13101 Columbia Pike
>
> > /Silver Spring, MD
>
> >
>
> >
>
>
>
> --

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD