Re: [Lsr] Publication has been requested for draft-ietf-lsr-ip-flexalgo-06

[Robert Raszuk <[e-mail]>]

Peter,

It is not about someone thinking if this is a good idea or not. It is
about practical aspects of real deployments.

But ok section 10 of the subject draft says something pretty interesting:






*10.  Protection   In many networks where IGP Flexible Algorithms are
deployed, IGP   restoration will be fast and additional protection
mechanisms will   not be required. *

*Question:* What makes networks with IGP flex-algo running any better then
networks without it in terms of protection needed or not ?

Sure when applicable ECMP can be used to locally protect the traffic. But
when you need to run flex-algo for mobile slicing requirements (as
discussed in section 3) the load on control plane CPUs and data plane FIBs
may become significant (especially when we are talking about lots of
"slices").

Thx,
R.











On Wed, May 18, 2022 at 9:45 AM Peter Psenak <[e-mail]> wrote:

> Robert,
>
> I really do not want to get into fallback between algorithms. If someone
> really thinks it is a good idea, he can write a separate document and
> describe the use case and how to do that safely. But please not in the
> base flex-algo specification.
>
> thanks,
> Peter
>
>
>
> On 17/05/2022 19:58, Robert Raszuk wrote:
> > Hi Peter,
> >
> > Enabling local protection on all nodes in all topologies may also not be
> > the best thing to do (for various reasons).
> >
> > While I agree that general fallback may be fragile, how about limited
> > fallback and only to one special "protection topology" which would have
> > few constraints allowing us to do such fallback safely ?
> >
> > I guess for ip flex-algo which is a subject of this thread this would
> > not be possible, but for SR flex-algo I think this may work pretty well
> > allowing N:1 fast connectivity restoration.
> >
> > Thx,
> > Robert
> >
> > On Tue, May 17, 2022 at 2:19 PM Peter Psenak <[e-mail]
> > <mailto:[e-mail]>> wrote:
> >
> >     Robert,
> >
> >     On 17/05/2022 14:14, Robert Raszuk wrote:
> >      > Ok cool - thx Peter !
> >      >
> >      > More general question - for any FlexAlgo model (incl. SR):
> >      >
> >      > Is fallback between topologies - say during failure of primary
> one -
> >      > only allowed on the ingress to the network ?
> >
> >     no. Fallback between flex-algos has never been a requirement and is
> not
> >     part of the flex-algo specification.
> >
> >     I consider it a dangerous thing to do. It may work under certain
> >     conditions, but may cause loops under different ones.
> >
> >     thanks,
> >     Peter
> >
> >
> >      >
> >      > If so the repair must be setup on each topology, otherwise repair
> >     will
> >      > be long as it would need to wait for igp flooding and ingress
> >     switchover
> >      > trigger ?
> >      >
> >      > Obviously for IP flex algo it would be much much longer as given
> >     prefix
> >      > needs to be completely reflooded network wide and purged from
> >     original
> >      > topo. Ouch considering time to trigger such action.
> >      >
> >      > Many thanks,
> >      > R.
> >      >
> >      > On Tue, May 17, 2022, 13:35 Peter Psenak <[e-mail]
> >     <mailto:[e-mail]>
> >      > <mailto:[e-mail] <mailto:[e-mail]>>> wrote:
> >      >
> >      >     Hi Robert,
> >      >
> >      >
> >      >     On 17/05/2022 12:11, Robert Raszuk wrote:
> >      >      >
> >      >      > Actually I would like to further clarify if workaround 1
> >     is even
> >      >     doable ...
> >      >      >
> >      >      > It seems to me that the IP flexalgo paradigm does not have
> >     a way for
> >      >      > more granular then destination prefix forwarding.
> >      >
> >      >     that is correct. In IP flex-algo the prefix itself is bound
> >     to the
> >      >     algorithm.
> >      >
> >      >      >
> >      >      > So if I have http traffic vs streaming vs voice going to
> >     the same
> >      >     load
> >      >      > balancer (same dst IP address) there seems to be no way to
> >     map some
> >      >      > traffic (based on say port number) to take specific
> topology.
> >      >
> >      >     no, you can not do that with IP flex-algo.
> >      >
> >      >
> >      >      >
> >      >      > That's pretty coarse and frankly very limiting for
> >     applicability
> >      >     of IP
> >      >      > flex-algo. If I am correct the draft should be very
> >      >     explicit about this
> >      >      > before publication.
> >      >
> >      >     please look at the latest version of the draft, section 3:
> >      >
> >      >
> >      >
> >
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#section-3
> >     <
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#section-3
> >
> >      >
> >       <
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#section-3
> <
> https://datatracker.ietf.org/doc/html/draft-ietf-lsr-ip-flexalgo#section-3
> >>
> >      >
> >      >     thanks,
> >      >     Peter
> >      >
> >      >      >
> >      >      > Kind regards
> >      >      > R.
> >      >      >
> >      >      > On Tue, May 17, 2022 at 12:01 PM Robert Raszuk
> >     <[e-mail] <mailto:[e-mail]>
> >      >     <mailto:[e-mail] <mailto:[e-mail]>>
> >      >      > <mailto:[e-mail] <mailto:[e-mail]>
> >     <mailto:[e-mail] <mailto:[e-mail]>>>> wrote:
> >      >      >
> >      >      >     Folks,
> >      >      >
> >      >      >     A bit related to Aijun's point but I have question to
> >      >     the text from
> >      >      >     the draft he quoted:
> >      >      >
> >      >      >         In cases where a prefix advertisement is received
> >     in both
> >      >     a IPv4
> >      >      >         Prefix Reachability TLV and an IPv4 Algorithm
> Prefix
> >      >     Reachability
> >      >      >         TLV, the IPv4 Prefix Reachability advertisement
> >     MUST be
> >      >     preferred
> >      >      >         when installing entries in the forwarding plane.
> >      >      >
> >      >      >     Does this really mean that I can not for a given
> >     prefix say
> >      >     /24 use
> >      >      >     default topology for best effort traffic and new
> flex-algo
> >      >     topology
> >      >      >     for specific application ?
> >      >      >
> >      >      >     Is the "workaround 1" to always build two new
> >     topologies for such
> >      >      >     /24 prefix (one following base topo and one new) and
> never
> >      >     advertise
> >      >      >     it in base topology ?
> >      >      >
> >      >      >     Is the "workaround 2" to forget about native
> >     forwarding and
> >      >     use for
> >      >      >     example SR and mark the packets such that SID pool
> >      >     corresponding to
> >      >      >     base topology forwarding will be separate from SID pool
> >      >      >     corresponding to new flex-algo topology ?
> >      >      >
> >      >      >     Many thx,
> >      >      >     Robert
> >      >      >
> >      >      >
> >      >      >     ---------- Forwarded message ---------
> >      >      >     From: *Acee Lindem via Datatracker* <[e-mail]
> >     <mailto:[e-mail]>
> >      >     <mailto:[e-mail] <mailto:[e-mail]>>
> >      >      >     <mailto:[e-mail] <mailto:[e-mail]>
> >     <mailto:[e-mail] <mailto:[e-mail]>>>>
> >      >      >     Date: Mon, May 16, 2022 at 3:36 PM
> >      >      >     Subject: [Lsr] Publication has been requested for
> >      >      >     draft-ietf-lsr-ip-flexalgo-06
> >      >      >     To: <[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]>>>>,
> >      >      >     <[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]>>>>,
> >      >     <[e-mail] <mailto:[e-mail]> <mailto:[e-mail]
> >     <mailto:[e-mail]>>
> >      >      >     <mailto:[e-mail] <mailto:[e-mail]>
> >     <mailto:[e-mail] <mailto:[e-mail]>>>>
> >      >      >
> >      >      >
> >      >      >     Acee Lindem has requested publication of
> >      >      >     draft-ietf-lsr-ip-flexalgo-06 as Proposed Standard on
> >     behalf
> >      >     of the
> >      >      >     LSR working group.
> >      >      >
> >      >      >     Please verify the document's state at
> >      >      >
> >     https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/
> >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/>
> >      >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/
> >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/>>
> >      >      >
> >       <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/
> >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/>
> >      >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/
> >     <https://datatracker.ietf.org/doc/draft-ietf-lsr-ip-flexalgo/>>>
> >      >      >
> >      >      >
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