Re: [Lsr] Question about draft-ppsenak-lsr-igp-ureach-prefix-announce

Robert Raszuk <robert@raszuk.net> Fri, 05 August 2022 13:09 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Fri, 05 Aug 2022 15:09:03 +0200
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To: Peter Psenak <ppsenak=40cisco.com@dmarc.ietf.org>
Cc: Huzhibo <huzhibo@huawei.com>, "lsr@ietf.org" <lsr@ietf.org>
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Subject: Re: [Lsr] Question about draft-ppsenak-lsr-igp-ureach-prefix-announce
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Peter,

Side question ...

Assume PE participates in 10 end to end flex-algos.

However BGP advertises 100K service routes with base 0 nh 1.1.1.1/32

Are you stating that BGP should advertise 100K routes 10 times with
different IP address ?

Note that mapping to flex-algo may not be prefix based on the number of
forwarding paradigms. Yet UPA seems to be only prefix based.

Was this case discussed in any document/thread so far ?

Thx,
R.
.



On Fri, Aug 5, 2022 at 12:16 PM Peter Psenak <ppsenak=
40cisco.com@dmarc.ietf.org> wrote:

> Zhibo,
>
> On 05/08/2022 05:49, Huzhibo wrote:
> > Peter:
> >
> >> -----Original Message-----
> >> From: Peter Psenak [mailto:ppsenak@cisco.com]
> >> Sent: Friday, August 5, 2022 1:55 PM
> >> To: Huzhibo <huzhibo@huawei.com>
> >> Cc: lsr@ietf.org
> >> Subject: Re: Question about draft-ppsenak-lsr-igp-ureach-prefix-announce
> >>
> >> Zhibo,
> >>
> >> On 03/08/2022 21:09, Huzhibo wrote:
> >>> Hi Peter:
> >>>        Please see inline.
> >>>
> >>>> -----Original Message-----
> >>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
> >>>> Sent: Wednesday, August 3, 2022 11:20 PM
> >>>> To: Huzhibo <huzhibo@huawei.com>
> >>>> Cc: lsr@ietf.org
> >>>> Subject: Re: Question about
> >>>> draft-ppsenak-lsr-igp-ureach-prefix-announce
> >>>>
> >>>> Hi Zhibo,
> >>>>
> >>>> On 29/07/2022 20:49, Huzhibo wrote:
> >>>>> Hi Peter:
> >>>>>
> >>>>> Supplement to yesterday's online questions, If a node that does not
> >>>>> support IP Flexalgo, which has a default route, should the node
> >>>>> process the IP Flexalgo prefix as a UPA?
> >>>>
> >>>> - I assume you are talking about the algo 0 default route. Because IP
> >>>> Flex-algo default route does not make much sense really.
> >>>>
> >>>> - If the node does not support IP flex-algo, than it would not use
> >>>> any IP algo prefix as BGP service endpoint or for any other purpose.
> >>>>
> >>>
> >>> Which IP Algo prefix as BGP service endpoint is not determined by the
> ingress
> >> node, Such as VXLAN and SRv6 VPN.
> >>> When the ingress node receives an BGP Service cayyied a IP algo prefix
> >>> as endpoint and it has a algo 0 default route, it should be process
> this BGP
> >> service. and this can not be affected by the IGP Flexalgo prefix.
> >>
> >> sorry, but above is completely wrong.
> >>
> >> When you want to use IP flex-algo forwarding, you must advertise the
> prefix as
> >> algo prefix, relying on the algo 0 default would not give you algo
> forwarding.
> >>
> >> Advertising IP algo prefix at the egress and relying in algo 0 default
> at the
> >> ingress is going to cause all sorts of problems. You CAN NOT mix/change
> algos
> >> along the path through the network - if you do, you may end up in a
> permanent
> >> loop.
> >
> >    If the ingress node does not support Flexalgo, the ingress node does
> not cause a
> > permanent loop because once the packet is forwarded to the Flexalgo
> node, it always
> > follows Flexalgo forwarding. If the packet does not reach the Flexalgo
> node, it always follows
> > Algo 0 forwarding.
>
> well, flex-algo was design for end to end forwarding. Switching between
> algos as packet traverses the network is not guaranteed to be loop free.
> If you don't trust me, I let you figure that out yourself when you do
> such a thing and it breaks.
>
> >
> >>
> >>> Therefore,
> >>> the IGP does only not generate the RIB/Fib for LSinfinity Metric
> prefix, but can
> >> not trigger BGP Service Down.
> >>> In addition, LSinfinity Metric may be applied to other scenarios in
> >>> the future. We cannot guarantee that LSinfinity Metric will not
> conflict with
> >> other purposes when being processed as a UPA.
> >>
> >> no, it can not, because the LSinfinity has a very strict definition -
> it means
> >> unreachable, which is exactly what the UPA is about.
> >>
> > I believe you are confusing a concept. The LSInfinity metric defined in
> RFC 5308
> > can be considered as zero route, but PUA/UPA actually defines a negative
> route.
> > It's not consistent
>
> I'm not confusing anything:
>
> rfc2328:
>
> LSInfinity
>          The metric value indicating that the destination described by an
>          LSA is unreachable.
>
> regards,
> Peter
>
>
>
> >
> >> Peter
> >>
> >>>
> >>>> - If such node receives the IP algo prefix and even if it treats it
> >>>> as UPA, given that such IP algo prefix was never reachable before on
> >>>> this node, the UPA would result in no action.
> >>>>
> >>>> thanks,
> >>>> Peter
> >>>>>
> >>>>> Thanks
> >>>>>
> >>>>> Zhibo
> >>>>>
> >>>>
> >>>
> >>>
> >>
> >
> >
>
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