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

[Huzhibo <[e-mail]>]

Peter:

> -----Original Message-----
> From: Peter Psenak [mailto:[e-mail]]
> Sent: Friday, August 5, 2022 1:55 PM
> To: Huzhibo <[e-mail]>
> Cc: [e-mail]
> 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:[e-mail]]
> >> Sent: Wednesday, August 3, 2022 11:20 PM
> >> To: Huzhibo <[e-mail]>
> >> Cc: [e-mail]
> >> 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.

> 
> > 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

> 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
> >>>
> >>
> >
> >
>