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

[Peter Psenak <[e-mail]>]

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]>> 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>
> 
>     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]>>> 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]>>>
>      >     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]>>>
>      >     Cc: <[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>,
>      >     <[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>,
>      >     <[e-mail] <mailto:[e-mail]>
>     <mailto:[e-mail] <mailto:[e-mail]>>>,
>     <[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/>>
>      >
>      >
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