Re: [spring] CRH is back to the SPRING Use-Case - Re: Size of CR in CRH

Peter Psenak <ppsenak@cisco.com> Fri, 29 May 2020 14:36 UTC

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Subject: Re: [spring] CRH is back to the SPRING Use-Case - Re: Size of CR in CRH
To: John Scudder <jgs@juniper.net>
Cc: "rtg-ads@ietf.org" <rtg-ads@ietf.org>, "spring@ietf.org" <spring@ietf.org>, 6man <6man@ietf.org>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Fri, 29 May 2020 16:36:49 +0200
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John,

On 29/05/2020 16:33, John Scudder wrote:
>> On May 29, 2020, at 10:28 AM, Peter Psenak <ppsenak@cisco.com 
>> <mailto:ppsenak@cisco.com>> wrote:
>>
>> how do nodes in the network learn about the local CRH identifier a node
>> X allocated for a prefix residing on node Y?
> 
> This is also answered in section 4, AFAICT:
> 
>     The CRH-FIB can be populated:
> 
>     o  By an operator, using a Command Line Interface (CLI).
> 
>     o  By a controller, using the Path Computation Element (PCE)
>        Communication Protocol (PCEP) [RFC5440  <https://tools.ietf.org/html/rfc5440>] or the Network
>        Configuration Protocol (NETCONF) [RFC6241  <https://tools.ietf.org/html/rfc6241>].
> 
>     o  By a distributed routing protocol [ISO10589-Second-Edition  <https://tools.ietf.org/html/draft-bonica-6man-comp-rtg-hdr-22#ref-ISO10589-Second-Edition>],
>        [RFC5340  <https://tools.ietf.org/html/rfc5340>], [RFC4271  <https://tools.ietf.org/html/rfc4271>].

well, advertising the local CRH identifier for every node and adjacency 
in the network from every other node is clearly a no-go from the IGP 
perspective.

Not to mention that the proposed encoding in 
draft-bonica-lsr-crh-isis-extensions only allows one to advertise the 
CRH identifier for a local prefix and adjacency, not for the remote ones.

thanks,
Peter

> 
> 
> I imagine the list isn’t meant to be exhaustive, some other minor 
> variations have been discussed on-list IIRC.
> 
> —John