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

Peter Psenak <> Fri, 29 May 2020 15:14 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 <>
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From: Peter Psenak <>
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Date: Fri, 29 May 2020 17:14:00 +0200
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On 29/05/2020 16:56, John Scudder wrote:
> Peter,
>> On May 29, 2020, at 10:36 AM, Peter Psenak < 
>> <>> wrote:
>> 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.
> (Of course this objection only applies to the final (“distributed 
> routing protocol”) bullet point.)


> We’re recapitulating conversation that has been done on-list at least 
> once. If I had time I’d find the reference and post, but as we know the 
> conversation is hundreds of messages deep (at least!) and I don’t; 

no worries, below summary is sufficient.

> sorry. Maybe someone else has a reference handy? If I recall correctly 
> (and I may not) one exemplary solution to your objection is to make use 
> of globally-unique (per domain, of course) identifiers, and yes, I do 
> mean something semantically similar to a SR Node-SID. Other solutions 
> are possible, depending on the use case — if the use case doesn’t 
> require any-to-any connectivity within the domain, you potentially don’t 
> need O(N^2) CRH identifiers to be present in the LS(P)DB even absent any 
> kind of global uniqueness. Granted that any-to-any is the most general case.

so if we design for a most general case, it's obvious that the locally 
unique CRH identifiers are problematic, at least when distributed 
routing protocol is being used to populate CRH-FIB.

>> Not to mention that the proposed encoding in
>> draft-bonica-lsr-crh-isis-extensions only allows one to advertise thener
>> CRH identifier for a local prefix and adjacency, not for the remote ones.
> That seems out of scope for discussion of CRH per se, unless you mean to 
> say “this problem cannot be solved” instead of “this particular solution 
> is deficient”. If it’s the latter, I think the LSR mailing list seems 
> like a better place to take it up with the authors 
> of draft-bonica-lsr-crh-isis-extensions.

sure, just tried to connect things together, but let's ignore it for a 
time being.


> —John