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 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 <jgs@juniper.net>
Cc: "rtg-ads@ietf.org" <rtg-ads@ietf.org>, "spring@ietf.org" <spring@ietf.org>, 6man <6man@ietf.org>
References: <9CF68CCE-B584-4648-84DA-F2DBEA94622D@cisco.com> <3bbb28c8-0106-ad63-abf9-c9dc4e428e0c@joelhalpern.com> <MW3PR11MB4570FD37ED32519C677F5E59C1B20@MW3PR11MB4570.namprd11.prod.outlook.com> <DM6PR05MB63486B842CD9DF5BE57FC1A5AEB30@DM6PR05MB6348.namprd05.prod.outlook.com> <MW3PR11MB45706D51FBE6CD63B58CDF15C1B30@MW3PR11MB4570.namprd11.prod.outlook.com> <DM6PR05MB634848BE997686F212FF9E49AEB30@DM6PR05MB6348.namprd05.prod.outlook.com> <MW3PR11MB457006B3ECAF2E812CD2E721C18E0@MW3PR11MB4570.namprd11.prod.outlook.com> <df0b518a11734e8f91dc2c0902f46df5@nokia-sbell.com> <DM6PR05MB6348EBA8F4E6C889393B5269AE8E0@DM6PR05MB6348.namprd05.prod.outlook.com> <a2876051-182b-f955-6e52-17740a612c74@cisco.com> <AC07D522-C10B-47CE-8B79-10EFDEA440D7@juniper.net> <ea9a0467-c9a6-11bf-5454-d6bc44b8d2ad@cisco.com> <3C511772-D3E8-4A80-AE73-43E644759C1D@juniper.net> <0ed7a981-d890-03e4-86b9-64d42c971552@cisco.com> <A049C501-EBB8-467E-96BB-6E01144DC527@juniper.net>
From: Peter Psenak <ppsenak@cisco.com>
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Date: Fri, 29 May 2020 17:14:00 +0200
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John,

On 29/05/2020 16:56, John Scudder wrote:
> Peter,
> 
>> On May 29, 2020, at 10:36 AM, Peter Psenak <ppsenak@cisco.com 
>> <mailto:ppsenak@cisco.com>> 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.)

correct.

> 
> 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.

thanks,
Peter

> 
> —John