RE: Size of CR in CRH

["Pablo Camarillo (pcamaril)" <[e-mail]>]

-----Original Message-----
From: ipv6 <[e-mail]> On Behalf Of Bob Hinden
Sent: miércoles, 20 de mayo de 2020 18:46
To: Ron Bonica <[e-mail]>
Cc: 6man <[e-mail]>; Bob Hinden <[e-mail]>
Subject: Re: Size of CR in CRH

<trimmed>

>> The O-RAN Alliance is exploring transport architectures in which each cell tower hosts a Cell Site Router (CSR) and each CSR can be the endpoint of a traffic engineered path. In that architecture, a 32-bit CR may be required, because there may be as many as 1,000,000 CSRs.
>> 
>> Yes, this is a bit speculative. But it may happen.

>CRH could start with a 16-bit identifier.   Once the O-RAN work is further along, a new routing header with 32-bit identifiers could be developed if needed.   As you said, there isn't a >shortage of routing header types and would make the specification and implementations simpler.

Bob,

If we consider that CRH-FIB only contains tag entries for each router/prefix in the network, then I agree with you: let's go with 2^16 which is more than enough in a single domain.
However, if we consider the original authors intent of re-spinning SRv6, then you will need Prefix SIDs, Adjacency SIDs, Binding SIDs -and perhaps also BGP EPE SIDs-. In this case the 2^16 number will fall short and likely you need 2^32 tags.

Hence how do we choose in between 16b or 32b? Either we blindly trust the authors, or we need some sort of document understanding what we are trying to solve here as to make the right decision. 

Thanks,
Pablo.