Re: Size of CR in CRH

[[e-mail]]

> The following factors figured into the decision to specify 2 Routing types, one with a 16-bit identifier and the other with a 32-bit identifier:
> 
> 	- Today, very few networks contain more than 65,000 routers. So, most networks could obtain best compression with a 16-bit identifier.
> 	- When 5G is deployed, we may see networks that contain more than 65,000 Cell Site Routers. These networks will need an identifier that is wider than 16 bits.
> 	- It is unlikely that we will ever see a network that contains more than 4,000,000 routers. So, we will never need an identifier that is wider than 32 bits.
> 
> If Routing header types were in short supply, and only one were available to us, we would have to do one of the following:
> 
> 	- Select a single length (16, 24 or 32 bits)
> 	- Use the fifth byte of the Routing header to indicate the identifier length.
> 
> The first option isn't very appealing. A 16-bit identifier is too short for some networks. A 24-bit identifier may be difficult for some ASICs to process. A 32-bit identifier gives suboptimal compression for all existing networks.
> 
> The second option isn't very appealing either. If we use the fifth byte to indicate the identifier length, and we want the first identifier to begin on a 32-bit boundary, the next 24 bits would be wasted.
> 
> Fortunately, Routing header types are not in short supply. The Routing Type registry has room for 255 entries. Since it was established 25 years ago, only 6 types have been allocated. Of those, two have been deprecated (RH0 and Nimrod) and two are for special use (Experiment 1 and Experiment 2).
> 
> So, allocating two Routing types may be the best solution.

I don't think we necessarily need to settle this as part of the adoption call.
Although it might influence someone's opionion if this adds 1 (additional) solution to the table or 2.

For clarification:
 - Are these tags meant to be unique within the controlled domain or do they only need to be unique per node?
 - A tag identifies a forwarding method. One node could then use many tags,
   e.g have one tag map to each of it's outgoing interfaces? Or a tag significy a VNI?
 - Method specific parameters. Are they meant to be embedded in the tag or somewhere else, if so where?

Best regards,
Ole