Re: [mpls] Concerns about ISD

[Tianran Zhou <[e-mail]>]

Hi Tony,

Please see in line.

Best,
Tianran

From: Tony Li [mailto:[e-mail]] On Behalf Of Tony Li
Sent: Monday, April 11, 2022 11:35 PM
To: Tianran Zhou <[e-mail]>
Cc: [e-mail]
Subject: Re: [mpls] Concerns about ISD


Hi Tianran,


Please see RFC 9088 and 9089.
While hardware continues to evolve, as we’ve discussed previously, we really want to try to maximize the value of the hardware that’s already in the field. That’s in  the operator’s best interests and thus in ours as well.

ZTR> I quickly go over this two RFCs. I did not see any limits on the number of readable labels. On the contrast, it allows devices with different capabilities. By using the flooding and notification mechanism, the controller or so knows the capability of each device, hence easy to program the stack on the head node.


Exactly.  This exists because there is a need to understand the readable label stack depth (RLSD) and operate within it.  RLSD is important for interoperability and pushing everything to PSD would hinder interoperability. People did things this way for a reason. It makes sense for us to continue to do so.

ZTR2> PSD can work with RLSD, I cannot see how it will hinder the interoperability.

I see hard coding an ASIC as a poor choice. But I’ve only been saying that since 1996. :)  All of the silicon that I’ve had a hand in has been microcoded for exactly this reason, with very little penalty.

ZTR> I disagree. New chips are combination of AICS part and microcode part. Microcode is for changes and flexibility. But ASIC is for performance.

Ok, clearly we operate with different silicon technology.

In a related matter, it does occur to me that if you dislike ISD, you are free to take any sub-stacks that you want to inject and push them to the bottom of the label stack. This would effectively push all of your ISD just above PSD, effectively doing the same thing as doing everything in PSD.  Of course, this would minimize your interoperability.  Other devices would be able to use MNA through your device, but you would not be able to send MNA through them. If this is what you want, we won’t stop you.

ZTR2> Of course I would not put ISD just above PSD. As PSD can provide all the functionalities, I do not see the reason why we need ISD anymore. Entropy label is a simple one, community chose to implement the in stack operation <optionally> as in RFC 6790. For ISD, I would not expect it to split the community effort. You can implement any fascinating ISD design privately, we won’t stop you. But I do not think we need any IETF standard on ISD.

Regards,
Tony