Re: [mpls] Concerns about ISD

Tony Li <tony.li@tony.li> Mon, 11 April 2022 15:42 UTC

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From: Tony Li <tony.li@tony.li>
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Date: Mon, 11 Apr 2022 08:42:45 -0700
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Cc: Tianran Zhou <zhoutianran@huawei.com>, "mpls@ietf.org" <mpls@ietf.org>
To: "Dongjie (Jimmy)" <jie.dong@huawei.com>
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Subject: Re: [mpls] Concerns about ISD
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Hi Jie,


> [Jie] IMO one of the difference between entropy label and ISD is whether the format of the label field, the TTL field and TC field are redefined or not. This will impact the parsing and processing implementation of network nodes. And concatenation of multiple fields in the same or different LSEs would be a very different behavior from the existing MPLS label processing. 


There is no doubt that the processing is different.  This is to be expected, we’re adding functionality.


> I strongly disagree.  Putting everything in PSD makes it impossible for devices with limited readable label stack depth to participate effectively.
>  
> [Jie] For backward compatibility, one thing to consider is the risk of ISD being exposed at the top of label stack on the legacy nodes, which may be misunderstood as forwarding labels.


I believe that we’ve been pretty clear: we’re using signaling to indicate which nodes support MNA. It’s up to the head end to do path selection that is MNA capable (and more specifically, action capable, if necessary).


>  [Jie] This shows that further hardware analysis is really needed. We’ve had some discussion about the hardware-friendly design principles, and the comparison between the optional encodings in terms of processing complexity and overhead.


What is it that you’re hoping to learn?  We’ve been through a few rounds of hardware analysis and had dissimilar results.

> I hope at least we can agree that MIAD or MNA requires new functionalities, then it would be helpful to understand what can and cannot be done with legacy hardware, what would be the requirements to new hardware, and hardware people’s feedback about these requirements.


I think we agree that it requires new functions. What can and cannot be done with legacy hardware varies with the specific hardware and no one is willing to disclose what their hardware can and cannot do. There are no requirements for new hardware as it is presumably more capable than existing hardware. The feedback from the various hardware analysis has been inconsistent.

Regards,
Tony