Re: [mpls] FW: New Version Notification for draft-jags-mpls-ps-mna-hdr-00.txt

Hi Tony,
please find my notes inline below under the GIM>> tag.

Regards,
Greg

On Thu, Apr 20, 2023 at 9:38 PM Tony Li <[email protected]> wrote:

>
> Hi Loa,
>
>
> > - will a non-MNA capable implementation have problems "processing" (aka
> as skipping over) the MNA label and the extra LSEs after the MNA Label? How
> does it know what is an extra LSE and what is a Label?
>
>
> This is an ISD question, not PSD.
>
> Non-MNA implementations should not be attempting to process MNA ISD.
> Assuming that we’ve specified ISD correctly and that implementations
> conform, the MNA ISD should never come to the top of stack at a non-MNA
> node.

GIM>> Yes, it should not, but things happen. If a non-MNA node
encounters MNA bSPL it will drop the packet. That's normal.

>
>
> If a transit node needs to find PSD, it can scan the entire label stack
> for the bottom of stack bit.  I can’t think of a good reason to ever do
> this, given that it’s a transit node and should be payload indifferent.
>
GIM>> I got confused. I am too not seeing the case when an LSR starts
looking for PSD unless it has found a proper NAS.

>
>
> > - we will only include the MNA first nibble if there is an MPLS Label in
> the packet. right? Existing (legacy) non-MMA capable implementations will
> not recognize the MNA first nibble as "MNA follows, only understand that
> this is something unrecognised. What does legacy implementations do with
> unrecognized first nibbles today?
>
>
> There is not much point in having an MNA first nibble unless there is also
> MNA PSD.  And there is not much point in MNA PSD unless there is a label
> stack involved. Therefore, yes, there should be a label in the label stack.
>
GIM>> More confusion in my head. Why it must be "an MNA first nibble" but
not any non-IPv4 and non-IPv6?

>
> AFAIK, legacy transit nodes should not be examining PSD at all, of any
> flavor.  That said, I cannot speculate on the behavior of all legacy
> implementations.
>
> Sending MNA PSD to a legacy terminating node is not something that we
> should be supporting.
>
>
> > - are there cases where PSD does not immediately follow the first nibble?
>
>
> MNA PSD and other forms of PSD must interoperate somehow.  We may decide
> that MNA PSD is not at the top of PSD.
>
GIM>> I am looking forward to seeing a proposal for that.

>
>
> > - shouldn't the behaviour in these two cases be documented in one of our
> drafts?
>
>
> We have tried to do so, but we are only human.
>
> Regards,
> Tony
>
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