Re: [mpls] [EXTERNAL] A comment on the TTL in draft-dong-mpls-mna-encaps-00

[Alexander Vainshtein <[e-mail]>]

Plese disregard my previous message.
In Uniform TTL handling mode the PHP node would decrement TTL of the label stack entry it has received as the top label and copy the result in the TTL filed of the MNA.

My 2c.

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________________________________
From: Alexander Vainshtein <[e-mail]>
Sent: Thursday, August 4, 2022, 16:37
To: Stewart Bryant <[e-mail]>
Cc: [e-mail] <[e-mail]>; mpls <[e-mail]>
Subject: RE: [EXTERNAL] [mpls] A comment on the TTL in draft-dong-mpls-mna-encaps-00

Hi all,
I concur with Stewart.

The relevant scenario could look as following:

  1.  The MPLS network uses the Uniform TTL processing mode
  2.  The Penultimate LSP forwards the packet to the node that would process the MNA after popping the top label it has received – and decrements TTL as part of the Uniform node processing.

Regards,
Sasha

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From: mpls <[e-mail]> On Behalf Of Stewart Bryant
Sent: Thursday, August 4, 2022 4:18 PM
To: mpls <[e-mail]>
Cc: [e-mail]
Subject: [EXTERNAL] [mpls] A comment on the TTL in draft-dong-mpls-mna-encaps-00








3<https://clicktime.symantec.com/15t5ZrYAQ2dsdrevzMjWB?h=kynp7kxM1KmWz21212MPDCSsDE1ueZsQ1YxpYnoQQD8=&u=https://datatracker.ietf.org/doc/html/draft-dong-mpls-mna-encaps%23section-3>.  MNA Indicator



   The MNA Indicator is introduced to indicate the presence of any MNA

   information in the packet.  It can be used to indicate the existence

   of MNA actions and the optional associated data in the ISD, or the

   PSD or both.  Since this indicator is generic for all types of MPLS

   network actions, it is reasonable to allocate a basic Special Purpose

   MPLS label (bSPL) for it.  The TC and TTL fields of the MNA Indicator

   are redefined as flags.



   The format of the MNA Indicator is shown as below:



       0                   1                   2                   3

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |       MNA Indicator=SPL (TBA)         |H|I|P|S|ISF|    RSV    |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1. The format of MNA Indicator



   Where:



<snip>





   *  RSV: The rest 6 bits in the original TTL field are reserved for

      future use.  They MUST be set to 0 on transmit and MUST be ignored

      on receipt.

SB> There might be some merit in setting the RSV to 0b111111

SB> Then if some router receiving the SPL predecremented the TTL (not unknown in hardware) the upper bits of the TTL and hence the indicators would be unchanged

- Stewart

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