The MPLS WG Archive

["David Allan" <dallan@nortelnetworks.com>]

Title: RE: MIBs and TTL

Thomas:

Pipe or uniform is the terminology adopted in the MPLS diffserv draft and carried forward into
http://www.ietf.org/internet-drafts/draft-agarwal-mpls-ttl-01.txt

The short story is:
- for uniform model TTL is independent of MPLS level. You copy TTL values up and down the stack as you push and pop.
- for pipe model, TTL is unique to each MPLS level.
So configuring this looks painful (get it from incoming label before x-connect entry, or get it from incoming IP payload, or set it to fixed value at ingress) :-(.

As to how to handle non-TTL capable links, an unsigned object added to InterfaceConfEntry (InterfaceTTLDec?) with a default value of 1 should be all that is required. The only wrinkle being that I don't fully grok pop and swap to be sure that a non-ttl link label under the top label would work correctly.

thanks
Dave

-----Original Message-----
From: Thomas Nadeau [mailto:tnadeau@cisco.com]
Sent: Monday, November 26, 2001 2:09 PM
To: Allan, David [CAR:NS00:EXCH]
Cc: mpls
Subject: Re: MIBs and TTL

From what I can see, none of the MPLS MIBs seem to acknowledge TTL. There's a couple of issues to address:

- what to do at the egress of a non-TTL capable link. (e.g. how much to decrement the value). This looks like an LSR-MIB "in-segment" table issue.

        That is true, but to-date, no neither the vendors implementing them nor the
SPs using them one has found it necessary to add them. What would you like to see?

- whether to use pipe or uniform model at an LSR ingress point
(which looks like it hits a bunch of places, FTN, MPLS-TE and LSR).

        I don't understand what you mean by a "pipe or uniform model" above.

        --Tom

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