Subject: RE: MIBs and TTL

From: "David Allan" <[email-masked]>
Date: Mon, 26 Nov 2001 14:49:58 -0500

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:[email-masked]]
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

------------------------------------------------------------------------
Mathematics is the supreme nostalgia of our time.

---

From: Thomas Nadeau <[email-masked]>
Date: Mon, 26 Nov 2001 15:00:23 -0500

><http://www.ietf.org/internet-drafts/draft-agarwal-mpls-ttl-01.txt>http://www.ietf.org/internet-drafts/draft-agarwal-mpls-ttl-01.txt 
>

         Sorry, from the original context, I wasn't sure.

>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.

         It looks painful, but is flexible as to support different 
implementations.

>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.

         This is certainly an option.

         --Tom

---

From: "David Allan" <[email-masked]>
Date: Mon, 26 Nov 2001 15:59:01 -0500

I meant painful from the point of view of the number of places it could
appear in the MIBs (which might not actually be that bad and looks like it
could be confined to the XCTable).  I'd assume the most useful definition
would be configurable per LSP with a default LSR setting. (per LSP default
is default specified for the LSR).
 
cheers
Dave.

-----Original Message-----
From: Thomas Nadeau [mailto:[email-masked]]
Sent: Monday, November 26, 2001 3:00 PM
To: Allan, David [CAR:NS00:EXCH]
Cc: mpls
Subject: RE: MIBs and TTL

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
<http://www.ietf.org/internet-drafts/draft-agarwal-mpls-ttl-01.txt>  

The short story is: 

        --Tom

---

From: Thomas Nadeau <[email-masked]>
Date: Mon, 26 Nov 2001 16:24:41 -0500

>is default specified for the LSR).

         Appearing in more than one place is not such a bad thing
if it is useful, and not done too often.

         --Tom

>>>Pipe or uniform is the terminology adopted in the MPLS diffserv draft 
>>>and carried forward into
>>>- for uniform model TTL is independent of MPLS level. You copy TTL 
>>>values up and down the stack as you push and pop.
>>>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.
>>