Subject: RE: New TTL Draft

From: Puneet Agarwal <[email-masked]>
Date: Fri, 23 Feb 2001 18:22:09 -0800

Eric,

Thanks for your comments. My comments are inline.

-Puneet

[...]
>> [...]
>> >
>> >    Finally, what is the mechanism which the PHP uses to determine
>> >whether or not the LSP is using the pipe or the uniform model?  I am
>> >not sure this information is currently available.
>>
>> You may be right. I looked through 
>"draft-ietf-mpls-diff-ext-08.txt", but
>> did not see any method to signal the model (pipe or uniform) 
>associated with
>> the LSP, using either RSVP or LDP. If it is a missing piece, 
>then I hope
>> that it will be addressed by the authors of that draft.
>
>This would address the case where you are just
>addressing the disparity between DS usage and
>TTL.  But what about the more general case -
>i.e. - where DS is not involved?
>
>The answer that how the PH knows this is out
>of scope, might be good enough, but I would like
>to know what people are thinking.  I am not sure
>that configuration makes sense since it is not
>necessarily clear in every case which LSRs are
>going to end up being the penultimate hop for
>which LSPs.  It really doesn't make a lot of
>sense to punt the issue if the current answer
>to the question "how could we make it work?" is
>"magic"...
>

You are correct. In my earlier reply I overlooked the fact that this could
be used in non DS cases.

The issue is in some sense broader than just PH knowing the model of the
LSP. The ingress and the egress LSRs also need to know the model (pipe or
uniform) of the LSP so they can consistent in their handling of TTL. The
ideal solution would be to add a new object to the PATH message (for RSVP)
indicating the LSP model being used so that ingress/PH/egress LSRs can be
consistent. Something similar can be done for LDP. In fact, even non
ingress/PH/egress LSRs may also need to know the LSP model to support
features, like "fast reroute", offered by some vendors.

I think you and I agree that there is a hole. I am not convinced that our
TTL draft is the correct place to define the signalling mechanism outlined
above. I can certainly look into addressing this is in a separate draft
depending on the response from the authors of
"draft-ietf-mpls-diff-ext-08.txt".

Hence I would rather add text to our TTL draft to the effect that "how the
LSR knows the model of any LSP is outside the scope of this draft".

-Puneet

>> -Puneet
>> [...]
>--
>Eric Gray

---

From: "S.Matsushima" <[email-masked]>
Date: Mon, 26 Feb 2001 15:01:46 +0900

Puneet,

I think you described very well the ttl processing on hierarchical
MPLS network.

> LSR knows the model of any LSP is outside the scope of this draft".

As a matter of fact, I have submitted an i-d which is described this
problem. Please see below url, and give me your thoughts on my i-d.

thanks,

http://www.net-work.ne.jp/~satoru/draft-satoru-mpls-1hop-lsp-00.txt

--
Satoru Matsushima