The MPLS WG Archive

[Puneet Agarwal <puneet@pluris.com>]

Hi Shahram,

Based on the tunnel mode definitions in the -07 version of mpls-diff draft,
the oTTL determination is not needed explicitly for the "Pop" case. After
you perform "Pop" (recursively), you need to route (determine the egress
interface etc) the exposed header (IP packet or label). You never "Pop" the
label you route on - you can only SWAP, SWAP+Push or PHP (+Push) the label.

Hence I never added the bullet for "Pop" when determining oTTL as it is not
a legal operation. If you want, I can add text in section 2.4 of the draft
that a "Pop" is not a legal operation for a label we route on. Would that
help?

Hope this clarifies.

-Puneet

>-----Original Message-----
>From: Shahram Davari [mailto:Shahram_Davari@pmc-sierra.com]
>Sent: Tuesday, February 27, 2001 11:19 AM
>To: 'Puneet Agarwal'; 'Eric Gray'
>Cc: 'mpls@uu.net'; 'flefauch@cisco.com'; 'liwwu@cisco.com';
>'bsd@cisco.com'; Bora Akyol
>Subject: RE: New TTL Draft
>
>
>Hi Puneet,
>
>Thanks for your reply. Please see my comments in-line:
>
>> >2) Section 2.4 does not discuss an important case that is: 
>> >egress processing of tunnels, i.e. pop and forwarding the 
>> >packet as MPLS. 
>> 
>> Pop (or Egress Pop to distinguish from PHP) is actually 
>> covered in section
>> 2.3. The possibly operation when forwarding the packet as 
>> MPLS are covered
>> in the 3 bullets  of section 2.4. Combine section 2.3 and 
>the relevant
>> section of 2.4 and I think your concern about the missing 
>> case should be
>> answered. Hence as far as I can see the case is convered, but 
>> please let me
>> know if you still think that it is not addressed.
>> >
>
>As you know there are at least 2 distinct operations that are needed 
>for TTL processing:
>
>1) Determining iTTL
>2) Determining oTTL
>
>Section 2.3 describes the iTTL determination for both PHP and 
>non-PHP case.
>Section 2.4 however describes the oTTL determination for PHP 
>case only. I 
>can't see anywhere in the draft that talks about oTTL 
>determination for non-PHP
>case. Do you see any?
> 
>
>Yours,
>Shahram 
>