The MPLS WG Archive

[Alia Atlas <aatlas@avici.com>]

I agree that removing the restriction that an explicit null only occur at 
the bottom of the stack would be a good idea.

It does raise some questions, because there is an IPv4 explicit null and an 
IPv6 explicit null.  What we really want is just an explicit null, which 
means "pop off this label and then forward based on whatever's underneath".

Alia

At 10:09 AM 1/29/2003 -0500, Eric Rosen wrote:

>Francis> Should the statement  that <the explicit null label  only occurs at
>Francis> the bottom of the stack> be relaxed?
>
>This statement causes a lot of problems, and no one can seem to remember why
>it is there.  Further, there are a number of cases in which it is awkward to
>prevent explicit  null from appearing in  mid-stack. Not only  that, but the
>specs  don't really say  what you  are supposed  to do  if you  do encounter
>explicit null above another label, or if you are instructed (via LDP) to put
>explicit null on a packet which already has a label stack.
>
>So I would favor removing the  requirement that explicit null only appear at
>the bottom of the stack.