The MPLS WG Archive

[Eric Rosen <erosen@cisco.com>]

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.