[j-nsp] MPLS implicit null question

[Chuck Anderson]

On Mon, Nov 17, 2008 at 05:56:26PM -0700, David Ball wrote:
>   This may sound strange, but if I don't explicitly have 'explicit
> null' configured under [edit protocols mpls], I'm doing implicit null
> by default, right?  So adjacent LERs should be sending me label 3 to
> instruct me to do penultimate hop popping?  Shouldn't I be able to see
> that label 3 anywhere, such as mpls.0 ?  I 'believe' my config would
> indicate that I'm doing PHP, but I"m now looking for evidence of it
> due to some anomalies I'm seeing.
> 
> I have a T-series connected to an MX in the lab, OSPF/BGP/LDP/RSVP
> between them, and an L2VPN built across them.  If I stick a switch
> between the 2 of them and sniff the data I"m sending across the L2VPN
> (with a test set), I'm seeing the traffic still MPLS-encapsulated,
> which, according to implicit null theory as I understand it, shouldn't
> be happening.

For L2/L3VPN, you would still see the inner MPLS label.  The outer 
label would be popped by PHP, leaving the inner label to distinguish 
which VPN the traffic is in.  The last hop router then pops the inner 
label.