MPLS forwarding "Instructions"
------------------------------
Inside the kernel the processing of MPLS packets and their label stacks
is down via "instructions".  By adding in and out labels and switch paths
you are modifing these instructions.  Sometimes it is useful to be able
to override these instructions, one specific case is when you want to
send or recieve packet with a label stack of size greater then 1.

Incoming labels and outgoing labels each have a set of instructions that
can be executed.  Certain instructions are only valid for incoming or
outgoing labels.

List of MPLS instructions
-------------------------
-pop - remove the top label from the label stack. (in/out)
-push - push another label on the label stack. (in/out)
-dlv - send this packet to the layer 3 protocol stored with this in label. (in)
-peek - look at the label on top of the label stack, look the label up in 
        the list of incoming label for this interface, and start executing
        the instructions associated with it.  If there is not a label,
        execute a dlv. (in)
-set - last step before transmitting a MPLS packet.  It copies the outgoing
       interface and the next hop layer 2 destination from the out going label
       structure. (out)
     - set the incoming interface to somethgin diffetn then the REAL incoming
       interface (in)
-fwd - send a packet to an outgoing label structure to be processed (in/out)

Format of each instruction
--------------------------

Incoming instructions
---------------------
pop
push:<label type>:<value>
dlv
peek
set:<intererface> 
fwd:<label type>:<value>:<interface>:<nh famliy>:<nect hop>

Outgoing instructions
---------------------
push:<label type>:<value>
set
fwd:<label type>:<value>:<interface>:<nh famliy>:<nect hop>

*Note: when using 'fwd' you are referencing an ougoing label, it must exist
in the outgoing label list, otherwise the command will fail

*Note: when using 'push' you can push any label values you would like.  They
do not need to exist in any table, nor do they have to correspond to the
label structure your operating on.  In the later case the label label value
specified by -I and -O can be thought of as keys, and not neccesaarily as
the label values in the resulting packets.

By adding in or out labels and switch paths your already setting up
instructions.  Here are some examples and what the resulting structure
and instrustions are:

mplsadm -A -I gen:34:0
----------------------
-create an in label structure with a key of (gen,34,0)
-set the instructions in the in label structure to be:
 pop:dlv
-set the layer 3 protocol to be IPv4

mplsadm -A -O gen:16:eth0:ipv4:128.104.17.130
---------------------------------------------
-create an out label structure with a key of (gen,16,eth0)
-set the instructions in the out label structure to be:
 push:gen:16:set

*Note: the key and the label being pushed do NOT have to match!

mplsadm -B -I gen:34:0 -O gen:16:eth0:ipv4:128.104.17.130
---------------------------------------------------------
-lookup in label structure with key (gen,34,0)
-lookup out label structure with key (gen,16,eth0)
-set the instructions in the in label structure to be:
 pop:fwd:gen:16:eth0
-the out label structures instructions do not change

The command line usage for instructions is straigh forward:

mpls -I gen:34:0 -i pop:dlv
mpls -O gen:16:eth0 -o push:gen:16:set
mpls -I gen:34:0 -i pop:fwd:gen:16:eth0