LSP Hierarchy can be acrhived via three mechanism:
-MPLS tunnel interface
-Multiple pushes
-forwarding

MPLS tunnel interface
---------------------
see README.tunnel

Multiple pushes
---------------
Conside the simple MPLS network:

    A------B--------C------D

where A,D are LERs and B,C are LSRs.  B,C have a LSP setup between them.
A,D would like to setup an LSP between them, but THOUGH the existing
LSP.  This is called hierachtical LSPs.

The desired label stacking is:

              101
      200     201     202
    A------B--------C------D

(We receive on eth1 and send on eth0)

First setup the LSP between B and C:

  On B:
  mplsadm -A -I gen:101:eth0:ipv4:C

  On C:
  mplsadm -L eth1:0
  mplsadm -A -I gen:101:0

Now setup the LSP between A,B:

  On A:
  mplsadm -A -O gen:200:eth0:ipv4:B

  On B:
  mplsadm -L eth1:0
  mplsadm -A -I gen:200:0

Now setup the LSP between C,D:

  On C:
  mplsadm -A -O gen:202:eth0:ipv4:B

  On D:
  mplsadm -L eth1:0
  mplsadm -A -I gen:202:0

Now setup another LSP between B,C inside of the first:

  On B:
  mpls -A -O gen:201:eth0:ipv4:C
  mpls -O gen:201:eth0 -o push:gen:201:push:gen:101:set

  *Note: that the set will use the data from the out going label
         structure with the key (gen,201,eth0) which isn't eactly
         ideal, but will have to do for now.  (maybe a fwd would work
         better?)

  On C:
  mpls -I gen:101:0 -i pop:peek
  mpls -A -I gen:201:0

  *Note: here we see when a peek is for.  If a packet arrives with 101 on
         top of the stack, 101 if popped, and if more labels exist, they
         are looked up, and there instructions are run, if not labels exist
         a 'dlv' is executed.  If we had use a 'dlv' as oppsed to a peek then
         all packets with a 101 on top would be send to a layer 3 protocol
         even if more labels existed.

Now tie the three LSPs togther (A,B),(B,C),(C,D):

  On B:
  mplsadm -I gen:200:0 -O gen:201:eth0 -B

  On C:
  mplsadm -I gen:201:0 -O gen:202:eth0 -B


Forwarding
----------

Considering the same example above:

The desired label stacking is:

              101
      200     201     202
    A------B--------C------D

(We receive on eth1 and send on eth0)

First setup the LSP between B and C:

  On B:
  mplsadm -A -I gen:101:eth0:ipv4:C

  On C:
  mplsadm -L eth1:0
  mplsadm -A -I gen:101:0

Now setup the LSP between A,B:

  On A:
  mplsadm -A -O gen:200:eth0:ipv4:B

  On B:
  mplsadm -L eth1:0
  mplsadm -A -I gen:200:0

Now setup the LSP between C,D:

  On C:
  mplsadm -A -O gen:202:eth0:ipv4:D

  On D:
  mplsadm -L eth1:0
  mplsadm -A -I gen:202:0

Now setup another LSP between B,C:

  On B:
  mplsadm -A -O gen:201:eth0:ipv4:C

  On C:
  mplsadm -A -I gen:201:0

Forward traffic for the 201 LSP to ride on the 101 LSP:

  On B:
  mplsadm -O gen:201:eth0 -o push:gen:201:fwd:gen:101:eth0

  On C:
  mplsadm -I gen:101:0 -i pop:peek

Tie the LSPs together:

  On B:
  mplsadm -B -I gen:200:0 -O gen:201:eth0

  On C:
  mplsadm -B -I gen:201:0 -O gen:202:eth0