The MPLS WG Archive

[Manish Godara <ml_manishg@yahoo.com>]

Hi Jane,

Apologies for the confusion.  I meant T2 is tunneled
inside T2.  Thanks for the clarification.  So it is
possible to pop two labels at one LSR.  Now I wonder
if it is efficient to implement this in hardware.

thanks,
manish

------------- your mail ----------------

Manish,

When you say "T2 is tunneled over T1", do you mean T1
is tunneled inside T2
or T2 is tunneled inside T1? 

After I sent out the email yesterday, I was getting
suspicious about what I
said.  If T1 is tunneled inside T2, then the packets
are traveling from L1
to L3, the MPLS label used for T2 will always be the
top label and
forwarding will be based on the top label, we would
not care about the
existence of T1.  So, T1 will not be involved when
packets travels from L1
to L3.  If T2 is tunneled inside T1, then from L1 to
L21, packets will be
forwarded based on the MPLS labels for T2.  When
packets get to L21, one
more layer of label will be pushed on and packet
forwarding will be based on
the newly added label layer.  When packets get to L22,
the top layer will be
popped as it is the end of the tunnel T1.  Also, due
to the negotiation
between L22 and L3, the current top label should also
be popped before the
packets are forwarded to L3.

Hope you did not mean to play the trick :-)

Regards,
Jane

-----Original Message-----
From: wiseguy@cs.stanford.edu
[mailto:wiseguy@cs.stanford.edu]
Sent: Tuesday, July 17, 2001 12:06 PM
To: mpls@UU.NET
Subject: [MPLS] Popping Multiple Labels



Hi,

I was wondering if there are any possible scenarios in
which
a node might pop multiple labels from the stack.  One
case
I was thinking of is : a node is endpoint of a tunnel
(T1) and
is also a penultimate hop for another tunnel (T2) and
T2 is
tunneled over T1!  Maybe this is not a valid scenario
but I
would like to check.

I appreciate any help.

thanks,
manish

PS: Scenario


  +-----+         +-------+               +-------+   
     +------+
  |     | ===~==  |       |  ====~~===    |      
+---------+      |
  | L1  |         | L21   |               | L2n   |   
     | L3   |
  +-----+         +-------+               +-------+   
     +------+

                  <------------  T1 -------------->
        
<--------------------------T2---------------------->



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