The MPLS WG Archive

["Jiang, Donghua (Donghua)" <djiang1@lucent.com>]

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---------------------->