Subject: Output features for MPLS2IP

From: Siddhartha Sen <[email-masked]>
Date: Tue, 24 Apr 2001 09:55:54 -0700

Hi:

  Say I have IP output features configured on a port on IP addresses.

Now I have a MPLS to IP packet (Removing the label at the penultimate
hop pop point). The question is will this packet be tested for output 
features. 

One school of thought says that it should not be done as it is strictly 
an MPLS packet with implicit NULL label. They also go further and say 
that what if the port is ATM (or explicit null configured) ? In that case,
it would be an MPLS packet and no test on IP output features will be done.
How can u build a system where the answer depends on the type of the port.

An opposing school of thought says that the protocol plane is independent
of the forwarding plane. The forwarding plane does not and should not 
distinguish between IP packets that came in as IP packets and IP packets
that was obtained from being penultimate-hop-popped. 

Who is correct ? Which way should I implement ? Also please give pointers
to any relevant RFC so as to defend myself.

Thanking you,

Siddhartha

---

From: [email-masked]
Date: Wed, 25 Apr 2001 12:01:29 +0530

hi Siddhartha!
     Presuming by "IP output features" you mean things like IP tunneling, GRE
etc, the solutio is quite staright forward. If we are doing penultimate hop
popping and our network is like

r1-------r2----------r3--------r4-------r5

where r4 is the penultimate LSR for the LSP from r1 to r5 then r4 should strip
the packet of the Label (pop operation) and forward the packet to r5 and hence
this is completely MPLS forwarding stuff. However when we reach the router r5 it
should ofcourse do all the L3 stuff needed to forward the packet to its outgoing
port. The key thing here is that between the r4 and r5 it is only L2 forawarding
(essentially enabled by MPLS) and when we reach the egress router then
everything should happen at L3 including evrything that needs to be done before
forwarding an IP packet to its outgoing port.

hope this helps!

ciao
sumit

Siddhartha Sen <[email-masked]> on 04/24/2001 10:25:54 PM

To:   [email-masked]
cc:    (bcc: Sumit Chauhan/HSS)

Subject:  Output features for MPLS2IP

Hi:

Thanking you,

Siddhartha