Re: [mpls-linux-general] Re: MPLS-Linux

[James R. L. <jl...@mi...>]

On Mon, Jun 25, 2001 at 02:08:43AM +0500, Saeed Akhter wrote:
> Hi Jim,
> 
> Thanks for you reply, can you please clarify following as well;
> 
> 1- When you say that there is some bug in mplsadm commands, does it mean all 
> commands or only few ? if so, which ones?

After looking at the code, it looks like it should work.  As far as 
know commands that are broken?  If I knew they were broken I would
fix them ;-)

> 2- Am I right in understanding LSP hierarchy as sending multiple labels in 
> the same packet or is it multiple labels in the same tunnel ? please 
> clarify.

Your statments mean about the same thing.

First, tunnel == LSP and LSP == tunnel.  MPLS tunnels were invented by Cisco
to make integration of MPLS into there routers easier, the usage of it has
proliferated to RFC and other documents in such away as to confuse people.

If you have LSP hierarchy you will have and LSP in which one of its hops is
an LSP.  As the packets traverse that hop of the outer LSP they will have two
labels.

   

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

               <----------- 100 ----------> (inner LSP)

   <----------------------- 200 ----------------------->  (outer LSP)

In this example:
-the inner LSP must be setup prior to the outer LSPs setup
-if the outer LSP was being setup via signalling (RSVP-TE or CR-LDP)
 the hop list for the outer LSP would be A B D E.  LSR C would not participate
 in the siganlling of the outer LSP, and would not even know of the existence
 of label 200
-as far as C is concerned it is only label switching packets for LSP 100
-packets traversing C would have 2 labels 100 on the top and 200 (with bos bit)
 on the bottom

If you need more clarification RFC 3031 does a good job of explaining
LSP hierarchy.

Jim
-- 
James R. Leu