The MPLS WG Archive

[Bora Akyol <akyol@pluris.com>]

Tony

Thank you for the explanation. I have a few more questions.

1. Do the RSVP messages for the second (hierarchical) tunnel get forwarded via the
previously established LSP or go hop by hop?

2. What happens to the bandwidth reserved for the original tunnel when a
hierarchical tunnel rides over it?

3. In the following example:

A-->B               E-->F
          \              /
           C---->D

Let there be an initial tunnel established between B & E with the ILMs from B to E
as follows

B--C: 23
C--D: 34
D--E: 45

Let us also assume that we want to establish a second tunnel from A to F.

When a PATH message goes from A to F, how does B, C, D, E know that this is a
hierarchical tunnel vs a regular tunnel (related to question 1 above).

What exactly are the steps that are performed?

I am asking these questions to make sure that I have the right understanding of
this use of RSVP-TE, and I appreciate your answer.

Regards

Bora





Tony Li wrote:

>  | How does one establish hierarchical tunnels using RSVP-TE?
>  |
>  | I know that the label object can be deeper than one label, but you need more
>  | than this to establish hierarchical tunnels.
>
> A hierarchical tunnel requires the participation of at least two LSRs.  The
> operation of the LSR creating the innermost tunnel is straightforward and
> is unchanged from what has been endlessly discussed here.
>
> For an LSR to create an outer tunnel, it simply creates another tunnel and
> specifies MPLS as the L3PID.  It then forwards packets received on the
> inner tunnel by pushing a label for the outer tunnel.  The RSVP control
> traffic for the inner tunnel is also forwarded through the outer tunnel
> after first being encapsulated with a null IP label.
>
> Recurse, ad nauseum.
>
> Simple, really.  ;-)
>
> Tony