The MPLS WG Archive

[Chris Metz <chmetz@cisco.com>]

Hello-
I had a question forwarding adjacencies.
http://search.ietf.org/internet-drafts/draft-ietf-mpls-lsp-hierarchy-00.txt
states that

> In general, creation/termination of a forwarding adjacency and its
>    FA-LSP could be driven either by mechanisms outside of MPLS (e.g.,
>    via configuration control on the LSR at the head-end of the
>    adjacency), or by mechanisms within MPLS (e.g., as a result of the
>    LSR at the head-end of the adjacency receiving LSP setup requests
>    originated by some other LSRs).

I am confused by the latter statement and the implied sequence of events. It seems to be saying that

"some other LSRs" (let's say A in the example below) would signal RSVP/CRLDP messages (towards H) that pass thru a "head-end" LSR (C) who in turn would establish a FA-LSP to F. 

A--B--C(head-end)====D====E====F--G--H

How does the A know to send an RSVP/CRLDP message thru C if the FA-LSP (C===F) does not already exist? Shouldn't the FA-LSP appear first as a link in A's topology database which would imply it has already been setup?

Thanks ...

Chris Metz

Lead IP Architect

Solutions Integration

Service Provider Line of Business

Cisco Systems

email: chmetz@cisco.com

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