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Hi, all:

I got a confused question. When I do some work about the MPLS TE, I
found I can not distinguish the different propuses of extended IGP and
RSVP. As I know, When used in MPLS TE, IGP is proposed to flood the
network resource information and let every MPLS hop getting the full
topology and calculate the best path with the CSPF. After that, the RSVP
is used to setup the path, namely LSP, with one hop by one hop
signaling. Am I right and making it clear?

If so, Does the RSVP's work is a must? I mean it's the IGP who announces
these resource information and make the paths calculations, then these
paths are there just like the common IP network working with normal IGP.
Please giving me some example of the RSVP is a must.

Sorry for my english, Thanks.