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OSPF TE topology, CBSPF look up

Hi everybody , Please consider the following scenario: We are using OSPF with TE enabled R1 ( the ingress LSR) needs to compute the LSP to reach with the following constraint: BW along the path should not be less than 20 Mig. 1)Will R1 only looks for the path that has least TE metric? 2) Will R1 first look for the all the paths which meet the constraint ( 20 Mig along the path) and then picks the one with the least TE metric? I appreciate your help
  • MPLS

Hi everybody I found the

Hi everybody


I found the answer,thanks to a good link on mpls by Jeff Doyle:


Just putting it here just in case if someone has a similar question




It can be bandwidh( most common), affinity ( aka coloring of the link) etc


If none constraints specified, ingress LSR  checks the TE topology and computes the shortest path based on TE cost If constraint such as bandwidth is specified, ingress first finds all the possible path to reach a particular destination, and then picks the one with the lowest TE metric.


In my example, R1 first finds all the possible paths meeting the constraint imposed ( 20 mig) and then selects the one with the least TE cost.





Have a great day


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