Vyatta Network OS Documentation

Learn how to install, configure and operate the Vyatta NOS, which helps drive our virtual networking & physical platforms portfolio.

Disabling CSPF path calculations

By default, CSPF is enabled for signaled LSP calculations, but you can disable CSPF. For example, to allow a TE tunnel LSP to traverse OSPF areas, disable CSPF.

Disabling CSPF means that the full CSPF path is not computed up front. Instead, the vRouter queries the RIB for the next-hop information. This information is needed to reach the egress vRouter. Then, the vRouter sends the RSVP PATH message to the next hop without an Explicit Route Object (ERO). A similar process occurs at each hop along the path.

If you configure a full or partial explicit path, the vRouter queries the RIB for the next-hop information to reach the first hop in the explicit path. The vRouter sends the RSVP PATH message with an ERO whose first hop is the actual first next hop, and whose subsequent hops are from the configured path. Each hop along the path removes the first hop from the ERO and performs a RIB lookup on the next hop in the list.

Note: If you configure constraints for a CSPF path, the next hop returned by the RIB query must meet the configured constraints or the session fails to come up—no alternative path can be found when CSPF is disabled. Each hop along the path checks whether its next hop meets any constraints present in the PATH message.

To disable constraint-based path selection for a TE tunnel, use the following command:

set protocols mpls-rsvp tunnels tunnel name { primary | secondary } no-cspf

For example, to disable constraint-based path selection for the primary and secondary path options for tunnel1, a TE tunnel, enter the following commands:
vyatta@vyatta# set protocols mpls-rsvp tunnels tunnel tunnel1 primary no-cspf
vyatta@vyatta# set protocols mpls-rsvp tunnels tunnel tunnel1 secondary no-cspf
vyatta@vyatta# commit
To verify that CSPF is disabled, run the following command:
vyatta@vyatta# show mpls rsvp session detail
Ingress (Primary) 
6.6.6.6
  From: 1.1.1.1, LSPstate: Up, LSPname: tunnel1 
  Ingress FSM state: Operational 
  Setup priority: 7, Hold priority: 0 
  CSPF usage: Disabled 
  Reoptimization: Disabled 
  IGP-Shortcut: Disabled, LSP metric: 65 
  LSP Protection: None
  Label in: -,  Label out: -
  Tspec rate: 0, Fspec rate: 0
  ...