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Establishing a Multiclass LSP on the Differentiated Services Domain
The following occurs when a multiclass LSP is established on the differentiated services domain:
- The IGPs advertise how much unreserved bandwidth is available for the traffic engineering classes.
- When calculating the path for a multiclass LSP, CSPF is used to ensure that the constraints are met for all the class types carried by the multiclass LSP (a set of constraints instead of a single constraint).
- Once a path is found, RSVP signals the LSP using an RSVP object in the path message. At each node in the path, the available bandwidth for the class types is adjusted as the path is set up. The RSVP object is a hop-by-hop object. Multiclass LSPs cannot be established through routers that do not understand this object. Preventing routers that do not understand the RSVP object from carrying traffic helps to ensure consistency throughout the differentiated services domain by preventing the multiclass LSP from using a router that is incapable of supporting differentiated services.
By default, multiclass LSPs are signaled with setup priority 7 and holding priority 0. A multiclass LSP configured with these values cannot preempt another LSP at setup time and cannot be preempted.
It is possible to have both multiclass LSPs and regular LSPs configured at the same time on the same physical interfaces. For this type of heterogeneous environment, regular LSPs carry best-effort traffic by default. Traffic carried in the regular LSPs must have the correct EXP settings.
