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DiffServ-Aware Traffic Engineered LSPs Operation

When configuring a DiffServ-aware traffic engineered LSP, you specify the class type and the bandwidth associated with it. The following occurs when an LSP is established with bandwidth reservation from a specific class type:

The IGPs advertise how much unreserved bandwidth is available for the traffic engineering classes.
When calculating the path for an LSP, CSPF is used to ensure that the bandwidth constraints are met for the class type carried by the LSP at the specified priority level.
CSPF also checks to ensure that the bandwidth model is configured consistently on each router participating in the LSP. If the bandwidth model is inconsistent, CSPF does not compute the path (except for LSPs from class type ct0).
Once a path is found, RSVP signals the LSP using the Classtype 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.

An LSP that requires bandwidth from a particular class (except class type ct0) cannot be established through routers that do not understand the Classtype object. Preventing the use of routers that do not understand the Classtype object helps to ensure consistency throughout the Differentiated Services domain by preventing the LSP from using a router that cannot support Differentiated Services.

By default, LSPs are signaled with setup priority 7 and holding priority 0. An LSP configured with these values cannot preempt another LSP at setup time and cannot be preempted.

It is possible to have both LSPs configured for DiffServ-aware traffic engineering 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 (either by remarking the EXP settings or by assuming that the traffic arrived with the correct EXP settings from the upstream router).

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