Bandwidth Management for RSVP-TE LSPs

If an RSVP-TE LSP is signaled through a switch with bandwidth parameters, the LSP bandwidth request is granted or rejected based on the availability of bandwidth resources on the physical ports that the LSP traverses.

Data traffic through these switches is not policed and there are no guarantees that the packets using the LSP are not dropped.

Note

Per LSP rate limiting is not supported in this release.

The available bandwidth for each OSPF (Open Shortest Path First) interface is continually updated within the OSPF area. As RSVP-TE LSPs are established and torn down, the reserved bandwidth associated with these LSPs is used to update the total bandwidth available through each OSPF interface. RSVP-TE and CSPF can use the bandwidth information to determine the appropriate path that each LSP should take through the network based on the LSP's profile parameters. LSP parameters that can affect the CSPF TE path calculation include the LSP setup priority and bandwidth configuration.

Available bandwidth is calculated for eight CoS (Class of Service) levels. Each CoS uniquely maps to an LSP hold priority. Thus, when an LSP is set up through the switch, the reserved bandwidth consumed is associated with a CoS based on the signaled LSP hold priority. The available bandwidth is recalculated and is advertised to its OSPF neighbors. Advertised bandwidth is calculated using graduated bandwidth reporting methodology. Using this scheme, higher CoS levels advertise available bandwidth that includes allocated bandwidth for lower CoS levels. The reasoning for doing this is that higher priority LSPs can preempt lower priority LSP. Thus, even though the bandwidth has been allocated to a lower priority LSP, it is still available for use by higher priority LSPs.

In the following example, an interface is configured to reserve 250 Mbps for MPLS (Multiprotocol Label Switching) traffic.

The following LSPs are established through this interface. Remember, hold priority value of 0 is the highest priority and 7 is the lowest.

LSP A, hold priority = 7, reserved = 50 Mbps
LSP B, hold priority = 5, reserved = 100 Mbps
LSP C, hold priority = 2, reserved = 25 Mbps
LSP D, hold priority = 1, reserved = 25 Mbps

OSPF advertises the following available bandwidth for each CoS.

CoS 0 is the highest and CoS 7 is the lowest:

CoS 0 (hold = 0): 250 Mbps (No LSPs; all bandwidth available)
CoS 1 (hold = 1): 225 Mbps (LSP D)
CoS 2 (hold = 2): 200 Mbps (LSP C & D)
CoS 3 (hold = 3): 200 Mbps (LSP C & D)
CoS 4 (hold = 4): 200 Mbps (LSP C & D)
CoS 5 (hold = 5): 100 Mbps (LSP B, C & D)
CoS 6 (hold = 6): 100 Mbps (LSP B, C & D)
CoS 7 (hold = 7): 50 Mbps (LSP A, B, C & D)

CSPF calculations only use the available bandwidth for the desired CoS, as specified by the LSP hold priority. Thus in this example, if LSP E, with a configured setup priority of 6, requires 150 Mbps, CSPF calculates a path to the destination that does not go through the above interface, since only 100 Mbps worth of bandwidth is available.

Published March 2020prev | next

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