In traffic engineered networks, IGP-TE advertisements are used to distribute bandwidth availability on each link. This bandwidth availability information only accounts for RSVP-TE LSP set-ups and tear-downs. However, network deployments often have labeled traffic (other than RSVP-TE LSP) flowing on the same links as these RSVP-TE LSPs, in particular when MPLS Segment Routing (MPLS-SR) is deployed. The bandwidth consumed by this labeled traffic is often referred to as dark bandwidth.
The bandwidth consumed by, for example, MPLS-SR traffic is not accounted for in IGP-TE advertisements. This unaccounted-for traffic may result in suboptimal constrained routing decisions or contention for the access to the bandwidth resource. SR OS enables accounting for dark bandwidth in IGP-TE advertisement and provides the means to control the behavior of this accounting.
To configure dark bandwidth accounting:
Enable collection of traffic statistics for dark bandwidth, using the command configure>router>mpls>aux-stats sr
Only one keyword parameter is available (sr) for this command, so only MPLS-SR is considered as contributing to dark bandwidth.
Enable dark bandwidth accounting on each SE, using the command configure>router>rsvp>dbw-accounting
After dark bandwidth has been enabled, auxiliary statistics collection cannot be disabled. Dark bandwidth accounting must be disabled (no dbw-accounting) before auxiliary statistics collection can be disabled.
Configure the dark bandwidth accounting parameters to control the behavior of the system.
When dark bandwidth accounting is enabled, the system samples dark bandwidth at the end of every sample interval and computes an average after sample-multiplier samples. The system applies a multiplier (dbw-multiplier) to the computed average dark bandwidth and then determines whether an IGP-TE update is required based on whether one of the thresholds (up-threshold or down-threshold) has been crossed. If an IGP-TE advertisement is required, the bandwidth information is updated, considering that dark bandwidth has the highest priority among the eight available priorities. These thresholds represent a change of Maximum Reservable Bandwidth (OSPF) or Maximum Reservable Link Bandwidth (IS-IS) compared to the previously advertised bandwidth. These parameters are generally global parameters, but it is possible to override the global value of some parameters on a per-interface basis.
The show>router>rsvp>status command allows the user to view, on a global or per-interface basis, key values associated with the dark bandwidth accounting process.