Auto-Bandwidth with RSVP-TE
Overview
Automatic bandwidth allows to dynamically adjust bandwidth reservation based on the measured traffic. RSVP automatic bandwidth monitors the traffic rate on a Label Switched Path (LSP) and resizes the bandwidth to align it closely with the traffic in the tunnel. RSVP automatic bandwidth is configured on individual LSPs at every headend router.
Auto bandwidth can be added to an operational LSP at any time, but no bandwidth change occurs until a future trigger event or auto bandwidth profile configured with initial bandwidth or minimum bandwidth. Auto bandwidth may also be removed from an operational LSP at any time and this would re-signal the LSP with no bandwidth reservation.
Feature Characteristics
The characteristics of the RSVP auto-bandwidth are:
| • | RSVP-TE auto bandwidth provides the means to automatically adjust the bandwidth allocation for traffic engineering tunnels based on their measured traffic load. |
| • | This feature samples the average output rate for each tunnel marked for automatic bandwidth adjustment. For each marked tunnel, this feature periodically adjusts the tunnel's allocated bandwidth to the largest eligible sample for the tunnel since the last adjustment. |
| • | The frequency with which tunnel bandwidth is adjusted and the allowable range of adjustments should be configurable on a per-auto-bandwidth profile basis. |
| • | In addition, the sampling interval and the interval over which to average tunnel traffic to obtain the average output rate is user-configurable on a per-auto-bandwidth profile basis. |
| • | Convergence on redundancy may require bidirectional traffic or MAC aging. |
| • | The feature relies on stat_id allocation to tunnel entities, and there is a limit on the maximum number of stat_ids (which varies based on the chip variant). If a tunnel is not associated with a stat entity, traffic rate samples cannot be fetched for those tunnels. |
| • | RSVP Graceful Restart is not supported for automatic bandwidth. When a GR is performed, RSVP will not store the current bandwidth for the reservation. It will use either the initial bandwidth (if configured), the minimum bandwidth, or the highest bandwidth of the on-boot sample (if auto-bandwidth-on-boot is configured). |
| • | The auto bandwidth feature relies on the hardware's ability to collect tunnel traffic counters. In Qumran1 devices, the “hardware-profile statistics tunnel-lif enable” command must be enabled, and the system must be reloaded for the change to take effect. Without the tunnel statistics profile, auto bandwidth will not process traffic rates and will be ineffective. Note that, only 2 statistics profiles shall be configured as this is the hardware limitation. |
| • | Auto bandwidth and manual bandwidth configurations are mutually exclusive. Auto bandwidth allows for configuring an initial bandwidth, which will be used as the session's initial bandwidth when auto bandwidth is associated with a trunk. If the initial bandwidth is not configured, the minimum bandwidth will be used to initialize the session bandwidth. |
| • | For tunnels with only one hop, the no PHP (default config) must be set for the rate to be computed correctly. |
Benefits
In large MPLS transport networks in service provider settings with this capability:
| • | The network can react faster to sudden bursts of traffic in near real-time and not rely on manual intervention. |
| • | Effective use of bandwidth resources by minimizing the over-subscription/padding of LSP bandwidth. |
| • | Maximizes the usage of available bandwidth and optimizes the network effectively to use preferred, shorter latency, paths first. |