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Configuring Optimized Auto-bandwidth Adjustments for MPLS LSPs

 

Auto-bandwidth functionality enables the RSVP-TE LSPs, either directly configured or automatically created using auto-mesh, to re-size based on the traffic rate. The traffic rate carried on each LSP is measured by periodically collecting samples of the traffic rate. The frequency of traffic statistics collection is controlled through the adjust-interval configuration statement. The minimum configurable value of adjust-interval is 300 seconds and the minimum configurable statistics interval is 1 second. The re-sizing of the LSPs is called adjustment and the frequency of adjustments is controlled through the adjust-interval statement.

Starting in Junos OS Release 20.4R1, the you can configure adjust-threshold-overflow-limit or adjust-threshold-underflow-limit only if the product of statistics interval and adjust-threshold-overflow-limit or adjust-threshold-underflow-limit less than or equal to 150 seconds. Therefore, it is required that:

statistics interval x adjust-threshold-overflow-limit or adjust-threshold-underflow-limit<= 150s

These values are checked during the commit operation. An error is returned if the value is less than 150 seconds.

Prior to Junos OS Release 20.4R1, the value for statistics interval x adjust-threshold-overflow-limit or adjust-threshold-underflow-limit is less than or equal to 300 seconds.

However, the minimum adjust-interval for an auto-bandwidth adjustment is 300 seconds if no overflow or underflow sample is detected.

In releases earlier than Junos OS Release 20.4R1, the adjust-interval is 300 seconds under overflow or underflow conditions.

With the implementation of auto-bandwidth adjustment optimization, the auto-bandwidth decreases the bandwidth of the LSP faster. The ingress label edge router (LER) is able to resize within 150 seconds because of the reduction in adjust-threshold-overflow-limit, provided the tear down of an old LSP instance post make-before-break (MBB) is accomplished within 150 seconds.

To optimize auto-bandwidth it is desirable to:

  • Reduce the probability of LSP route change—This is to reduce the probability of LSP route change when an auto-bandwidth adjustment occurs.

  • Reduce the probability of LSP reroute—This is to reduce the probability of the LSP reroute because of the higher priority LSPs that demand the same resource.

Therefore, auto-bandwidth adjustments optimization supports the following:

  1. In-place LSP Bandwidth Update—Enables the ingress label edge router (LER) to to reuse the existing LSP instance when signaling the bandwidth change on the LSP.

    Note

    In-place LSP bandwidth update is not applicable for an inter-domain LSP.

    In certain scenarios, the LSP route next hop carries the LSP bandwidth either directly or indirectly. Even though in-place LSP bandwidth update is supported in these scenarios, the performance improvement from the functionality is limited because of the LSP route change. That is, because of the change in the inet.3 route table after auto-bandwidth (MPLS Tunnel). For example, performance enhancement is limited when you configure either or both the statements:

    • auto-policing configured under MPLS.

    • The option bandwidth under the statement load-balance configured under RSVP.

    Note

    In-place LSP bandwidth update through LSP-ID reuse fails and the ingress LER immediately triggers MBB with a new LSP-ID if:

    • no-cspf is configured for the LSP.

    • LSP is controlled by the Path Computation Element (PCE).

    • LSP optimization timer fires.

    • clear mpls lsp optimize-aggressive command is executed.

  2. Per-priority Subscription—In order to utilize the network resources more efficiently, per-priority subscription enables you to configure a lower RSVP subscription percentage for LSPs of lower priorities.

    For example, instead of setting RSVP subscription percentage as 90% for LSPs for all priorities, you can configure a lower RSVP subscription percentage (say 75%) for LSPs of lower priorities

Note

Per-priority subscription does not interoperate with Differentiated Services (DiffServ)-aware traffic engineering (TE). Differentiated Services (DiffServ)-aware traffic engineering offers more flexible and statistical sharing of TE link bandwidth than per-priority subscription.

To Configure In-place LSP Auto-bandwidth Resizing:

  1. Configure the device interface to enable MPLS.
  2. Configure MPLS protocol on the interface.
  3. Configure MPLS and the LSPs and configure link protection for the LSP.
  4. Configure in-place-bandwidth-update for the LSP to enable automatic bandwidth LSP resizing.
  5. Enter commit from the configuration mode.

Verification

From configuration mode, confirm your configuration by entering the, show protocols show interfaces commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

To Configure Per-priority Subscription:

  1. Configure RSVP protocol on the interface.
  2. Configure the bandwidth subscription value for the interface. It can be a value from 0 through 65,000 percent. The default subscription value is 100 percent.
  3. Configure the subscription priority over the interface.
  4. Configure the subscription percentage for the priority.
  5. Enter commit from the configuration mode.

Verification

From configuration mode, confirm your configuration by entering the, show protocols show interfaces commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.