Tuning ISIS-SPB LSP timers

Change LSP timer settings depending on network stability to increase the network convergence speed and protect CPU from unnecessary route recalculations.

Table 5: ISIS-SPB LSP timers

LSP timer	Functionality	Tuning guidelines
LSP lifetime	Sets the amount of time that an LSP can be retained in an LSDB.	Set the lifetime to a higher value than the LSP refresh interval.
LSP refresh interval and LSP generation timer	Control the update interval for an LSP.	Increase the interval to protect the CPU from frequent LSP generation. Decrease the interval for quick reaction to topology change events.
Minimum LSP transmit interval	Sets the minimum interval for transmitting LSPs out of an interface. You can also set the number of LSPs that can be sent at each interval.	Increase the interval to reduce LSP traffic in the network. Decrease the interval for quick LSDB synchronization.
Fast flooding of LSPs	Floods the first several LSPs that invoke SPF before SPF computation is started.	Enable this feature for quick LSDB synchronization.

Configuring the LSP lifetime

The LSP lifetime specifies the maximum amount of time for an LSP to be retained in an LSDB.

SPBM nodes add a lifetime in each LSP they have advertised. If an SPBM node does not receive an update for an LSP before its lifetime expires, the SPBM node removes the LSP from the LSDB.

To configure the maximum LSP lifetime:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter SPBM view.	spbm	N/A
3. Configure the maximum LSP lifetime.	timer lsp-max-age seconds	The default maximum LSP lifetime is 1200 seconds.

Tuning the LSP refresh interval and LSP generation timer

To prevent LSPs from age-out and synchronize LSDBs, ISIS-SPB performs periodic and event-driven LSP updates:

LSP refresh interval—Sets the interval at which ISIS-SPB regularly regenerates an LSP, regardless of whether any change has occurred to the LSP.
LSP generation timer—Sets the delay for ISIS-SPB to generate a new version of an LSP in response to an LSP change. For example, an update occurs because of a change in adjacency, interface metric value, system ID, or area address.

The LSP generation timer is an exponential generation timer. With this timer, ISIS-SPB quickly responds to the first events for an LSP and then slows down to protect the CPU from frequent LSP generation.

The LSP generation timer value is derived from the following parameters:

minimum-interval—Minimum LSP generation interval.
incremental-interval—Base number for the incremental interval.
maximum-interval—Maximum LSP generation interval.

When the network is stable, the LSP generation timer is set to the minimum interval for each LSP generation. When the network is unstable, the LSP generation timer increments by incremental-interval×2^n-² (n is the number of generation times) for each LSP generation until the maximum interval is reached. If an event triggers LSP generation after the maximum interval is reached, the LSP generation timer re-initiates with the minimum interval.

NOTE:

The network is considered unstable if the interval between consecutive LSP generation events is smaller than two times the maximum interval.

To tune the LSP refresh interval and the LSP regeneration timer parameters:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter SPBM view.	spbm	N/A
3. Configure the LSP refresh interval.	timer lsp-refresh seconds	The default refresh interval is 900 seconds.
4. Configure the LSP generation timer parameters.	timer lsp-generation maximum-interval [ minimum-interval [ incremental-interval ] ]	Default values for the LSP generation timer parameters: maximum-interval—2 seconds. minimum-interval—0 milliseconds. incremental-interval—0 milliseconds.

Configuring the minimum LSP transmit interval and the maximum number of LSPs sent at each interval

To control ISIS-SPB traffic on a circuit, tune the minimum interval for the device to transmit LSPs out of the circuit and the maximum number of LSPs sent at each interval. Before the minimum interval expires, newly generated LSP updates must wait in queue before they can be sent out.

To control ISIS-SPB traffic on the SPBM network:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Configure the minimum LSP transmit interval and the maximum number of LSP segments sent at each interval.	spbm timer lsp time [ count count ]	By default, the minimum LSP transmit interval is 33 milliseconds, and a maximum of five LSP segments can be sent at each interval.

NOTE:

ISIS-SPB requires acknowledgement for each LSP sent on a point-to-point circuit. ISIS-SPB will retransmit an LSP at 5-second interval until it receives an acknowledgement for the LSP. This retransmission interval is not user configurable.

Enabling fast flooding of LSPs

Fast flooding of LSPs enables ISIS-SPB to flood the first several LSPs that invoke SPF before SPF computation is started. This mechanism improves ISIS-SPB convergence time. The number of LSPs that can be fast flooded is user configurable.

To configure fast flooding of LSPs:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter SPBM view.	spbm	N/A
3. Configure fast flooding of LSPs.	flash-flood [ flood-count flooding-count \| max-timer-interval flooding-interval ] *	By default, fast flooding of LSPs is disabled.

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