Configuring Attributes for LSPs

Context

LSPs are used to exchange link state information. You can configure attributes for LSPs to control the length and maximum lifetime of LSPs. To accelerate network convergence, you can enable LSP fast flooding or reduce the minimum interval for sending LSPs and the interval for updating LSPs to speed up LSP flooding. However, too many CPU resources will be consumed if the network topology changes frequently. In this situation, configure the intelligent timer for generating LSPs. This timer can quickly respond to emergencies, speed up network convergence, and improve CPU resource efficiency because its interval becomes longer when the network changes frequently. The function and implementation of different parameter configurations are shown in the following table.

Parameter Configuration	Function	Implementation
Set the maximum length for LSPs	Set the size for LSPs to be generated and LSPs to be received.	When the volume of link status information increases, the length of LSPs to be generated can be increased to carry more information in each LSP.
Set the maximum lifetime for LSPs	Set the maximum lifetime for LSPs to ensure the validity of an LSP before its updated LSP is received.	When a switch generates the system LSP, it fills in the maximum lifetime for this LSP. After this LSP is received by other switches, the lifetime of the LSP is reduced gradually. If the switch does not receive any more update LSPs and the lifetime of the LSP is reduced to 0, the LSP will be deleted from the LSDB 60s later if no more updated LSPs are received.
Set the refresh interval for LSPs	Set the refresh interval for LSPs to synchronize LSDBs.	On an IS-IS network, LSDB synchronization is implemented through LSP flooding. During LSP flooding, a switch sends an LSP to its neighbors and then the neighbors send the received LSP to their respective neighbors except the switch that first sends the LSP. In this manner, the LSP is flooded among the switches of the same level. LSP flooding allows each switch of the same level to have the same LSP information and synchronize its LSDB with each other.
Set the minimum interval at which LSPs are sent	Set the interval for sending an LSP during LSP update.	Reducing the minimum interval for sending LSPs speeds up LSP flooding.
Configure the intelligent timer used to generate LSPs	Control the interval for generating LSPs intelligently to speed up route convergence and reduce system load.	On an IS-IS network, if the local routing information changes, a switch needs to generate a new LSP to notify this change. If the local routing information changes frequently, a large number of new LSPs are generated. This occupies a lot of system resources and decreases system performance. To speed up network convergence and prevent system performance from being affected, configure an intelligent timer for generating LSPs. This timer can adjust the delay in generating LSPs based on the routing information change frequency.
Enable LSP fast flooding	Control the number of LSPs flooded each time on an interface to speed up IS-IS network convergence.	When an IS-IS switch receives new LSPs from other switches, it updates the LSPs in the local LSDB and periodically floods out the updated LSPs according to a timer. LSP fast flooding updates the preceding method. When a device configured with LSP fast flooding receives one or more new LSPs, it floods out the LSPs with a number smaller than the specified number before calculating routes. This speeds up LSDB synchronization.
Set an interval at which LSPs are retransmitted over a P2P link	Control the interval for retransmitting LSPs to ensure LSDB synchronization on a P2P network.	On a point-to-point network, devices at both ends of a link synchronize LSDBs with each other by flooding LSPs. The device at one end of the link sends an LSP. If the device at the other end receives this LSP, it replies with a PSNP. If the device that has sent an LSP does not receive a PSNP from the other end in a period of time, the device will retransmit the LSP.

Procedure

Set the maximum length for LSPs.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Set the maximum length for LSPs.
  - Run lsp-length originate max-size
    The maximum length is set for each generated LSP.
  - Run lsp-length receive max-size
    The maximum length is set for each received LSP.
  By default, the IS-IS system generates and receives 1497-byte LSPs.
  Ensure that the value of max-size for LSPs to be generated is less than or equal to the value of max-size for LSPs to be received.
  The value of max-size set through the lsp-length command must meet the following requirements; otherwise, the MTU status on the interface is considered Down.
  The MTU of an Ethernet interface must be greater than or equal to the sum of the value of max-size and 3.
  
  The MTU of a P2P interface must be greater than or equal to the value of max-size.
Set the maximum lifetime for LSPs.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run timer lsp-max-age age-time
  The maximum lifetime is set for LSPs.
  
  By default, the maximum lifetime of LSPs is 1200 seconds.
Set the refresh interval for LSPs.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run timer lsp-refresh refresh-time
  A refresh interval is set for LSPs.
  
  By default, the LSP refresh interval is 900s.
  
  Ensure that the LSP refresh interval is at least 300s less than the maximum LSP lifetime. This allows new LSPs to reach all devices in an area before existing LSPs expire.
  
  The larger a network, the greater the deviation between the LSP refresh interval and the maximum LSP lifetime.
Set the minimum interval at which LSPs are sent.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. Run isis timer lsp-throttle throttle-interval [ count count ]
  The minimum interval for sending LSPs on an IS-IS interface and the maximum number of LSPs sent within the interval are set.
  
  By default, the minimum interval for sending LSPs is 50 ms, and the maximum number of LSPs sent each time is 10.
Configure the intelligent timer used to generate LSPs.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run timer lsp-generation max-interval [ init-interval [ incr-interval ] ] [ level-1 | level-2 ]
  The intelligent timer used to generate LSPs is set.
  
  If no level is configured, both Level-1 and Level-2 are configured.
  
  The initial delay for generating the same LSPs (or LSP fragments) is init-interval. The delay for generating the same LSPs (or LSP fragments) in the next iteration is incr-interval. When the routes change each time, the delay for generating the same LSPs (or LSP fragments) is twice as the previous value until the delay is up to max-interval. After the delay reaches max-interval for three times or the IS-IS process is reset, the interval is reduced to init-interval.
  
  When incr-interval is not used and the same LSPs (or LSP fragments) are generated for the first time, init-interval is used as the initial delay. Then, the delay for generating the same LSPs (or LSP fragments) is max-interval. After the delay reaches max-interval for three times or the IS-IS process is reset, the interval is reduced to init-interval.
  
  When only max-interval is used, the intelligent timer changes into a normal one-short timer.
Enable LSP fast flooding.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run flash-flood [ lsp-count | max-timer-interval interval | [ level-1 | level-2 ] ]^*
  The LSP fast flooding is enabled.
  
  The lsp-count parameter specifies the number of LSPs flooded each time, which is applicable to all interfaces. If the number of LSPs to be sent is greater than the value of lsp-count, lsp-count takes effect. If the number of LSPs to be sent is less than the value of lsp-count, all the LSPs are sent. If a timer is configured and the configured timer does not expire before the route calculation, the LSPs are flooded immediately when being received; otherwise, the LSPs are sent when the timer expires.
  
  When LSP fast flooding is enabled, Level-1 LSPs and Level-2 LSPs are fast flooded by default if no level is specified.
Set an interval at which LSPs are retransmitted over a P2P link.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. (Optional) On an Ethernet interface, run undo portswitch
  The interface is switched to Layer 3 mode.
  
  By default, an Ethernet interface works in Layer 2 mode.
  
  Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.
4. (Optional) Run isis circuit-type p2p [ strict-snpa-check ]
  A broadcast interface is simulated as a P2P interface.
  
  If the interface type is P2P, this step is not required.
5. Run isis timer lsp-retransmit retransmit-interval
  The interval at which LSPs are retransmitted over a P2P link is set.
  
  By default, the interval for retransmitting LSPs over a P2P link is 5 seconds.