Setting Flooding Parameters of SNPs and LSPs

To speed up LSDB synchronization between devices, set flooding parameters of SNPs and LSPs to proper values.

Context

SNPs consist of CSNPs and PSNPs. CSNPs carry summaries of all LSPs in LSDBs, ensuring LSDB synchronization between neighboring routers. SNPs are processed differently on broadcast links and P2P links.

On a broadcast link, CSNPs are periodically sent by a DIS device. If a router detects that its LSDB is not synchronized with that on its neighboring router, the router will send PSNPs to apply for missing LSPs.
On a P2P link, CSNPs are sent only during initial establishment of neighbor relationships. If a request is acknowledged, a neighboring router will send a PSNP in response to a CSNP. If a router detects that its LSDB is not synchronized with that on its neighboring router, the router will send PSNPs to apply for missing LSPs.

To speed up LSDB synchronization, perform the following operations on the NetEngine 8000 F:

Set an interval at which CSNPs are sent.
Configure the intelligent timer to control LSP generation.
Set the size of an LSP.
Set the LSP update interval.
Set the maximum lifetime for LSPs.
Set the maximum holdtime for the largest IS-IS route cost in local LSPs.
Enable LSP fast flooding.
Set an interval at which LSPs are retransmitted over a P2P link.
Configure automatic IS-IS LSP Remaining Lifetime adjustment.

Procedure

Set an interval at which CSNPs are sent.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run isis timer csnp csnp-interval [ level-1 | level-2 ]
  The interval at which CSNPs are sent is set on the specified interface.
  
  Configure Level-1 and Level-2 only when a broadcast interface is specified.
4. Run commit
  The configuration is committed.
Configure the intelligent timer to control LSP generation.
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 is configured to control LSP generation.
  Before using the timer lsp-generation command, note the following:
  - When only max-interval is specified, the intelligent timer functions as a one-shot timer.
  - If init-interval and incr-interval are specified, init-interval is used as the LSP generation interval for the first time, and incr-interval is used as the LSP generation interval for the second time. From the third time on, the LSP generation interval doubles each time until the interval reaches max-interval. If the local routing information keeps being updated within the max-interval period, the interval remains at max-interval until the time the local routing information is not updated within the max-interval period or the IS-IS process is restarted. Then the interval decreases to init-interval.
  - If init-interval is specified, but incr-interval is not, init-interval is used as the LSP generation interval for the first time, and then max-interval is used as the interval. If the local routing information keeps being updated within the max-interval period, the interval remains at max-interval until the time the local routing information is not updated within the max-interval period or the IS-IS process is restarted. Then the interval decreases to init-interval.
4. Run commit
  The configuration is committed.
Set the size of an LSP.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. Run lsp-length originate max-size
  The size of an LSP to be generated is set.
4. Run lsp-length receive max-size
  The size of an LSP to be received is set.
  
  max-size of an LSP to be generated must be less than or equal to max-size of an LSP to be received.
  The value of max-size in the lsp-length command must meet the following conditions.
  - The MTU of an Ethernet interface must be greater than or equal to the sum of the value of max-size plus 3.
  - The MTU of a P2P interface must be greater than or equal to the value of max-size.
5. Run commit
  The configuration is committed.
Set the LSP update interval.
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-value
  An LSP update interval is set.
  
  To synchronize all LSPs in the areas, IS-IS regularly transmits all the current LSPs to neighbors.
  
  Ensure that the LSP update interval is at least 300s shorter than the maximum LSP lifetime so that new LSPs can reach all devices in an area before existing LSPs expire.
  
  The larger a network, the greater the deviation between the LSP update interval and the maximum LSP lifetime.
4. Run commit
  The configuration is committed.
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 max-age-value
  The maximum lifetime is set for LSPs.
  
  When a device generates the system LSP, it fills in the maximum lifetime for this LSP. The lifetime of the LSP decreases with time. If the device does not receive any updated LSPs and the lifetime of the LSP is reduced to 0, the device keeps the LSP for another 60s. If the device fails to receive any updated LSPs within the 60s, it deletes the LSP from the LSDB.
4. Run commit
  The configuration is committed.
Set the maximum holdtime for the largest IS-IS route cost in local LSPs.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run isis [ process-id process-id ] peer hold-max-cost timer timer-val
  The maximum holdtime for the largest IS-IS route cost in local LSPs is set.
  
  When a Down IS-IS interface goes Up, IS-IS neighbor relationships are re-established on the interface, and traffic is switched back to this Up interface after IGP route convergence. IGP route convergence is fast, but many services that depend on IGP routes may not expect such fast traffic switchback. To delay traffic switchback after IGP route convergence, run the isis peer hold-max-cost command to set the maximum holdtime for the largest IS-IS route cost (16777214 in wide mode and 63 in narrow mode) in local LSPs. In this manner, before the specified maximum holdtime expires, traffic is not switched back to this route due to its large cost. After the specified maximum holdtime expires, the route cost reverts to the original value, and then traffic is switched back to this route.
4. (Optional) Run isis peer hold-cost cost-val timer timer-val
  The period during which IS-IS keeps the specified cost in local LSPs is set.
5. Run commit
  The configuration is committed.
Enable LSP fast flooding.
1. Run system-view
  The system view is displayed.
2. Run interface interface-type interface-number
  The interface view is displayed.
3. Run isis timer lsp-throttle throttle-interval [ count count ]
  The minimum interval at which LSPs are sent by the interface and the maximum number of LSPs that can be sent within the interval are set.
  
  The count parameter specifies the maximum number of LSPs that can be sent within the interval specified by throttle-interval. The value of count is an integer ranging from 1 to 1000.
4. Run commit
  The configuration is committed.
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) Run isis circuit-type p2p
  The broadcast interface is simulated as a P2P interface.
  
  An interval at which LSPs are retransmitted takes effect only on P2P interfaces. Therefore, to configure the interval on a broadcast interface, change the broadcast interface to a P2P interface first.
4. Run isis timer lsp-retransmit retransmit-interval
  The interval at which LSPs are retransmitted over a P2P link is set.
5. Run commit
  The configuration is committed.
Configure automatic IS-IS LSP Remaining Lifetime adjustment.
1. Run system-view
  The system view is displayed.
2. Run isis [ process-id ]
  The IS-IS view is displayed.
3. (Optional) Run undo lsp-remaining-lifetime refresh disable
  Automatic IS-IS LSP Remaining Lifetime adjustment is enabled.
4. Run lsp-remaining-lifetime refresh timer { refreshvalue | lsp-max-age }
  An IS-IS LSP Remaining Lifetime value is set.
5. Run commit
  The configuration is committed.