Configuring LSP parameters
Configuring LSP timers
Specify the maximum age of LSPs.
Each LSP has an age that decreases in the LSDB. Any LSP with an age of 0 is deleted from the LSDB. You can adjust the age value based on the scale of a network.
To specify the maximum age of LSPs:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Specify the maximum LSP age. | timer lsp-max-age seconds | The default setting is 1200 seconds. |
Specify the LSP refresh interval and generation interval.
Each router needs to refresh its LSPs at a configurable interval and send them to other routers to prevent valid routes from aging out. A smaller refresh interval speeds up network convergence but consumes more bandwidth.
When the network topology changes, for example, a neighbor is down or up, or the interface metric, system ID, or area ID is changed, the router generates an LSP after a configurable interval. If such a change occurs frequently, excessive LSPs are generated, consuming a large amount of router resources and bandwidth. To solve the problem, you can adjust the LSP generation interval.
When network changes are not frequent, the minimum-interval is adopted. If network changes become frequent, the LSP generation interval is incremented by incremental-interval × 2n-2 (n is the number of calculation times) each time a generation occurs until the maximum-interval is reached.
To specify the LSP refresh interval and generation interval:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Specify the LSP refresh interval. | timer lsp-refresh seconds | By default, the LSP refresh interval is 900 seconds. |
4. Specify the LSP generation interval. | timer lsp-generation maximum-interval [ minimum-interval [ incremental-interval ] ] [ level-1 | level-2 ] | By default:
|
Specify LSP sending intervals.
If a change occurs in the LSDB, IS-IS advertises the changed LSP to neighbors. You can specify the minimum interval for sending these LSPs to control the amount of LSPs on the network.
On a P2P link, IS-IS requires an advertised LSP be acknowledged. If no acknowledgement is received within a configurable interval, IS-IS will retransmit the LSP.
To configure LSP sending intervals:
Step | Command | Remarks | |
|---|---|---|---|
1. Enter system view. | system-view | N/A | |
2. Enter interface view. | interface interface-type interface-number | N/A | |
3. Specify the minimum interval for sending LSPs and the maximum LSP number that can be sent at a time. | isis timer lsp time [ count count ] | By default, the minimum interval is 33 milliseconds, and the maximum LSP number that can be sent at a time is 5. | |
4. Specify the LSP retransmission interval on a P2P link. | isis timer retransmit seconds | By default, the LSP retransmission interval on a P2P link is 5 seconds. | |
Specifying LSP lengths
IS-IS messages cannot be fragmented at the IP layer because they are directly encapsulated in frames. IS-IS routers in an area must send LSPs smaller than the smallest interface MTU in the area.
If the IS-IS routers have different interface MTUs, configure the maximum size of generated LSP packets to be smaller than the smallest interface MTU in the area as a best practice. Otherwise, the routers must dynamically adjust the LSP packet size to fit the smallest interface MTU, which takes time and affects other services.
To specify LSP lengths:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Specify the maximum length of generated Level-1 LSPs or Level-2 LSPs. | lsp-length originate size [ level-1 | level-2 ] | By default, the maximum length of generated Level-1 LSPs or Level-2 LSPs is 1497 bytes. |
4. Specify the maximum length of received LSPs. | lsp-length receive size | By default, the maximum length of received LSPs is 1497 bytes. |
Enabling LSP flash flooding
Changed LSPs can trigger SPF recalculation. To advertise the changed LSPs before the router recalculates routes for faster network convergence, enable LSP flash flooding.
To enable LSP flash flooding:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Enable LSP flash flooding. | flash-flood [ flood-count flooding-count | max-timer-interval flooding-interval | [ level-1 | level-2 ] ] * | By default, LSP flash flooding is disabled. |
Enabling LSP fragment extension
Perform this task to enable IS-IS fragment extension for an IS-IS process. The MTUs of all interfaces running the IS-IS process must not be less than 512. Otherwise, LSP fragment extension does not take effect.
To enable LSP fragment extension:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter IS-IS view. | isis [ process-id ] [ vpn-instance vpn-instance-name ] | N/A |
3. Enable LSP fragment extension. | lsp-fragments-extend [ level-1 | level-1-2 | level-2 ] | By default, this feature is disabled. |
4. Configure a virtual system ID. | virtual-system virtual-system-id | By default, no virtual system ID is configured. Configure at least one virtual system to generate extended LSP fragments. |