Setting the Parameters of LSP

This describes how to set attributes such as the Link State PDUs (LSP) update period, LSP size, Mesh-Group feature, and LSP fragment extension. These attributes can be adjusted according to the actual condition of the IS-IS network.

Context

You can adjust attributes such as the LSP update period and packet size according to the actual condition of the IS-IS network.

LSPs are used to exchange link status information. To ensure the synchronization of the LSPs in the entire area, IS-IS sends all current LSPs periodically.
When the router generates the system LSP, the maximum validity period of the LSP is filled in the LSP. When the LSP is received by other routers, the validity period decreases as time goes by. If the router does not receive the update LSP, the validity period of the LSP decreases to 0. If a new LSP is not received after 60 seconds, the LSP is deleted from the LSDB.
On the NBMA network, if one interface of the router receives a new LSP, the LSP is flooded to other interfaces of the router. On the network with high interconnectivity and multiple point-to-point links, this processing mode causes the repetition of LSP flooding, resulting in the waste of bandwidths.

To avoid the previous problem, you can aggregate certain interfaces into a Mesh Group. The interfaces of the same group do not flood the LSP received by one interface of the local group to other interfaces in the group, but the interfaces of other groups or the interfaces that the Mesh Group is not configured.

Procedure

Configure the LSP update period.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the LSP update period.
  timer lsp-refresh refresh-interval
By default, the LSP refreshment period is 900 seconds, and the maximum lifetime of an LSP is 1200 seconds. When performing configurations, ensure that the LSP refresh interval is 300 seconds shorter than the maximum LSP Keepalive time. In this way, new LSPs can reach all routers in an area before existing LSPs expire.

The difference between the LSP update period and maximum validity period needs to be configured according to the actual network scale.
Set the maximum validity period.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the maximum validity period.
  timer lsp-max-age age-time
  
  When a router generates an LSP, it sets the max lifetime for the LSP. After the LSP is received by other routers, its lifetime decreases as time passes. If a router does not receive any updated LSP and the lifetime of this LSP decreases to 0, the lifetime of the LSP lasts 60s. If a new LSP is still not received, this LSP is deleted from the LSDB.
Set the used intelligent timer generated by the LSP.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the intelligent timer generated by the LSP.
  timer lsp-generation max-interval [ initial-interval [ incremental-interval ] ] [ level-1 | level-2 ]
- If the level is not specified, it regards that both Level-1 and Level-2 are specified at the same time.
- The delay for generating the same LSP (or LSP fragment) for the first time is init-interval, and the delay for generating the same LSP (or LSP fragment) for the second time is incr-interval. Subsequently, for each change, the delay time is twice that of the former change until the max-interval. The required delay keeps stable at the max-interval for three changes or the IS-IS process is restarted, the delay returns to the init-interval.
  
  If the incr-interval is not adopted, the init-interval is adopted as the delay time for the first generated same LSP (or LSP fragment). Then, the max-interval is adopted as the delay time. The required delay keeps stable at the max-interval for three changes or the IS-IS process is restarted, the delay returns to the init-interval.
- If only the max-interval is adopted, the intelligent timer turns into a common one-time triggering timer.
Configure the LSP size.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Set the size of the generated LSP.
  lsp-length originate max-size
4. Set the size of the received LSP.
  lsp-length receive max-size
- During the setting of parameter max-size, the max-size of the generated LSP must be smaller than or equal to the max-size of the received LSP.
- The max-size value configured through the lsp-length originate command must meet the following requirements; otherwise, the MTU status of the interface is regarded as Down.
  - The MTU value of the Ethernet interface must be larger than or equal to max-size + 3.
  - The MTU value of the P2P interface must be larger than or equal to max-size.
  To forward packets normally, you should ensure that the max-size value configured through the lsp-length receive command meets the same requirements.
Configure the Mesh-Group feature of the interface.
1. Access the system view.
  system-view
2. Access the interface view.
  interface interface-type interface-number
3. Add the interfaces to the mesh group.
  isis mesh-group { mesh-group-number | mesh-blocked }
On the Non Broadcast Multiple Access (NBMA) network, after receiving an LSP, the interface of a router floods the LSP to the other interfaces. In a network with higher connectivity and multiple P2P links, however, the flooding method causes repeated LSP flooding and wastes bandwidth.

To avoid the preceding problem, you can configure several interfaces to form a mesh group. The router in the mesh group does not flood the LSP received from an interface of the group to the other interfaces of the group, but floods it to interfaces of other groups or interfaces that do not belong to any group.

If parameter mesh-blocked is specified for the interface, the interface is blocked, and does not flood LSPs to the external. All the interfaces added into the Mesh Group ensure the synchronization of all the LSDBs on the entire network segment through the CSNP and PSNP mechanisms.
Configure the LSP fragment extension.
1. Access the system view.
  system-view
2. Access the IS-IS process view.
  isis [ process-id ]
3. Enable the LSP fragment extension of the IS-IS process.
  lsp-fragments-extend [ [ mode-1 | mode-2 ] | [ level-1 | level-2 | level-1-2 ] ]^*
4. Configure a virtual system.
  virtual-system virtual-system-id
- To make the router generate extended LSP fragments, at least one virtual system ID should be specified. The virtual system ID must be unique in the entire routing domain.
- A maximum of 50 virtual system IDs can be configured for each IS-IS process.
- During the configuration of the LSP fragment extension, if not being specified, the mode and level are mode-1 and level-1-2 respectively by default.