timer lsp-refresh (IS-IS view)

Usage Scenario

Link states on an IS-IS network are synchronized through LSP flooding. The flooding of LSPs is a mode in which a device sends an LSP to its neighboring devices and the neighboring devices send the received LSP to their respective neighbors except the device that first sends the LSP. In this manner, the LSP is flooded among the devices of the same level. By this flooding, each device of the same level can learn the same LSP information to synchronize its LSDB.

The flooding of LSPs needs to be refreshed periodically, because when a device generates the system LSP, it fills in the maximum lifetime for this LSP. After other devices receive this LSP, the Keepalive time of the LSP is reduced continuously. If a device does not receive any more refreshed LSPs and the lifetime of the LSP is reduced to 0, the LSP will be deleted 60s later if no more new refreshed LSPs are received.

The timer lsp-refresh command configures an LSP refresh interval to keep the LSPs valid and control the network convergence speed.

Prerequisites

An IS-IS process has been created using the isis command.

Configuration Impact

If the LSP refresh interval is too short, the LSPs will be refreshed frequently, which causes excessive usage of bandwidth; If the refresh interval of LSPs is too long, the network cannot receive information about changes of link states in time.

Precautions

The LSP refresh interval must be at least 300 seconds shorter than the maximum Keepalive time of an LSP specified in the timer lsp-max-age command. In this manner, new LSPs can reach all devices in an area before old LSPs expire.