The isis memory-overload exception-threshold discard new-lsp command enables IS-IS to set the Overload bit in its LSP fragment zero (to be sent) to 1 and discard new LSPs (received) if the system memory is overloaded and the memory usage of the IS-IS LSDB component is not among the top 3.
The undo isis memory-overload exception-threshold discard new-lsp command disables this function.
By default, if the system memory is overloaded and the memory usage of the IS-IS LSDB component is not among the top 3, IS-IS does not set the Overload bit in its LSP fragment zero (to be sent) to 1 or discard new LSPs (received).
Usage Scenario
If the system memory is overloaded, each module needs to take necessary measures to control the memory usage increase or even reduce the memory usage. In this case, if the memory usage of the IS-IS LSDB component is among the top 3, IS-IS sets the Overload bit in its LSP fragment zero (to be sent) to 1 and discards new LSPs (received) by default to improve IS-IS resilience. However, if the memory usage of the IS-IS LSDB component is not among the top 3 and new IS-IS services are added, the IS-IS LSDB component will consume more memory resources, aggravating the system memory overload issue. To prevent the issue in this case, run the isis memory-overload exception-threshold discard new-lsp command, which enables IS-IS to set the Overload bit in its LSP fragment zero (to be sent) to 1 and discard new LSPs (received). To disable this function, run the undo isis memory-overload exception-threshold discard new-lsp command.
Prerequisites
IS-IS memory overload control has been enabled using the undo isis memory-overload control disable command.