Features

When a router running in an IS-IS domain restarts, it typically causes routers in that domain to reset their adjacencies, thus generating unnecessary LSP flooding and shortest-path-first (SPF) calculations throughout the domain. Enabling graceful restart minimizes these effects by providing a mechanism by which a restarting router can do the following:

• Notify neighboring IS-IS routers that it is restarting and request help resynchronizing its LSP database. Neighbors with active adjacencies to the restarting router can thereby reestablish these adjacencies without having to reset them.
• Determine when complete LSP database synchronization with its neighbors has occurred.
• Optimize the process of LSP database synchronization while minimizing temporary routing disruption.

IS-IS graceful restart on E-series routers supports both restart and helper capabilities. These capabilities mean that an E-series router can not only notify neighboring IS-IS routers that it is restarting and request help resynchronizing its LSP database, but can also cooperate with other restarting routers to help them with the restart process.

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