DHCP State Persistence

The extended DHCP relay agent maintains the state of active DHCP client leases in persistent storage on the router. It can recover this state if the DHCP relay agent process fails or is manually restarted, or if you manually reboot (gracefully shut down) the router. DHCP state persistence prevents the loss of active DHCP clients in either of these circumstances. If a power failure occurs or if the kernel stops operating on a single Routing Engine, however, the state of active DHCP client leases is lost.

DHCP state persistence is automatically enabled when you configure the extended DHCP relay agent on the router by including the dhcp-relay statement.

The DHCP relay agent records in persistent storage only those DHCP clients that are fully bound, which means that they currently have an active lease on an IP address from a DHCP server. DHCP clients in a renewal or rebind state are considered to be fully bound, and their state is also maintained in persistent storage. When a DHCP client lease expires or the client is released, the DHCP relay agent removes the client state from persistent storage.

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