Dynamic Data Persistency (DDP) Access Optimization for DHCP Leases

A high rate of DHCP renewals can create a load on the compact flash file system when subscriber management and DHCP server persistence is enabled. To optimize the access to the Dynamic Data Persistency (DDP) files on the compact flash, a lease-time threshold can be specified that controls the eligibility of a DHCP lease for persistency updates when no other data other than the lease expiry time is to be updated.

configure
    system
        persistence
            subscriber-mgmt
                location cf2:
            exit
            dhcp-server
                location cf2:
            exit
            options
                dhcp-leasetime-threshold [days <days>] [hrs <hours>] 
[min <minutes>] [sec <seconds>]
            exit
        exit
    exit

When the offered lease time of the DHCP lease is less than the configured threshold, the lease is flagged to skip persistency updates and is installed with its full lease time upon a persistency recovery after a reboot.

The dhcp-leasetime-threshold command controls persistency updates for:

To check if a DHCP relay or proxy lease is flagged to skip persistency updates, use the tools dump persistence submgt record record-key CLI command. When flagged to skip persistency updates, the persistency record output includes ‟Skip Persistency Updates: true”.

To check if a DHCP server lease is flagged to skip persistency updates, use the tools dump persistence dhcp-server record record-key CLI command. When flagged to skip persistency updates, the persistency record output includes ‟lease mode : LT” (LT = Lease Time) and a ‟lease time : …” field. When not flagged to skip persistency updates, the persistency record output includes ‟lease mode : ET” (ET = Expiry Time) and an ‟expires : …” field.