System Management
7750 SR OS Basic System Configuration Guide Page 223
Persistence
The persistence feature allows information learned through DHCP snooping across reboots to be
kept. This information can include data such as the IP address, MAC binding information, lease-
length information, and ingress sap information (required for VPLS snooping to identify the
ingress interface). This information is referred to as the DHCP lease-state information.
When a DHCP message is snooped, there are steps that make the data persistent in a system with
dual CPMs. In systems with only one CPM, only Step 1 applies. In systems with dual CPMs, all
steps apply.
1. When a DHCP ACK is received from a DHCP server, the entry information is written to the
active CPM Compact Flash. If writing was successful, the ACK is forwarded to the DHCP
client. If persistency fails completely (bad cflash), a trap is generated indicating that persis-
tency can no longer be guaranteed. If the complete persistency system fails the DHCP
ACKs are still forwarded to the DHCP clients. Only during small persistency interruptions or
in overload conditions of the Compact Flash, DHCP ACKs may get dropped and not for-
warded to the DHCP clients.
2. DHCP message information is sent to the standby CPM and also there the DHCP informa-
tion is logged on the Compact Flash. If persistency fails on the standby also, a trap is gener-
ated.
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