System Management
Basic System Configuration Guide 249
Figure 12: Management Ethernet: Redundancy Mode (FID 120 placeholder)
Persistence
The persistence feature on the 7750 SR 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 persistency 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 forwarded to the DHCP clients.
2. DHCP message information is sent to the standby CPM and also there the DHCP
information is logged on the Compact Flash. If persistency fails on the standby also,
a trap is generated.
Active
CPM
Standby
CPM
X
Management
Network
Management Ethernet:
Down
Management Ethernet:
IP Address of Active
IP Address of Standby
25168
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