Dell PowerConnect 7048P User Manual - Page 142

Checkpointing Switch applications (features) that build up a list of data such as neighbors or clients can significantly improve their restart behavior by remembering this data across a warm restart. This data can either be stored persistently, as DHCP server and DHCP snooping store their bindings database, or the Management Unit can checkpoint this data directly to the standby unit. Persistent storage allows an application on a standalone unit to retain its data across a restart, but since the amount of storage is limited, persistent storage is not always practical. The NSF checkpoint service allows the Management Unit to communicate certain data to the backup unit in the stack. When the stack selects a backup unit, the checkpoint service notifies applications to start a complete checkpoint. After the initial checkpoint is done, applications checkpoint changes to their data. NOTE: The switch cannot guarantee that a backup unit has exactly the same data that the Management Unit has when it fails. For example, the Management Unit might fail before the checkpoint service gets data to the backup if an event occurs shortly before a failover. Table 8-1 lists the applications on the switch that checkpoint data and describes the type of data that is checkpointed. Table 8-1. Applications that Checkpoint Data Application ARP Auto VOIP Captive Portal DHCP server DHCP snooping DOT1Q DOT1S DOT1X DOT3ad Checkpointed Data Dynamic ARP entries Calls in progress Authenticated clients Address bindings (persistent) DHCP bindings database Internal VLAN assignments Spanning tree port roles, port states, root bridge, etc. Authenticated clients Port states 142 Managing a Switch Stack