438 Configuring Switching Information
The DHCP binding database is persisted on a configured external server or locally in flash, depending on
the user configuration. A row-wise checksum is placed in the text file that is going to be stored in the
remote configured server. On reloading, the switch reads the configured binding file to build the DHCP
snooping database. When the switch starts and the calculated checksum value equals the stored
checksum, the switch reads entries from the binding file and populates the binding database. A
checksum failure or a connection problem to the external configured server will cause the switch to loose
the bindings and will cause a host’s data loss if DAI is enabled.
When a switch learns of new bindings or when it loses bindings, the switch immediately updates the
entries in the database. The switch also updates the entries in the binding file. The frequency at which
the file is updated is based on a configurable delay, and the updates are batched.
If the absolute lease time of the snooping database entry expires, then that entry will be removed. You
should take care of the system time to be consistent across the reboots. Otherwise, the snooping entries
will not expire properly. If a host sends a DHCP release while the switch is rebooting then, when the
switch receives the DHCP discovery or request, the client’s binding will go to the tentative binding as
shown in the following figure.
Figure 7-120. States of Client Binding
To access the DHCP Snooping Static Bindings Configuration page, click Switching
→
DHCP
Snooping
→
Static Bindings Configuration in the navigation tree.
No Binding
Tentative
Binding
Complete
Binding
RELEASE, NACK
DISCOVER
ACK
DISCOVER,
REQUEST
DECLINE,
NACK
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