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NS3503-16P-4C User Manual
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4.9.7.6 Database Agent
Overview of the DHCP Snooping Database Agent
When DHCP snooping is enabled, the switch uses the DHCP snooping binding database to store
information about untrusted interfaces. The database can have up to 8192 bindings.
Each database entry (binding) has an IP address, an associated MAC address, the lease time (in
hexadecimal format), the interface to which the binding applies, and the VLAN to which the interface
belongs. A checksum value, the end of each entry, is the number of bytes from the start of the file to end
of the entry. Each entry is 72 bytes, followed by a space and then the checksum value.
To keep the bindings when the switch reloads, you must use the DHCP snooping database agent. If the
agent is disabled, dynamic ARP or IP source guard is enabled, and the DHCP snooping binding
database has dynamic bindings, the switch loses its connectivity. If the agent is disabled and only DHCP
snooping is enabled, the switch does not lose its connectivity, but DHCP snooping might not prevent
DCHP spoofing attacks.
The database agent stores the bindings in a file at a configured location. When reloading, the switch
reads the binding file to build the DHCP snooping binding database. The switch keeps the file current by
updating it when the database changes.
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 file is not
updated in a specified time (set by the write-delay and abort-timeout values), the update stops.
The DHCP Snooping Database and Information screens in Figure 4-9-40 and Figure 4-9-41 appear.
Figure 4-9-40 DHCP Snooping Database Setting Page Screenshot
The page includes the following fields:
Object
Description
Database Type
Select database type
File Name
The name of file image
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