User’s Manual of WGS Managed Series
256
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 4-9-39
&
Figure 4-9-40
appear.
Figure 4-9-39
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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