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set dhcpsnooping trust
17-6 DHCP Snooping and Dynamic ARP Inspection
Mode
Switch command, read ‐ write.
Usage
When a switch learns of new bindings or when it loses bindings, the switch updates the entries in
the bindings database according to the write delay timer. The switch also updates the entries in
the binding file. The frequency at which the file is updated is based on the delay configured with
this command, and the updates are batched.
Example
The following example specifies that the stored database should be updated once an hour.
C3(rw)->set dhcpsnooping database write-delay 3600
set dhcpsnooping trust
Use this command to enable or disable a port as a DHCP snooping trusted port.
Syntax
set dhcpsnooping trust port port-string { enable | disable }
Parameters
Defaults
By default, ports are untrusted.
Mode
Switch command, read ‐ write.
Usage
In order for DHCP snooping to operate, snooping has to be enabled globally and on specific
VLANs, and the ports within the VLANs have to be configured as trusted or untrusted. On
trusted ports, DHCP client messages are forwarded directly by the hardware. On untrusted ports,
client messages are given to the DHCP snooping application.
The DHCP snooping application builds the bindings database from client messages received on
untrusted ports. DHCP snooping creates a “tentative binding” from DHCP DISCOVER and
REQUEST messages. Tentative bindings tie a client to the port on which the message packet was
received. Tentative bindings are completed when DHCP snooping learns the client’s IP address
from a DHCP ACK message on a trusted port.
The ports on the switch through which DHCP servers are reached must be configured as trusted
ports so that packets received from those ports will be forwarded to clients. DCHP packets from a
DHCP server (DHCP OFFER, DHCP ACK, DHCP NAK) are dropped if received on an untrusted
port.
port port ‐ string Specifies the port or ports to be enabled or disabled as trusted ports. The
ports can be physical ports or LAGs that are members of a VLAN.
enable | disable Enables or disables the specified ports as trusted ports.