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7 dhcp snooping, 1 enabling dhcp snooping, 2 dhcp trust state – Siemens S223 User Manual

Page 258: Dhcp snooping, 1 enabling dhcp snooping 8.8.7.2 dhcp trust state

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UMN:CLI User Manual

SURPASS hiD 6615 S223/S323 R1.5

258 A50010-Y3-C150-2-7619

8.8.7 DHCP

Snooping

For enhanced security, the hiD 6615 S223/S323 provides the DHCP snooping feature.
The DHCP snooping filters untrusted DHCP messages and maintains a DHCP snooping
binding table. An untrusted message is a message received from outside the network,
and an untrusted interface is an interface configured to receive DHCP messages from
outside the network.

The DHCP snooping basically permits all the trusted messages received from within the
network and filters untrusted messages. In case of untrusted messages, all the binding
entries are recorded in a DHCP snooping binding table. This table contains a hardware
address, IP address, lease time, VLAN ID, interface, etc.

It also gives you a way to differentiate between untrusted interfaces connected to the
end-user and trusted interfaces connected to the DHCP server or another switch.

8.8.7.1

Enabling DHCP Snooping

To enable the DHCP snooping on the system, use the following command

Command Mode

Description

ip dhcp snooping

Enables the DHCP snooping on the system.

no ip dhcp snooping

Global

Disables the DHCP snooping on the system. (default)

Upon entering the ip dhcp snooping command, the DHCP_OFFER and DHCP_ACK
messages from all the ports will be discarded before specifying a trusted port.

To enable the DHCP snooping on a VLAN, use the following command

Command Mode

Description

ip dhcp snooping vlan

VLANS

Enables the DHCP snooping on a specified VLAN.

no ip dhcp snooping vlan

VLANS

Global

Disables the DHCP snooping on a specified VLAN.

You must enable DHCP snooping on the system before enabling DHCP snooping on a
VLAN.

8.8.7.2

DHCP Trust State

To define a state of a port as trusted or untrusted, use the following command.

Command Mode

Description

ip dhcp snooping trust

PORTS

Defines a state of a specified port as trusted.

no ip dhcp snooping trust

PORTS

Global

Defines a state of a specified port as untrusted.

Note that, the DHCP snooping only sees the DHCP_OFFER and DHCP_ACK messages
which are received from untrusted interfaces.

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