Edge-Core ECS4660-28F, Management Manual, Page: 1119 / 2020

C
HAPTER
29
| General Security Measures
DHCPv4 Snooping
– 1119 –
just their MAC address. DHCP client-server exchange messages are
then forwarded directly between the server and client without having to
flood them to the entire VLAN.
◆
DHCP snooping must be enabled for the DHCP Option 82 information to
be inserted into packets. When enabled, the switch will only add/
remove option 82 information in incoming DCHP packets but not relay
them. Packets are processed as follows:
■
If an incoming packet is a DHCP request packet with option 82
information, it will modify the option 82 information according to
settings specified with ip dhcp snooping information policy
command.
■
If an incoming packet is a DHCP request packet without option 82
information, enabling the DHCP snooping information option will
add option 82 information to the packet.
■
If an incoming packet is a DHCP reply packet with option 82
information, enabling the DHCP snooping information option will
remove option 82 information from the packet.
E
XAMPLE
This example enables the DHCP Snooping Information Option.
Console(config)#ip dhcp snooping information option
Console(config)#
ip dhcp snooping
information policy
This command sets the DHCP snooping information option policy for DHCP
client packets that include Option 82 information.
S
YNTAX
ip dhcp snooping information policy { drop | keep | replace }
drop - Drops the client’s request packet instead of relaying it.
keep - Retains the Option 82 information in the client request, and
forwards the packets to trusted ports.
replace - Replaces the Option 82 information circuit-id and
remote-id fields in the client’s request with information about the
relay agent itself, inserts the relay agent’s address (when DHCP
snooping is enabled), and forwards the packets to trusted ports.
D
EFAULT
S
ETTING
replace
C
OMMAND
M
ODE
Global Configuration
C
OMMAND
U
SAGE
When the switch receives DHCP packets from clients that already include
DHCP Option 82 information, the switch can be configured to set the action