Brocade Communications Systems Brocate Ethernet Access Switch 6910 - Manual (Page 269)

Brocade 6910 Ethernet Access Switch Configuration Guide 219
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DHCP Snooping
10
• When the DHCP Snooping Information Option 82 is enabled, the requesting client (or an
intermediate relay agent that has used the information fields to describe itself) can be
identified in the DHCP request packets forwarded by the switch and in reply packets sent back
from the DHCP server.
• When the DHCP Snooping Information Option is enabled, clients can be identified by the switch
port to which they are connected rather than 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.
Example
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.
Syntax
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.
Default Setting
replace
Command Mode
Global Configuration