Brocade BigIron RX Series Configuration Guide - Manual (Page 1167)

BigIron RX Series Configuration Guide 1089
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DHCP snooping
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How DHCP snooping works
When enabled on a VLAN, DHCP snooping stands between untrusted ports (those connected to
host ports) and trusted ports (those connected to DHCP servers). A VLAN with DHCP snooping
enabled forwards DHCP request packets from clients and discards DHCP server reply packets on
untrusted ports, and it forwards DHCP server reply packets on trusted ports to DHCP clients, as
shown in the following figures.
FIGURE 144 DHCP snooping at Work - on untrusted port
FIGURE 145 DHCP snooping at Work - on trusted port
System reboot and the binding database
To allow DAI and DHCP snooping to work smoothly across a system reboot, the binding database is
saved to a file in the system flash memory after the user issues the "reload" command. DHCP
learnt entries are written to the system flash memory before the router reboots. The flash file is
written and read only if DHCP snooping is enabled.
Configuring DHCP snooping
Configuring DHCP snooping consists of the following steps.
Brocade Device
Trusted
Un trusted
reply packet
DHCP server
DHCP
Server
Snooping
DHCP
request packet
DHCP client
DHCP
Client
Brocade Device
DHCP server
reply packet
Trusted
Untrusted
DHCP
Server
DHCP
Snooping