How Dhcp Snooping Works; System Reboot And The Binding Database; Configuring Dhcp Snooping - Dell PowerConnect B-RX Configuration Manual

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 129
FIGURE 130

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.
1. Enable DHCP snooping on a VLAN. Refer to
2. For ports that are connected to a DHCP server, change their trust setting to trusted. Refer to
BigIron RX Series Configuration Guide
53-1001810-01
DHCP snooping at Work - on untrusted port
DHCP client
request packet
DHCP server
reply packet
DHCP snooping at Work - on trusted port
DHCP
Client
"Enabling trust on a port"
DHCP
Snooping
Foundry Device
DHCP
Snooping
Foundry Device
"Enabling DHCP snooping on a VLAN"
on page 996.
35
DHCP snooping
DHCP
Server
DHCP server
reply packet
DHCP
Server
on page 996.
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