Cisco 350 Series Administration Manual page 384

IP Configuration
IPv4 Management and Interfaces
Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
DHCP Relay
VLAN with IP Address
Option 82 Packet is sent
Insertion without Option
Disabled 82
Option 82 Packet is sent
Insertion without Option
Enabled 82
DHCP Snooping Binding Database
DHCP Snooping builds a database (known as the DHCP Snooping Binding database) derived
from information taken from DHCP packets entering the device through trusted ports.
The DHCP Snooping Binding database contains the following data: input port, input VLAN,
MAC address of the client and IP address of the client if it exists.
The DHCP Snooping Binding database is also used by IP Source Guard and Dynamic ARP
Inspection features to determine legitimate packet sources.
DHCP Trusted Ports
Ports can be either DHCP trusted or untrusted. By default, all ports are untrusted. To create a
port as trusted, use the Interface Settings page. Packets from these ports are automatically
forwarded. Packets from trusted ports are used to create the Binding database and are handled
as described below.
If DHCP Snooping is not enabled, all ports are trusted by default.
DHCP Relay
VLAN without IP Address
Packet is sent Relay discards
with the Option 82
original Option
Bridge -
82
Packet is sent
without Option
82
Packet is sent Relay –
without Option discards
82 Option 82
Bridge –
Packet is sent
without Option
82
16
Relay
1. If reply originates
on the device, packet is
sent without Option 82
2. If reply does not
originate on the
device, discards the
packet
Bridge – Packet is sent
with the original
Option 82
Packet is sent without
Option 82
297