IP Configuration
IPv4 Management and Interfaces
359 Cisco 500 Series Managed Switch Administration Guide
18
The following describes how DHCP reply packets are handled when both DHCP
Snooping and DHCP Relay are enabled
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.
DHCP Relay
VLAN with IP Address
DHCP Relay
VLAN without IP Address
Packet
arrives
without
Option 82
Packet
arrives with
Option 82
Packet
arrives
without
Option 82
Packet arrives with
Option 82
Option
82
Insertion
Disabled
Packet is
sent without
Option 82
Packet is
sent with the
original
Option 82
Relay
discards
Option 82
Bridge -
Packet is
sent without
Option 82
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
Option
82
Insertion
Enabled
Packet is
sent without
Option 82
Packet is
sent without
Option 82
Relay –
discards
Option 82
Bridge –
Packet is
sent without
Option 82
Packet is sent
without Option 82
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