Cisco 500 series Administration Manual page 387

Configuring DHCP
Interactions Between DHCP Snooping, DHCP Relay and Option 82
Cisco 500 Series Stackable Managed Switch Administration Guide
DHCP Relay
VLAN with IP Address
Relay – is sent
Option 82
Insertion with Option 82
Enabled
Bridge – Option
82 is added
(if port is
trusted, behaves
as if DHCP
Snooping is not
enabled)
The following describes how DHCP Reply packets are handled when DHCP
Snooping is disabled:
DHCP Relay
VLAN with IP Address
Packet arrives
without
Option 82
DHCP Relay
VLAN without IP Address
Packet is Relay – is sent
sent with the with Option 82
original
Bridge –
Option 82
Option 82 is
inserted
(if port is
trusted,
behaves as if
DHCP
Snooping is
not enabled)
DHCP Relay
VLAN without IP Address
Packet arrives Packet arrives
with Option without
82 Option 82
23
Relay –
discards the
packet
Bridge –
Packet is sent
with the
original
Option 82
Packet arrives
with Option
82
387