Cisco 500 series Administration Manual page 389

Configuring DHCP
Interactions Between DHCP Snooping, DHCP Relay and Option 82
Cisco 500 Series Stackable Managed Switch Administration Guide
The following describes how DHCP reply packets are handled when both DHCP
Snooping and DHCP Relay are enabled
DHCP Relay
VLAN with IP Address
Packet
arrives
without
Option 82
Option 82 Packet is
Insertion sent without
Disabled Option 82
Option 82 Packet is
Insertion sent without
Enabled Option 82
DHCP Relay
VLAN without IP Address
Packet Packet
arrives with arrives
Option 82 without
Option 82
Packet is Relay
sent with the discards
original Option 82
Option 82
Bridge -
Packet is
sent without
Option 82
Packet is Relay –
sent without discards
Option 82 Option 82
Bridge –
Packet is
sent without
Option 82
23
Packet arrives with
Option 82
Relay
1. If reply originates
on the switch,
packet is sent
without Option 82
2. If reply does not
originate on the
switch, discards the
packet
Bridge – Packet is
sent with the
original Option 82
Packet is sent
without Option 82
389