Configuring DHCP
Interactions Between DHCP Snooping, DHCP Relay and Option 82
Cisco 500 Series Stackable Managed Switch Administration Guide
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The following describes how DHCP reply packets are handled when both DHCP
Snooping and DHCP Relay are enabled
Transparent DHCP Rely
For Transparent DHCP Relay where an external DHCP relay agent is being used,
do the following:
•
Enable DHCP Snooping.
•
Enable Option 82 insertion.
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 will
be sent
without
Option 82
Packet will
be sent with
the original
Option 82
Relay will
discard
Option 82
Bridge -
Packet will
be sent
without
Option 82
Relay
1. If reply originates
on the switch,
packet will be sent
without Option 82
2. If reply does not
originate on the
switch, will discard
the packet
Bridge – Packet will
be sent with the
original Option 82
Option
82
Insertion
Enabled
Packet will
be sent
without
Option 82
Packet will
be sent
without
Option 82
Relay – will
discard
Option 82
Bridge –
Packet will
be sent
without
Option 82
Packet will be sent
without Option 82