Cisco Catalyst 4500 series Administration Manual page 1381

Chapter 53 Configuring DHCP Snooping, IP Source Guard, and IPSG for Static Hosts
The DHCP server unicasts the reply to the switch if the request was relayed to the server by the
•
switch. The switch verifies that it originally inserted the Option 82 data by inspecting the remote ID
and possibly the circuit ID fields. The switch removes the Option 82 field and forwards the packet
to the switch port that connects to the DHCP client that sent the DHCP request.
In the default suboption configuration, when the described sequence of events occurs, the values in these
fields in
Circuit ID suboption fields
•
–
–
–
–
• Remote ID suboption fields
–
–
–
–
Figure 53-2
default suboption configuration is used. For the circuit ID suboption, the module number corresponds to
the switch module number. The switch uses the packet formats when you globally enable DHCP
snooping and enter the ip dhcp snooping information option global configuration command.
Figure 53-2
Circuit ID Suboption Frame Format
Suboption
type
1
1 byte
Remote ID Suboption Frame Format
Suboption
type
2
1 byte
OL_28731-01
Figure 53-2 do not change:
Suboption type
Length of the suboption type
Circuit ID type
Length of the circuit ID type
Suboption type
Length of the suboption type
Remote ID type
Length of the remote ID type
shows the packet formats for the remote ID suboption and the circuit ID suboption when the
Suboption Packet Formats
Circuit
ID type
Length Length
6 0 4 VLAN
1 byte 1 byte 1 byte 2 bytes
Remote
ID type
Length Length
8 0 6
1 byte 1 byte 1 byte
Module Port
1 byte 1 byte
MAC address
6 bytes
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
About DHCP Snooping
53-5