Cisco 3750G - Catalyst Integrated Wireless LAN Controller

22-5
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 22 Configuring DHCP Features and IP Source Guard
Understanding DHCP Features
In the default suboption configuration, when the described sequence of events occurs, the values in these
fields in Figure 22-2 do not change:
• Circuit-ID suboption fields
– Suboption type
– Length of the suboption type
– Circuit-ID type
– Length of the circuit-ID type
• Remote-ID suboption fields
– Suboption type
– Length of the suboption type
– Remote-ID type
– Length of the remote-ID type
In the port field of the circuit-ID suboption, the port numbers start at 3. For example, on a switch with
24 10/100 ports and small form-factor pluggable (SFP) module slots, port 3 is the Fast Ethernet x/0/1
port, port 4 is the Fast Ethernet x/0/2 port, and so forth, where x is the stack member number. Port 27 is
the SFP module slot x/0/1, and so forth.
Figure 22-2 shows the packet formats for the remote-ID suboption and the circuit-ID suboption when
the default suboption configuration is used. For the circuit-ID suboption, the module number
corresponds to the switch number in the stack. The switch uses the packet formats when you globally
enable DHCP snooping and enter the ip dhcp snooping information option global configuration
command.
Figure 22-2 Suboption Packet Formats
Length Length
Circuit
ID type
Suboption
type
Circuit ID Suboption Frame Format
Remote ID Suboption Frame Format
6 bytes
MAC address
1 byte 1 byte 1 byte
Suboption
type
1 byte
Length Length
Remote
ID type
1 byte 1 byte 1 byte1 byte
116300
4061
6082
Module Port
1 byte 1 byte2 bytes
VLAN