Cisco Catalyst 3750-X Software Configuration Manual page 627

Chapter 24 Configuring DHCP Features and IP Source Guard
In the port field of the circuit ID suboption, the port numbers start at 3. For example, on a
Catalyst 3750-E switch with 24 10/100/1000 ports and four small form-factor pluggable (SFP) module
slots, port 3 is the Gigabit Ethernet 1/0/1 port, port 4 is the Gigabit Ethernet 1/0/2 port, and so forth.
Port 27 is the SFP module slot Gigabit Ethernet1/0/25, and so forth.
Figure 24-2
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 24-2
Circuit ID Suboption Frame Format
Suboption
type
1
1 byte
Remote ID Suboption Frame Format
Suboption
type
2
1 byte
Figure 24-3
switch uses these packet formats when DHCP snooping is globally enabled and when the ip dhcp
snooping information option format remote-id global configuration command and the ip dhcp
snooping vlan information option format-type circuit-id string interface configuration command are
entered.
The values for these fields in the packets change from the default values when you configure the
remote-ID and circuit-ID suboptions:
Circuit-ID suboption fields
•
–
–
Remote-ID suboption fields
•
–
–
OL-21521-01
shows the packet formats for the remote-ID suboption and the circuit-ID suboption when
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
shows the packet formats for user-configured remote-ID and circuit-ID suboptions The
The circuit-ID type is 1.
The length values are variable, depending on the length of the string that you configure.
The remote-ID type is 1.
The length values are variable, depending on the length of the string that you configure.
Module Port
1 byte 1 byte
MAC address
6 bytes
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Understanding DHCP Features
24-5