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21-5
Cisco Catalyst Switch Module 3110 and 3012 for IBM BladeCenter Software Configuration Guide
OL-12189-01
Chapter 21 Configuring DHCP Features and IP Source Guard
Understanding DHCP Features
• 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 1. For example, on a Catalyst Switch
Module 3110X, which has 15 ports, port 1 is the internal Gigabit Ethernet 1/0/1 port, port 2 is the internal
Gigabit Ethernet 1/0/2 port, and so on. Port 15 is the 10-Gigabit Ethernet 1/0/15 port.
Figure 21-2 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 21-2 Suboption Packet Formats
Figure 21-3 shows the packet formats for user-configured remote-ID and circuit-ID suboptions The
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.
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