20-5
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
OL-8915-03
Chapter 20 Configuring DHCP Features and IP Source Guard
Understanding DHCP Features
In the port field of the circuit ID suboption, the port numbers start at 1. For example, on a Cisco Catalyst
Blade Switch 3020 for HP, which as 24 ports, port 1 is the Gigabit Ethernet 0/1 port, port 2 is the Gigabit
Ethernet 0/2 port, port 3 is the Gigabit Ethernet 0/3 port, and so on. Ports 17 to 20 are dual-purpose SFP
module/RJ-45 copper Ethernet uplink ports Gi0/17 to Gi0/20. Ports 21x and 22x are copper
10/100/1000BASE-T ports Gi0/21 and Gi0/22. Ports 23x and 24x are dual-purpose external/internal
10/100/1000BASET copper uplink ports Gi0/23 and Gi0/24.
Figure 20-2
shows the packet formats for the remote-ID suboption and the circuit-ID suboption when
the default suboption configuration is used.The switch uses the packet formats when you globally enable
DHCP snooping and enter the
ip dhcp snooping information option
global configuration command.
Figure 20-2
Suboption Packet Formats
Figure 20-3
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.
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
–
The circuit-ID type is 1.
–
The length values are variable, depending on the length of the string that you configure.
•
Remote-ID suboption fields
–
The remote-ID type is 1.
–
The length values are variable, depending on the length of the string that you configure.
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 byte
1 byte
116300
4
0
6
1
6
0
8
2
Module Port
1 byte 1 byte
2 bytes
VLAN