Configuring Dhcp Features - Cisco Catalyst 2950 Software Configuration Manual

Chapter 19

Configuring DHCP Features

The port numbers in the port field of the circuit ID suboption start at 0. For example, on a
Catalyst 2950G-24-EI switch, port 0 is the Fast Ethernet 0/1 port, port 1 is the Fast Ethernet 0/2 port,
port 2 is the Fast Ethernet 0/3 port, and so on. Port 24 is the Gigabit Interface Converter (GBIC)-based
Gigabit module slot 0/1, and port 25 is the GBIC-based Gigabit module slot 0/2.
Figure 19-2
switch uses the packet formats when DHCP snooping is globally enabled and when the ip dhcp
snooping information option global configuration command is entered. For the circuit ID suboption,
the module field is always zero
Figure 19-2
Circuit ID Suboption Frame Format
Suboption
type
1 byte
Remote ID Suboption Frame Format
Suboption
type
1 byte
Configuring DHCP Features
These sections describe how to configure DHCP snooping and option 82on your switch:
•
•
•
•
78-11380-12
Remote ID type
–
Length of the remote ID type
–
shows the packet formats for the remote ID suboption and the circuit ID suboption. The
Suboption Packet Formats
Circuit
ID type
Length Length
1 6 0 4
1 byte 1 byte 1 byte
Remote
ID type
Length Length
2 8 0 6
1 byte 1 byte 1 byte
Default DHCP Configuration, page 19-6
DHCP Snooping Configuration Guidelines, page 19-6
Configuring the DHCP Server, page 19-7
Enabling DHCP Snooping and Option 82, page 19-7
VLAN Module Port
2 bytes 1 byte 1 byte
MAC address
6 bytes
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
Configuring DHCP Features
19-5