Dell PowerConnect J-EX4200-24T Software Manual page 2690

Dell PowerConnect J-Series Ethernet Switch Complete Software Guide for Junos OS
Requirements
Overview and Topology
2618
This example describes how to configure DHCP option 82 on a switch with DHCP clients,
DHCP server, and switch all on the same VLAN:
Requirements on page 2618
Overview and Topology on page 2618
Configuration on page 2619
This example uses the following hardware and software components:
One J-EX Series switch
A DHCP server to provide IP addresses to network devices on the switch
Before you configure DHCP option 82 on the switch, be sure you have:
Connected and configured the DHCP server.
NOTE: Your DHCP server must be configured to accept DHCP option 82.
If it is not configured for DHCP option 82, it does not use the DHCP option
82 information in the requests sent to it when it formulates its reply
messages.
Configured the
employee
the clients and the server connect to the switch with that VLAN. See "Configuring
VLANs for J-EX Series Switches (CLI Procedure)" on page 1136.
If DHCP option 82 is enabled on the switch, then when a network device—a DHCP
client—that is connected to the switch on an untrusted interface sends a DHCP request,
the switch inserts information about the client's network location into the packet header
of that request. The switch then sends the request to the DHCP server. The DHCP server
reads the option 82 information in the packet header and uses it to implement the IP
address or other parameter for the client.
DHCP option 82 is enabled on an individual VLAN or on all VLANs on the switch.
When option 82 is enabled on the switch, then this sequence of events occurs when a
DHCP client sends a DHCP request:
The switch receives the request and inserts the option 82 information in the packet
1.
header.
The switch forwards the request to the DHCP server.
2.
The server uses the DHCP option 82 information to formulate its reply and sends a
3.
response back to the switch. It does not alter the option 82 information.
The switch strips the option 82 information from the response packet.
4.
The switch forwards the response packet to the client.
5.
VLAN on the switch and associated the interfaces on which