IP Routing Features

Configuring DHCP Relay

However, Option 82 relay agents should be positioned at the DHCP policy boundaries in a network to provide maximum support and security for the IP addressing policies configured in the server.

Option 82 Server Support

To apply DHCP Option 82, the routing switch must operate in conjunction with a server that supports Option 82. (DHCP servers that do not support Option 82 typically ignore Option 82 fields.) Also, the routing switch applies Option 82 functionality only to client request packets being routed to a DHCP server. DHCP relay with Option 82 does not apply to switched (non-routed) client requests.

For information on configuring policies on a server running DHCP Option 82, refer to the documentation provided for that application.

Relay Agent “1” (Routing Switch) with DHCP Option 82 Enabled

 

 

 

 

 

 

 

 

 

 

 

VLAN

VLAN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10

20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

10.10.10.1

10.10.20.1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch “B”

 

 

 

 

Switch “A”

 

 

 

 

 

 

 

10.10.20.3

 

 

 

 

 

10.10.10.2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Client

 

 

Client

 

 

Client

Client

 

 

Client

 

 

Client

 

 

4

 

 

5

 

 

6

1

 

 

2

 

 

3

 

 

 

 

 

 

 

 

 

 

 

 

 

Policy Boundaries

10.10.30.1DHCP

10.10.20.2

 

 

 

Option

 

 

 

 

 

 

82

 

 

 

 

Server

Relay Agent “2” (Routing

Switch) without DHCP

Option 82 Enabled

Subnets 10 and 20 in relay agent “1” form policy boundaries that can be defined by the IP address of the subnet on which the client request is received.

Figure 7-10. Example of a DHCP Option 82 Application

Terminology

Circuit ID: In Option 82 applications, the number of the port through which the routing switch receives a DHCP client request. On ProCurve fixed- port switches, the Circuit ID of a given port corresponds to the port number appearing on the front of the switch for that port. On ProCurve chassis switches, the port number for a given port corresponds to the internal ifIndex number for that port. This value is included as a suboption in an Option 82 field that the relay agent appends to a Client DHCP request before forwarding the request toward a DHCP server. (For more on Circuit ID, refer to “Circuit ID” in the bulleted list on page <zBlue>33.)

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