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DES-7200 Configuration Guide Chapter 5 DHCP Relay Configuration
5-8
5.2.6 Configuring DHCP
option VPN
To enable DHCP Relay in the MPLS VRF environment, execute the ip dhcp
relay information option vpn command in the global configuration mode by
setting VPN-ID, Subnet-Selection and Server-id Override options.
The VPN-ID option carried with the DHCP request message indicates the VPN
(VRF environment) from which the DHCP Request message comes. The DHCP
response message from the DHCP server to the DHCP relay also carries with
VPN-ID based on which the DHCP relay forwards the DHCP response
message to the right VRF.
In traditional process of DHCP relay, the gateway address field of the DHCP
message indicates the subnet where the DHCP client locates in and the
communication address of the DHCP Server and the DHCP relay. In multi-VRF
environment, however, the IP address of the interface through which the DHCP
relay connects to the DHCP Server belogns to the global routing table. The
gateway address field of the DHCP message from the DHCP relay to the DHCP
Server indicates the communication address of the DHCP Server and the
DHCP relay. The Subnet-Selection option carries with the IP address of the
interface through which the DHCP relay connects to the DHCP Server to notify
the DHCP server of the subnet where the DHCP client locates in.
In the MPLS VPN environment, the DHCP client cannot send RENEW and
RELEASE messages from the VRF to which it belongs to the global DHCP
Server. The Server-id-Override option carries with the IP address of the VRF
interface through which the DHCP relay connects to the DHCP Server. For the
DHCP response message from the DHCP Server to the DHCP relay, the
Server-id-Override option is used to override the Server ID address field. As a
result, the DHCP client sends RENEW and RELEASE messages to the
corresponding DHCP Relay which then forwards the messages to the DHCP
Server.
Command Function
DES-7200(config)# ip dhcp relay
information option vpn
Enable the DHCP Aware VRF
function.
DES-7200(config)# no ip dhcp relay
information option vpn
Disable the DHCP Aware VRF
function.