DHCP relay support for MPLS VPN
Specifically, this information is used by the relay agent to tell the DHCP server the VPN for every DHCP request it passes to the DHCP server. It is also used to forward the DHCP replies that the DHCP server sends back to the DHCP relay agent. The VPN ID configured on the incoming interface (or the VRF name if no VPN ID is configured) is contained in the VPN identifier option.
This mechanism can also be observed by looking at Syslog messages similar to the following:
*Jun 15 01:31:38.582: DHCPD: client's VPN is .
This message indicates that there is no VLAN ID/VRF information contained within option 82, thus the value given is ".". In the following example, a VLAN ID/VRF of
Customer_A has been specified:
*Apr 24 00:13:19.935: DHCPD: client's VPN is Customer_A.