16. Client Source Address and Interface Selection

16. Client Source Address and Interface Selection

When a client sends a DHCP message to the All_DHCP_Relay_Agents_and_Servers address, it SHOULD send the message through the interface for which it is requesting configuration information. However, a client MAY send a message through another interface attached to the same link if and only if the client determines that the two interfaces are attached to the same link. The client MUST use the link-local address assigned to the interface for which it is requesting configuration information as the source address in the IP datagram header.

When a client uses unicast to send a DHCP message directly to a server (after receiving a Server Unicast option from that server), the source address in the IP datagram header MUST be an address assigned to the interface for which the client wishes to obtain configuration, and that address MUST be appropriate for the server to use in responding to the client.