Methods and apparatuses for dynamically provisioning a dynamic host configuration protocol (DHCP) client as a clientless internet protocol services (CLIPS) subscriber on a last-resort interface

A non-transitory computer-readable storage medium implemented in computer hardware that provides instructions, which when executed by a computer, cause the computer to perform a method in a network element to enable clientless IP services (CLIPS) for a Dynamic Host Configuration Protocol (DHCP) client on a last-resort interface comprising:

• receiving, over a network, on the last-resort interface of the network element a request packet containing a request for an IP address, the request packet originating from the DHCP client, wherein the request packet passes through a DHCP relay located between the network element and one or more DHCP client subnets, wherein the request packet includes a gateway IP (GI) address field having an IP address of an interface of the DHCP relay, and wherein the interface of the DHCP relay is located within the DHCP relay;
• in response to the request packet, on behalf of the DHCP client, forwarding a modified request packet to a set of one or more DHCP servers, the modified request packet including an IP address of the last-resort interface in the GI address field;
• receiving a response packet forwarded from one of the DHCP servers of the set of DHCP servers, the response packet at least including an IP address to be allocated to the DHCP client, a default network gateway address of the DHCP server, and a GI address field having the IP address of the last-resort interface;
• processing the received response packet by-passing the DHCP relay located between the DHCP client and the network element;
• responding to the DHCP client with respect to the request packet as if the network element is an IP address provider, on behalf of the DHCP server;
• intercepting an Address Resolution Protocol (ARP) request originated from the DHCP client and destined for the DHCP server that requests a Media Access Control (MAC) address corresponding with the default network gateway address of the DHCP server;
• and
• communicating to the DHCP client, in response to intercepting the ARP request, an ARP acknowledgement packet that includes a MAC address of the network element;
• checking a learned router identification (RID) data structure to determine whether the learned RID was previously learned, the previously learned RID having been previously placed within a learned RID data structure;
• and
• if the learned RID is not already located within the learned RIDs data structure:
• placing the learned RID into the learned RIDs data structure to enable the network element to alias for the DHCP server;
• and
• placing the learned RID into an Address Resolution Protocol (ARP) data structure to enable the network element to respond to ARP queries from the DHCP client, the ARP queries required for the DHCP client to obtain a MAC address to enable clientless IP services on the last-resort interface.

An apparatus comprising:

• a network element, coupled between a Dynamic Host Configuration Protocol (DHCP) relay and a set of one or more DHCP servers, to act as a DHCP proxy on behalf of the set of DHCP servers and to provide clientless IP services (CLIPS) to a plurality of DHCP clients coupled to the DHCP relay, the network element including,
• a port coupled to the DHCP relay, the port including an interface configured as a last-resort interface for CLIPS subscribers;
• a forwarding component coupled to said port to receive over the last-resort interface requests for IP addresses originating from the DHCP clients, the requests including a gateway IP (GI) address field having an IP address of an interface of the DHCP relay, wherein the interface of the DHCP relay is at located within the DHCP relay, and to forward modified requests to the set of DHCP servers, the modified requests including an IP address of the last-resort interface in the GI address field;
• a snoop component to receive response packets forwarded from the set of DHCP servers responsive to said requests, to process the received response packets as if by-passing the DHCP relay is not located between the DHCP client and the network element including snoop the response packets to learn a default network gateway address of the responding ones of the set of DHCP servers, and to respond to the respective DHCP clients as if the network element is an IP address provider, on behalf of the set of DHCP servers;
• and
• an Address Resolution Protocol (ARP) process to:
• intercept ARP requests originated from the DHCP clients and destined for the set of DHCP servers that each request a Media Access Control (MAC) address corresponding with one of the default network gateway addresses of one of the responding ones of the set of DHCP servers, and
• responsive to each intercepted ARP request, communicate an ARP acknowledgement packet that includes a MAC address of the network element to that DHCP client that originated that intercepted ARP request;
• a learned router identification (RID) data structure to store previously learned RIDs;
• and
• an Address Resolution Protocol (ARP) data structure coupled to the snoop component and the ARP process to store ARP entries corresponding to the previously learned RIDs.