Abstract:
The management of DHCP address leased based on client properties is described. According to a method of operation, clients are managed in a wireless digital network by modifying a requested lease time for an assigned Internet Protocol (IP) address based on properties of a client requesting the lease time. The assigned IP address is released if (i) no communication activity is detected by the client for a prescribed duration or (ii) upon detecting a DHCP Release message from the client. When the DHCP server receives a renewal request, it checks if the client has generated more than a predetermined amount of traffic. If the client has generated traffic exceeding this threshold level, the lease is renewed for a longer period. If the client traffic has not met the threshold level, the lease is renewed with the short lease time.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to wireless digital networks, and more particularly, to the problem of managing addresses assigned to clients through DHCP. 
         [0002]    Data networks, particularly wireless data networks, have become an expected or necessary resource in more and more situations. Once present only in the workplace environment, they are now nearly ubiquitous, present in schools, libraries, retail environments, and just about anyplace where people gather. 
         [0003]    Operating wireless networks, particularly in environments handling large numbers of users and/or devices present a number of challenges. The operating environment has changed dramatically within the last few years, from a user having a single device such as a laptop computer with wireless capability, to a single user having multiple devices each with such capability, such as laptops, smart phones, tablets, and portable music players. 
         [0004]    To work with a local wireless network, a device first uses the DHCP protocol to request an address which the device will use while associated to the network. This address is supplied by a DHCP server. The number of distinct addresses available to the DHCP server is determined by its configuration and is finite. A DHCP server is considered to own the IP addresses it manages, and leases them to clients. A DHCP server responds to requests by returning an address (if one is available) which is valid for a predetermined period of time, known as the DHCP lease time. DHCP servers may also work through DHCP relays, which are used to administer subnets. 
         [0005]    DHCP is known to the art, described for example in RFC 2131 for IPv4 networks, and described in RFC 3315, RFC 3633 and RFC 3736 for DHCPv6 in IPv6 networks. 
         [0006]    Particularly in IPv4 environments where multiple users with multiple devices congregate, the finite number of distinct addresses available through a DHCP server may turn out to be a limiting factor in supporting users on the network. 
         [0007]    It has also become apparent in monitoring such networks that while there may be a large number of devices associated to a network, only a fraction of those devices are active. Yet each associated device is tying up an address. 
         [0008]    It is known to the art that in environments where the number of users may exceed the number of addresses available, short lease times should be used to free up unused addresses and make them available. 
         [0009]    The seemingly simple and straightforward solution of having the DHCP server only grant short leases, two minutes, for example, does not work. To be motivated to attempt such a solution, one has to have a network environment in which users exceed available addresses; a very busy environment. In such an environment, issuing only short leases will result in an overloaded DHCP server and network segments flooded with DHCP traffic. 
         [0010]    What is needed is a better way to manage DHCP leases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention may be best understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention in which: 
           [0012]      FIG. 1  shows devices in a network, 
           [0013]      FIG. 2  illustrates an aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Embodiments of the invention relate to methods of managing DHCP leases based on client properties. Short or long lease times are assigned to clients based on properties such as device type, OUI, client location, or client activity. 
         [0015]    In one embodiment, device type may be identified from the device OUI or derived from device OUI. Based on device type, highly mobile devices such as smart phones and tablets may be assigned short lease times. 
         [0016]    In one embodiment, short lease times may be assigned to devices based on client location, such as through one or more access points covering a particular area. 
         [0017]    In one embodiment lease times are based on client activity. A DHCP server allocates addresses with an initial short lease time, as an example, a few minutes. When a DHCP Renew request is received, the DHCP server queries client network activity. If client activity is above a predetermined level, the DHCP server renews the lease with a longer interval, for example, an hour. If the client activity is below the predetermined level, another short lease time is given. 
         [0018]    In one embodiment, a DHCP Relay mediates between the client and DHCP server. The DHCP Relay monitors the offer—ack process by returning a short lease to the client. If this short lease expires, or the client device disconnects, the DHCP relay issues a release to the DHCP server. The DHCP Relay handles client DHCP Renew requests, renewing for a short lease if the client activity is below the predetermined level, otherwise renewing for a long lease time. 
         [0019]    According to the present invention and as shown in  FIG. 1 , a client device  300  wishing to communicate with network  100  first acquires an address by communicating with DHCP server  200 . 
         [0020]    As shown in  FIG. 1 , wireless client devices  300  and  310  wish to communicate with other devices on network  100 . Client devices  300  and  310  are served by wireless access points  250  and  260 . Wireless access point  250  is in direct communication with DHCP Server  200 , while wireless access point  260  goes through DHCP Relay  400 . 
         [0021]    As is understood in the art, wireless access points  250  and  260  are purpose-built digital devices, each containing a processor, a memory hierarchy, and input/output interfaces. Such devices typically operate under the control of an operating system such as Linux, running specific programs to provide for access point operation. A MIPS-class processor such as one from Cavium or NetLogic—RMI may be used. Wired network interfaces typically are IEEE 802.3 Ethernet interfaces. Wireless interfaces are typically IEEE 802.11 WiFi interfaces. The memory hierarchy of the device typically contains fast read-write memory for holding programs and data during device operation, and a hierarch of persistent memory such as ROM, EPROM, and Flash for holding instructions and data needed for device startup, and a file system for device operation. 
         [0022]    DHCP server  200  and DHCP relay  400  may be hosted on distinct hardware platforms, each containing one or more processors, a memory hierarchy, and input/output interfaces, or the DHCP server and DHCP relay functionality may be hosted on another network device, such as a router, switch, controller, or access point. 
         [0023]    Client devices  300  and  310  are also digital devices containing a processor, memory hierarchy, and input/output interfaces, including a wireless interface such as an IEEE 802.11 wireless interface for communicating with wireless access points  250  and  260 . Typical wireless client devices  300 ,  310  include but are not limited to laptop and netbook computers, wireless phones, wireless music players, and other wireless devices such as barcode scanners, instruments, and the like. 
         [0024]    For clarity,  FIG. 1  does not show other typical network devices such as switches, routers, firewalls, and the like which are well understood by the art. 
         [0025]    According to the present invention, and as shown in  FIG. 2 , for a client device  300  to operate on a digital network, it must first acquire an address, which it does using the DHCP protocols. These protocols are used in both wired (such as IEEE 802.3) and wireless (such as IEEE 802.11) networks. 
         [0026]    DHCP is known to the art, described for example in RFC 2131 for IPv4 networks, and described in RFC 3315, RFC 3633 and RFC 3736 for DHCPv6 in IPv6 networks. While the examples herein given are with respect to IPv4 networks, they are equally applicable to IPv6 networks. 
         [0027]    Client device  300  begins the process by sending out a DHCP discover request. This request contains the client&#39;s unique MAC address. As is known in the art, the first three octets of the MAC address are the OUI as assigned by the IEEE Registration Authority and identify the manufacturer of the device. 
         [0028]    In one embodiment of the invention, lease time is based on client device type. DHCP server  200  receives the client request, whether direct from the client or through a DHCP relay, and allocates an IP address with a lease time based on client device type. Device type may be based on the device OUI, derived from the device OUI, or may be derived from previous operating characteristics of the device recorded by MAC address. Tables mapping OUIs or MAC addresses to device types may be kept in the DHCP server, or elsewhere on the network for lookup use. As an example, highly mobile devices such as smart phones and tablets may be given short lease times, while less mobile devices, such as workstations or printers may be given longer lease times. 
         [0029]    In one embodiment of the invention, address lease time may be based on client location. As an example, an educational institution may wish to have a 1 hour lease time in lecture hall and lab locations, longer lease times in faculty/staff areas, and short lease times in high-mobility locations such as cafeterias and commons areas. 
         [0030]    In one embodiment of the invention, address lease time may be based on time of day or other calendar/time basis. As an example, a college library may wish to use short lease times during peak usage periods, but fall back to longer lease times in periods of lower use, such as Friday and Saturday nights. 
         [0031]    In one embodiment of the invention address lease time is based on client activity. Assume client  300  is in direct communication with DHCP Server  200 . Client  300  sends out a DHCP discover request. DHCP server  200  responds with a DHCP Offer, allocating an IP address to the client and according to the invention, assigning a short lease time to the offer. 
         [0032]    Client  300  accepts the offer by responding with a DHCP Request, accepting the IP address for the short duration specified in the DHCP Lease. 
         [0033]    DHCP Server  200  responds with a DHCP ACK, and the IP address is assigned to the client device MAC for the short lease duration. 
         [0034]    According to the invention, using an initial short lease quickly ages out inactive devices. After the short initial DHCP lease period, if client  300  has gone inactive, the lease expires and DHCP Server  200  returns the address to the DHCP pool, where it may be reused by a different client device seeking an address. 
         [0035]    Prior to the expiration of the short DHCP lease period, a client  300  may renew the DHCP lease through a DHCP Request. 
         [0036]    According to the present invention, DHCP server  200  tests to see if client  300  has been active on the network. This may be accomplished, for example, by querying a controller or access point through which client  300 &#39;s traffic flows. Traffic may be measured for example in terms of sessions, packets, bytes, or other measures of network use by the client. For example in the case of the wireless network shown in  FIG. 1 , client  300  connects to the network through wireless access point  250  All data to and from client  300  flows through AP  250 . The AP may, for example, track sessions initiated by client  300 , or may track data to and from the device. 
         [0037]    According to the invention, if client  300  has been active, a DHCP ACK is returned renewing the lease for a long period. If client  300  has not been active, a DHCP ACK is returned renewing the lease for another short period. Renewing the lease for a short period on devices which have not met an activity threshold continues the goal of aging out inactive devices through the use of short lease times. 
         [0038]    In an additional embodiment of the invention where lease time is based on client activity, a DHCP Relay  400  is between client  310  and DHCP server  200 . DHCP Relays are known to the art, and are used when a single DHCP server is used to provide IP addresses over multiple subnets. In such instances, DHCP Relays are used in each subnet to provide DHCP services to clients which do not have direct access to a DHCP server. In operation a client on a local subnet broadcasts a DHCP request, which is received by the DHCP Relay. The DHCP Relay then unicasts the DHCP request to the DHCP Server, which unicasts a response to the DHCP Relay. The DHCP Relay then retransmits the response on the local subnet. 
         [0039]    Performing the steps of the present invention in a DHCP Relay allows the invention to be performed in a system using an older, legacy DHCP server, without needing to alter or replace that DHCP server. 
         [0040]    DHCP Relay  400  may then take generic leases returned by DHCP server  200  and return lease times to clients based on client properties. As described above, these properties may include device type, OUI, client location, and/or client activity. 
         [0041]    DHCP Relay  400  also issues DHCP Releases to DHCP server  200  when a short lease to a client expires, or the client disconnects from the network without issuing a DHCP Release. 
         [0042]    According to an embodiment of the invention, when client  310  issues a DHCP discover, this request is received by DHCP Relay  400  and unicast to DHCP Server  200 . DHCP Server  200  unicasts a DHCP Offer to DHCP Relay  400 , allocating an address in the local subnet for client  310 . DHCP Relay  400  rewrites the lease time in this DHCP Offer to a short lease time and retransmits the DHCP Offer on the local subnet to client  310 . DHCP Relay  400  mediates the DHCP Request response from client  310 , forwarding it to DHCP Server  200 , which responds with a DHCP ACK, which DHCP Relay  400  sends to client  310 . 
         [0043]    According to the present invention, even if, for example, DHCP Server  200  issues uniform 8 hour DHCP leases, DHCP Relay  400  rewrites these to short DHCP Leases. If the short DHCP lease to client  310  expires, DHCP Relay  400  issues a corresponding DHCP Release to DHCP Server  200  to return that address to the available IP pool for the subnet supported by DHCP Relay  400 . DHCP Relay  400  will also initiate a DHCP Release to DHCP Server  200  on behalf of client  310  if client  310  disconnects without initiating a DHCP Release. This reinsures that context is cleared for short-lived clients, and their IP addresses are returned to the available pool. 
         [0044]    DHCP Relay  400  mediates DHCP Renew requests from client  310 . As previously described, in one embodiment of the invention, if client  310  has been active, a DHCP ACK is returned by DHCP Relay  400  renewing the lease for a long period. If client  310  has not been active, a DHCP ACK is returned by DHCP Relay  400  renewing the lease for another short period. Renewing the lease for a short period on devices which have not met an activity threshold continues the goal of aging out inactive devices through the use of short lease times. 
         [0045]    It should be understood that the steps and processes of the present invention are performed by a DHCP Server and/or DHCP Relay being hosted on a suitable device on the network such as a controller, a dedicated host, or an access point. Similarly, the client device may be a laptop or desktop computer, tablet, handheld device, or fixed-function device capable of performing the methods described herein. 
         [0046]    The present invention may be realized in hardware, software, or a combination of hardware and software. A typical combination of hardware and software may be a network server or access point with a computer program that, when being loaded and executed, controls aspects of the host device such that it carries out the methods described herein. 
         [0047]    The present invention also may be embedded in nontransitory fashion in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form. 
         [0048]    This invention may be embodied in other forms without departing from the spirit or essential attributes thereof. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.