Abstract:
A system and method is described for providing policy-based Network Address Translation (NAT) configurations wherein each user/resource policy within a network protection device may use a different set of address translation mappings.

Description:
RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This present application claims priority to and is a continuation of U.S. Non-Provisional application Ser. No. 10/857,225, entitled “Policy Based Network Address Translation”, filed on May 28, 2004, which claims the benefit of and priority to U.S. Provisional Patent Application No. 60/473,964, filed May 28, 2003, both of which are incorporated herein by reference in their entirety. This patent application incorporates by reference in its entirety each of the following U.S. patent applications: 1) “Method and System for Identifying Bidirectional Packet Flow” filed on May 28, 2004, having U.S. application Ser. No. 10/857,703, now abandoned; 2) “Method, System and Software for State Signing of Internet Resources” filed on May 28, 2004, having U.S. application Ser. No. 10/857,536, now abandoned; and 3) “Multilayer Access Control Security System” filed on May 28, 2004, having U.S. application Ser. No. 10/857,224 and co-pending with the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     Network Address Translation (NAT) is an Internet technology that was originally developed to work around the growing scarcity of Internet Protocol (IP) addresses on the Internet. The current, and most widely used, Internet Protocol (IPv4) supports more than four billion addresses. However, because of inefficient allocation of addresses, routing constraints, and the Internet&#39;s phenomenal growth, this number has proven insufficient. The NAT solution is to use private addresses on a company&#39;s (or homeowner&#39;s) internal network and only convert those internal addresses to globally routable IP addresses when communicating through a gateway (e.g., router, firewall, other switching or routing device) to hosts (other computers/servers) on the Internet. In some applications, hosts currently communicating will get their own globally routable IP address, while in other applications, as few as one globally routable IP address may be used for multiple internal hosts. Ideally, this translation will be invisible to the underlying networking applications and protocols. NAT functionality can also be exploited for its security features (internal IP addresses are effectively “hidden” to the external world) and has been employed in session redirection and load balancing. 
     There are many products available today that employ NAT functionality, including routers for business and home use, firewalls, and Internet/residential gateways. Some computer operating systems also implement NAT functionality so that a server or workstation running such an operating system can act as a NAT-enabled software router or firewall. Applications of NAT have been focused on address translations based on network structure, resource availability, and simple application requirements. 
       FIG. 1  illustrates an exemplary use of a NAT map (functionality)  100  within a NAT router  110  connecting an internal network  120  to the Internet  130 . The internal network  120  includes the NAT router  110 , an application server  140  and a file server  150 . External users  160 ,  170  can connect to the internal network  120  via the Internet  130 . The NAT map  100  includes a list of external IP addresses  180  and a list of internal IP addresses  190 . 
     As is understood in the prior art, the first user  160  transmits packets to the externally known IP address for the application server  140  (196.28.43.2). With no regard for who the user is or what the resource is, the NAT router  110  receives the packets containing the externally known destination IP address  180  (196.28.43.2) and utilizes the NAT map  100  to translate the external address (196.28.43.2) to a corresponding internal IP address (10.33.96.5)  190  and routes the packets accordingly. The second user  170  sends packets to the file server  150  (using external IP address 196.29.74.4) and the NAT router  110  translates the external address to the internal IP address (10.33.96.9) and forwards to the file server  150 . If the application server  140  or file server  150  communicates with an external user, the NAT router  110  utilizes the NAT map  100  to translate the source address from the internal IP address  190  (10.33.96.5 and 10.33.96.9 respectively) to the externally known IP address  180  (196.28.43.2 and 196.29.74.4) prior to forwarding the packets externally. The external users therefore do not know the internal IP addresses. Although as illustrated in  FIG. 1  the user&#39;s addresses are not translated, the NAT map  100  may optionally perform user address translation. 
     Session flow, also referred to herein as flow, is well known to those skilled in the art and is described in detail in the Internet Engineering Task Force (IETF) Request for Comments (RFC) 2663, which is incorporated herein by reference. Session flow is a combination of inbound and outbound packets that form part of a session initiated in one direction. Packet flow is defined in RFC 2663 as the direction in which the packet has traveled with reference to a network interface. As an example, a session (session flow) initiated by a user on a server for telnet would consist of packet flows in both the inbound and outbound directions. 
     As network applications and Web application services have proliferated and corporate networks have become more distributed, there has been a growing need for more flexibility in address translation functionality. NAT is a process in which IP addresses are mapped from one group to another, transparent to end users. Network Address Port Translation (NAPT) is a method by which many network addresses and their TCP/UDP (Transmission Control Protocol/User Datagram Protocol) ports are translated into a single network address and its TCP/UDP ports. NAPT works well to share a single globally routable IP address when an internal user initiates the contact and receives a reply on the same port. The processes of NAT and NAPT are well known to those skilled in the art and are described in detail in ETF document RFC 3022, which is incorporated herein by reference. However, when multiple applications using the same well-known port (such as TCP port  443  for secure socket layer) are placed behind an NAPT enabled device some of the applications may become inoperative for inbound flows. 
     Other features of NAT have been developed, including the use of NATs for load sharing, where a session load can be distributed across a pool of servers, instead of directed to a single server. The use of NATs for load sharing is described in the IEETF document RFC 2391, which is incorporated herein by reference. A type of NAT has been developed for interfacing between end-nodes using version 6 of the Internet protocol (V6) trying to communicate with end-nodes using version 4 (V4) and vice versa. This type of Network Address Translation—Protocol Translation (NAT-PT) is described in RFC 2766, which is incorporated by reference herein. 
     The prior art systems essentially use address maps to provide address translations regardless of who the client is and what the service is. This limited flexibility results in unrestricted user access and uniform address translation. What is needed is a way to create and adjust network address translation configurations based on user and resource-specific network policies. Such capability would result in higher security based on user authorization, greater control of network resources and the general ability to vary network address translation for a wide range of purposes. 
     SUMMARY OF THE INVENTION 
     A network protection device (firewall or network access management system) may be responsible for establishing and enforcing packet traffic policies into and out of a corporate or home network. Each packet entering a piece of network protection equipment may be classified into a particular flow and, based on the established policies, either forwarded to a destination or dropped. In some cases, the source and/or destination addresses and ports may be modified for all packets in a particular flow. This may be done for a number of reasons, including security, load balancing, and to work around equipment failures. This rewriting of addresses and ports is referred to herein as “translation.” The set of translations that are active at any particular time is called a NAT configuration. 
     In an advanced access management system, resources may be made available (authorized) for specific users at specific times and in user-specific ways. A “policy” may be defined by the precise rules for how a particular resource is made available to a particular user at a particular time. An advanced access management system may filter some or all packets entering the system based on all of the policies in force when the packet arrives. In one embodiment, each policy within an access management system may employ a different NAT configuration. In this way, the address translation may vary from policy to policy (user to user). In an embodiment, no two policies need carry the same set of NAT translation parameters. This allows for resources to be given customized access rules and address translation functionality for each user. 
     Before explaining at least one embodiment in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be used as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and, together with the description serve to explain the principles of the invention. 
         FIG. 1  illustrates an exemplary use of a NAT map within a router for inbound access to enterprise applications; 
         FIG. 2  illustrates an exemplary system architecture of a network connecting to the Internet through two layers of network protection equipment, according to one embodiment; 
         FIG. 3  illustrates an exemplary policy-based NAT map, according to one embodiment; 
         FIG. 4  illustrates an exemplary network utilizing an access management system (AMS), according to one embodiment; 
         FIGS. 5A and 5B  illustrate an exemplary policy-based NAT map, according to one embodiment; and 
         FIG. 6  illustrates an exemplary policy-based network address translation processor, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In describing an embodiment of the invention illustrated in the drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
       FIG. 2  illustrates an exemplary system architecture of a network  200  (or network segment) connecting to the Internet  250  through at least two layers of network protection equipment. The network  200  may be internal to a location or facility (e.g. corporate network). The network  200  as illustrated includes two layers of network security: application servers  210 , and an authentication server  220 . An access management system (AMS)  230  and a firewall  240  provide protection for the network  200  (protected network/network segment). The application servers  210  and the authentication server  220  are connected to the AMS  230  which is connected to the Internet  250  through the firewall  240 . An external/partner company  260  and/or a public Internet user  270  are also connected to the Internet  250 . An exemplary operating scenario may be that an operator of the network  200  (e.g., company) desires to enable the external/partner company  260  to access the application servers  210  while blocking the public Internet user  270 . It should be understood that the exemplary system architecture is a simplified architecture for illustrative purposes. That is, system architecture is likely to include many more servers, external and partner companies, and public Internet users. 
     The firewall  240  may provide traditional proxy/firewall protection based on simple packet rules. The typical proxy/firewall will block most or all external intruders, while allowing users within the company to access internal resources as well as resources connected to the Internet  250 . The AMS  230  provides for authenticated, secure access to internal server equipment (e.g., application servers  210 ) by utilizing policies established by, for example, a system administrator. The policies define the use of more complex, multi-layer packet filtering rules, along with a means for authenticating users wishing to access resources within the company. The AMS  230  may also perform network address translation based on policies defined (e.g., authenticated users). 
       FIG. 3  illustrates an exemplary policy based NAT map  300 . The NAT map  300  is divided by user  310  (identified by source IP address at a given time) and for each user  310  external IP addresses  320  are associated with internal IP addresses  330  for the internal resources. Note that different users may access internal resources with different external IP addresses  320  but having the same internal IP address (e.g., 198.76.29.2 for user  1  and 198.76.29.5 for user  2  both translate to 10.33.96.5) where the resource resides. It is also possible that the same external IP address can be used by different users to equate to different internal addresses (not illustrated). That is, utilizing the user (destination of the packet) in the NAT map provides flexibility. The exemplary policy based NAT map  300  utilizes users and maps or associates different externally known IP addresses to internal IP addresses for each internal resource. 
       FIG. 4  illustrates an exemplary network (or network segment)  400 . It should be noted that there are similar components in both the exemplary network  400  and the exemplary network  200  of  FIG. 2  (e.g., firewall, AMS). The similar components are referred to by different reference numbers in each of the figures to illustrate that they may be different embodiments. The network  400  includes a firewall  410 , an AMS  420 , an application server  430 , and a file server  440 . The network  400  communicates via the Internet  450  with an external/partner company  460  and an external user  470 . The AMS  420  utilizes the NAT map  300  for network address translations. Initially it is pointed out that the AMS  420  authenticates a user at the external/partner company  460  and the external user  470  prior to the users accessing anything with the network  400 . According to one embodiment, user authentication may involve logging into a Web-Page hosted by the AMS  420  and entering a user name and password. Other methods of authentication, familiar to those skilled in the art, can be used. 
     We will now discuss an embodiment of network address translation for communications with this network  400  with respect to the NAT map  300  of  FIG. 3 . The user at the external/partner company  460  accesses the application server  430  by transmitting packets having an externally known IP address (198.76.29.2) as the destination address. The user transmitting the packets is determined based on the source address of the packets (198.76.28.4). The AMS  420  then utilizes the NAT map  300  to find the externally known IP address  320  for that particular user  310  to determine the internal IP address  330  (10.33.96.5). The AMS  420  accordingly translates the destination address on all packets with this flow from 198.76.29.2 to 10.33.96.5 and the packets are forwarded to the application server  430 . Likewise, when the external user  470  (68.151.70.32) transmits packets to the file server  440  utilizing the externally known IP address (198.76.29.6) the AMS  420  then finds the externally known IP address  320  for that particular user  310  and translates it to the internal IP address  330  (10.33.96.9). 
     Packets in the return flow (from application server  430  or file server  440 ) have their source address translated from local address (10.33.96.5 and 10.33.96.9 respectively) to the externally known address (198.76.29.2 and 198.76.29.6 respectively based on the user the packet is destined for). The AMS  420  determines the user by looking at the destination IP address. TCP/UDP port numbers are also mapped, as necessary, in a similar fashion. In this way, the user at the external/partner company  440  has no direct knowledge of the host IP addresses internal to the company and cannot directly access hosts within the company. 
       FIGS. 5A and 5B  illustrate an exemplary policy based NAT map  500  for User  1  ( FIG. 5A ) and User  2  ( FIG. 5B ). Although shown as separate tables, these maps may exist in a contiguous table and are simply shown as separate figures for convenience. Referring to  FIG. 5A , the first column contains external user IP addresses  510 , the second column contains external resource IP addresses  520 , the third column contains internally mapped user IP addresses  530 , the fourth column contains internally mapped resource IP addresses  540 , and the fifth column specifies the resource name  550 , as known to the device implementing the policy based NAT. 
     Referring back to  FIG. 4 , we will now discuss network address translation for communications with network  400  with respect to the policy based NAT map  500  of  FIGS. 5A and 5B . For a flow from User  1  to Resource  1 , the user will use an external IP address (198.76.28.4) as the originating source address and will use an external resource address (198.76.29.2) as the destination address. When the first packet of the flow traverses the device implementing the policy based NAT, the device can identify the user and the flow ID of the user and will use the map selector to select address maps for the internal user&#39;s IP address (10.33.96.2) as well as the internal resource address (10.33.96.5). These address maps would be used for translation of all subsequent packets pertaining to this flow. 
     Referring to  FIG. 5B , User  2  bearing the IP address of 68.151.70.32 goes through a different address map for translating the external user IP address and the external resource IP address to access the same Resource  1 . The ability to select different address maps based on user parameters results in a policy based NAT. 
     When used herein the term policy refers to a set of access or security rules associated with one or more parameters of a user including, but not limited to, group membership, level of authorization or clearance, current network address, time of day, or location. Policies allow users access to certain network resources, and deny them access to other resources, either temporarily (e.g. for time of day based rules or location based rules) or permanently (level of authorization or clearance). In one embodiment, a user logs onto a system with a user ID and a password, and based on the policies associated with that user, they receive access to, or are denied access to, certain network resources. Other mechanisms can be used to determine which policies are applicable, including determinations based on information transmitted from the user. 
     According to one embodiment, an AMS may utilize a NAT map where the user address map and the resource address map can be divided into internal maps and external maps. That is, the NAT map may include a user address map as well as a resource address map. 
       FIG. 6  illustrates a policy based NAT processor  600  that is able to perform policy based address translation. Referring to  FIG. 6 , when an incoming packet arrives at the policy based NAT processor  600 , the flow identifier is determined  610  from the packet. A determination  620  of whether the packet establishes a new flow  613  or is part of an existing flow  617 . If the packet constitutes the start of a new flow  613 , the flow identifier is directed to a map selector  640  which looks up the address map storage  630 , uses appropriate policies pertaining to the user and resource being accessed (and other policy determining parameters) and identifies an address bind  625  that should be applied to the flow. This address bind may be stored into the active address bind  650  for subsequent use. Subsequent packets of the flow may also be subject to the same translation using the same address bind(s) applied to address translator  670 . Address translator  670  may use address bind  625  to translate the incoming packet buffer  665  and perform the appropriate address translations on the incoming packet to generate an outgoing packet. 
     In the event that the incoming packet belongs to an existing flow  617 , the bind selector  660  will look up the active address binds  650  against the existing flow ID and determine the appropriate address bind to be applied for the flow associated with the incoming packet. 
     For flows originating from the internal network to the external network, the AMS may utilize a particular policy based NAT table. Similarly, for flows originating from the external network to the internal network, a different policy based NAT table may be utilized. 
     For example, if an internal user wishes to access an external web server (an external resource) and has a specific IP address they use for the web server, the internal user address map may identify the resource associated with the unique IP address as an external resource. The outside resource address map may then identify the common IP address for that resource. 
     NAT address maps may be generated automatically, and they may optionally be edited by a system administrator. In addition, the administrator may set policies for the generation and/or selection of NAT address maps. The particular NAT address map that is used at any given time may depend on the policy that applies to the particular packet flow that is being routed. For example, the NAT resource address maps are typically generated by the AMS at the time of resource definition. User address maps may be automatically generated from policies established during system configuration, but may also be edited manually to fine tune policies. According to one embodiment, default NAT address maps are generated during the initialization and configuration of the AMS. 
     Computer program instructions to implement a software embodiment of the present invention may be stored in a computer program memory or on a computer readable carrier such as a disk, memory stick, portable memory device, communications signal or carrier wave. The instruments may be carried out in any computer programming language. 
     The many features and advantages of the invention are apparent from the detailed specification. Since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described. Accordingly, all appropriate modifications and equivalents may be included within the scope of the invention.