Abstract:
A system maintains a dormant state in the host, in which no beacons (or “bubbles”) are transmitted from the host when no application or service (collectively, “processes”) of the host is accepting unsolicited traffic via the edge traversal service. When at least one application or service begins to accept unsolicited traffic via the edge traversal service, the host enters a qualified state and begins transmitting the beacons. As each additional application or service begins to accept such traffic, the number of accepting applications and services is maintained. As applications and services terminate acceptance of such traffic, the number of accepting applications and services is decremented. When the last application or service terminates acceptance of unsolicited traffic via the edge traversal service, the host re-enters the dormant state and ceases transmission of its beacons.

Description:
BACKGROUND 
       [0001]    Many computer hosts are connected within a local network to certain entry points to that local network, such as a network address translation (NAT) device or a firewall application or device positioned at an “edge” of the local network. Certain edge traversal technologies have emerged to allow legitimate unsolicited inbound traffic to traverse such edge entities. One particular implementation of such technology is an edge traversal service designed to send UDP (uniform data packet) “bubbles” from the host to artificially maintain address mapping states on edge devices in order to allow the unsolicited UDP traffic to traverse back through said edge devices. Without the bubbles, the address mapping state on the edge device may time out or close, thereby disabling the edge traversal feature until the mapping state is reinitialized or re-opened at some later point in time. Note that the host is generally unable to receive unsolicited external traffic when the edge traversal feature is disabled. In summary, an edge traversal service allows a host to receive unsolicited, inbound traffic through its local network edge. 
         [0002]    In one implementation, UDP bubbles are transmitted from a host in the local network to maintain an open state on one or more edge devices. However, the UDP bubbles sent from such hosts inside the local network act as beacons that notify both legitimate and illegitimate entities outside the local network of the host&#39;s existence, and importantly, of the host&#39;s ability to received unsolicited traffic, even when no application or service in the host is actively accepting unsolicited traffic. As such, the UDP bubbles can expose the host, and therefore the local network, to undesirable security risks, even when the host is not actively accepting unsolicited traffic. Furthermore, the bubbles can also create unnecessary traffic on a network and present privacy concerns. 
       SUMMARY 
       [0003]    Implementations described and claimed herein address the foregoing problems by maintaining a dormant state in the host, in which no beacons (or “bubbles”) are transmitted from the host when no application or service (collectively, “processes”) of the host is accepting unsolicited traffic via the edge traversal service. When at least one application or service begins to accept unsolicited traffic via the edge traversal service, the host enters a qualified state and begins transmitting the beacons. As each additional application or service begins to accept such traffic, the number of accepting applications and services (representing active edge traversal endpoints) is maintained. As applications and services terminate acceptance of such traffic, the number of accepting applications and services is decremented. When the last application or service terminates acceptance of unsolicited traffic via the edge traversal service, the host re-enters the dormant state and ceases transmission of its beacons. 
         [0004]    In some implementations, articles of manufacture are provided as computer program products. One implementation of a computer program product provides a computer program storage medium readable by a computer system and encoding a computer program. Another implementation of a computer program product may be provided in a computer data signal embodied in a carrier wave by a computing system and encoding the computer program. Other implementations are also described and recited herein. 
         [0005]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates an example host computer connected to a communications network beyond the edge of its local network. 
           [0007]      FIG. 2  illustrates an example host adding an active edge traversal endpoint. 
           [0008]      FIG. 3  illustrates example operations for adding an active edge traversal endpoint. 
           [0009]      FIG. 4  illustrates an example host deleting an active edge traversal endpoint. 
           [0010]      FIG. 5  illustrates example operations for deleting an active edge traversal endpoint. 
           [0011]      FIG. 6  illustrates an example host updating active edge traversal endpoints. 
           [0012]      FIG. 7  illustrates example operations for updating active edge traversal endpoints. 
           [0013]      FIG. 8  illustrates an example system that may be useful in implementing the described technology. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates an example host computer  100  connected to an IPv4 communications network  102  beyond the edge  104  of its IPv4 local network  106 . A NAT device  108  represents an edge device that provides an entry point for traffic into the local network  106 . Other examples of edge devices may include without limitation routers, firewalls, intrusion protection systems, intrusion detection systems, VPN gateways, edge switches, edge translators, etc. The local network  106  also includes other computing and communications entities, including without limitation another host computer  110 , a router  112 , and another host computer  114 . 
         [0015]    The host  100  includes a host firewall (HFW)  116  that is configured control traffic between the host  100  and other entities, such as computer  112 . The hosts  110  and  114  are also shown with host firewalls  117  and  118 , respectively. The host firewall  116  filters (e.g., allows or blocks) certain traffic transmitted to or from the host  100  according to specified firewall rules. In one implementation, a default firewall rule may block all inbound traffic. Given this default, one or more firewall rules can be specified as exceptions to the default in order to allow certain traffic to pass through the host firewall. For example, a firewall rule may allow all inbound traffic received by the host  100  and destined to a service Foo executing on the host  100  via TCP port  321 . Other exceptions may also be specified. The local network  106  also includes an enterprise firewall (FW)  120 , which is tasked with controlling traffic between the local network  106  and the IPv4 communications network  102 . 
         [0016]    The local network  106  and the IPv4 communications network  102  are connected within an aggregate network  122 , which also includes an IPv6 communications network  124  and an IPv6 host  126  and may include many other host computers, communication entities, security entities, etc. An edge traversal technology has been implemented within the aggregate network  122  to allow unsolicited inbound traffic to traverse the edge devices of the local network  106 , such as the NAT  108  and the enterprise firewall  120 . In one implementation, the host  100  represents an edge traversal client that supports an edge traversal tunneling protocol through which packets are tunneled from other hosts outside the local network  106 . In this manner, the host  100  supports IPv6 addressing from behind the NAT  108  in order to access the IPv6 communications network  124  and the IPv6 host  126 . 
         [0017]    The host  100  communicates with an edge traversal server  128  to obtain an address prefix from which a valid IPv6 address is configured or to help initiate communication with other clients or hosts on the IPv6 communications network  124 . The edge traversal server  128  is an IPv6/IPv4 node that is connected to both the IPv4 communications network  102  and the IPv6 communications network  124  and supports an edge traversal tunneling interface over which packets are received. In one implementation, the edge traversal server  128  assigns the host  100  an IPv6 address that incorporates its IPv4 address and the port through which it is communicating. An edge traversal relay  130  serves as a remote end of an edge traversal tunnel, forwarding data received on behalf of the edge traversal clients it serves. 
         [0018]    To allow unsolicited traffic to traverse an edge device, such as the NAT device  108 , the host sends periodic traffic  132  (i.e. edge traversal service beacons) through the edge device to the edge traversal server  128 . The beacons  132  cause the NAT device  108  to maintain the address mapping state, for example, preventing it from timing out and closing. In this manner, the beacons  132  keep a channel open through which the unsolicited emails can traverse the edge  104  to the host computer  100 . 
         [0019]    However, when no process associated with the edge traversal service is accepting unsolicited edge traversal traffic, the edge traversal service is maintained in a dormant beacon transmission state, so that no beacons  132  are transmitted through the edge device. When a process associated with the edge traversal service begins to accept unsolicited edge traversal traffic, such as through a bind or listen operation, the edge traversal service transitions to a qualified beacon transmission state, subject to other networking conditions such as host firewall rules, and initiates the transmission of the beacons  132 . When the number of processes associated with the edge traversal service that are accepting unsolicited edge traversal traffic drops to zero, the edge traversal service transitions back to the dormant beacon transmission state and ceases the transmission of the beacons  132 . 
         [0020]    Through these or similar mechanisms, the aggregate network  122 , and particularly the host  100 , can support edge traversal technology. If the edge security devices on the local network (e.g., the edge firewall  120 ) allow unsolicited traffic to an edge traversal service of hosts in the local network  106 , then the host firewall  116  will be able to make the determination about whether to pass the traffic to a target application or service within the host  100 . In order for the host  100  to securely control such edge traversal traffic, the traffic is evaluated against one or more firewall rules of the host firewall  116 . In one implementation, the host firewall  116  and an edge traversal service within the host  100  determine whether the traffic has traversed an edge of the local network, generate an edge traversal context for the traffic and evaluates the traffic, including the edge traversal context, against the applicable firewall rules to determine whether to allow traffic to be received by target in the host  100 . The firewall rule includes an edge traversal criterion that influences whether the traffic is blocked or allowed. 
         [0021]      FIG. 2  illustrates an example host  200  adding an active edge traversal endpoint, which represents a host process that is accepting unsolicited edge traversal traffic. The host  200  is capable of executing processes (e.g., application Foo  202  and service Bar  204 ) capable of accepting such traffic. To accept such traffic, a process configures the host  200  to enable network communications to the process. In one implementation, the process opens a socket to support the network communications and binds/listens to a port via a temporary edge traversal adapter address. For example, a service Foo  202  calls to a socket module  206  to open a socket. The socket module  206  communicates with a protocol module  208  (such as a TCP/IP stack module) to open the socket. The protocol module  208  calls to an application layer enforcement (ALE) module  210  in a filtering platform  212 . The protocol module  208  and the ALE module  210  establish corresponding states representing the open socket. A reference to the socket is then communicated back to the process. 
         [0022]    Having created and obtained an open socket, the process then attempts to establish a local association with the socket by assigning a local name to the socket (e.g., in step  1 , identified by the circle labeled “1” in  FIG. 2 ). In one implementation, the process creates the association for TCP via a bind command, although other commands may establish this association, such as a listen command. The association operation works through the socket module  206 , the protocol module  208 , and the filtering platform to perform a resource assignment using a filter in an edge traversal sub-layer  214  (e.g., in step  2 , identified by the circle labeled “ 2 ” in  FIG. 2 ) of the ALE module  210 . By virtue of its filters, the ALE module  210  determines whether to permit edge traversal traffic to the process (e.g., application Foo  202 ) and executes a callout function  216  (e.g., in step  3 , identified by the circle labeled “ 3 ” in  FIG. 2 ), if the association operation (e.g., bind) satisfies the filter and is otherwise permitted by the ALE module  210 . The callout causes a count of active edge traversal endpoints to be incremented in a Network Service Interface (NSI) Provider structure  218  in a framing layer module  220 , which monitors for a transition from zero to one (0→1) in this count and for a transition from one to zero (1→0) in this count. The framing layer module  220  registers (e.g., in step  4 , identified by the circle labeled “4” in  FIG. 2 ) a notification with the ALE module  210 , responsive to the addition of the active edge traversal endpoint. This registration identifies the newly added active edge traversal endpoint to the ALE module  210  so that the ALE module  210  can decrement the active edge traversal endpoint count when the endpoint is deleted at a later time. 
         [0023]    In the case of adding active edge traversal endpoints, as described with regard to  FIG. 2 , when the framing layer module  220  detects a 0→1, the framing layer module  220  notifies the kernel-mode NSI module  222  of the transition (e.g., in step  5 , identified by the circle labeled “5” in  FIG. 2 ). The kernel-mode NSI module  222  then communicates a representation of the notification to the user-mode NSI module  224  (e.g., in step  6 , identified by the circle labeled “6” in  FIG. 2 ). The user-mode NSI module  224  then communicates (e.g., step  7 , identified by the circle labeled “7” in  FIG. 2 ) a representation of the notification to the edge traversal service  226 . The edge traversal service  226 , which generally initializes to a “dormant” beacon transmission state in which no beacons are transmitted, interprets the communication as an instruction to transition from the “dormant” beacon transmission state to a “qualified” beacon transmission state in which beacons are transmitted through an edge device of the local network. 
         [0024]    As will be described below, in one implementation, the edge traversal sub-layer  214  resides in a prioritized listing of filter sub-layers (e.g., wherein the edge traversal sub-layer  214  has a lower priority or weighting than a host firewall sub-layer or network service hardening sub-layer). In this manner, if a higher priority filter sub-layer blocks the association operation (e.g., because of a rule preventing socket operations by the process, such as socket creation), the block supersedes any permission that may be allocated by the edge traversal sub-layer  214 , thereby preventing the incrementing of the active edge traversal endpoint count and blocking the transmission of any beacons based solely on the present association operation. It should be understood, however, that other applications and/or association operations may have already caused a 0→1 transition and initiated the transmission of beacons. 
         [0025]    Also illustrated in  FIG. 2  are a host firewall service  228  and a base filtering engine  230 , which communicate with the filtering platform  212  to block or permit traffic destined for processes in the host  200 . In the illustrated implementation, both the firewall features and the edge traversal features rely on a single filtering platform, although other implementations may be configured differently (e.g., different filtering platforms, non-filtering implementations, etc.). For examine, an NDIS (Network Driver Interface Specification) driver or TDI (Transport Data Interface) hook could be utilized to intercept and act upon edge traversal traffic. 
         [0026]      FIG. 3  illustrates example operations  300  for adding an active edge traversal endpoint. An association operation  302  associates a process, such as an executing application or service, to a socket. Example operations implementing an association operation may include a bind or listen command. A resource assignment operation  304  uses classification against filters in an edge traversal layer of an ALE module to execute the bind or listen command. The resource assignment is implemented using a prioritized listing of filter sub-layers. An example of the prioritized listing is illustrated below, wherein the higher weight represents a higher priority, although other implementations are contemplated: 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Example ALE Sub-layer Weighting 
               
             
          
           
               
                 Weight 
                 Sub-layer 
               
               
                   
               
               
                 . . . 
                 . . . 
               
               
                 3 
                 Firewall 
               
               
                 2 
                 Network Service 
               
               
                   
                 Hardening 
               
               
                 1 
                 Edge Traversal 
               
               
                 0 
                 Inspection 
               
               
                   
               
             
          
         
       
     
         [0027]    The resource assignment operation  304  evaluates the sub-layers from highest priority (or weight) to lowest priority (or weight). If all higher priority sub-layers permit the socket operation, the edge traversal layer may permit the socket operation, if the association operation satisfies filter in the edge traversal sub-layer. If the requesting process satisfies the filters, which coordinate to permit or block such traffic, then a decision operation  306  directs processing to a callout operation  308  to execute the callout. 
         [0028]    In contrast, if a higher priority sub-layer (e.g., a firewall sub-layer) blocks the socket operation by the requesting process, then even if there is a filter in the edge traversal sub-layer that matches the requesting process and permits the socket operation, the resource assignment operation  304  will not satisfy the process&#39;s request and will not add a new active edge traversal endpoint because the higher priority sub-layer blocks the socket operation. In both cases, a decision operation  306  will direct processing to a maintenance operation  322 , which maintains the current state (e.g., qualified or dormant) without incrementing the active edge traversal endpoint count. 
         [0029]    The callout operation  308  instructs a framing layer to increment an active edge traversal endpoint count in an NSI provider structure. A registration operation  310  registers the new active edge traversal endpoint with the ALE module. The registration instructs the ALE module to call the framing layer when the new active edge traversal endpoint is later terminated by the process (e.g., the process terminates and closes its sockets). 
         [0030]    A decision operation  314  detects whether the incrementing operation  310  causes the count to transition from zero to one. If not, processing proceeds to a maintenance operation  322 , which maintains the current beacon transmission state (e.g., qualified or dormant). If the 0→1 transition is detected, then a notifying operation  316  notifies a kernel-mode NSI module of the new qualified beacon transmission state, another notifying operation  318  notifies a user-mode NSI module of the new qualified beacon transmission state, and yet another notifying operation  320  notifies an edge traversal service of the new qualified beacon transmission state. A state operation  324  sets the current beacon transmission state to “qualified”, and a beacon operation  326  initiates transmission of the beacons from the edge traversal service. 
         [0031]      FIG. 4  illustrates an example host  400  deleting an active edge traversal endpoint. The host  400  executes processes (e.g., application Foo  402  and service Bar  404 ) capable of accepting unsolicited edge traversal traffic. To terminate acceptance of such traffic by the process or in response to a request to terminate the process, the process terminates the network communications supporting such traffic. In one implementation, the process communicates (e.g., in step  1 , identified by the circle labeled “1” in  FIG. 4 ) with a socket module  406  to effect closure of the socket through which Such traffic is communicated. The socket module  406  communicates with a protocol module  408  (such as a TCP/IP stack module) to close the socket. The protocol module  408  calls (e.g., in step  2 , identified by the circle labeled “2” in  FIG. 4 ) to an application layer enforcement (ALE) module  410  in a filtering platform  412 . The protocol module  408  and the ALE module  410  terminate their corresponding states representing the open socket, as part of the process of closing the socket. 
         [0032]    In the case of deleting an active edge traversal endpoint, as described with regard to  FIG. 4 , an endpoint deletion module  432  within the filtering platform  412  uses the registration of the active edge traversal endpoint associated with the closed socket (see e.g., step  4  of  FIG. 2 ) to cause the decrementing of the count of active edge traversal endpoints in an NSI provider structure  418 . When the framing layer module  420  detects a  10  transition in the count, the framing layer module  420  notifies the kernel-mode NSI module  422  of the transition (e.g., in step  4 , identified by the circle labeled “4” in  FIG. 4 ). The kernel-mode NSI module  422  communicates a representation of the notification to the user-mode NSI module  424  (e.g., in step  5 , identified by the circle labeled “5” in  FIG. 4 ). The user-mode NSI module  424  then communicates (e.g., step  6 , identified by the circle labeled “6” in  FIG. 4 ) a representation of the notification to the edge traversal service  426 . The edge traversal service  426 , which would have been in a “qualified” beacon transmission state prior to this notification, interprets the communication as an instruction to transition from the “qualified” beacon transmission state to a “dormant” beacon transmission state in which the transmission of beacons through an edge device of the local network are terminated. 
         [0033]    Also illustrated in  FIG. 4  are a host firewall service  428  and a base filtering engine  430 , which communicate with the filtering platform  412  to block or permit traffic destined for processes in the host  400 . In the illustrated implementation, both the firewall features and the edge traversal features rely on a single filtering platform, although other implementations may be configured differently (e.g., different filtering platforms, non-filtering implementations, etc.). 
         [0034]      FIG. 5  illustrates example operations for deleting an active edge traversal endpoint. A termination operation  502  initiates termination of a process, such as an executing application or service, and/or termination of a network connection. Example operations implementing an association operation may include a close command in reference to a TCP connection. A protocol module processes a resulting instruction to close the network connection and communicates with an application layer enforcement (ALE) module in a filtering platform. The protocol module and the ALE module coordinate termination of their corresponding states representing the open socket, as part of the process closing the socket. 
         [0035]    A deletion operation  508  uses the registration of the active edge traversal endpoint associated with the closed socket (see e.g., step  4  of  FIG. 2 ) to cause the decrementing of the count of active edge traversal endpoints in an NSI provider structure, in a decrementing operation  510 . A decision operation  512  detects whether the decrementing operation  510  causes the count to transition from one to zero (1→0). If not, processing proceeds to a maintenance operation  524 , which maintains the current beacon transmission state (e.g., dormant). If the 1→0 transition is detected, then a notifying operation  514  notifies a kernel-mode NSI module of the new dormant beacon transmission state, another notifying operation  516  notifies a user-mode NSI module of the new dormant beacon transmission state, and yet another notifying operation  518  notifies an edge traversal service of the new dormant beacon transmission state. A state operation  520  sets the current beacon transmission state to “dormant”, and a beacon operation  522  terminates transmission of the beacons from the edge traversal service. 
         [0036]      FIG. 6  illustrates an example host  600  updating active edge traversal endpoints. An edge traversal service  602  in the host may momentarily shut down and restart for a variety of reasons (e.g., system problems, programming error, etc.). As a result, if the edge traversal service  602  is restarted after one or more active edge traversal endpoints had previously been added, the edge traversal service  602  determines whether it should restart in qualified or dormant beacon transmission state. 
         [0037]    Accordingly, the edge traversal service  602  restarts and queries (e.g., in step  1 , identified by the circle labeled “1” in  FIG. 6 ) a user-mode network service interface  604  to obtain the current beacon transmission state. The user-mode network service interface module  604  passes (e.g., in step  2 , identified by the circle labeled “2” in  FIG. 6 ) the query along to a kernel-mode network service interface module  606 . The kernel-mode network service interface module  606  queries (e.g., in step  3 , identified by the circle labeled “3” in  FIG. 6 ) a framing layer  608  to determine the current count of active edge traversal endpoints maintained by a NSI provider structure  610 . Based on this determination, the framing layer  608  determines whether the current count is greater then zero (&gt;0), for which the beacon transmission state is determined to be “qualified”, or equal to zero (=0), for which the beacon transmission state is determined to be “dormant” and passes (e.g., in step  4 , identified by the circle labeled “4” in  FIG. 6 ) a notification of the beacon transmission state to the kernel-mode network service interface module  606 . The kernel-mode network interface module  606  passes (e.g., in step  5 , identified by the circle labeled “5” in  FIG. 6 ) a representation of the notification of the beacon transmission state to the user-mode network interface module  604 , which notifies (e.g., in step  6 , identified by the circle labeled “6” in  FIG. 6 ) the edge traversal service  602  of its current beacon transmission state. The edge traversal service  602  therefore transmits or does not transmit edge traversal beacons according to this notification of the beacon transmission state. 
         [0038]      FIG. 7  illustrates example operations  700  for updating active edge traversal endpoints. An initialization operation  702  restarts the edge traversal service. A query operation  704  (e.g., initiated by the edge traversal service or some other service) queries the user-mode NSI module for the beacon transmission state. Another query operation  706  queries the kernel-mode NSI module for the beacon transmission state. Yet another query operation  708  queries the framing layer, and specifically the NSI provider structure, beacon transmission state based on the count of active edge traversal endpoints. 
         [0039]    If the count is greater than zero, processing proceeds through notification operations  714 ,  716 , and  718  by communicating through the kernel-mode and user-mode NSI modules to notify the edge traversal service that it should achieve a qualified beacon transmission state. Responsive to this notification, the edge traversal service initiates beacon transmission in an initiation operation  720  and maintains the qualified beacon transmission state in a maintenance operation  722 . 
         [0040]    If the count is equal to zero, processing proceeds through notification operations  724 ,  726 , and  728  by communicating through the kernel-mode and user-mode NSI modules to notify the edge traversal service that it should achieve a dormant beacon transmission state. Responsive to this notification, the edge traversal service does not initiate or otherwise terminates beacon transmission in an initiation operation  730  and maintains the dormant beacon transmission state in a maintenance operation  732 . 
         [0041]    The example hardware and operating environment of  FIG. 8  for implementing the invention includes a computing device, such as general purpose computing device in the form of a gaming console or computer  20 , a mobile telephone, a personal data assistant (PDA), a set top box, or other type of computing device. In the implementation of  FIG. 8 , for example, the computer  20  includes a processing unit  21 , a system memory  22 , and a system bus  23  that operatively couples various system components including the system memory to the processing unit  21 . There may be only one or there may be more than one processing unit  21 , such that the processor of computer  20  comprises a single central-processing unit (CPU), or a plurality of processing units, commonly referred to as a parallel processing environment. The computer  20  may be a conventional computer, a distributed computer, or any other type of computer; the invention is not so limited. 
         [0042]    The system bus  23  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, a switched fabric, point-to-point connections, and a local bus using any of a variety of bus architectures. The system memory may also be referred to as simply the memory, and includes read only memory (ROM)  24  and random access memory (RAM)  25 . A basic input/output system (BIOS)  26 , containing the basic routines that help to transfer information between elements within the computer  20 , such as during start-up, is stored in ROM  24 . The computer  20  further includes a hard disk drive  27  for reading from and writing to a hard disk, not shown, a magnetic disk drive  28  for reading from or writing to a removable magnetic disk  29 , and an optical disk drive  30  for reading from or writing to a removable optical disk  31  such as a CD ROM or other optical media. 
         [0043]    The hard disk drive  27 , magnetic disk drive  28 , and optical disk drive  30  are connected to the system bus  23  by a hard disk drive interface  32 , a magnetic disk drive interface  33 , and an optical disk drive interface  34 , respectively. The drives and their associated computer-readable media provide nonvolatile storage of computer-readable instructions, data structures, program modules and other data for the computer  20 . It should be appreciated by those skilled in the art that any type of computer-readable media which can store data that is accessible by a computer, such as magnetic cassettes, flash memory cards, digital video disks, random access memories (RAMs), read only memories (ROMs), and the like, may be used in the example operating environment. 
         [0044]    A number of program modules may be stored on the hard disk, magnetic disk  29 , optical disk  31 , ROM  24 , or RAM  25 , including an operating system  35 , one or more application programs  36 , other program modules  37 , and program data  38 . A user may enter commands and information into the personal computer  20  through input devices such as a keyboard  40  and pointing device  42 . Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  21  through a serial port interface  46  that is coupled to the system bus, but may be connected by other interfaces, such as a parallel port, game port, or a universal serial bus (USB). A monitor  47  or other type of display device is also connected to the system bus  23  via an interface, such as a video adapter  48 . In addition to the monitor, computers typically include other peripheral output devices (not shown), such as speakers and printers. 
         [0045]    The computer  20  may operate in a networked environment using logical connections to one or more remote computers, such as remote computer  49 . These logical connections are achieved by a communication device coupled to or a part of the computer  20 ; the invention is not limited to a particular type of communications device. The remote computer  49  may be another computer, a server, a router, a network PC, a client, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  20 , although only a memory storage device  50  has been illustrated in  FIG. 8 . The logical connections depicted in  FIG. 8  include a local-area network (LAN)  51  and a wide-area network (WAN)  52 . Such networking environments are commonplace in office networks, enterprise-wide computer networks, intranets and the Internet, which are all types of networks. 
         [0046]    When used in a LAN-networking environment, the computer  20  is connected to the local network  51  through a network interface or adapter  53 , which is one type of communications device. When used in a WAN-networking environment, the computer  20  typically includes a modem  54 , a network adapter, a type of communications device, or any other type of communications device for establishing communications over the wide area network  52 . The modem  54 , which may be internal or external, is connected to the system bus  23  via the serial port interface  46 . In a networked environment, program modules depicted relative to the personal computer  20 , or portions thereof, may be stored in the remote memory storage device. It is appreciated that the network connections shown are example and other means of and communications devices for establishing a communications link between the computers may be used. 
         [0047]    In an example implementation, an application layer enforcement module, a host firewall module, an edge traversal service module, a framing layer module, and other modules may be embodied by instructions stored in memory  22  and/or storage devices  29  or  31  and processed by the processing unit  21 . A beacon, an NSI provider structure, and other data may be stored in memory  22  and/or storage devices  29  or  31  as persistent datastores. 
         [0048]    The technology described herein is implemented as logical operations and/or modules in one or more systems. The logical operations may be implemented as a sequence of processor-implemented steps executing in one or more computer systems and as interconnected machine or circuit modules within one or more computer systems. Likewise, the descriptions of various component modules may be provided in terms of operations executed or effected by the modules. The resulting implementation is a matter of choice, dependent on the performance requirements of the underlying system implementing the described technology. Accordingly, the logical operations making up the embodiments of the technology described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language. 
         [0049]    The above specification, examples and data provide a complete description of the structure and use of example embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. In particular, it should be understood that the described technology may be employed independent of a personal computer. Other embodiments are therefore contemplated. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. Changes in detail or structure may be made without departing from the basic elements of the invention as defined in the following claims. 
         [0050]    Although the subject matter has been described in language specific to structural features and/or methodological arts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claimed subject matter.