Abstract:
A test method for Internet-Protocol packet networks that verifies the proper functioning of a dynamic pinhole filtering implementation as well as quantifying network vulnerability statistically, as pinholes are opened and closed is described. Specific potential security vulnerabilities that may be addressed through testing include: 1) excessive delay in opening pinholes, resulting in an unintentional denial of service; 2) excessive delay in closing pinholes, creating a closing delay window of vulnerability; 3) measurement of the length of various windows of vulnerability; 4) setting a threshold on a window of vulnerability such that it triggers an alert when a predetermined value is exceeded; 5) determination of incorrectly allocated pinholes, resulting in a denial of service; 6) determining the opening of extraneous pinhole/IP address combinations through a firewall which increase the network vulnerability through unrecognized backdoors; and 7) determining the inability to correlate call state information with dynamically established rules in the firewall.

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 10/678,328, now U.S. Pat. No. 7,421,734, which was filed on Oct. 3, 2003, and which is hereby expressly incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of communications and, in particular, to methods and apparatus for testing certain security aspects of firewalls used in packet networks. 
     BACKGROUND OF THE INVENTION 
     The transmission of voice signals over a packet network offers economies of scale which make it likely that common carriers will, over time, evolve their circuit switched voice networks into converged services packet switched networks that will transport voice traffic in packets. The full realization of this voice over packet network paradigm, however, will likely be delayed until the security of the voice traffic carried over the packet network is improved to the point at which it rivals that of present day circuit switched networks. 
     A likely protocol to be employed in a voice over packet network is Internet Protocol, or more conveniently, IP. Accordingly, such networks are oftentimes referred to as voice over Internet Protocol networks (VoIP). 
     IP has become attractive for such applications, in part, because of its ubiquity. Unfortunately however, IP and networks designed thereon suffer from a lack of security as a legacy of how IP networks were originally designed with little or no security functions built in. Recent attempts to remedy the security deficiencies of IP have focused on protocol enhancements such as those which include the incorporation of IPSecurity (IPSec) at the Network Layer, and other schemes at the Application Layer (e.g., application security protocols). 
     In VoIP networks, these new security enhancements can be difficult to implement, either because of the distributed nature of VoIP networks (many hops), or because they frequently utilize digital certificate-based key systems which are difficult to manage—especially for large, common carrier size networks. One alternative is to protect crucial network assets, such as server farms of media gateways, signaling gateways, and softswitches by employing network perimeter protection devices that block unwanted and/or potentially nefarious traffic from reaching those assets. Unfortunately however, VoIP networks have specific requirements that make using traditional perimeter protection devices, such as firewalls, not practical as such devices, and in particular firewalls, typically block unwanted traffic on a specific IP port in a static manner, i.e., specific ports are allowed/excluded independent of time. 
     In a VoIP network, ports used to carry the media part of a call are normally dynamically assigned through signaling, released upon call termination, and reused for subsequent call(s) later. As a result, a scheme was designed that permitted firewalls to open and close ports dynamically, for a specific call, from signaling information obtained from a signaling channel at call setup and call termination. This scheme and related method(s) are sometimes referred to as “dynamic pinhole filtering”, as the firewalls filter traffic dynamically by opening/closing ports (pinholes) depending upon the state and progress of a call. When implemented correctly at the network perimeter, dynamic pinhole filtering advantageously provides protection at a level of granularity not realizable through other current security technologies. 
     As can be appreciated, strict verification of the correctness of a dynamic pinhole filtering implementation is of paramount importance as a defective implementation could result in “windows of vulnerability” which could be maliciously exploited to invade the very assets being protected. Worse still, a partially correct implementation may contribute to a false sense of security, while leaving network assets exposed to malicious attack or takeover. Such windows of vulnerability can, in turn, be used by a malicious attacker for Denial of Service Attacks in simple cases. In more complex cases, such windows of vulnerability can be used by a malicious attacker to takeover network assets that can be used to control and disrupt other parts of the network. 
     Accordingly, a continuing need exists for methods that provide or otherwise facilitate the strict verification of security measures employed in VoIP networks, and in particular networks utilizing dynamic pinhole filtering. In particular, there is a need for methods of verifying firewall operation prior to deployment, a need for methods of determining the maximum loading that is possible on a firewall prior to an unacceptable degradation in security and/or service, and there is also a need for methods of monitoring a firewall while deployed in an active system to insure that it is operating properly with port opening and closing delays remaining within preselected limits. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to firewall testing methods and apparatus. The results of the testing methods can be used to verify compliance of firewalls to design specifications and/or engineer firewalls to meet expected loading conditions while providing the desired level of responsiveness, e.g., in terms of port opening and closing times. The methods and apparatus of the present invention can also be used to monitor and test a firewall system while in use in a network application. Failures of various tests, e.g., excessive port opening and/or closing times, are detected and reported to a management system. The management system responds to such alarms by limiting traffic flow, redirecting traffic, performing time and space correlations, root cause analyses, and/or notifying the system administrators of the problem. 
     The testing methods and apparatus of the invention are well suited for testing firewalls which open and close ports in a dynamic manner to support VoIP calls. 
     Among the features to which the present invention is directed are 1) test apparatus and a testing system; 2) testing methods involving: a) checking whether firewall ports are open and/or closed as dictated by various firewall rules and/or b) opening and/or closing delays associated with opening and closing ports in response to session signals used to establish and/or terminate media sessions; 3) determining the effect of increasing traffic loads, e.g., session signaling loads, on firewall port opening and/or closing delays; and 4) the monitoring of an active firewall to a) detect the effect of traffic loading on port opening and/or closing delays, b) generate an alarm when a detected opening and/or closing delay exceeds a pre-selected threshold; and c) taking one or more actions in response to a generated port opening or closing delay alarm to reduce the load on the firewall to which the alarm corresponds and/or take other measures to ensure that firewall security is maintained. Additionally, by way of example, a time/spatial fault detector coupled with a root-cause analysis engine could help sectionalize in time and space where and when one or more security violations have occurred in a large network. This may be done by correlating the output of various port opening and closing delay time monitoring devices deployed throughout the network to determine the cause and locality of actions which interfere with proper firewall operation. The time/spatial fault detector and root-cause analysis engine are, in some embodiments, included in a security management system which receives input from multiple firewalls and/or monitoring systems distributed throughout the network. 
     A test system implemented in accordance with the invention includes at least two novel test apparatus of the present invention, referred to as an Integrated Intelligent End Points (IIEPs). At least one of the test apparatus includes a traffic generator, e.g., a session signal generator, and a probe signal generator. The traffic generation module, included in an IIEP, is used for generating call and/or other media traffic as part of the test process. The probe signal generator module is used to generate test signals which are used to probe whether ports are opened and/or closed. Each EEP also normally includes a traffic/probe signal analysis and/or report generation module included that is used to perform analysis on signals, e.g., probe signals, detected passing through the firewall. A timing/synchronization module is included in each of IIEP. The timing/synchronization module is used to synchronize the timing of the IIEP, e.g., to an external clock source or another IIEP. 
     An originating IIEP is positioned “outside” of the firewall within an untrusted zone and a target IIEP is positioned “inside” of the firewall within a trusted zone. The two devices work together to test the firewall&#39;s operation. Each IIEP includes “intelligence”, e.g., control logic and/or software routines which allow the analysis module and various other modules, such as traffic generation and probe signal generation modules, to work together in a coherent manner and to interoperate with other IIEPs to implement the testing method of the present invention which will be discussed in detail below. 
     Thus, the test apparatus of the present invention includes traffic and probe signal generators located in the untrusted zone outside a firewall and an analysis device located inside a trusted zone positioned behind the firewall. The probe test signal generator and the analysis device, e.g., analysis module of the IIEP located in the trusted zone, operate in a synchronized manner, with the probe test generator directing test signals at the firewall&#39;s ports, which may be used for media traffic, and the analysis device looking to determine what test signals, if any, pass through the ports and whether such signals should have been allowed through the firewall in accordance with the firewall rules. Such rules may include rejecting signals from source devices having IP addresses which have not been legitimated to the firewall, e.g., not associated with an ongoing media session through the use of session signaling. The firewall rules may also include rejecting traffic directed from a device having a legitimated IP address but which is directed to a port which should not be open. Firewall processing will also normally involve dynamically opening and closing ports in the firewall for media sessions, e.g., voice or data sessions, associated with an IP address that has been legitimated through the use of appropriate session establishment signaling. 
     In accordance with one feature of the invention, the ability of a firewall to block media signals corresponding to a source address which has not been legitimated through session signaling is tested by directing traffic at the firewall&#39;s media ports from an IP address which has not been associated by the firewall with an active media session. Signals which are allowed to pass through the firewall&#39;s media ports from the source that does not have an IP address associated with an ongoing media session are detected and interpreted as indications that the firewall filtering on IP addresses is not working properly. 
     In addition to address filtering, port filtering is also tested. The combination of IP address and port identifier is used to identify the port to be accessed. An IP address is legitimated with the firewall by initiating a media session, e.g., a call. A pair of ports are opened, assuming proper firewall operation for the legitimated IP address, for the initiated call while the other ports that may be associated with the legitimated IP address, and used for media signals, should remain closed. To test the port filtering, test signals are directed at the firewall&#39;s full range of ports using the legitimated IP address as the source address for the test signals. The test signals should pass the IP address filtering portion of the firewall filtering process but should be rejected based on the port portion of the testing process with the exception of the signals directed to the ports that were associated with the established call. The analysis device monitors during this phase of the testing process for signals passing through the firewall and notes any ports through which a signal is received as an open port. The generated list of detected open ports is compared to a list of ports associated with the source IP address which should be open, e.g., the ports assigned to the ongoing call. Ports through which signals were received that should not have been open are identified as erroneously open ports. If a port should have been open, and it is a port for traffic going in the direction of the analysis device, and a signal was not received through the port, the port is identified as being erroneously closed. The testing of the port open/closed status for the legitimated IP address is indicative of how the firewall would respond to signals directed from another legitimated IP address to such ports. 
     In addition to IP address and basic port filtering, the rate at which ports are opened and closed in response to session establishment and session termination signals, e.g., traffic signals, is monitored. Probe test signals are directed at the firewall&#39;s ports associated with a source IP address that was used to initiate a call or other media session. The time between the session establishment signal, which should trigger port opening, and the time a port corresponding to the session being established is opened is measured. In various embodiments this is done by detecting the time between the signal which should cause a port to open and the time a test probe signal passes through the firewall port associated with the established session as detected by the analysis device located on the trusted side of the firewall. Port closing delay is tested in a similar manner with the analysis module measuring the time delay between a session signal which should cause the port corresponding to an established session to close and the time probe test signals cease passing through the port associated with the terminated session. 
     To generate a more representative measure of opening and closing delays, multiple calls may be initiated and then terminated. The multiple calls may each have the same source IP address but use, e.g., be assigned to, different ports in the firewall. The calls may be initiated and terminated in parallel. The measured opening delays corresponding to the multiple calls can, and in various embodiments are, statistically averaged to generate an average measured opening delay. Similarly measured closing delays corresponding to the multiple calls can, and in various embodiments are, statistically averaged to generate an average measured closing delay. Plots of opening and closing delays, e.g., average delays, measured under different system conditions or measured for different systems may be generated and used as an engineering tool in accordance with the invention. 
     The effect of traffic loading is tested in various embodiments by increasing firewall traffic, e.g., session signaling which triggers the opening and/or closing ports, and measuring the corresponding opening and closing delays for different traffic loads. A given firewall may be specified with maximum acceptable port opening and/or closing delay threshold values, e.g., pinhole opening and/or closing delay threshold times. It is possible, based on testing, in accordance with the present invention, to determine the maximum traffic load for the given firewall before the operational opening and/or closing delays will exceed the maximum acceptable threshold values, e.g., maximum opening and/or closing delay times. Different thresholds may be used to define the maximum acceptable opening and closing delays. Determining this information facilitates correct engineering of a firewall system so that it will handle the expected loads. 
     Different processors may be tested in a given firewall application to determine the maximum traffic load they can support for a maximum permitted closing and/or opening delay. By combining this information with expected traffic load information, processors are, in some implementations, selected based on the testing methods of the present invention to match anticipated traffic loads thereby permitting cost effective investment and hardware deployment. 
     The test methods of the present invention which are used to determine port opening and closing delays may be, and in some embodiments are, used in an active network. In such cases, the amount of test traffic generated at any given time is kept to a minimal amount to avoid interfering with actual traffic. A maximum closing delay threshold is set in some embodiments. The closing delay is monitored through limited testing on an ongoing and/or periodic basis. This may be done by establishing a call from a device having a particular IP addresses associated with it, directing probe signals at the range of ports which can be associated with the particular IP address and measuring opening and/or port closing times based on the time signals are detected passing through the firewall and/or stop passing through the firewall through one or more ports associated with the particular IP address being used for the test call. Closing delays approaching and/or exceeding the maximum acceptable closing delay are reported to the security management system. The security management system then takes steps to reduce the load on the firewall, e.g., by modifying network routing parameters to reduce the traffic directed to the firewall and/or by controlling the node in which the firewall is located to drop traffic, e.g., traffic above a pre-selected threshold. System administrators are notified of closing delay problems so that they can upgrade the affected firewall and/or take other steps to address firewall problems. Correlation from various firewall monitoring modules and/or other devices distributed throughout the network can be used to analyze in space and time when/where a security problem, such as excessive port closing delays, is occurring and feed the information into an analysis tool to identify a root cause of the problem and/or the location of the cause of the problem, thereby enabling further action. 
     During testing of a system in use, test probe signals are normally directed to the ports corresponding to a call which is established for testing purposes with care being taken to avoid directing signals to IP address/port combinations which may be used for other calls. Accordingly, the test call and probe test signals do not directly affect calls associated with IP addresses that are different from the one being used by the test device of the present invention. 
     In most but not all embodiments, the IIEPs of the present invention include both signal generation, e.g., traffic and test probe signal generation, capabilities as well as monitoring/analysis abilities. Thus, when used in pairs with one IIEP located inside the trusted zone and another located in the untrusted zone, it is possible to generate traffic in both directions and determine if the firewall operates properly in regard to each of a pair of uni-directional ports that may be involved in an established test call. The IIEPs of the present invention include sufficient logic that one device is able to initiate a call with each device then generating and transmitting test probe signals to check the status of the ports in each direction. The results of the firewall testing, determined by each of the IIEPs e.g., in regard to one direction of probe test signal flows, may be combined into a single report by the IIEPs which operate together in a synchronized manner. The analysis module in the IIEP on the trusted side of the firewall may perform this function. 
     Our inventive method may proceed in stages, by verifying pinhole operation according to a set of static rules (IP address and/or port rules) as well as verifying pinhole operation according to a set of dynamic rules, e.g., rules associated with opening and/or closing ports in response to session signaling in a timely manner. Our inventive method advantageously verifies the dynamic rule operation from a traffic source compliant with the static rules, adding further credence to the certification of proper dynamic rule operation and compliance. 
     It should be appreciated that specific potential security vulnerabilities that may be addressed through our inventive testing method include: 1) excessive delay in opening pinholes, resulting in an unintentional denial of service; 2) excessive delay in closing pinholes, creating a closing delay window of vulnerability; 3) measurement of the length of various windows of vulnerability; 4) setting a threshold on a window of vulnerability such that it triggers an alert when a predetermined value is exceeded; 5) determination of incorrectly allocated pinholes, resulting in a denial of service; 6) determining the opening of extraneous pinhole/IP address combinations through a firewall which increases the network vulnerability through unrecognized backdoors; and 7) determining the inability to correlate call state information with dynamically established rules in the firewall. 
     Advantageously, our inventive method is applicable to dynamic pinhole filtering as used in conjunction with specific VoIP protocols currently in use. More specifically, our method is applicable to the H.323 series of recommendations originating from the International Telecommunications Union (ITU) in versions 1 and 2, and the Session Initiation Protocol (SIP) defined by the Internet Engineering Task Force (IETF) in versions RFC 2543 and RFC 3261. 
     Numerous additional features and benefits of the methods and apparatus of the present invention will be apparent from the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a network arrangement according to the present invention for SIP call flows. 
         FIG. 2  illustrates a testing device which may be used as a source of firewall test signals an/or as a device for receiving and analyzing test signals which pass through a firewall being tested. 
         FIG. 3  is an alternative representation of the network of  FIG. 1  with test signals directed to and passing through the firewall being shown. 
         FIG. 4  is a timeline depicting various SIP signaling points and a window of vulnerability associated with opening and closing ports in response to SIP signaling. 
         FIG. 5 , which comprises the combination of  FIGS. 5A and 5B , is a flow chart illustrating the steps of an exemplary firewall test method implemented in accordance with the invention. 
         FIG. 6  depicts a network test arrangement according to the present invention which may be used to test firewall operation in the case of H.323 signaling. 
         FIG. 7  is a timeline illustrating various H.323 signaling points and a window of vulnerability associated with opening and closing ports in response to H.323 signaling. 
         FIG. 8  illustrates an active system subject to firewall monitoring and security control implemented in accordance with one embodiment of the invention. 
         FIG. 9  illustrates the firewall monitoring and security steps performed in an active network in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is particularly well suited for testing firewalls which open and close ports in a dynamic manner, e.g., to support session signaling such as for VoIP calls. In such applications, a firewall&#39;s ability to reject signals from IP addresses which have not initiated a media session, e.g., call, or are not being used in an ongoing media session is important. A firewall&#39;s ability to close and keep closed ports which are not being used in active media sessions, e.g., calls, and the ability to open and close ports to allow call signals to pass through on a dynamic, e.g., per call basis, in a timely manner are important to insure network security and a satisfactory level of service. 
     VoIP calls are commonly implemented using SIP or H.323 signaling to manage call establishment and termination. The methods and apparatus of the present invention are well suited for testing firewalls intended for either type of signaling application. For purposes of explaining the invention, the firewall testing methods and apparatus of the present invention will first be discussed in the context of a SIP application. As will become apparent, from the discussion which follows, the invention is not limited to SIP and can be used with a wide range of signaling protocols and firewall applications where ports in a firewall are opened and closed dynamically, e.g., H.323 protocol. 
     SIP calls are typically conducted in three steps, namely, 1) Call Registration, 2) Call Signaling, and 3) Call Media Exchange. The Call Registration and Call Signaling steps are both carried out using a well known port (p: 5060) and for which firewall static rules may be defined. 
     The signaling exchange includes a negotiation/selection of two logical ports (talking and listening), which then carry the media exchange (voice conversation) for a normal call. These talking and listening ports are dynamically chosen from a range of allowed ports, used for the duration of the call, and then released. Since they are chosen dynamically, their identification normally cannot be predicted in advance. 
     The port information can however, be determined from the specific signaling message(s) that include the logical port assignment functions (INVITE, 200 OK). Thus, the port information can be determined by monitoring and/or examining the appropriate messages as is done in various embodiments of the invention. Once this information is derived, a state machine may be constructed for the two logical ports involved in the call and/or a set of information indicating the status of the ports (open/closed) may be generated. The state of the call may then be monitored for the duration of the call. At the end of the call, corresponding messages (BYE) may be used to trigger the tear-down of the state machine and the closure of the two logical ports. The time between the BYE message and the actual closing of the ports should be relatively small and is monitored in accordance with the invention. 
     As can be appreciated, the determination of the port information and call-state monitoring which are used to trigger port closure is an important function for the proper operation of dynamic pinhole filtering. The architectural placement of these functions depends upon the processing power of the firewall involved and any performance and/or scalability requirements. Consequently, these functions may be implemented in, e.g., a router or other device such as device  140  shown in  FIG. 1  which operates as a firewall, or distributed to an external server, e.g., proxy  150 , that communicates to the firewall the identity of the ports to be opened and closed and the initiation of same. The incorporation of the firewall control proxy functionality  150  into the firewall  140  is largely an implementation issue which has little bearing on the test methods of the invention. For purposes of explaining the invention, a firewall  240  will be discussed with the understanding that this firewall  240  may be implemented as a single firewall device  140  which includes firewall control proxy functionality or as a combination of a firewall device  140  and a separate firewall control proxy  150 . 
     With further reference now to  FIG. 1 , there is shown a VoIP network arrangement that we will use to describe our inventive test method. Specifically, network  100  includes both a trusted user zone  120  and an untrusted zone  110  separated by a firewall system  240 . The firewall system  240 , referred to hereafter as firewall  240 , includes, a firewall  140  which may be implemented, e.g., as part of a router, and a Firewall Control Proxy (FCP)  150  which is coupled to the firewall  140 . As discussed above, FCP  150  may be incorporated directly into firewall device  140 . Shown further are Integrated Intelligent End Points (IIEPs)  130 ,  132  implemented in accordance with the present invention. IIEPs  130 ,  132  are placed at appropriate locations within the VoIP network. In particular, originating IIEP  130  is positioned “outside” of the firewall within the untrusted zone  110  and target IIEP  132  is positioned “inside” of the firewall within the trusted zone  120 . 
     When implemented in the distributed manner shown in  FIG. 1 , dynamic pinhole function state information (DPFSI)  151  is not located in the firewall device  140 , but rather in the external FCP  150  coupled to the firewall device  140 . The external device, FCP  150 , communicates the required port (pinhole) information to the firewall  140 . The pinhole information  151  includes port information, e.g., source port address, destination port address, source port number, destination port number and protocol information for on-going media sessions, e.g., calls. Source and/or Destination IP address information may also be included in the pinhole information, e.g., DPFSI  151 , so that a media signal associated with IP addresses which do not correspond to an active media session can be blocked, e.g., prior to performing filtering on port number information. In embodiments where the FCP functionality is included in the firewall  140 , the firewall device  140  includes DPFSI  151 . 
     Using a system  240  such as the one shown in  FIG. 1 , pinhole applications, such as those under consideration by the IETF MIDCOM working group which open and close ports in a firewall dynamically in response to session signaling, may be implemented using a combination of a firewall  140  and a firewall control device FCP  150 . In VoIP applications, this FCP device  150  is normally application level aware and is able to forward messages to other Proxy machines or end stations. While signaling messages, e.g., call setup and termination messages, are statically allowed to pass through the firewall from “untrusted” sources, as outlined in a firewall rule set, ports for media traffic, e.g., voice signals, are dynamically opened and closed as indicated from messages sent from the FCP  150  with the DPFSI  151  reflecting the intended media port status at any given time. 
     So that the invention can be appreciated in the context of a VoIP call, a typical call flow initiated by a device in the untrusted zone  110  will now be explained with continued reference to  FIG. 1 . To further aid the reader in following the call flow, it is noted that each of the steps that comprise a call flow are numbered sequentially. 
     In our example, a call is initiated by originating IIEP  130  situated in the untrusted zone  110  by launching 1:Invite message through firewall  140  and then received by firewall control proxy  150 . Although firewall control proxy is shown in  FIG. 1  as a separate unit, it is possible that the functions provided by FCP  150  may exist in firewall  140 , as an integrated unit as discussed previously. 
     Upon receipt of 1:Invite message by FCP  150 , proxy  150  generates a 2:100 Trying message and transmits it to originating IIEP  130  and also sends a 3:Invite message to destination IIEP  132 , situated in trusted user zone  120 . 
     Destination IIEP  132  then sends 4:180 Ringing message back to FCP  150  which then sends a 5:180 Ringing message through firewall  140  to originating IIEP  130 . Message 6:200 OK is transmitted from destination IIEP  132  to FCP  150  indicating that the call is being established. FCP  150  launches 7:150 Request Pinhole message to firewall  140  and notifies originating IIEP  130  that call is being set up by forwarding 8:200 OK message through firewall  140  to originating IIEP  130 . When firewall  140  opens the requested pinhole, it sends 9:Pinhole Opened message to FCP  150 . Lastly, originating IIEP  130  sends 10:ACK message through firewall  140  to FCP  150  where it is forwarded to destination IIEP  132  as 11:ACK message. At this point, the call is established, the pinhole is opened through firewall  140 , and 12:RTP Media Traffic messages carry media, e.g., voice traffic, through the established pinhole, e.g., dynamically opened port(s) in the firewall  240 . 
     A guiding thesis in the development of our inventive test method is that testing should verify that the firewall rule-sets and thus the firewall system  240  are properly filtering traffic based upon source and destination IP addresses, port numbers, and the protocol being used. The firewall interface should have ports used for media flows closed, except for those involved in an ongoing session, while those ports specifically used for signaling should remain open. 
     In theory, verifying that ports excluded by firewall rules are closed may be accomplished through the use of a port scanning tool or by reviewing firewall logs. Unfortunately, the design of the User Datagram Protocol (UDP) which is the foundation of Real Time Protocol (RTP), which is often used for SIP Media Traffic, usually makes the use of port scanners inconclusive in VoIP applications. In particular, SIP devices do not respond to UDP scans with the expected “ICMP-unreachable” messages which are the primary way to identify what ports are closed on a system. Because of this non-responsiveness, media ports will therefore appear to be open regardless of the actual state of the firewall pinholes. Consequently, open and closed pinholes will appear to be open, whether or not they have been filtered at the firewall. While firewall logs, e.g., copies of DPFSI information  151  with time information, can be used to approximate the window that these ports are open, there is no certainty that only appropriate traffic is being allowed to pass at a given time. 
     In accordance with the present invention, IIEPs ( 130 ,  132 ) can be used to accurately determine port status and firewall functionality. Advantageously, the IIEPs ( 130 ,  132 ) may have traffic generation (both VoIP traffic generation and scanning probes) and analysis tools incorporated within them. In addition, IIEPs ( 130 ,  132 ) should, and often do, possess the following capabilities: VoIP SIP traffic generation for both signaling and media; the ability to generate scanning probes; a promiscuous mode packet analysis; and timing and synchronization with an external clock thereby permitting accurate synchronization of IIEPs  130 ,  132  located inside and outside the firewall  240 . Traffic generation may be performed by softclients, e.g., one or more software modules or applications which are used to establish and terminate VoIP test calls. 
       FIG. 2  illustrates an exemplary IIEP  130  which may be used as the IIEP  130  or  132  shown in  FIG. 1 . The IIEP  130  includes an input/output (I/O) device  170  which operates as an interface to the firewall  240  and to additional devices and/or systems, e.g., a network management system and/or external clock signal  260 . The IIEP  130  also includes an input device  172 , output device  174 , processor, e.g., CPU,  176  and a memory  160  which are coupled together and to the I/O device  170  via a bus  171 . 
     Input device  172  may be implemented as a keyboard through which a system administrator can enter commands and/or other data. Output device  174  may be implemented as, e.g., a display and/or printer, and can be used to display and/or print generated reports and information relating ongoing tests, monitoring and/or firewall test results. CPU  176  controls operation of the IIEP  130  including the generation of test signals and reports under control of one or more of the modules stored in memory  160  which are executed by CPU  176 . Memory  160  includes reports and other information  169  which are generated by monitoring firewall status and performing various tests as discussed below. Various modules included in memory include an IP address and/or Port scanning probe generation module  162 , a traffic analysis and/or report generation module  164 , timing/synchronization module  166  and VoIP signaling and media generation module  168 . IP and/or port scanning probe generation module  162  is used to generate test signals in accordance with the invention. Traffic analysis and/or report generation module  164  is used to analyze detected signals passing through the firewall and generate a report on firewall operation there from. Timing/synchronization module  166  is used to synchronize the operation of the IIEP  130  with another IIEP device, e.g., by synchronizing the IIEP operation to an external clock signal source  260 , which is also used by at least one other IIEP device. VoIP signaling and media generation module  168  is used to generate SIP and/or H.323 compliant call setup and termination signals as required by the testing process of the present invention. While shown as software modules in  FIG. 2 , modules  162 ,  164 ,  166 ,  168  may be implemented using hardware, software, or a combination of hardware and software. In the case of full hardware implementations, modules  162 ,  164 ,  166 ,  168  are implemented using circuits outside of memory  160 . 
     Generally speaking, and as used with our method, IIEPs  130 ,  132  serve as traffic injection tools at a call generation end of a VoIP network and as a traffic analyzer at a target end of the call. Such an implementation is shown in  FIG. 3 . In such a case, traffic is launched into the VoIP network  100  at an originating end, e.g., in untrusted zone  110 , and subsequently examined at a target end, e.g., inside trusted zone  120 , to determine what portion of the launched traffic is able to traverse the firewall  240  and under what conditions. Advantageously, our inventive test method may be performed in stages, thereby permitting the test measurements made to be fine-tuned to varying degrees of granularity as may be needed for a particular application. 
     Turning our attention now to  FIG. 3 , there is shown a simplified schematic of the VoIP network  100  as tested by our inventive method. In particular, as in  FIG. 1 , the network  100  comprises both untrusted zones  110  and trusted zones  120 , separated by firewall  240 . IIEP Traffic Generator  130 , located in untrusted zone  110 , uses its port scanning module  162  and soft client signaling and media generation module  168  as well as its timing synchronization module  166 . IIEP Traffic Analyzer  132 , which is located in trusted zone  120 , uses its traffic analyzer module  164  for processing detected traffic signals passing through the firewall  240  and soft client signaling and media generation module  168 . Timing and Synchronization signals  260  are received from an external clock source and/or are exchanged between the IIEP Traffic Generator  130  and IIEP Traffic Analyzer  132  to support timing synchronization between the two IIEPs  130 ,  132 . IIEP  132  may also use its port scanning probe generation module to generate probe signals from inside the firewall allowing UUEP  130  to monitor the status of ports used to communicate from inside the trusted user zone  120  to untrusted user zone  110 . Thus, it is possible to test pairs of unidirectional ports associated with a call to determine opening and closing delays in each direction of signal flow. 
     According to our inventive method, in a first stage of testing, the firewall  240  is probed for compliance with static rules regarding accepted origination and destination IP addresses. Additionally, and as can be appreciated by those skilled in the art, it is important to verify that dynamic rule-sets are operating correctly as well. In order to verify that the dynamic rule-sets are operating correctly, one or more of the following parameters should be varied through the use of traffic generation outside the firewall and detection within the trusted user zone  120 :
         Source and Destination Addresses (including addresses on the trusted  120  and untrusted  110  sides of the firewall  240 , across the supported address ranges);   Source and Destination Port Numbers (Across the supported UDP and TCP range);   and IP Protocol Numbers.       

     In one firewall implementation, IP addresses not legitimated by SIP signaling as being associated with a call should be rejected regardless of the port being accessed. Thus, for a media signal having an IP source address that is not listed in the DPFSI information  151 , the firewall should block the signal regardless of the port which is being accessed. As a result, when the scanning probe generation module  162  of the originating IIEP  130  launches test signals from an IP address not associated with a current call, the firewall&#39;s media ports should be completely closed to those scans originating from the unassociated addresses, e.g., the IP address which is not listed in DPFSI information  151 . Accordingly, in such a situation, the scanning probe should not be detected across the firewall  240  by the target IIEP  132 , as such traffic, e.g., test signals, should be blocked by the firewall at the IP address filtering state of the firewall filtering process. 
     In the next stage of testing, and to verify that media ports that are not defined within the firewall rule-set and not currently dynamically allocated are closed, traffic is generated across the supported UDP and TCP port ranges from a source having a legitimated IP address, while monitoring this traffic on the destination end. The IP address from which these test signals are launched is legitimated by initiating a media session, e.g., call, from the IP address prior to generating the port test signals. In particular, the IIEP probe generation module  162  of IIEP  130 , has an IP address associated with it. This specific IP address is used to launch a call, thereby legitimating the specific IP address, and resulting in a pair of legitimately opened pinholes, e.g., uni-directional pinholes, associated with it. From that specific IP address however, no traffic directed to any other port used for media traffic should be visible by the IIEP analysis module  164  at the destination end assuming proper operation of firewall  240 . 
     More specifically, the port scanning probe generation module  162  of the traffic generator  130  probes the full TCP and UDP range with test signals directed at the firewall&#39;s media ports using its legitimated IP address as the source address for the test signals. The IIEP analysis module  164  of the IIEP  132  analyzes arriving traffic that passed through the firewall  240  and discriminates between allowed traffic—according to the firewall rules—and searches for the presence of traffic from the originating IIEP Traffic generator  130  addressed to any ports other than the port or ports which were associated with the call established by the source IIEP  130 . The expected result is that no traffic other than that addressed to ports dynamically set for the established call should appear at the IIEP traffic analysis module  164  of the IIEP  132  at the destination end. Accordingly, the presence of traffic proceeding through any ports other than those dynamically allocated is indicative of a failure in the pinhole implementation and will be reflected in a report generated by the analysis and report generation module  164  of IIEP  132 . 
     As may now be appreciated by those skilled in the art, there exists a component to the “window of vulnerability” that results from the closing delay of the pinhole during the time period between a call effectively ending and a firewall, being instructed, closing the pinhole. During this “window” component, scanning traffic may still be able to “punch-through” and use the pinhole. 
     It should be noted that the “window of vulnerability” has at least two components, namely, the actual duration of the call when malicious traffic may penetrate the firewall and the closing delay window which, as defined above, is the period of time between the call ending and the firewall closing the pinhole. Of course, if malicious traffic interrupted a call during its progress, such call disruption may alert the user or customer to an intrusion. Unfortunately however, detecting malicious traffic during the closing delay window of vulnerability (CDWoV) is not so straightforward therefore its duration is important to quantify. Fortunately, our inventive method makes this determination. 
     As noted before and now alternatively stated, the “window of vulnerability is that period of time beginning when a first media packet is allowed to pass through a firewall pinhole and ending when a last packet is able to pass through. With reference now to  FIG. 4 , there is shown a timeline  300  depicting “window of vulnerability”  380  for a SIP based call. Specifically, the timeline  300  shown therein depicts the window of vulnerability  380 , as that period of time between the pinhole opening  320  and the pinhole closing  360 . 
     Of particular interest in a SIP call and as shown in  FIG. 4 , is opening delay  330  and closing delay  370 . With continued reference to  FIG. 4 , the opening delay  330  is that period of time between the receipt of an “200 OK” message  310  and the opening of the pinhole  320 , and the closing delay  370  is that period of time between the transmission of a “BYE” message  350  and the pinhole actually closing  360 . 
     Of additional interest from a timing perspective are the time periods between an INVITE message and corresponding “200 OK” messages being sent by IIEPs ( 130  and  132  respectively), to when the window opens at call initiation  320 , and the time period between the sending of the “BYE” message  350  to the window&#39;s actual closing—subsequent to call termination. Fortunately, these values may be determined, by streaming packets at the pinhole, from a time prior to its opening until after the pinhole&#39;s closing and detecting the passage of signals through the pinhole, e.g., port or ports assigned to be used for a call being established. The start of packet streaming at ports to detect pinhole opening is shown in  FIG. 4  as point  385  while stopping of streaming of packets is shown at point  387 . The time interval between the start of packet streaming to detect pinhole opening  385  and the stoppage of packet streaming to detect pinhole opening  387  is identified as media/packet generation/probing interval  390  in  FIG. 4 . 
     Advantageously, our inventive SIP testing method can be used to verify a number of important aspects of calls proceeding according to timeline  300  including:
         a) the speed with which a firewall will correlate information from the INVITE/200 OK messages ( 305 ,  310 ) and the opening of the pinhole  320 , thereby identifying potential “throttling” of calls; and   b) the length of time a pinhole remains open after a call has terminated, or “closing delay”  370 .       

     In our inventive method, the Closing Delay Window of Vulnerability (CDWoV) may be determined from the time the last packet sent from an originating IIEP  130  is detected by a target IIEP  132 , less the time of the BYE message generation. In practice, there are at least two factors that will affect the closing delay window, and in particular, the firewall processing the information from a BYE packet, and the existence of a timeout default in the absence of a BYE packet. Additionally, the amount of processing needed to process this information in real-time is dependent upon the speed at which the pinhole is closed and therefore the “width” of the CDWoV. Generally, an overloaded system will not be able to carry out these functions within established specifications. 
     The test methods of the present invention can be used to determine the effect of large loads, e.g., numerous simultaneous or nearly simultaneous requests, to open and/or close pinholes may have on the ability of a firewall  240  to open and close ports in a timely manner. To load the system for purposes of performing stress testing, the IIEP  130  operates as a bulk traffic generator. The volume of requests to open and close ports can be slowly increased permitting for stress testing and thereby permitting the benchmarking of performance for the firewall&#39;s CPU, beyond which the Closing Delay Window of Vulnerability will become so large and so persistent, due to CPU degradation, that the firewall system  240  is no longer effective. This benchmarking can be done to predict how closing window delays will vary based on traffic load. Plots of closing window delay versus traffic load (pinhole open/closing request signals) can be useful in determining maximum acceptable traffic loads based on a selected maximum acceptable closing delay for a particular firewall system  240 , e.g., for a firewall with a particular fixed CPU speed. 
     Other benchmarking that can be performed can be firewall CPU speed vs. traffic load that can be supported given a pre-selected maximum closing delay. This benchmarking of CPU speed vs. maximum traffic load can have widespread use in engineering VoIP networks, as important criteria for performance will be determined by establishing upfront the correct match between an interface rate, and the processing power of a firewall CPU needed to maintain the dynamic pinhole filtering functionality for that given rate at the perimeter protection devices exposed to that traffic load. Traffic engineering information generated by stress tests implemented in accordance with the invention can be a useful new tool for security companies and other service providers trying to design and maintain firewalls which can support dynamic firewall operations for various traffic loads. 
     Firewall stress testing implemented in accordance with the invention is intended to be performed off-line in a testing environment and not in a live system as the stress-testing is likely to cause disruptions to a real-time system and interfere with actual network traffic. However, as will be discussed below, limited testing of firewall operation can, and in various embodiments is, performed in accordance with the present invention in operational systems as part of a security management system. 
     To perform stress testing, two IIEPs  130 ,  132  are situated on either side of the firewall  240  as shown in  FIG. 3  for the SIP case. The H.323 system will look functionally the same for stress testing, e.g., the setup shown in  FIG. 6  may be used. The originating IIEP traffic generator  130  operates in bulk mode during maximum stress testing injecting traffic, e.g., signals to cause pinholes to open and/or close, at the maximum rate allowed by the firewall interface. The target IIEP  132  monitors the ever lengthening of the Closing Delay Window of Vulnerability as the firewall CPU is stressed by increasing amounts of traffic and becomes unable to process the “close pinhole” messages, e.g., due to firewall CPU overloading. 
     A graphic display of the Closing Delay Window of Vulnerability is generated in some embodiments on the IIEP&#39;s output device providing an indication of the cutoff point at which the firewall&#39;s CPU can no longer process the dynamic pinhole filtering function in a timely manner, leaving pinholes open for increasingly longer times. From the graphic display a system administrator can determine a maximum permissible traffic flow above which traffic is to be cutoff to maintain proper firewall operation. Upon encountering the cutoff threshold in an actual implementation, traffic is dropped. A new CPU may be added to the firewall device, or to FCP, in order to return system to normal performance within specifications at actual level of loading encountered. 
       FIG. 5 , which comprises the combination of  FIGS. 5A and 5B , illustrates the steps  500  of an exemplary firewall test method of the present invention. The method  500  is applicable to both SIP signaling applications and H.323 applications but for purposes of explaining the invention will be discussed in the context of the SIP compatible testing system shown in  FIG. 3 . The method includes steps for testing both static firewall rules as well as dynamic firewall filtering, e.g., filtering corresponding to the opening and closing of pinholes. Static rule testing is performed first. The testing method concludes with testing based on increasing volumes of traffic which provide stress based test results and information about pinhole closing delays corresponding to different levels of traffic, e.g., levels of signaling used to cause pinholes to be opened and/or closed. 
     The testing method  500  begins in start step  502  wherein IIEPs  130 ,  132  are initialized. In step  504 , the traffic generator IIEP  130  sends probe signals directed at the firewall  240  using as a source address, an IP address that is not associated with any ongoing media session, e.g., a call. Since the IP address has not been legitimated through SIP session signaling, it will not be listed in DPFSI information  151  and the probe signals should be blocked by firewall  240 . In step  506 , the target IIEP  132  monitors to detect any probe signals passing through the firewall that were generated in step  504 . Next, in step  508  an error report is generated by the destination IIEP  132  listing any ports used for media traffic through which probe signals from the illegitimate IP address passed. 
     With testing of the firewall&#39;s ability to block signals from IP addresses which have not be legitimated through session signaling completed, operation proceeds to step  510  wherein a session signal, e.g., call establishment signaling, is initiated by the signal generator IIEP  130  using an IP address associated with IIEP  130 . As a result of this signaling, the firewall system  240  will assign one or more ports, e.g., a pair of ports, to be used with this specific IP address for the call being established and a corresponding IP address and port information entry will be made in DFSI information  151 . Once legitimated in this manner, the specific IP address associated with IIEP signal generator  130  will be used to transmit test probes at the full set of ports supported by the firewall  240  through which media traffic can be directed. In regard to the port assigned for call signals from the trusted zone  120  to the untrusted zone  110 , an IP address assigned to the IIEP  132  will be indicated as the source address in DFSI information  151  and the IP address associated with IIEP  130  may be indicated as a destination address. 
     In step  512 , the signal generator IIEP  130  sends port test probe signals directed at the port(s) capable of carrying media signals from outside the firewall  240  using the IP address legitimated in step  510 . Then, in step  514 , the IIEP  132  monitors to detect test probe signals which pass through the firewall to detect port opening time(s) and to determine which ports are open and which ports are closed. Then in step  515  a port opening delay is determined from the time a signal is detected passing through the opened port and the time of a signal used to initiate port opening. A list of open and closed ports generated in step  514  is compared in step  516  to a list of ports which should be open, e.g., a list of ports included in DFSI information  151 . In this manner, in step  516 , ports which are erroneously open and/or closed are detected. 
     Next, in step  518 , the IIEP  132  generates a report including a list of any detected open ports which should be closed and any detected closed ports which should be open. Operation proceeds from step  518  to step  524  via connecting node  520 . 
     In step  521 , as session signal to terminate the initiated call is generated. Then, in step  522 , the IIEP  132  monitors to determine when probe signals stop passing through port(s) associated with the initiated call. Next, in step  523 , at least one port closing delay is determined from the time difference between a signal used to initiate port closing and the actual closing of the port as indicated by the cessation of signals passing through the port(s) associated with the call being terminated. With the opening and closing delays having been determined for the single test call, in step  524  probe signals directed to the ports corresponding to the terminated test call are stopped. Then, in step  525 , a control signal generation control parameter X is initialized to 2. 
     Step  525  marks the start of firewall load testing. The parameter X controls the number of calls opened or closed at a given point in time. As will be discussed below, this number is incremented to achieve stress testing beyond the case of low load testing, e.g., as in the case of a single call setup and close procedure. 
     Operation proceeds to step  528  wherein X calls are initiated at the same time causing X ports in the firewall to be opened in each direction. In step  529  the IIEP  130  acting as a test signal generator transmits probe signals to the full range of firewall ports which can be used to communicate media, e.g., voice, signals for the IP addresses used to initiate the test calls. Then, in step  530  the IIEP  132  monitors to determine the time(s) and corresponding port opening delays, corresponding to individual calls and/or an average time, to open the ports for the calls initiated in step  528 . Next, in step  532  the signal generator IIEP  130  generates session signals to terminate the X calls started in step  528 . Then, in step  534 , the destination IIEP  132  monitors to determine the closing delay associated with individual calls and/or to determine the average closing delay for the X calls being terminated. The IIEP  132  can determine the time of port closing by detecting when probe signals cease to penetrate the firewall through a port associated with one of the X calls, while the start time from which the closing delay can be determined from the time of a session signal used to trigger the closing of the port. 
     With the closing delay times and/or average closing delay having been determined for the X calls in step  534 , operation proceeds to step  535  wherein generation of the test probe signals associated with the IP addresses used to initiate the X calls are terminated. Then in step  536  a report is generated on the detected opening and closing times for a load corresponding to X calls. 
     Next, in step  538 , a check is made to determine if a stop criterion has been satisfied. The stop criteria may be a maximum average port closing delay to which the average generated in step  534  is compared. If a stop criterion has been satisfied in step  538 , e.g., a stop threshold was meet or exceeded, operation proceeds to step  544 . However, if a stop criterion was not satisfied in step  538  operation proceeds to step  540  wherein X is incremented prior to operation proceeding again to step  528 , e.g., for testing at a higher level of loading. X may be incremented by a small or large step size depending on the desired resolution, in terms of load size, of the statistics indicating increased loading effects. 
     As mentioned before, upon some preselected stop criteria being satisfied in step  538 , operation proceeds to step  544  wherein an overall test report is generated. The overall test report includes information indicating holes in IP address filtering detected in the static firewall rule testing steps, detected errors in port open/closed status that were detected, opening and/or closing delays for a single call, and/or information indicating the effect of increasing loads, e.g., calls, on the time required to open and/or close ports in the firewall  240 . The report is output in step  546  e.g., in the form of printed and/or displayed charts and/or text information listing the detected errors and pinhole opening and closing delays for different loads. 
     With the generated reports being output by the IIEP  132 , the test procedure stops in step  548 . 
     Advantageously, as discussed above the inventive methods of the present invention are not limited to specific protocols. In particular, it is well suited to H.323 based calls as well as others. H.323 calls and signaling will now be briefly discussed to facilitate an understanding of how the test methods of the present invention can be used in H.323 based systems. As will become apparent, the  FIG. 5  test method is applicable to firewall systems that work with H.323 signaling. 
     H.323 calls are typically conducted in three steps, namely, 1) Call Registration, 2) Call Signaling, and 3) Call Media Exchange. The Call Registration and Call Signaling steps are carried out using well known port(s) (p: 1719/1720) which are the same and for which firewall static rules may be defined. 
     The session establishment signaling exchange includes a negotiation/selection of two logical ports (talking and listening), which carry the media exchange (voice conversation) for a normal call. These talking and listening ports are dynamically chosen from a range of allowed ports, used for the duration of the call, and then released. Since they are chosen dynamically, their identification normally cannot be predicted in advance. 
     They can however, be determined from the specific signaling message(s) that include the “open logical channel” function (H.225/H.245 OpenLogicalChannel, H.225/H.245 OpenLogicalChannel ACK). The port information may be determined by examining the appropriate messages. Once this information is derived, a state machine may be constructed for the two logical ports involved in the call and the state of the call may then be monitored for the duration of the call. An information table, the same as or similar to, the DPFSI  151  shown in  FIG. 1  is normally also constructed in the firewall system  641  shown in  FIG. 6 . At the end of the call, corresponding messages (CALL RELEASE) may be used to trigger the tear-down of the state machine and the close of the logical ports just used for the call. 
     As can be appreciated, the determination of the port information and call-state monitoring are two functions which are important for the proper operation of dynamic pinhole filtering. The architectural placement of these functions depends upon the processing power of the firewall involved and any performance and/or scalability requirements as in the case of the SIP implementation previously discussed. Consequently, and as noted before with SIP architectures, these functions may be implemented for H.323 architectures in a firewall device  640 , or distributed to an external firewall control proxy  650  that communicates to the firewall device  640  the identity of the ports to be opened and closed and the initiation of same as shown in  FIG. 6 . 
     Turning our attention now to  FIG. 6 , there is shown a VoIP network arrangement  600  that we will use to describe our inventive test method as it applies to the H.323 protocols. Specifically, network  600  includes both a trusted user zone  620  and an untrusted zone  610  separated by a firewall device  640 . The firewall device  640  operates in conjunction with firewall control proxy  650  as a firewall system  641  which may be referred to simply as the firewall  641 . 
     Shown further are Integrated Intelligent End Points (IIEPs)  630 ,  632 , placed at appropriate locations within the VoIP network  600 . In particular, originating IIEP  630  is positioned “outside” of the firewall within the untrusted zone  610  and target IIEP  632  is positioned “inside” of the firewall within the trusted zone  620 . 
     As with the SIP protocols described earlier, the IIEPs ( 630 ,  632 ) used for H.323 protocols may have traffic generation (both VoIP traffic generation and scanning probes) and analysis tools incorporated within them. Additionally, H.323 IIEPs should possess the following capabilities: VoIP SIP traffic generation (softclients) for both signaling and media; the ability to generate scanning probes; a promiscuous mode packet analysis; and timing and synchronization with an external clock. The exemplary IIEP  130  shown in  FIG. 2  may be used in the system  600  as any one of the IIEPs  630 ,  632 . In such an embodiment, the IIEP  130  generates signals compliant with H.323. 
     Generally speaking, and as noted before, IIEPs  630 ,  632  serve as traffic injection tools at a call generation end of a VoIP network  600  and as a traffic analyzer at a target end of the call. As such, traffic is launched into the VoIP network at an originating end and subsequently examined at the target end to determine what portion of the launched traffic is able to traverse the firewall  641  and under what conditions. As with the SIP method, our inventive method for H.323 protocols may be performed in stages. 
     A typical H.323 call flow can be understood with continued reference to  FIG. 6 . Specifically, a call is initiated by originating IIEP  630  situated in the untrusted zone  610  by launching 1:OpenLogicalChannel message through firewall device  640  which is then received by FCP  650 . As noted before with the SIP method(s), the functions provided by FCP  650  may be integrated into firewall device  640 . 
     Upon receipt of 1:OpenLogicalChannel message by FCP  650 , FCP  650  generates a 2:OpenLogicalChannel ACK message and transmits it to originating IIEP  630  and also sends a 3:OpenLogicalChannel message to destination IIEP  632 , situated in trusted user zone  620 . 
     Destination IIEP  632  then sends 4:OpenLogicalChannel ACK message back to FCP  650  and then sends a 5:OpenLogicalChannel message to FCP  650 . FCP  650  then sends a 5a:OpenLogicalChannel ACK message to IIEP  632  and a 6:OpenLogicalChannel message through firewall device  640  to originating IIEP  630 . 
     FCP  650  launches 7: Request Pinhole message to firewall device  640 . Originating IIEP  630  acknowledges the channel opening with 8: OpenLogicalChannel ACK message sent to FCP  650 . When firewall device  640  opens the requested pinhole, it sends 9: Pinhole Opened message to FCP  650 . 
     At this point, the call is established, the pinhole is opened through firewall  641 , and 12: RTP Media Traffic messages carry media through the established pinhole. 
     According to our inventive method and similar to that described for the SIP protocol, in a first stage of testing, the firewall  641  is probed for compliance with static rules regarding accepted origination and destination IP addresses. Additionally, and as can be appreciated by those skilled in the art, it is important to verify that dynamic rule-sets are operating correctly as well. In order to verify that the dynamic rule-sets are operating correctly, the following parameters may be varied in traffic generation:
         Source and Destination Addresses (including addresses on the trusted  620  and untrusted  610  sides of the firewall  641 , across the supported address ranges);   Source and Destination Port Numbers (Across the supported UDP and TCP ranges);   and IP Protocol Numbers.       

     According to our method, IP addresses not legitimated by H.323 signaling as being associated with an ongoing media session, e.g., call, should be rejected regardless of the port being accessed. Additionally, when the scanning probe generation module  162  of the originating IIEP  630  is launched from an IP address not associated with a current call, the firewall ports used for media traffic should be completely closed to those scans originating from the unassociated IP addresses. Accordingly, in such a situation, the scanning probe signals should not be detected across the firewall  641  by the target IIEP  632 , as such traffic should be blocked by the firewall  641  at the IP address level of filtering. 
     In the next stage of H.323 testing, and to verify that ports that are not currently allocated to a media session are closed, traffic is generated across the full UDP and TCP port ranges from source  630  having a legitimated IP address, while monitoring this traffic on the destination end at IIEP  632 . In particular, the IIEP  630  which operates as a traffic generator, having an IP address associated with it, is used to launch a call that will have a pair of legitimately opened pinholes, e.g., ports, associated with it. From that specific legitimated IP address however, no traffic directed to other ports used for media flows should be visible to the analysis module of the IIEP  632  at the destination end. 
     More specifically, the scanning probe signals launched from the IIEP  630  which operates as a test signal generator uses the legitimate IP address to probe the full TCP and UDP range of ports which may be used for media traffic. The IIEP  632  operating as a traffic analyzer performs analysis on the arriving traffic that passes through the firewall  641  to detect which ports were erroneously opened and/or closed. The expected result is that no traffic other than that addressed to ports associated with the established call should appear at the IIEP  632  at the destination end. Accordingly, the presence of traffic proceeding through any ports used for media flows other than those dynamically allocated as part of the established call is indicative of a failure in the pinhole implementation. 
     With reference to  FIG. 7 , which shows a timeline of H.323 call events and resulting windows of vulnerability and delays, the opening delay  730  may be measured as the period of time between the receipt of an “OpenLogicalChannel ACK” message  710  and the opening of the pinhole  720 , while the closing delay  770  can be measured as the period of time between the transmission of a “CloseLogicalChannel ACK” message  750  and the pinhole actually closing  760 . 
     Of additional interest for the H.323 protocol are the time periods between an CallSetUp/CallProceeding message and corresponding “H.225/H.245 OpenLogicalChannel/OpenLogicalChannel ACK” messages being sent by IIEPs  630 ,  632 , to when the window opens at call initiation  720 , and the time period between the sending of the “H.225/H.245 CloseLogicalChannel/CloseLogicalChannel ACK” message  750  to the window&#39;s actual closing—subsequent to call termination. Fortunately, and according to our inventive method, these values may be determined by streaming packets at the pinhole, from a time prior to its opening until after the pinhole&#39;s closing, a media packet generation/probing time interval  790  of  FIG. 7 . Start and end time of media packet generation/probing time interval  790  are shown on the timing diagram  700  of  FIG. 7  as points  785  and  787  respectively. 
     Advantageously, and similar to the advantages for the SIP method described before, our inventive H.323 testing method verifies a number of important aspects of calls proceeding according to timeline  700  including:
         the speed with which a firewall will correlate information from the H.225/H.245 OpenLogicalChannel/OpenLogicalChannel ACK messages ( 710 ) and the opening of the pinhole  720 , thereby identifying potential “throttling” of calls; and the length of time a pinhole remains open after a call has terminated, or “closing delay”  770 .       

     As used with the H.323 protocol, the Closing Delay Window of Vulnerability (CDWoV) may be measured as the time the last packet sent from an originating IIEP  630  is detected by a target IIEP  632 , minus the time of the CloseLogicalChannel message generation. As before, there are at least two factors that will affect the closing delay window, and in particular, the firewall processing the information from a H.225/H.245 CloseLogicalChannel/CloseLogicalChannel ACK packet, and the existence of a timeout default in the absence of a H.225/H.245 CloseLogicalChannel ACK packet. 
     Of course, the amount of processing needed to process this information in real-time is dependent upon the speed at which the pinhole is closed and therefore the “width” of the CDWoV. Generally, an overloaded system will not be able to carry out these functions within established specifications, and an alert may be generated when a predetermined threshold width of the CDWoV is met or exceeded in a system which monitors for such delays while in use as will be discussed below. 
       FIG. 8  a communications network system  800 , wherein the firewall testing and firewall control methods of the present invention are used in an active communications network to detect firewall faults, excessive opening and/or closing delays and to generate alert signals which are used to alert a security management system to firewall problems. In response to receiving a firewall alert signal, the security management system  815  can take one or more of a variety of actions to address the firewall problem. 
     The communications network  800  includes an untrusted zone  810  and a trusted zone  820 . First and second firewall systems  810 ,  820  are used to separate the untrusted zone  810  from the trusted zone  820 . The untrusted zone  810  includes a plurality of nodes, e.g., end node Y  830  and end nodes  832 ,  834 . End nodes may be, e.g., user terminals or other user devices. End node  830  is coupled to the first firewall system  810  by network node  1  and to the second firewall system  820  by network node  2 . Network nodes may be e.g., routers, which route traffic according to routing information including, in some cases weights associated with particular paths. End nodes  832  and  834  are coupled to the second firewall system by network node  2   836  and to the first firewall system  810  through network node  1  via its connection to network node  2   836 . Thus, end nodes  830 ,  832 ,  834  have two available paths over which media signals can be routed into the trusted network zone  820 . 
     Trusted network zone  820  includes a security management system  815  which has routing control links  841 ,  843  to network nodes  836 ,  838 . It is also coupled to firewall system  1   810  and firewall system  2   820 . In addition the security management system  815  is coupled to a pinhole firewall management system which generates alarms that are sent to the security management system  815  when a pinhole closing delay is detected to have been exceeded at one of the firewall systems  810 ,  820 . Pinhole firewall management system  822  receives pinhole information  824  form each of the firewall systems  810 ,  820  and generates alarms as needed. The first and second firewall systems  810  and  820  are both coupled to the third network node  840  which, in turn, is coupled to end node X  842 . Thus, the end nodes on both sides of the trusted zones have multiple paths through which messages can be communicated between the trusted and untrusted zones  820 ,  810 . Security management system  815  can take several actions in response to receiving a closing delay alarm including signaling the firewall device  140  which triggered the alarm to drop or refuse to pass new session requests to thereby reduce loading, signal system administers to upgrade or take other action in regard to the firewall system  810 ,  821  which generated the alarm and or signal network routers  838 ,  836  to modify the network routing to reduce the load on the firewall which trigger the alarm. In this manner, assuming the threshold for generating the alarm is set at a level where security has not yet been jeopardized due to excessive delays, corrective measure can be taken before a security problem occurs. 
     Each of the first and second firewall systems  810 ,  820  includes a firewall  130  as well as IIEPs  130 ,  132 . In the active network embodiment, the IIEPs provide ongoing and/or periodic testing using signaling which places relatively little loading on the firewall system  130 . Thus, during active system use, stress testing is avoided to reduce the risk of interfering with legitimate traffic passing through the firewall system  130 . In the active system embodiment, care is taken to avoid directing test signals to ports which are in used for ongoing media sessions as indicated by DPFSI information  151  and to avoid stress testing. Otherwise, testing may be performed in the same way as described with regard to the  FIG. 5  example. In some embodiments, testing of active systems is limited to determining closing delay. In some cases, this is done by having the IIEP  132  monitor signaling and port closing log information  131  obtained from firewall device  140 . In such an embodiment transmission of test signals from IIEP  130  can be minimized or avoided. In other embodiments opening and/or closing delays are determined by the IIEP  132  through the use of test signals as previously described. 
       FIG. 9  illustrates the firewall monitoring and security steps  900  performed in an active network in accordance with one embodiment of the present invention. 
     The monitoring/testing process  900  begins in step  902  with operation proceeding to step  904  wherein firewall operation is tested and/or the current pinhole closing delay associated with at least one communication session is established. Next, in step  906 , the determined pinhole closing delay is reported to the pinhole firewall management system  822 . The pinhole firewall management system  822  compares the reported closing delay to a threshold, e.g., a predetermined threshold slightly below the maximum acceptable pinhole closing delay. If the threshold is not exceeded no alarm is generated and monitoring operation continues from step  904 . 
     However, if the closing delay threshold is exceeded, indicating a loading or other firewall problem, operation proceeds to step  910 . In step  910  and alarm is generated and sent to the security management system  815 . The alarm signal normally indicates the firewall that was responsible for the generation of the alarm, i.e., the firewall  810  or  821  exhibiting large port closing delays. 
     The security management system  815  responds to the alarm by performing one or more actions including: 1) adjusting network routing to reduce the load on the firewall system  810  or  821  which triggered the alarm; 2) control the firewall system  810  or  821  which triggered the alarm to re drop traffic or refuse new sessions to reduce the closing delay and/or 3) generate a signal or other output to notify a system administrator of the alarm condition so that corrective measures can be taken such as upgrading of the firewall system  810  or  821  which generate the alarm. 
     Operation proceeds from step  912  back to step  904  so that monitoring of the firewall system can continue while the network  800  remains in operation. 
     Thus, a system  800  implemented in accordance with the invention can monitor to make sure that the windows of vulnerability remain within criteria according to a design specification, with the issuance of alarms in the event of threshold crossings of windows of vulnerability permitted widths and/or excessive closing delays. The system will alert security monitoring personnel in real-time when a firewall system  810 ,  821  is leaving open windows of vulnerability that can be exploited by an intruder to gain access to network. This methodology is equally applicable to H.323 and SIP based systems. The testing method of the invention can be used to monitor whether a firewall implementation is working properly during operation, free of software malfunctions, or is subject to problems because of intermittent faults when the firewall system  810 ,  821  is performing at the limit of its traffic capabilities. The monitoring system  822  is a real-time system that monitors firewall interfaces at periodic intervals or on a continuous basis feeding information up to the security management system  815 . 
     The testing component set up may be generally the same as that described in regard to  FIG. 1 . The setup shown in  FIG. 8  can work with SIP or H.323 signaling. 
     In various implementations, the two IIEPs  130 ,  132  are situated on either side of the firewall device  140  which is included in each of the first and second firewall systems  810 ,  821 . The originating IIEP  130  sends test traffic probes periodically across the firewall device  140 . The purpose of the intermittent test probes is to obtain measurements of the CDWoV and to verify that illegitimate traffic originated from the IIEP  130  will not pass through the firewall device  140 . These measurements are performed using the previously described methodologies. It is likely that as the firewall device  140  is stressed with user traffic, the window of vulnerability may increase or the firewall  140  may be breached by packets that have not been validated through signaling. Either event should be detected resulting in a report to the pinhole firewall management system  822  and generation of an alarm which is sent to the security management system  815 . 
     Security management system  815 , in some embodiments, operates as a root cause analysis tool which uses logic, e.g., one or more analysis software modules, to process alarm signals received from the alarm generation components of various firewalls over a period of time. The analysis is used to locate the cause, e.g., source of signals, causing one or more alarms. The security management system  815  also includes a module for predicting future alarms so that preventive actions, e.g., upgrading of firewall hardware, can be taken. 
     Thus, in at least some embodiments the security management system  815  includes a receiver for receiving alarms from a plurality of different alarm generation devices located at different locations, e.g., in different firewalls and a module for analyzing alarms received from different alarm generation devices, over a period of time, to identify the location of one or more traffic sources causing alarms during said period of time. The security management system  815  also includes another module or uses the same analysis module to analyze alarms received from different alarm generation devices, over a period of time, to predict the occurrence of future security alarms. Thus, the security management system  185  uses distributed probes, e.g., test probes at different firewalls through out the communications network which result in different alarms being received and uses time and space information corresponding to the information obtained from said probes to feed into a root-cause analysis tool that helps sectionalize a pinhole vulnerability problem in time and space for further action in a “predictive” and/or “reactive” manner. 
     A graphic display of the CDWoV widths may be, and often is, generated and used to indicate the threshold point at which a firewall CPU can no longer process the dynamic pinhole filtering function according to specifications, leaving pinholes open for increasingly longer times. The graphic display may be used to indicate dynamically at the pinhole management system  822  when this threshold has been exceeded and to generate an alert (e.g., an authenticated SNMPv3 trap) which can be sent up to a monitoring device capable of understanding traps. 
     The methodology and management system  822  can be used to correlate information from multiple firewall systems  810 ,  821 , which may be implemented as MIDCOM systems, from devices  151  which control the “pinholes” within the firewalls, and end-to-end testing devices  130 ,  132  used to intermittently verify the functionality and vulnerability of the complete firewall system  810 ,  821 . The information from multiple devices can be correlated and fed into a “root analysis” tool that will provide spatial information of where anomalies are occurring within the overall network  800 . 
     It will be apparent to those skilled that many variations to our inventive methods may be realized. In particular, numerous alternative network architectures and/or protocols may be tested by those skilled in the art without departing from the spirit and scope of the present invention.