Patent Publication Number: US-8122482-B2

Title: Cryptographic peer discovery, authentication, and authorization for on-path signaling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS; PRIORITY CLAIM 
     This application claims domestic priority under 35 U.S.C. §120 as a Continuation of prior application Ser. No. 11/115,542, filed Apr. 26, 2005, the entire contents of which are hereby incorporated by reference as if fully set forth herein. 
     This application is related to U.S. patent application Ser. No. 10/756,634, entitled “ENABLING STATELESS SERVER-BASED PRE-SHARED SECRETS”, filed Jan. 12, 2004; U.S. patent application Ser. No. 10/756,633, entitled “AVOIDING SERVER STORAGE OF CLIENT STATE”, filed Jan. 12, 2004; and U.S. patent application Ser. No. 10/411,964, entitled “METHOD AND APPARATUS FOR SECURELY EXCHANGING CRYPTOGRAPHIC IDENTITIES THROUGH A MUTUALLY TRUSTED INTERMEDIARY”, filed Apr. 10, 2003. The entire contents of these applications are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein. 
     FIELD OF THE INVENTION 
     The present invention generally relates to authentication, authorization, and peer discovery mechanisms for computer networks. The invention relates more specifically to a method and apparatus for cryptographic peer discovery, authentication, and authorization for on-path signaling. 
     BACKGROUND OF THE INVENTION 
     The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     In packet-switched networks consisting of multiple network elements such as routers and switches, an on-path signaling protocol such as Resource Reservation Protocol (“RSVP”) may be used to reserve routing paths for the purpose of providing optimized routing of specified kinds of network traffic, such as voice traffic. RSVP is described in Braden et al., “Resource ReSerVation Protocol (RSVP)—Version 1, Functional Specification,” Request for Comments (RFC) 2205 of the Internet Engineering Task Force (IETF), September 1997. In general, RSVP can be used to reserve resources in order to achieve a desired quality of service (QoS) for a particular kind of traffic. Resource reservations established using RSVP messages expire over time unless the reservations are refreshed. 
     RSVP defines sessions and flow descriptors. A session encompasses a data flow that is identified by its destination. A flow descriptor is a resource reservation that encompasses a filter specification (filterspec) and a flow specification (flowspec). When the reservation is implemented at a router, packets that pass a filter defined by the filterspec are treated as defined by the flowspec. RSVP operation is controlled using Path messages and Resv (reservation) messages. 
     In general, RSVP operation at a host such as a router proceeds as follows. A sender issues a Path message; a receiver receives the message, which identifies the sender. As a result, the receiver acquires reverse path information and may start sending Resv messages to reserve resources at intermediate hosts. The Resv messages propagate through the Internet and arrive at the sender. The sender then starts sending data packets and the receiver receives them. 
     In some cases, the only paths existing between the sender and receiver contain one or more firewalls. In order for data packets to pass through a firewall, the firewall might need to be configured to allow a certain class of data packets of pass through the firewall; the firewall&#39;s policy might need to be changed. For example, the firewall&#39;s policy might need to be changed to expressly allow data packets that originate from the sender&#39;s Internet Protocol (IP) address to be forwarded to devices that lie on the other side of the firewall from the sender. 
     However, firewalls are implemented for a good reason: to keep unauthorized data flows from invading portions of a network. If the general public were permitted to alter the firewall&#39;s policy, then the purpose of the firewall would be defeated. Only certain entities should be allowed to alter the firewall&#39;s policy. If a firewall is to remain sound, the firewall must require some proof that each entity that attempts to alter the firewall&#39;s policy is actually authorized to do so. 
     In theory, the firewall could use an authentication system like Kerberos to authenticate each entity that attempted to alter the firewall&#39;s policy. However, such an authentication system would be separate from RSVP. If Kerberos were used in conjunction with RSVP, then both RSVP messages and Kerberos messages would be passing through the network. Available network bandwidth would be reduced. Furthermore, because of the separate nature of the RSVP and Kerberos protocols, there would be some delay between the RSVP resource-reservation operations and the Kerberos authentication operations. A significant amount of time might need to pass between the time that the sender begins using RSVP to reserve resources along a path, and the time that the sender can begin sending data packets along that path. Implementing a solution that used multiple separate protocols for different purposes would be complex and require a high degree of skill and organization. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a block diagram that illustrates an overview of a system in which a combined peer-discovery, authentication, and authorization protocol is used for on-path signaling; 
         FIG. 2  depicts a flow diagram that illustrates one embodiment of a method whereby two intermediary network devices authenticate each other using a shared secret cryptographic key and group identifier; 
         FIG. 3  depicts a flow diagram that illustrates an alternative embodiment of a method; and 
         FIG. 4  is a block diagram that illustrates a computer system upon which an embodiment may be implemented. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A method and apparatus for cryptographic peer discovery, authentication, and authorization for on-path signaling is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention. 
     Embodiments are described herein according to the following outline:
         1.0 General Overview   2.0 Structural and Functional Overview   3.0 Implementation Examples   4.0 Implementation Mechanisms—Hardware Overview   5.0 Extensions and Alternatives
 
1.0 General Overview
       

     The needs identified in the foregoing Background, and other needs and objects that will become apparent for the following description, are achieved in the present invention, which comprises, in one aspect, a method for cryptographic peer discovery, authentication, and authorization for on-path signaling. 
     According to one embodiment, the method includes at least the following steps, which may be performed by an intermediary network device such as a router, firewall, or network address translator, for example; in other embodiments, the method may include additional or alternative steps. One or more data packets are intercepted at an intermediary network device. Rather than being addressed to the intermediary network device, the data packets (e.g., IP data packets) are addressed to a destination device other than the intermediary network device. 
     The data packets collectively contain certain information. Among this information are a group identifier and a request. For example, the request may ask the intermediary network device to allocate sufficient resources to a particular data flow so that the particular data flow will be communicated with at least a specified QoS. For another example, the request may ask a firewall to allow a particular data flow to pass through. 
     One or more different shared secret cryptographic keys are stored at the intermediary network device. Each cryptographic key is mapped to a different group identifier. From among these keys, a particular key is selected—the key that is mapped to the group identifier that was contained in the intercepted data packets. 
     A first message is sent toward an “upstream” device from whence the data packets came. The first message contains, at least, a challenge. A second message is received in response to the first message. The second message contains, at least, a response to the challenge. 
     A verification value is generated based, at least, on the particular key and the first challenge. A comparison is made between the verification value and the response. If the verification value matches the response, then the challenge has been satisfied, and the upstream device is authentic. In some embodiments, some of which are described in greater detail below, one or more additional steps are also taken whereby the upstream device can ascertain the authenticity of the intermediary network device. 
     One or more separate sets of authorizations are stored on the intermediary network device. Each set is mapped to a group identifier; different sets may be mapped to different group identifiers, and some sets may be mapped to more than one group identifier. Each set indicates the extent to which the intermediary network device&#39;s policy is permitted to be modified by an entity that is within a group that is associated with the group identifier that is mapped to that set. 
     If the upstream device is authentic, then the following steps are performed. From among the sets of authorizations, a particular set is selected—the set that is mapped to the group identifier that was contained in the intercepted data packets. A determination is made as to whether the request that was contained in the intercepted data packets is allowed by the selected set of authorizations. If the request is allowed, then the intermediary network device&#39;s policy is configured based on the request. For example, a firewall&#39;s policy may be configured to allow the forwarding of data packets that belong to a specified data flow. For another example, the intermediary network device&#39;s policy may be configured in such a way that data packet that belong to a specified data flow will be communicated with at least a specified QoS. 
     Because the group identifier is associated with a shared secret cryptographic key that is stored on the intermediary network device, cryptographic keys do not need to be exchanged between network devices every time that a network device needs to be authenticated. Because the cryptographic key is associated with a group of entities that are associated with the group identifier, fewer cryptographic keys need to be maintained. 
     Moreover, because the request and the group identifier are carried together, there is no need for separate resource reservation and authentication protocols to be used in the network. As a result, fewer messages are needed to achieve the desired reservation and authentication purposes, and less network bandwidth is consumed in the process. 
     In other aspects, the invention encompasses a computer apparatus and a computer-readable medium configured to carry out the foregoing steps. 
     2.0 Structural and Functional Overview 
       FIG. 1  is a block diagram that illustrates an overview of a system  100  in which a combined peer-discovery, authentication, and authorization protocol is used for on-path signaling. System  100  comprises a network  102 , source device  104 , destination device  106 , and intermediary network devices  108 - 118 . The term “network device” as used herein encompasses the term “network element.” 
     Network  102  may be a computer network such as a local area network (LAN), a wide area network (WAN), or an internetwork such as the Internet. Intermediary network devices  108 - 118  may be network elements such as network routers, network switches, network bridges, network address translators, firewalls, etc. Intermediary network devices  108 - 118  may differ from each other. Source device  104  and destination device  106  may be hosts of any kind. Source device  104  and destination device  106  may be personal computers with network interfaces. 
     As shown in  FIG. 1 , source device  104  can only communicate with destination device  106  via one or more of intermediary network devices  108 - 118 . Therefore, data packets that source device  104  sends to destination device  106  over network  102  travel through some path that contains one or more of intermediary network devices  108 - 118 . 
     At least some of source device  104 , destination device  106 , and intermediary network devices  108 - 118  are members of a group. Different devices may be members of different groups, and some devices may be members of more than one group. Each group is associated with a different group identifier. For example, intermediary network devices  108 ,  110 , and  118  may be members of a group whose group identifier is “1.” Intermediary network devices  110 - 114  may be members of a group whose group identifier is “2.” Intermediary network devices  112 - 116  may be members of a group whose group identifier is “3.” Intermediary network devices  114 - 118  may be members of a group whose group identifier is “4.” Intermediary network devices  116 ,  118 , and  108  may be members of a group whose group identifier is “5.” 
     Each group identifier is associated with a different shared secret cryptographic key. Each shared secret cryptographic key is stored locally on the devices that are members of the group whose group identifier is associated with that shared secret cryptographic key. According to one embodiment, no shared secret cryptographic key is possessed by any network device that is not a member of the group whose group identifier is associated with that shared secret cryptographic key. Therefore, using the above example, the cryptographic key that is associated with the group identifier of “1” would be stored on intermediary network devices  108 ,  110 , and  118 , but not on intermediary network devices  112 - 116 . 
     In one embodiment, each intermediary network device stores mappings between the cryptographic keys that are stored on that device, and the group identifiers that are associated with those cryptographic keys. Therefore, using the above example, intermediary network device  108  would store three different cryptographic keys, a mapping between the first cryptographic key and the group identifier of “1, ” a mapping between second cryptographic key and the group identifier of “2, ” and a mapping between the third cryptographic key and the group identifier of “6.” 
     In one embodiment, each group identifier is also mapped to a set of authorizations, or “authorization set.” Different group identifiers can be mapped to different authorization sets, and a particular authorization set may be mapped to more than one group identifier. Intermediary network devices  108 - 118  each store mappings between the group identifiers of the groups to which those devices belong and the corresponding authorization sets. 
     According to one embodiment, before source device  104  sends substantive data toward destination device  106 , source device  104  uses an on-path signaling protocol to reserve resources along a network path over which the substantive data will be communicated. The on-path signaling protocol discussed herein is called the “Network Layer Signaling” (NLS) Protocol. Some features of the NLS Protocol are disclosed in an IETF Network Working Group Internet Draft which, at the time of the filing of the present patent application, is found at the following URL: http://www.ietf.org/internet-drafts/draft-shore-nls-tl-00.txt. The NLS Protocol works through the mechanism of NLS messages. NLS messages may be carried within the data packets of lower-level protocols, such as IP. An example of the use of the NLS protocol is provided below. 
     For example, sender device  104  may send an NLS message within an IP packet that is addressed to an IP address that is associated with destination device  106 . Intermediary network device  108  may intercept the IP packet, determine that the IP packet contains an NLS message, and determine whether authentication needs to occur between source device  104  and intermediary network device  108 . 
     Assuming that no authentication needs to occur between these two devices, intermediary network device  108  may determine a request that is contained in the NLS message. For example, the request may ask each intermediary network device to reserve specified resources for a specified data flow. Intermediary network device  108  may allocate the requested resources for the specified data flow, and then forward the IP packet towards a next hop that is associated with the destination IP address, as indicated in the routing tables of intermediary network device  108 . For example, intermediary network device  108  may forward the IP packet toward intermediary network device  110 . 
     Some network devices in network  102  might not recognize the NLS Protocol. For example, intermediary network device  110  might not be able to determine that the IP packet contains an NLS message. Therefore, without allocating any resources, intermediary network device  110  may simply forward the IP packet towards a next hop that is associated with the destination IP address, as indicated in the routing tables of intermediary network device  110 . For example, intermediary network device  110  may forward the IP packet toward intermediary network device  112 . 
     Both intermediary network devices  112  and  114  may be NLS-aware. Furthermore, intermediary network device  114  may be, or implement, a firewall. Upon inspecting the NLS message, intermediary network device  114  may determine that the request in the NLS message asks for a “pinhole” to be opened in each firewall along the path, so that a data flow that satisfies specified criteria can pass through each firewall along the path. Before intermediary network device  114  modifies its policy to allow the specified network traffic to be forwarded through, intermediary network device  114  may engage in a mutual authentication process with the device from which the NLS message was received-namely, intermediary network device  112 . 
     The mutual authentication process in which intermediary network devices  112  and  114  engage involves a group identifier of a group to which both devices belong. In this case, using the above example, both devices mutually belong to two different groups: group “2” and group “3, ” referring to the group identifiers of those groups. One of these group identifiers is selected and used in the mutual authentication process. The mutual authentication process also involves the shared secret cryptographic key that is mapped to the selected group identifier. An example of one implementation of the mutual authentication process is described below with reference to  FIG. 2 . 
     If the mutual authentication process is successful, then, at the conclusion of the mutual authentication process, both intermediary network devices  112  and  114  are assured of the other&#39;s authenticity. Intermediary network device  114  then selects, based on locally stored mappings, an authorization set that is mapped to the group identifier that was used in the mutual authentication process. Intermediary network device  114  determines whether the request contained in the NLS message falls within the boundaries of the policy modifications that can be made, according to the selected authorization set. Assuming that the request is allowable, intermediary network device  114  modifies its policy as indicated in the request, and then forwards the IP packet to destination device  106 . For example, intermediary network device  114  may modify its policy by making an exception to its firewall policy and by allocating requested resources to a specified data flow. 
     Destination device  106  receives the IP packet. According to one embodiment, the network path through which data flows from source device  104  to destination device  106  can differ from the network path through which data flow back from destination device  106  to source device  104 . In such an embodiment, network device  106  may send, toward source device  104 , another IP packet that contains another NLS message. Whereas the IP packet sent from source device  104  might have traveled the path comprising intermediary network devices  108 ,  110 ,  112 , and  114 , the IP packet sent from destination device  106  might travel a path comprising intermediary network devices  114 ,  116 ,  118 , and  108 , for example. Thus, the techniques described herein can be used to reserve resources and authenticate intermediary network devices along either symmetrical or asymmetrical routes. 
     The techniques described herein can be used to authenticate intermediary network devices along a route even under circumstances where the sender (e.g., source device  104 ) does not know the route before the intermediary network devices along the route are authenticated. The NLS messages perform a peer-discovery function. The pre-organization of intermediary network devices into groups, and the pre-sharing of secret cryptographic keys among intermediary network devices that are potential next hops relative to each other, make this “spontaneous” style of authentication possible. 
     3.0 Implementation Examples 
       FIG. 2  depicts a flow diagram  200  that illustrates one embodiment of a method whereby two intermediary network devices authenticate each other using a shared secret cryptographic key and group identifier. For example, any of intermediary network devices  108 - 118 , shown in  FIG. 1 , may perform the method shown. The method encompasses a mutual authentication process as described above. 
     Referring to  FIG. 2 , in block  202 , one or more data packets are intercepted at an intermediary network device. The data packets are addressed to a destination device that is separate from the intermediary network device. For example, intermediary network device  114  may intercept an IP packet that intermediary network device  112  sent. The IP packet may specify a destination IP address that is associated with destination device  106 . 
     In block  204 , it is determined whether the data packets collectively contain an NLS message. Continuing the example, intermediary network device  114  may determine whether the IP packet contains an NLS message. The NLS message may be identified by a specified bit pattern that occurs at the start of every NLS message, for example. If the data packets collectively contain an NLS message, then control passes to block  206 . Otherwise, control passes to block  226 . 
     In block  206 , a secret cryptographic key that is mapped to a group identifier is selected. The group identifier is contained in the NLS message, but the secret cryptographic key is not. Continuing the example, intermediary network device  114  may consult locally stored mappings and determine that a particular cryptographic key is associated with the group identifier that is contained in the NLS message. If the NLS message contains more than one group identifier that corresponds to a group to which intermediary network device  114  belongs, then intermediary network device  114  may choose one of those group identifiers to be the “active” group identifier, and ignore the others. 
     In block  208 , a first response to a first challenge is generated. The first challenge is contained in the NLS message. The first response is generated based on both the secret cryptographic key and the first challenge. Continuing the example, the first challenge may be a random nonce that intermediary network device  112  generated. Intermediary network device  114  may generate the first response by inputting both the “first” NLS message (including the first challenge) and the secret cryptographic key into a cryptographic function such as HMAC SHA1 (Keyed Hashing for Message Authentication). The output of the cryptographic function is the first response. In one embodiment, the cryptographic function is chosen such that the inputs to the cryptographic function cannot be derived mathematically from the output of the cryptographic function. 
     In block  210 , a second challenge is generated. Continuing the example, intermediary network device  114  may generate a random nonce and use the nonce as the second challenge. 
     In block  212 , an NLS message is sent to the upstream device from whence the data packets, intercepted in block  202 , were sent. This “second” NLS message contains the group identifier, the first response, and the second challenge. Continuing the example, intermediary network device  114  may send such a “second” NLS message toward intermediary network device  112 . 
     Intermediary network device  112  also stores a copy of the secret cryptographic key that is mapped to the group identifier. Upon receiving the “second” NLS message from intermediary network device  114 , intermediary network device  112  may verify the correctness of the first response by inputting (a) the secret cryptographic key that is mapped to the group identifier, and (b) a copy of the “first” NLS message that intermediary network device  112  previously sent to intermediary network device  114 , into the same cryptographic function that intermediary network device  114  used to generate the first response. If the output of the cryptographic function matches the first response, then intermediary network device  112  “knows” that intermediary network device  114  is authentic. 
     Intermediary network device  112  may generate a second response to the second challenge by inputting both the “second” NLS message received from intermediary network device  114  (including the second challenge) and the secret cryptographic key into the cryptographic function. The output of the cryptographic function is the second response. Intermediary network device  112  may send both the second response and the group identifier to intermediary network device  114  in a “third” NLS message. 
     In block  214 , an NLS message is received. The NLS message contains the second response and the group identifier. Continuing the example, intermediary network device  114  may receive the “third” NLS message that intermediary network device  112  sent. 
     In block  216 , a verification value is generated. The verification value is generated based on both (a) the secret cryptographic key that is mapped to the group identifier and (b) the second challenge. Continuing the example, intermediary network device  114  may generate the verification value by inputting both the secret cryptographic key and a copy of the “second” NLS message (including the second challenge) into the cryptographic function. The output of the cryptographic function is the verification value. 
     In block  218 , it is determined whether the second response matches the verification value. For example, intermediary network device  114  may compare the second response with the verification value. If the second response matches the verification value, then intermediary network device  114  “knows” that intermediary network device  112  is authentic, and control passes to block  220 . Otherwise, control passes to block  228 . 
     In block  220 , an authorization set that is mapped to the group identifier is selected. Continuing the example, intermediary network device  114  may consult locally stored mappings and determine that a particular authorization set is mapped to the group identifier. 
     In block  222 , it is determined whether a request is allowed by the particular authorization set. The request is contained in the NLS message that was originally received in block  202 . For example, if the request asks for a “pinhole” to be opened in a firewall to allow a data flow that satisfies specified criteria to pass through the firewall, then intermediary network device  114  may determine whether a pinhole associated with the specified criteria is allowable according to the particular authorization set. It may be that the authorization set indicates that some pinholes may be opened in the firewall, but only for data flows that satisfy certain criteria, which may or may not be narrower than the criteria specified in the request. 
     For another example, if the request asks for resources to be allocated to a data flow that satisfies specified criteria so that the data flow will be accorded at least a certain QoS, then intermediary network device  114  may determine whether the allocation of such resources is allowable according to the particular authorization set. It may be that the authorization set indicates that some resources may be reserved for data flows that satisfy the specified criteria, but possibly not as many resources as the request asks. 
     Thus, different groups may be allowed different privileges in the extent to which entities within those groups are permitted to modify an intermediate network device&#39;s policy. Entities within one group may be allowed to make sweeping changes to a network device&#39;s policy, while entities within another group may be allowed to make only minor adjustments to the network device&#39;s policy. 
     If the request is allowed by the particular authorization set, then control passes to block  224 . Otherwise, control passes to block  228 . 
     In block  224 , a policy of the intermediate network device is configured based on the request. For example, if the request asks intermediary device  114  to open a pinhole in a firewall implemented on intermediary device  114 , then intermediary device  114  may adjust its firewall policy so that data flows that satisfy the criteria specified in the request will be forwarded through. For another example, if the request asks intermediary device  114  to allocate resources sufficient to accord a specified data flow a specified QoS, then intermediary device  114  may allocate as many resources (e.g., bandwidth) to such a data flow as will be necessary to accord that data flow the specified QoS. 
     In block  226 , the data packets that were intercepted in block  202  are forwarded toward the destination device. For example, intermediary network device  114  may forward the originally intercepted IP packet toward destination device  106 . Prior to doing so, intermediary network device may modify the NLS message contained within the IP packet, if the IP packet contained an NLS message. 
     Alternatively, in block  228 , the request that is contained in the original NLS message is denied. For example, intermediary network device  114  may refuse to modify its policy (e.g., firewall and/or resource allocation) as asked in the request. 
     Thus, resource reservation, authentication, and authorization may be handled via the messages of a single on-path signaling protocol, thereby eliminating the need to use several different protocols to perform these functions. Because the request and the group identifier are carried together within the same message, in one embodiment, there is no need for separate resource reservation and authentication protocols to be used in the network. As a result, fewer messages are needed to achieve the desired reservation and authentication purposes, and less network bandwidth is consumed in the process. 
     The use of group keys allows the foregoing technique to function successfully even when “next hops” are not known beforehand, and even when network topology changes. Fewer cryptographic keys are required. The use of a single protocol rather than many protocols reduces administrative complexity. 
     Because very refined and specific authorization sets may be associated with group identifiers, authorizations may be very fine-grained. Because group identifiers are transmitted through the network, the authorization sets themselves do not need to be. 
       FIG. 3  depicts a flow diagram  300  that illustrates an alternative embodiment of a method. Referring to  FIG. 3 , in block  302 , one or more data packets, which collectively contain a request, are intercepted. In block  304 , a particular cryptographic key is selected from among one or more cryptographic keys. In block  306 , a challenge is sent toward an upstream device. In block  308 , a response is received. In block  310 , a verification value is generated based on the particular cryptographic key and the challenge. In block  312 , it is determined whether the response matches the verification value. If the response matches the verification value, then control passes to block  316 . Otherwise, control passes to block  322 . In block  316 , a particular authorization set is selected from among one or more authorization sets. In block  318 , it is determined whether the request is allowed by the particular authorization set. If the request is allowed by the particular authorization set, then control passes to block  320 . Otherwise, control passes to block  322 . In block  320 , in response to determining that the request is allowed by the particular authorization set, an intermediary network device is configured based on the request. Alternatively, in block  322 , the request is denied, and the intermediary network device is not configured based on the request. 
     4.0 Implementation Mechanisms—Hardware Overview 
       FIG. 4  is a block diagram that illustrates a computer system  400  upon which an embodiment of the invention may be implemented. The preferred embodiment is implemented using one or more computer programs running on a network element such as a router device. Thus, in this embodiment, the computer system  400  is a router. 
     Computer system  400  includes a bus  402  or other communication mechanism for communicating information, and a processor  404  coupled with bus  402  for processing information. Computer system  400  also includes a main memory  406 , such as a random access memory (RAM), flash memory, or other dynamic storage device, coupled to bus  402  for storing information and instructions to be executed by processor  404 . Main memory  406  also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor  404 . Computer system  400  further includes a read only memory (ROM)  408  or other static storage device coupled to bus  402  for storing static information and instructions for processor  404 . A storage device  410 , such as a magnetic disk, flash memory or optical disk, is provided and coupled to bus  402  for storing information and instructions. 
     A communication interface  418  may be coupled to bus  402  for communicating information and command selections to processor  404 . Interface  418  is a conventional serial interface such as an RS-232 or RS-422 interface. An external terminal  412  or other computer system connects to the computer system  400  and provides commands to it using the interface  414 . Firmware or software running in the computer system  400  provides a terminal interface or character-based command interface so that external commands can be given to the computer system. 
     A switching system  416  is coupled to bus  402  and has an input interface  414  and an output interface  419  to one or more external network elements. The external network elements may include a local network  422  coupled to one or more hosts  424 , or a global network such as Internet  428  having one or more servers  430 . The switching system  416  switches information traffic arriving on input interface  414  to output interface  419  according to predetermined protocols and conventions that are well known. For example, switching system  416 , in cooperation with processor  404 , can determine a destination of a packet of data arriving on input interface  414  and send it to the correct destination using output interface  419 . The destinations may include host  424 , server  430 , other end stations, or other routing and switching devices in local network  422  or Internet  428 . 
     The invention is related to the use of computer system  400  for secure network device policy configuration on computer system  400 . According to one embodiment of the invention, computer system  400  provides for such configuration in response to processor  404  executing one or more sequences of one or more instructions contained in main memory  406 . Such instructions may be read into main memory  406  from another computer-readable medium, such as storage device  410 . Execution of the sequences of instructions contained in main memory  406  causes processor  404  to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory  406 . In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software. 
     The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor  404  for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as storage device  410 . Volatile media includes dynamic memory, such as main memory  406 . Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus  402 . Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. 
     Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. 
     Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor  404  for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system  400  can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to bus  402  can receive the data carried in the infrared signal and place the data on bus  402 . Bus  402  carries the data to main memory  406 , from which processor  404  retrieves and executes the instructions. The instructions received by main memory  406  may optionally be stored on storage device  410  either before or after execution by processor  404 . 
     Communication interface  418  also provides a two-way data communication coupling to a network link  420  that is connected to a local network  422 . For example, communication interface  418  may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface  418  may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface  418  sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information. 
     Network link  420  typically provides data communication through one or more networks to other data devices. For example, network link  420  may provide a connection through local network  422  to a host computer  424  or to data equipment operated by an Internet Service Provider (ISP)  426 . ISP  426  in turn provides data communication services through the worldwide packet data communication network now commonly referred to as the “Internet”  428 . Local network  422  and Internet  428  both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network link  420  and through communication interface  418 , which carry the digital data to and from computer system  400 , are exemplary forms of carrier waves transporting the information. 
     Computer system  400  can send messages and receive data, including program code, through the network(s), network link  420  and communication interface  418 . In the Internet example, a server  430  might transmit a requested code for an application program through Internet  428 , ISP  426 , local network  422  and communication interface  418 . In accordance with the invention, one such downloaded application provides for secure network device policy configuration as described herein. 
     Processor  404  may execute the received code as it is received and/or stored in storage device  410  or other non-volatile storage for later execution. In this manner, computer system  400  may obtain application code in the form of a carrier wave. 
     5.0 Extensions and Alternatives 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.