Abstract:
A network device for distributing authentication information between authorized nodes for purposes of concurrently “pre-authenticating” a mobile user at a plurality of points throughout a LAN is disclosed. When a client attempts to access the network through the network device, the network device attempts to authenticate the client based on the credentials presented by the user. If authenticated, the client is admitted into the network at the network device and the client&#39;s pre-authentication information transmitted to one or more network nodes associated with an authentication group. Upon receipt of the pre-authentication information, the one or more network nodes are authorized to admit the client into the network at those nodes in addition to the network device at which the client was initially authenticated, thereby concurrently pre-authorizing the client at multiple points across the network.

Description:
FIELD OF INVENTION 
     The present invention relates to a technique for securely sharing authentication information between network nodes to facilitate user access. In particular, the invention relates to a system and method for automatically sharing client authentication information between switching devices and access points to permit the client to roam through the network without being re-authenticated at each network node. 
     BACKGROUND 
     Network with multiple edge devices or access points typically require that all clients be authenticated using a central authentication server. The authentication server thus becomes a bottleneck in the network through which all authenticated traffic must flow. Moreover, when a client moves from one access point or edge device to another, the client must be re-authenticated by the authentication server to establish connectivity to the core network again. The process of being re-authenticated consumes time, disrupts client connectivity, may result in loss of data, and is unnecessary where the client is merely moving between secure nodes in a private network, for example. 
     There is therefore a need for a system and method for securely distributing authentication information of a client between participating edge devices or access points, reduce the need to access the authentication server, and reduce time and effort to repeatedly re-authenticate clients that move within a network between different edge devices and or access points. 
     SUMMARY 
     The invention features a network device for distributing authentication information between authorized nodes for purposes of concurrently “pre-authenticating” a mobile user, for example, at a plurality of points throughout a local area network (LAN) or other network domain. The preferred embodiment is a network device for advertising security authentication in a network comprising one or more network nodes associated with an authentication group, an authentication server, and a client having an associated client identifier and credentials. The network device preferably comprises at least one port adapted to receive a packet and credentials from the client; a table for retaining the client identifier of one or more authenticated clients; and an authentication manager. The authentication manager is adapted to determine whether the client has been pre-authenticated by querying the table using information from the packet, e.g. the source MAC address; determine whether to authenticate the client from the authentication server based on the client credentials if not pre-authenticated; and transmit the client identifier to the one or more network nodes if the client is authenticated by the authentication server. Upon receipt of the client identifier, the one or more network nodes are authorized to admit the client to the network at those nodes, thereby concurrently pre-authorizing the client at multiple points across the network. The client credentials presented in the initial packet transmitted by the client generally comprises the client&#39;s user identifier and password. The network device may be selected from the group comprising a router, a bridge, a multi-layer switch, a network access point, a wireless network access point, and a combination thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, and in which: 
         FIG. 1  is a data communications network including a plurality of network devices adapted to exchange pre-authentication information, in accordance with the preferred embodiment; 
         FIG. 2  is a functional block diagram of a multi-layer switching device for performing secure authentication advertisement, in accordance with the preferred embodiment; 
         FIG. 3  is a functional block diagram of a switching module for performing secure authentication advertisement, in accordance with the preferred embodiment; 
         FIG. 4  is a schematic of a shared admission table for preauthorizing clients within a network, in accordance with the preferred embodiment; 
         FIG. 5  is a functional block diagram of an authentication manager for pre-authorizing clients within a network, in accordance with the preferred embodiment; and 
         FIG. 6  is a message diagram produced within the network as a client is initially authenticated and then pre-authenticated within the network, in accordance with the preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrated in  FIG. 1  is a data communications network including a plurality of network devices adapted to exchange pre-authentication information. The network  100  in the preferred embodiment may include or operatively couple to a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), an Internet Protocol (IP) network, the Internet, or a combination thereof, for example. The network  100  includes a plurality of switching devices  102 - 105 , a plurality of clients  110 - 114 , an application server  130 , and an authentication server  120 . Any of the switching devices  102 - 105  may include or be operatively coupled to a wireless access point such as access points  108 - 109 . Similarly, one or more of the clients  110 - 114  may include wired or wireless capability permitting the device to migrate through the network  100 , as mobile client  110  migrates from the first switching device  110  to the access point  108 . 
     The first switching device  103  and third switching device  105  of the preferred embodiment are enabled with Ethernet and Internet Protocol (IP) protocol, although various other network layer protocols-including Connectionless Network Protocol (CLNP) or Internetwork Packet eXchange (IPX)/Sequenced Packet Exchange (SPX)—and link layer protocols—including token ring and asynchronous transfer mode (ATM) WAN/serial protocols such as T1/E1—may be implemented. 
     As described in more detail below, the switching devices of the network  100  may be associated with one or more virtual pre-authentication networks (VPANs) authentication groups, each of which is designated by a unique VPAN identifier. The first VPAN  110 , for example, includes the first switching device  103 , the router  102 , the third switching device  105 , as well as the wireless access point  108 . 
     Illustrated in  FIG. 2  is a functional block diagram of a multi-layer switching device for performing secure authentication advertisement. The switching device  103  preferably comprises a plurality of switching modules  210  operatively coupled to one another by means of a switch fabric  250  for transmitting protocol data units (PDUs) between switching modules. A switching module  210  may take the form of a switch processor, switching element, or switching blade adapted to detachably engage a slot or bus system (not shown) in the backplane  252  that operatively couples each of the switching modules  210  together. 
     Each of the plurality of switching modules  210  comprises a plurality of external ports  203  operatively coupled to the network  100  via a network communications link. Each switching module  210  in the preferred embodiment further includes at least one switching controller  206  generally capable of, but not limited to, Layer 2 (Data Link) switching and Layer 3 (Network) routing operations as defined in the Open Systems Interconnection (OSI) reference model. As such, each of the modules  210  is adapted to transmit protocol data units (PDUs) to and receive PDUs from the network via ports  203 , and to transmit PDUs to and receive PDUs from every other switching module by means of the switch fabric  250 . 
     For purposes of this application, PDUs flowing into a switching module  210  from a communications link toward the switch fabric  250  are referred to herein as ingress PDUs, and the switching module  210  through which the ingress PDUs enters the switching device  103  is generally referred to as an ingress switching module. PDUs flowing from the switching fabric  250  to a communications link are referred to herein as egress PDUs, and the switching module from which they are transmitted is referred to as an egress switching module. Each of the plurality of switching modules  210  of the present embodiment may serve as both an ingress switching module and an egress switching module depending on the flow and its direction. The switching device  103  is one of a plurality of network nodes that may be adapted to perform secure authentication advertisement including routers, bridges, traffic classifiers, rate policers, accounting devices, editing devices, and address look-up devices. 
     Illustrated in  FIG. 3  is a functional block diagram of a switching module for performing secure authentication advertisement. The switching module  210  preferably comprises a plurality of network interface modules (NIMs)  304 , at least one switching controller  206 , a management module  320 , and a fabric interface module  308 . Each of the NIMs  304  is operatively coupled to one or more external ports  203  for purposes of receiving and transmitting data traffic. The NIMs  304 , preferably enabled with Institute of Electrical and Electronics Engineers (IEEE) 802.3, IEEE 802.2 and or IEEE 802.11 for example, are adapted to perform physical layer and data link layer control that operably couple the switching device  103  to communication media including wired, wireless, and optical communications links. 
     Ingress PDUs received by NIMs  304  are transmitted via an internal data bus  305  to the switching controller  206  where a routing engine  330  generally makes filtering and forwarding decisions before the PDUs are buffered in a queue manager  340  en route to the destination node. The routing engine  330  of the preferred embodiment comprises a classifier  332 , a forwarding processor  334 , and an egress processor  336 . The classifier  332  extracts one or more fields of the ingress PDUs, queries a content addressable memory (CAM)  333  using one or more properties associated with the ingress PDU including the extracted fields, and classifies the PDUs into one of a plurality of flows. The PDU properties generally include, for example, the destination and source addresses, ingress port number, protocol type, priority information, and virtual local area network (VLAN) information including 802.1Q tags. 
     The switching controller  206  in the preferred embodiment also employs an authentication manager  360  to perform admission testing prior to executing the applicable forwarding operations identified by classifier  332 . If the ingress PDU originated from an authenticated client that is currently logged into the switching device  103 , for example, the client identity and associated access privileges are recorded in a shared admission table (SAT)  362  retained internal to the switching device  103 . If the client has not been authenticated or is not currently logged in, the client is prompted to provide credentials, preferably a user name and password, for determining the client&#39;s access profile from an external database such as authentication server  120 . If the access privilege sought by the client is denied by the switching device&#39;s SAT  362  or the authentication server  120 , the ingress PDU is filtered. 
     If the access sought by the client is granted by the SAT  362  or the authentication server  120 , however, the classifier  332  retrieves the associated PDU forwarding instructions from the forwarding table  354  and transmits the instant PDU to the forwarding processor  334 . Subsequent PDUs originating from the same client are also admitted to the switching device  103  as long as the client is logged in or the session between the client and destination node maintained. 
     When a client entering the network  100  is authenticated by the authentication server  120 , the authentication manager  360  is adapted to update the SAT  362  with an associated client identifier (ID). In accordance with the preferred embodiment of the present invention, the authentication manager  360  is further adapted to transmit a pre-authentication status message to one or more network nodes associated with the same VPAN authentication group as the switching device  103 . The pre-authentication status message in the preferred embodiment comprises the client identifier of the newly-authenticated client and its associated access privileges. Upon receipt of a pre-authentication status message, the recipients update their respective shared admission tables with the client identifier and the access privileges of the newly-authenticated client. In this manner, a client is effectively logged into each of the members of the VPAN security group once the client affirmatively logs into one member of the security group. 
     Once the client is authenticated at the node to which it is transmitting, the ingress PDU is transmitted to the forwarding processor  334  where the forwarding operations identified by the retrieved forwarding instructions are executed. If the destination media access control (MAC) address is known to and reachable through the switching device  103 , the PDU is generally switched to the appropriate egress port without alteration. If unknown, the source MAC address may be associated with the ingress port  203  by a source learning mechanism and the PDU broadcast to every other egress port within the VLAN associated with the ingress port. If the destination node of the PDU is within another network, the forwarding processor  334  generally decrements the time to live (TTL) counter and re-encapsulated the packet with a new data link layer header, for example, before routing the packet to the appropriate destination. 
     The forwarding processor  334  in some embodiments is also adapted to perform packet processing operations including, but are not limited to, header transformation for re-encapsulating data, VLAN tag pushing for appending one or more VLAN tags to a PDU, VLAN tag popping for removing one or more VLAN tags from a PDU, quality of service (QoS) for reserving network resources, billing and accounting for monitoring customer traffic, Multi-Protocol Label Switching (MPLS) management, authentication for selectively filtering PDUs, access control, higher-layer learning including Address Resolution Protocol (ARP) control, port mirroring for reproducing and redirecting PDUs for traffic analysis, source learning, class of service (CoS) for determining the relative priority with which PDUs are allocated switch resources, and coloring marking used for policing and traffic shaping, for example. 
     After packet processing by the routing engine  330 , PDUs destined for nodes reachable through other switching modules of switching device  103  are temporarily buffered by the queue manager  340  within the priority queues  342  in accordance with their Class of Service (CoS) and or Quality of Service (QoS) requirements until the bandwidth is available to transmit the PDUs through the switching fabric  250 . The PDUs are then transmitted via the fabric interface module  308  to the appropriate egress switching module for transmission in the direction of the PDU&#39;s destination node. 
     In the preferred embodiment, the fabric interface module  308  is adapted to both transmit ingress PDUs to the switching fabric  250  as well as receive egress PDUs from each of the other one or more switching modules. In the preferred embodiment, the egress data received from the fabric interface module  308  are buffered in priority queues  342 , passed through the routing engine&#39;s egress processor  336  for statistical processing, for example, and transmitted from the appropriate egress port via one of the NIMs  304 . 
     Illustrated in  FIG. 4  is a schematic of a shared admission table  362  for preauthorizing clients within a network. The SAT  400  comprises one or more fields that are used to identify an authenticated client and the associated access privileges of the client. In the preferred embodiment, an authenticated client is identified by its address, preferably the MAC source address (SA)  401 , although the address may also be an IP source address for example. The access privileges associated with the client preferably include one or more VLAN identifiers (VIDs)  402 , although the access privileges may also include one or a plurality of access controls specifying the right of the user to view, download, or change various files. 
     The client identifiers recited in the SAT  362  include those clients that directly logged into the network node hosting the SAT  362 , e.g., switch  103 , as well as the clients that directly logged into other network nodes associated with the same VPAN authentication group. As explained in more detail below, the client IDs of clients that directly logged into other network nodes in the VPAN are learned in one or more authentication status messages generated by the authorization manager  360  of those other network nodes. The SAT  362  is embodied in the authentication manager  360  in the preferred embodiment, although it may also be integrated with the bridging and routing information of the forwarding table  354  or in the central command processor  260 . The client may be a node within or external to the network  100  or an application running thereon, for example. 
     Illustrated in  FIG. 5  is a function block diagram of an authentication manager  360  for pre-authorizing clients within a virtual pre-authentication area network. The authentication manager  360  of the preferred embodiment includes an authentication status module  502 , security module  506 , a SAT  362 , a pre-authentication message generator  510 , and a pre-authentication message receiver  512 . Upon receipt of a PDU from a client seeking to connect to the switching device  103  or a node reachable through the device  103 , the routing engine  330  determines whether the client is authenticated to do so. In particular, the routing engine  330  transmits one or more fields extracted from the ingress PDU to the status module  502 , which is adapted to first query the shared admission table  362  to determine the admission status of the client. 
     If the status manager  502  cannot authenticate the client based in the SAT  362 , the status manager  502  notifies the routing engine  330  that the client is provisionally denied authentication, causing the routing engine  330  to prompt the client for credentials, preferably a user identifier and password. Upon receipt of the user identifier and password, the status manager  502 , i.e., and more particularly the retrieval agents  504 , generates an authentication query transmitted to an external database, e.g., the authentication server  120 , to determine the admission status of the client. In the preferred embodiment, the authentication query and the subsequent response are encrypted and decrypted, respectively, by the security module  506 . 
     If the authentication server  120  issues a response granting the authentication, the status module  502  triggers the update control  508  to add the client identifier to the internal SAT  362 . The pre-authentication generator  510  in the preferred embodiment then determines the destination addresses of the each of the other members of the authentication group table (AGT)  514  to which the first switching device  103  belongs. The pre-authentication generator  510  then sends a pre-authentication grant message encrypted by the security module  506  to each member of VPAN authentication group. Similarly, the pre-authentication generator  510  also transmits a pre-authentication rescind message to each member of the authentication group when the clients logs-off or authentication otherwise revoked. 
     The update control  508  is also adapted to receive pre-authentication grant and rescind messages from other members of the authentication group. Upon receipt of pre-authentication grant message, the update control  508 , particularly the pre-authentication receiver  512 , causes the client identifier and associated access privileges therein to be added to the local SAT  362 . Similarly, the pre-authentication receiver  512  causes a client identifier and privileges to be removed from the local SAT  362  upon receipt of a pre-authentication direction to rescind privileges, that is, a rescind message from another member of the authentication group. 
     In this manner, a client is able to quickly gain access to each and every member of an authentication group without the formality of a user log-in procedure. Although the authentication manager  360  in the preferred embodiment is configured to provisionally deny authentication to each client not explicitly listed in the SAT  362 , one skilled in the art will appreciate that the authentication manager  360  may be configured with different default authentication rules. 
     Illustrated in  FIG. 6  is a message diagram produced within the network as a client is initially authenticated and then pre-authenticated within the network. The first message transmitted by the mobile client  110 , for example, to a node within a VPAN is referred to herein as an access request message  602 . Upon receipt of the access request message  602 , the first switching device  103  queries its SAT  362  using the MAC source address of the mobile node  110 . If the source address is not present and the mobile client  110  provisionally denied authentication, the switching device  103  transmits an identifier request message  604  prompting the client  110  to enter a user ID and password  606 . If the authentication server  120  is able to authenticate the client  103  based on the received user ID and password  606 , the server  412  transmits an authentication message  610 - 611  including the authentication confirmation. Upon receipt of the authentication confirmation, the first switching device  103  permits the mobile client  110  to transmit to and establish a communications session  612  with the requested resource such as application server  130 . 
     In accordance with the preferred embodiment, the first switching device  103  also transmits a pre-authentication grant message  614  to each member of the VPAN authorization group  150 , including the router  102  which forwards the grant message  614  to the third switching device  105  which forwards it to the access point  108 . Each of the nodes in the VPAN  150  that receives the grant message updates its SAT  362  with the mobile user&#39;s client ID to signify that the mobile client  110  is logged in at that node. 
     At a later time, if and when the mobile client  110  migrates within the VPAN  150  as illustrated in  FIG. 1 , the mobile client  110  can continue the ongoing session with the application server  130  in real-time without disruption. As the mobile client  110  swaps the connection to the first switching device  103  with the wireless connection to the access point  108 , for example, the mobile client  110  continues to transmit session messages  620 - 621  to and receive messages from the application server  130  as part of the pre-existing session  612 . As described above, the access point  108  authenticates the mobile user based on the MAC source address and VLAN association information extracted from the session messages  620  without prompting the mobile client  110  again for a user ID and password, which would disrupt the ongoing session with the application server  130  and result in the loss of data and inconvenience to the user. 
     Note that a network node consistent with the preferred embodiment is assigned at least one of a plurality of VPAN authentication group identifiers by the network administrator. In this manner, a network may be segmented into multiple virtual pre-authentication subnets. For example, a corporate network may be subdivided into separate, and to some degree overlapping, subnets for an engineering department, a financial department, and a sales department. A client that is authenticated in one portion of the network may then be required to log in at a different portion of the network if the node to which access is sought has a different VPAN authentication association than that portion of the network to which the client is currently authenticated. Referring to  FIG. 1  as an example, the mobile client  110  would need to log in to connect to either the second switching device  104  or its associated access point  109  because the client&#39;s pre-authenticated is valid only among the first switching device  103 , router  102 , third switching device  105 , and access point  108 . 
     At a later time, if and when the mobile client  110  logs off the node to which it is connected, the node revokes the pre-authentication at the connected node and at each of the other nodes associated with the VPAN authentication group. If the mobile client  110  logs off  630  from the access point  108 , for example, the access point  108  generates a pre-authentication rescind message  632  transmitted to each of the other members of the VPAN  150  including the third switching device  105  which forwards the rescind message  632  to the router  102  which forwards it to the first switching device  103 . Upon receipt of the rescind message  632 , each of the nodes removes the mobile client ID from its SAT, thereby preventing the mobile client  110  from accessing the network  100  without logging in once again. 
     In the preferred embodiment, the network nodes associated with a particular VPAN, i.e., the members of a VPAN authentication group, are adapted to discover one another using a neighbor discovery protocol known to those skilled in the art. The neighbor discover protocol is preferably a Layer 2 protocol that employs “hello” messages transmitted to a reserved multicast MAC address to enable each network device to advertise its own identity, preferably an IP address, to other nodes in the LAN, discover the identities of its neighbors, determine which of the neighbors are running the same pre-authentication protocol of the present invention, and which of the one or more VPANs the neighbors support or which of the one or more VPANs are supported by nodes reachable through those neighbors. In the preferred embodiment, each device wanting to share authentication is provided an encryption key that is unique for the VPAN and the key used to open an encrypted communication stream between the network nodes over which the client identification information can be shared. An example neighbor discovery protocol with which the present invention may utilize is IEEE 802.1A/B, hereby incorporated by reference. 
     Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. 
     Therefore, the invention has been disclosed by way of example and not limitation, and reference should be made to the following claims to determine the scope of the present invention.