Abstract:
Conventional methods of addressing a Distributed Denial of Service attack include taking the target node offline, and routing all traffic to an alternate countermeasure, or “sinkhole” router, therefore requiring substantial lag time to reconfigure the target router into the network. In a network, a system operator monitors a network for undesirable message traffic. Upon a notification of such undesirable message traffic, traffic is rerouted to a filter complex to separate undesirable traffic. The filter complex establishes an alternate route using a second communications protocol, and uses the alternate route to redirect the desirable message traffic to the target node. The use of the second protocol avoids conflict between the redirected desirable traffic and the original, or first, protocol which now performs the reroute. In this manner, the filter complex employs a second alternate communications protocol to reroute and redirect desirable message traffic to the target node while diverting undesirable message traffic, and therefore avoids widespread routing configuration changes by limiting the propagation breadth of the second protocol.

Description:
BACKGROUND OF THE INVENTION 
   Computer networks transport a large volume of message traffic between users. The network interconnects the users by way of routing devices and physical communication lines. The routing devices switch message traffic between users by address information in the message traffic which conforms to a particular protocol. The message traffic travels in a series of “hops” among the routing devices conversant in the protocol to arrive at the destination, or target node. 
   In such a computer network, certain activities may cause an influx of an inordinate amount of message traffic to particular target node. Malicious, intentional inundation of messages to a particular target node overwhelm the resources of the target node to process the barrage of incoming message traffic. This so called “denial of service” attack results in the inability of the target node to provide routing service to users due to the consumption of resources by the undesirable incoming message traffic. Such denial of service attack attempts may be made by disgruntled employees, hackers, pranksters, and others for a variety of reasons. Further, such attacks also occur unintentionally due to unfamiliarity or ignorance, for example, an employee erroneously addressing an email to an entire company mailing list with delivery confirmation. 
   Such conventional computer networks employ a plurality of routing devices. The routing devices include edge routers, which communicate directly with the user nodes, or hosts/servers, and core routers, which communicate with other routing devices in the computer network. Each of the edge routers and core routers (routing devices) has one or more routing tables for routing message traffic according to address information in each of the messages included in the message traffic. The routing devices lookup the address information in the routing tables to determine where to send, or route, the message. 
   In a conventional computer network, the information in the routing table propagates between the routing devices so that each routing device will know where to forward a particular message for the next “hop.” An edge router nearest a particular host advertises itself as the preferred routing device for that host. Other routers will store information in their routing tables indicating that message traffic for the host is to be sent to the preferred routing device. The edge router serving the host, therefore, becomes the focal point for the denial of service attack on the host. 
   SUMMARY 
   Conventional countermeasures for defending against denial of service attacks include analyzing the incoming message traffic to determine the source. An inordinate quantity of transmissions from a particular, unknown source is often indicative of such improper transmissions. In such a scenario, the solution is to isolate the messages emanating from the offending source. However, a particularly malicious hacker or other scenario causes in the inundating message traffic to emanate from a plurality of sources. For example, a virus disseminates via an email to a rather large distribution list. Upon opening the email, the virus results in a transmission sent from the email recipient to the target node. Since all the recipients unknowingly cause a transmission back to the same target node, the target node receives an inordinate amount of messages, each from a different source. None of the senders may be aware that they are, in effect, participating in a denial of service attack, as they simply opened an email, and since each email emanates once from each remote node, the target node observes no inordinate pattern of transmission from a single remote source. Such an attack is called a Distributed Denial of Service attack (DDOS), since it emanates from a plurality of distributed sources. 
   Conventional methods of addressing a DDOS attack include removing the victim target node from the routing tables of the network configuration by taking the target node offline. A system operator then reroutes message traffic to a countermeasure destination by replacing the target node address with the countermeasure, or “sinkhole” router node address such that the countermeasure destination, typically another node, receives all message traffic for analysis. 
   Once the system or network administrator diagnoses and finds the offending source or sources and corrects the DDOS attack condition, the administrator reconfigures the target node back into the network by replacing the countermeasure destination with the target node, reversing the conventional DDOS approach. However, reconfiguration with the original target node is subject to a time lag, depending on the breadth of the target node&#39;s user base. Intervening message traffic may be lost during the downtime of the victim target node. 
   Unfortunately, there are such drawbacks associated with the above described conventional recovery techniques for inundating or excessive message delivery, such as brought about by distributed denial of service (DDOS) attacks. If the affected target node, or host, is taken offline, it will typically require approximately between 4 to 36 hours to repropagate the new name to network address binding and corresponding preferred route across the network. Further, in this instance, a malicious DDOS attacker is at least somewhat successful, because the affected target node was taken offline, opening the window for lost message traffic. 
   Another conventional alternative is to collect the message traffic at the countermeasure router, separate the undesirable message traffic, and forward the desirable benign, or clean, message traffic to the target victim node without taking the affected node offline. However, this conventional approach requires a modification to each collected message and/or to routing information at each intermediate router between the sinkhole router and the edge router serving the host, since each conventional intermediate router needs to be reconfigured allow the desirable “clean” message traffic to pass. 
   It would be beneficial, therefore, to allow a system operator to defend against a DDOS attack by identifying a target node, or host, under attack, and assigning a filter complex to intercept and filter all message traffic originally sent to the target node, and without taking the target node offline or modifying numerous routing devices between the filter complex and the target node. The filter complex separates desirable, or clean, message traffic from the undesirable, or bad, message traffic and forwards the desirable message traffic onto the target node without burdening the target node with the voluminous undesirable traffic and without taking the target node offline or otherwise requiring time consuming reconfiguration to occur. 
   The present invention substantially overcomes the drawbacks associated with the above described conventional reroute of undesirable message traffic. In a computer network system suitable for use with the invention claimed herein, a system operator monitors a network for undesirable message traffic. Upon a notification of such undesirable message traffic inundating a node, the system operator reroutes message traffic from the target node to a filter complex. The filter complex becomes the reroute destination temporarily replacing the target node, and propagates a network address according to a network protocol in use by the target node. A preferred target router formerly serving the target node also receives notification that it (the former preferred target router) is no longer the preferred router for the target node, and likewise propagates such routing information to other nodes in communication via the network protocol. The filter complex filters the message traffic to separate desirable “clean” message traffic from undesirable “bad” message traffic, and may discard or analyze the latter. 
   The filter complex establishes an alternate route using a second communications protocol or transport mechanism different from the protocol used to redirect message traffic to the filter complex, and uses the alternate route to redirect the desirable message traffic from the filter complex to the target node. The use of the second protocol avoids conflict between the redirected desirable traffic and the original, or first, protocol (transport mechanism) which now performs the reroute. In this manner, the filter complex employs a second, alternate, transport mechanism to reroute and redirect desirable message traffic to the target node while preventing undesirable message traffic due to a DDOS attack or other inundating sources from reaching the target node. The system employs the second, alternate transport mechanism protocol by reconfiguring routing information only at the preferred target node edge router and the filter complex, and avoids reconfiguring every intermediate router between the filter complex and the target node. 
   The second, alternate routing mechanism may, in particular arrangements, be a virtual private network (VPN) having a separate set of routing tables in an overlay arrangement with the first, primary network protocol under which the rerouting to the filter complex occurs. In such an arrangement, the routing devices operate (i.e. are conversant) in both the first, or primary protocol and in the second, VPN protocol. Such routing devices may be MPLS (Multi-Protocol Layer Service) routing devices, marketed commercially by Cisco Systems, Inc. of San Jose, Calif. The MPLS devices allow the same physical network for both the first and second protocols. In conjunction with the invention, the second transport protocol operates as an MPLS shunt, using a predefined or dynamic Virtual Routing or Forwarding table, to reach the target node. Alternatively, the second protocol follows a separate path on alternate lines and/or communication devices. 
   The system further provides directing the filter complex to filter the message traffic to subdivide desirable message traffic from undesirable message traffic. A security filter in the filter complex has filtering logic for performing filtering. The security filter identifies sequences in the message traffic indicative of undesirable message traffic. The filtering logic parses message content and identifies undesirable messages by content tags, keywords, token identification, or other suitable method. 
   In a particular configuration, the filter complex further includes a filter routing device in communication with other routing devices in the communications network and coupled to a filtering device operable to employ the security filter to analyze message traffic. Such a filter routing device is operable to communicate according to the first transport mechanism and the second transport mechanism. 
   In another particular configuration, a network management server is in communication with the filtering complex, and operable to send messages to direct the filter complex in rerouting and redirecting the message traffic. 
   The network management server operable to send a reroute message to the filtering complex. Such a reroute message is indicative of the filtering complex receiving message traffic in the first transport mechanism intended for the target node via the target node router serving the target node. 
   The network management server is further operable to communicate with a target node router serving the target node from the network management server, the network management server operable to send a redirect message to the target node router. Such a redirect message is indicative that the target router serving the target node is not to receive message traffic in the first transport mechanism corresponding to the target node. The redirect message is further indicative that the target node router serving the target node receives message traffic in the second transport mechanism corresponding to the target node. 
   In particular configurations, the first transport mechanism corresponds to a public access protocol adapted for communication via a plurality of dissimilar network switching devices, such as TCP/IP via the Internet. The second transport mechanism corresponds to a virtual private network operable to encapsulate message packets of dissimilar protocols such that the encapsulated message packets are recognized by a routing protocol of the virtual private network, and may also be TCP/IP based. 
   Rerouting includes propagating, via a standard protocol corresponding to the first transport mechanism, a node address other than the node address corresponding to the target node. Redirecting includes propagating routing information according to a predetermined protocol, the routing information operable to designate the target node as the destination of the message according to the second Transport mechanism. Such predetermined and standard protocols may be TCP/IP compliant, or may correspond to other transport mechanisms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the embodiments, principles and concepts of the invention. 
       FIG. 1  is a context diagram of a communications system which is suitable for use with the present invention. 
       FIG. 2  is a flowchart depicting message traffic rerouting in the network of  FIG. 1 . 
       FIG. 3  is a block diagram of a communications network for transmitting message traffic in the system of  FIG. 1 . 
       FIGS. 4   a - 4   c  are flowcharts depicting message traffic rerouting as in  FIG. 2  in greater detail. 
       FIG. 5  is an example of a Virtual Private Network (VPN) transmitting redirected message traffic in the communications network of  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   Configurations of the invention provide for countermeasures to undesirable message traffic such as that presented by DDOS (Distributed Denial of Service) attacks. In a computer network system suitable for use with the invention claimed herein, a system operator monitors a network for undesirable message traffic. Upon a notification of such undesirable message traffic inundating a node, the system operator reroutes message traffic from the target node to a filter complex. The filter complex becomes the reroute destination temporarily replacing the target node, and propagates a network address according to a network protocol in use by the target node. A preferred target router formerly serving the target node also receives notification that it (the former preferred target router) is no longer the preferred router for the target node, and likewise propagates such routing information to other nodes in communication via the network protocol. The filter complex filters the message traffic to separate desirable “clean” message traffic from undesirable “bad” message traffic, and may discard or analyze the latter. 
   The filter complex establishes an alternate route using a second transport mechanism different from the transport mechanism used to reroute message traffic to the filter complex, and uses the alternate, second transport mechanism to redirect the desirable message traffic from the filter complex to the target node. In this manner, the filter complex employs the second alternate transport mechanism to reroute and redirect desirable message traffic to the target node while preventing undesirable message traffic due to a DDOS attack or other inundating sources from reaching the target node. The system employs the second, alternate transport mechanism by reconfiguring routing information only at the preferred target node edge router and at the filter complex, and avoids reconfiguring every intermediate router between the filter complex and the target node over which the redirected message traffic passes. 
   The second, alternate transport mechanism may, in particular arrangements, be a virtual private network (VPN) having a separate set of routing tables in an overlay arrangement with the first, primary transport mechanism under which the rerouting to the filter complex occurs. In such an arrangement, the routing devices operate (i.e. are conversant) in both the first, or primary transport mechanism and in the second, VPN transport mechanism. Such routing devices may be, by way of example only, the MPLS (Multi-Protocol Layer Service) routing devices described above. The MPLS devices allow the same physical network for both the first and second protocols. Alternatively, the second protocol follows a separate path on alternate lines and/or communication devices. 
     FIG. 1  is a context diagram of a communications system which is suitable for use with the present invention. Referring to  FIG. 1 , a communications network  10  includes a filter complex (FC)  12 , a host target router  14 , a network management server  16 , a host target node  20 , a management server console  18 , and remote nodes  22  sending message traffic  24 . The communications system  10  also includes a plurality of routers  26 - 1 - 26 - 2  ( 26 - n  generally). 
   The routers  26 - n  interconnect the filter complex  12 , the host target router  14 , and the other routers  26 - n . The host target router  14  connects to the host target node  20 , and the network management server  16  connects to the filter complex  12  and the host target router  14 , and also to a network management server console  18 . Message traffic  24  travels among the routers  26 - n  from a source node  22  to a destination node, typically an edge router such as the exemplary host target router  14  serving a user. The host target router  14  and filter complex  12 , for purposes of the discussion herein, also include functionality found in routers  26 - n  for routing message traffic  24 , discussed further below. 
   In operation, message traffic emanates from an originating remote node  22  and travels as a stream of packets, or message traffic  24 , according to a particular transport protocol. In the exemplary network shown, such a transport protocol may be the TCP/IP protocol, having message traffic  24  in the form of TCP/IP compliant packets. The message traffic  24  travels from router  26 - n  to router  26 - n  according to address information in the message traffic  24  and recognized by the transport protocol. 
   During normal message traffic  24  routing, all message traffic  24  follows a series of hops determined by the routers  26 - n . In the example shown, the message traffic  24  flows to router  26 - 1 , then to router  26 - 2  as shown by arrow  28 - 1 , then to the host target router  14 , as shown by arrow  28 - 2 . As the host target router  14  (target router) is an edge router serving the host target node  20  (target node), message traffic  24  delivery occurs via an Internet gateway link  26 , such as a telephone line modem or broadband drop (not shown), to the target node  20 . 
   In the event of an inundation of excessive message traffic  24  to the target node  20 , such as a DDOS attack, the target node  20  detects the potentially harmful message traffic  24  and alerts the network management server  16 . Alternatively, an automated or manual inspection process triggers such a detection, such as via an operator at the server console  18 . In response, the network management server  16  directs the filter complex  12  to receive message traffic  24  directed (addressed) to the target node  20 . The network management server  16  also informs the target router  14  that it is no longer the preferred router to access the target node  20 . Accordingly, the network  10  redirects the message traffic  24  to the filter complex  12 , as shown by arrow  30 . 
   At the filter complex  12 , described further below, the message traffic  24  bifurcates into undesirable message traffic  32  and desirable message traffic  34 . The filter complex  12  diverts the undesirable message traffic  32  for analysis or discard (i.e. the so called “bit bucket”), and redirects the desirable message traffic  34  to the host target router  14 . The filter complex  12  redirects the desirable message traffic  34  by a second communications transport protocol (mechanism), since the management server  16  has already rerouted message traffic sent via the primary, or first, transport protocol (mechanism) from the target node  20  to the filter complex  12 . Accordingly, an attempt to transmit message traffic  24  from the filter complex  12  to the target router  14  via the first transport mechanism would result in the message traffic returning to the filter complex  12 . The second transport mechanism  34 , however, allows the redirected message traffic  34  to travel to the host target router  14  and on to the target node  20  regardless of the reroute in the first transport mechanism. 
     FIG. 2  is a flowchart depicting message traffic  24  rerouting and redirecting in the network of  FIGS. 1 and 2 . Referring to  FIG. 2 , the method for redirecting network message traffic  24  in response to a DDOS attack or other rerouting trigger involves, at step  102 , receiving an indication of undesirable message traffic  24  directed to a particular target node  20  via the first transport mechanism in the communications network  10 . The indication occurs according to a variety of warning triggers. An operator at the target node  20  may observe an influx of message traffic  24  impeding performance, or obstruction via an automated daemon (not shown) or other component executing on the target node  20  may occur. The network management server  16  may also observe a high traffic volume at the target router  14  for routing to the target node  20 . Other trigger and/or detection mechanisms may be used. 
   At step  104 , in response to detecting in step  102 , the network management server  16  initiates rerouting all message traffic  24  carried via the first transport mechanism in the communications network and directed to the particular target node  20 , to the filter complex  12  operable to distinguish desirable message traffic from undesirable message traffic. The rerouting, in the configuration shown in  FIG. 1 , occurs as a message sent from the network management server  16  to the filter complex  12 . Additionally, the network management server  16  sends a second message to the target router  14  to indicate that the target router  14  is no longer the preferred route for the target node  20 . The management server  10  therefore designates the filter complex  12  as the edge router for message traffic routing for the target node  20  address. Accordingly, the message traffic  24  follows the reroute path to the filer complex  12 , as shown by arrow  30 . Both the filter complex  12  and the target router  14  propagate the routing information directing the target node  20  message traffic  24  to the filer complex  12  according to the protocol of the first transport mechanism, which automatically disseminates such routing information to the routing tables at routers  26 - n  across the communications network, described further below. However, the network management server need only transmit the reroute messages to the filter complex  12  and to the target router  14 . 
   At step  106 , the network management server  16  sends a message directing the filter complex  12  to transmit, via a second transport mechanism (described further below) over the communications network  10 , the desirable message traffic  34  to the target node  20 , as shown by arrow  34 . Since the desirable, redirected message traffic  34  follows the second transport mechanism, it is unaffected by the routing changes in the first transport mechanism which redirect the target node  20  message traffic  30  to the filter complex  12 . At the filter complex  20 , undesirable message traffic deviates off on an alternate path, shown by arrow  32 , as the filter complex does not send the undesirable message traffic  32  to the target node  20 , as will now be described with respect to  FIGS. 3 and 4   a - 4   c.    
     FIG. 3  is a block diagram of a computer communications network  10  for transmitting message traffic  24  in the system of  FIG. 1 . Referring to  FIG. 3 , the communications network  10  includes a plurality of routers  26 - n , including routers  26 - 1 - 26 - 5  shown. Further, the target router  14  has routing capability similar to that of  26 - n , and the filter complex  12  includes a filter routing device  36  also with similar routing capability. The filter complex  12  also includes a security filter  38  having filter logic  40 , and a repository  50  for deleting and/or storing for analysis the undesirable message traffic  34  shown by arrow  208 . The network management server  16  includes a network interface  42 , a network monitor  44 , or daemon, a routing processor  46  and a routing table DB  48 . 
   As indicated above, each of the routers  26 - 1 - 26 - 5  interconnect each other, the target router  14  and the filter routing device  36 . Each of the routing devices  26 - n ,  14  and  36  send messages  201 - 208 , described further below with respect to  FIGS. 4   a - 4   c , according to either the first or second transport mechanisms. The filter complex includes the security filter  38 , in communication with the filter routing device  36  and operable to distinguish and subdivide the undesirable message traffic  208  from desirable message traffic  207 - 1 . The filter logic  40  in the security filter  36  includes instructions and operations for parsing the incoming message traffic  205 - 2  to distinguish and bifrucate the undesirable and desirable message traffic. One method for distinguishing undesirable message traffic is disclosed by Riverhead Networks, of Cupertino, Calif. Other mechanisms will be apparent to those skilled in the art regarding such security filters, and include various parsing and token matching procedures and routines for detecting certain known incriminating patterns in the message traffic  205 - 2 . 
   The network management server  16  enables operator management of the network  10  via the server console  18  ( FIG. 1 ). The network interface  42  couples to the network  10  for receiving and sending routing information to the routing devices  26 - n  and other status information. The network monitor  44  detects and receives indications of message influx and other indications, either automated or via manual inspection, of a need to reroute and redirect traffic via the filter complex  12 , such as those corresponding to step  100  above. The routing processor  46  computes and determines messages  200 - 208  to send in response to detection by the network monitor  44 . The routing table DB  48  stores information regarding routing tables in the first and second transport mechanisms, enabling the routing processor to determine which routing devices  26 - n ,  14  and  36  to send rerouting and redirection instructions, as will now be describe in  FIGS. 4   a - 4   c.    
     FIGS. 4   a - 4   c  are flowcharts depicting message traffic rerouting as in  FIG. 2  in greater detail. Referring to  FIGS. 4   a - 4   c ,  1  and  3 , at step  102 , the network management server  16 , receives an indication of undesirable message traffic, as shown by arrow  202 - 1 . At step  102 - 1 , the indication further includes detecting a pattern of undesirable message traffic in quantity sufficient to be recognized. As indicated above, the DDOS attack emanates from a plurality of sources. Detection of an attack involves identifying inundating message traffic from multiple sources, none of which on their own may indicate an abnormal condition. Therefore, a threshold or other indication of an attack or abnormal influx triggers the detection. At step  102 - 2 , a check is performed to determine the existence of undesirable message traffic emanating from a plurality of sources  22 , shown by arrow  201 - 1 , even when each of the plurality of sources independently contributing substantially insignificant volume of message traffic. Therefore, a volume of predetermined message throughput load is deemed to be significant enough to trigger the reroute and redirection as disclosed herein. 
   At step  104 , a particular arrangement of rerouting is described in an exemplary manner. Alternate mechanisms operable to perform basing routing functions will be apparent to those skilled in the art, without deviating from the scope of the invention. Accordingly, rerouting to the filter complex  12  further includes, at step  104 - 1  directing the filtering complex to filter the message traffic  24  to subdivide desirable message traffic  34  from undesirable message traffic  32 . At step  104 - 1 A, the rerouting message  203 - 1  is, in a particular configuration, sent from the network management server  16  in communication with the filtering complex  12 , the network management server  16  being operable to send the reroute message  203 - 1  to the filtering complex  12 . 
   As indicated above, the filter complex  12  further includes the security filter  38  having filtering logic  40  for performing filtering, the security filter  38  operable to parse the message traffic and identify sequences in the message traffic indicative of undesirable message traffic. At step  104 - 2 , the filter complex  12  invokes the security filter  38  to analyze the incoming rerouted message traffic, shown by arrows  205 - 1  and  205 - 2 , according to the filter logic  40 . 
   At step  104 - 3 , in response to the reroute message  203 - 1 , the filtering complex  20  reroutes and receives message traffic sent according to the first transport mechanism and intended for the target node  20  via the target node router  14  serving the target node. Therefore, the rerouting causes the filter routing device  36  to now receive message traffic  205 - 1 ,  205 - 2  which had originally been addressed to travel to the host target router  14 , as shown by arrows  201 - 1 - 201 - 3 . 
   At step  104 - 4 , since the filter complex further  20  includes a filter routing device  36  in communication with other routing devices  26 - n  in the communications network, the filter routing device  36  receives the message traffic and employs the security filter  38  to analyze the message traffic  205 - 2 . 
   At step  104 - 5 , the filter routing device  36  in the filtering complex  12  is operable to communicate according to the first transport mechanism and the second transport mechanism, and at step  104 - 5 A, rerouting all message traffic further includes propagating, via a standard protocol corresponding to the first transport mechanism, a node address other than the node address corresponding to the target node  20 , as shown by arrows  204 - 1 . The first transport mechanism corresponds to a primary routing protocol, such as TCP/IP in a particular configuration, and involves advertising the filter routing device  36  as the preferred route for the target node  20  rather than the target router  14 . In addition to or alternatively, at step  104 - 5 B, the network management server  16  establishes a static route, according to the first transport mechanism, from the single target router  14  serving the target node  20  to the filter routing device  36  serving the filter complex  12 . Therefore, the filter routing device  36  becomes the preferred router for message traffic  201 - 1  in the first transport protocol sent to the target node  20 . Accordingly, message traffic  201 - 1  which would have traveled to the target router  14  absent the reroute, as shown by arrows  201 - 2  and  201 - 3 , is rerouted by router  26 - 1 , as shown by arrow  205 - 1 . 
   At step  104 - 6 , a check is performed to examine the result of the security filter  38  in filtering the rerouted message traffic  205 - 1 ,  205 - 2 . Typically, the message traffic  205 - 1 ,  205 - 2  is a stream of message units or segments upon which the check applies. In a particular arrangement, in which the first transport mechanism corresponds to the TCP/IP protocol, the message traffic  205 - 2  is a series of message packets. The check at step  104 - 6  applies on a per packet basis. Therefore, if the message packet is undesirable, the filter complex sends the message packet to a disposal repository  50 , such as an analysis file or “bit bucket,” as shown by arrow  208 - 1  and, at step  104 - 7 , terminates the undesirable message traffic. 
   At step  106 , If the message packet is desirable, as determined by the check at step  104 - 6 , the network management server  16  directs the filter complex  12  to transmit, via the second transport mechanism over the communications network  10 , the desirable message traffic to the target node  20 . At step  106 - 1 , directing the filter complex  12  includes directing the target router  14  serving the target node  20  from the network management server  16 , the network management server  16  being  203 - 2  operable to send a redirect message  203 - 2  to the target node router  14 . 
   At step  106 - 1 A, the redirect message  103 - 2  is indicative that the target router  14  (edge router) serving the target node  20  is not to receive message traffic  201 - 3  in the first transport mechanism corresponding to the target node. Accordingly, the target router  14  advertises, via messages  206 - 1 , that it is not the preferred route to the target node  20 . Alternatively, rather than explicit messages  206 - 1  indicating the change in preferred routers  26 - n , the reroute notification of messages  204 - 1  above, may, in particular embodiments, prevail. 
   At step  106 - 1 B, in particular arrangements, the first transport mechanism corresponds to a public access protocol adapted for communication via a plurality of dissimilar network switching devices, such as routing devices  26 - n ,  36  and  14 . Such dissimilar network switching devices are nonetheless conversant in the first transport mechanism, such as TCP/IP. Therefore, any TCP compliant device is operable to perform the redirection of step  106 . 
   At step  106 - 2  the redirect message  203 - 2  is further indicative that the target node router  14  serving the target node  20  receives message traffic in the second transport mechanism corresponding to the target node  20 . This message  103 - 2  may be sent as one message effectively performing  106 - 1  and  106 - 2 , or may be sent as multiple messages. 
   At step  106 - 2 A the redirect message  203 - 2  propagates routing information according to a predetermined protocol, the routing information operable to designate the target node  20  as the destination of the message according to the second transport mechanism. The second transport mechanism allows the filter router  36  to send the rerouted  205 - 2 , desirable message traffic to the target node, as shown by arrows  207 - 1 ,  207 - 2  and  207 - 3 . The second transport mechanism provides an alternate set of routing tables stored in the routing table DB  48 . The network management server  16  determines the redirect message from the target router  14  and the filter routing device  36 , and provides that the message traffic  207 - 1 - 207 - 3  in the second transport mechanism follows the route to the target node  20 . 
   At step  106 - 2 B, establishing the redirection according to the second transport mechanism corresponds to a virtual private network operable to encapsulate message packets of dissimilar protocols such that the encapsulated message packets are recognized by a routing protocol of the virtual private network. Therefore, the second transport mechanism defines routing tables and information corresponding to the VPN for message redirection. The desirable message traffic is, in the particular configuration shown, rerouted to the filter complex  12  by the TCP/IP reroute according to the first transport mechanism, and redirected to the target node  20  by the VPN according to the second transport mechanism. 
   At step  106 - 3  therefore, directing and rerouting occur via messages in which the first and second transport mechanisms coexist on a common physical network  10 . Therefore, the same physical network  10 , such as a public access network including the Internet, has physical lines which carry the message traffic according to both the first transport mechanism and the second transport mechanism. The routers  26 - n  employ parallel sets of routing tables corresponding to the Internet and VPN, respectively, and determine and lookup routing hops according to the transport mechanism by which a particular message packet travels. Further, the routing devices  26 - n ,  36 , and  14  employ routing operable in at least the first transport mechanism and the second transport mechanism. Such operation is available, by way of example only, in the MPLS (Multi-Protocol Layer Service) conversant routing devices referenced above. In conjunction with the invention, the second transport mechanism operates as an MPLS shunt, using a predefined or dynamic Virtual Routing or Forwarding (VRF) table, to reach the target node. 
     FIG. 5  is an example of a Virtual Private Network (VPN) transmitting redirected message traffic in the communications network of  FIG. 3 . In the computer network  10 , several sights have become infected with a virus for propagating a DDOS attack. Three sights: Seattle  61 , San Jose  62  and Melbourne  63  transmit message traffic to the host target  20 . Suppose further that the target host  20  is in Washington, D.C. The message traffic emanating from these sites follows the path shown by the arrows  211 - 1 - 211 - 7  to the filter complex, all via the first transport mechanism  52 . As the sights are all distributed across the U.S., the illustrated number of routers  26 - n  is exemplary; many more routers  26 - n  would be used for routing of such distributed hosts  61 - 63 . The network management server  16  directs the message traffic  211 - n  to the filter complex  12  via the first transport mechanism  52 . The filter complex  12 , router  26 - 4 , and the target router  14  are all conversant in both the first transport mechanism  52  and the second transport mechanism  54 . As can be seen by  FIG. 5 , the first and second transport mechanism  52 ,  54  may be illustrated as overlays on the same physical routing devices  26 - n ,  12  and  14 . 
   The filter complex  12 , after filtering the undesirable message traffic as described above, redirects the desirable message traffic via router  26 - 4  to the target router  14  via the VPN corresponding to the second transport mechanism  54 . In this manner, the VPN denoting the second transport mechanism  54  operates as an alternate (VRF) providing a second virtual path from the filter complex  12  to the target node  20 . 
   The exemplary first and second transport mechanisms discussed above correspond to, in a particular configuration, to a TCP/IP protocol on the Internet on a VPN, respectively. It should be understood that the system and methods disclosed herein are applicable to a plurality of transport mechanisms, including alternate protocols, transmission lines, and virtual facilities/overlay schemes. 
   The first and second transport mechanisms  52 ,  54 , in particular, configuration disclosed above, propagate routing information according to a routing table mechanism, as is known to those skilled in the art. Such a routing table matches an IP address with a destination along each hop through the network. The first and second transport mechanisms, in a particular arrangement, reference separate sets of routing tables. Alternate data structures and lookup methods to distinguish and separate the logic deterministic of the routing operations will be apparent to those skilled in the art without deviating from the scope of the claimed invention. 
   Further, the rerouting and redirection of undesirable message traffic is disclosed above in an exemplary manner in terms of defending against a distributed denial of service (DDOS) attack. The operations and methods discussed above are, in alternate configurations, applicable to a variety of other circumstances as well. For example, such rerouting and filtering is applicable to detecting and eliminating transmissions such as email SPAM or so-called “push” medium pop-up windows. Other uses can be envisioned. 
   The operations and functions disclosed above for rerouting and redirecting undesirable message traffic are described, by way of example only, as initiating from an operator console of a network management server, such as an SNMP console. The operations and functions claimed herein my also be performed in the routing devices themselves, such as in the filter complex or in the target routing devices. Further, such operations may be initiated manually, by operator inspection, or automatically by a watchdog daemon in the network monitor or other monitoring component. The above described arrangement is not meant to be limiting of the invention; the invention claimed herein is intended to be limited only by the following claims. 
   Those skilled in the art should readily appreciate that the programs and methods for network message traffic redirection as defined herein are deliverable to a processing device in many forms, including but not limited to a) information permanently stored on non-writeable storage media such as ROM devices, b) information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media, or c) information conveyed to a computer through communication media, for example using baseband signaling or broadband signaling techniques, as in an electronic network such as the Internet or telephone modem lines. The operations and methods may be implemented in a software executable object or as a set of instructions embedded in a carrier wave. Alternatively, the operations and methods disclosed herein may be embodied in whole or in part using hardware components, such as Application Specific Integrated Circuits (ASICs), state machines, controllers or other hardware components or devices, or a combination of hardware, software, and firmware components. 
   While the system and method for network message traffic redirection has been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. Accordingly, the present invention is not intended to be limited except by the following claims.