Abstract:
A performance enhancing proxy network device is configured to operate in a virtual inline mode, in which selected network traffic is redirected to and through the network device by a router using simple routing policies. In this way, the network device can be coupled to the router in series but can still operate as if it were physically connected inline.

Description:
RELATED APPLICATION 
       [0001]    This present application claims priority to and is a continuation of U.S. patent application Ser. No. 11/380,004, entitled “Virtual Inline Configuration for a Network Device”, filed Apr. 25, 2006, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Network devices, such as performance enhancing proxy network devices, are used in a variety of applications for enhancing the network traffic across a data connection or other characteristics of the connection. Deployed in the communication path of a network between a sender and recipient of data packets, these performance enhancing proxy network devices operate on the packets so as to increase reliability, speed, bandwidth, compression, security, and/or many other features of the existing network connection. To perform any function for the network, however, these devices must be coupled to the network in some way to receive and then retransmit at least some of the data packets being sent over the data connection. 
         [0003]    In typical configurations, such as that shown in  FIG. 1 , a performance enhancing proxy network device  10 , or proxy, is often deployed inline with the WAN link of a router  20 . In this way, all traffic from a WAN  30  passes through the network device  10  before arriving at its destination computing system  15  on a LAN  5 . This inline configuration requires a modest amount of physical re-wiring and downtime to establish the link. To deploy a network device  10  inline, the link must be broken, and then the device  10  to be installed must be connected in between the broken link. The installation is manually intensive, and it interrupts the network services unless there is a backup mechanism in place. In addition, it may be physically or electrically challenging to place a network device in line due to incompatible standards, such as a network device that uses Ethernet while the WAN link uses fiber optics. 
         [0004]    Systems have been designed to allow for parallel installation of intermediate network devices, but these systems generally require that the data packets be addressed to the network devices. When the data packets are passed on to the true destination system, the destination address of the data packet must be changed so that the data packet is routed to its true destination. Such systems are undesirable for several reasons, primarily in that they lack transparency. The sending system must know of the existence and the address of the network device so that the data packet can be addressed to it. This limits the ability to implement one-sided optimization of network traffic, since remote senders must be configured for the local network device. 
         [0005]    Alternatively, systems have been designed that allow transparency to be maintained from the point of view of the source and destination systems, but require that the packets be encapsulated in a different protocol to facilitate routing. One example of this is the WCCP protocol, used to connect network devices (typically Web proxy caches) to routers, encapsulating packets using the GRE protocol to allow the path taken between router and network appliance to be independent of the original packet routing. This method is transparent to the endpoints, but it is not transparent along the path between the router and the network device. Encapsulation is also accompanied by overhead and thus loss of performance. 
         [0006]    Accordingly, there is a need for a method to allow a parallel installation of a network device while preserving the transparency and other benefits that an inline installation offers. 
       SUMMARY OF THE INVENTION 
       [0007]    A performance enhancing proxy network device is deployed in a virtual inline configuration, which combines the benefits of inline and parallel configurations. With the network device installed in a configuration other than inline with the WAN link, a router redirects network traffic to the network device when data packets are to be sent over the network. The network device then performs any desired processing on the received data packets. Once the processing is completed, the network device sends packets to the router to be transferred to the destination over the network. In this way, the network device can be coupled to the router in parallel but can still operate as if it were inline. This requires less physical rewiring and downtime for a communication link. This method also provide transparency in the rerouting of data packets, as the source and destination addresses and port information are preserved for each data packet as the packet (or its transformed equivalent) is routed through the network from source to destination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic network diagram of a typical inline configuration for a network device, as found in the prior art. 
           [0009]      FIG. 2  is a schematic network diagram of a virtual inline configuration for a network device, in accordance with an embodiment of the invention. 
           [0010]      FIG. 3  is a schematic diagram of a router and network device in a virtual inline configuration, showing the policy based routing rules that reroute certain incoming and outgoing data packets, in accordance with an embodiment of the invention. 
           [0011]      FIG. 4  is a schematic diagram of a local side of a network configuration in which multiple routers share a network device, in accordance with an embodiment of the invention. 
           [0012]      FIG. 5  is a schematic diagram of a local side of a network configuration in which multiple routers share multiple network devices, in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]      FIG. 2  illustrates a network architecture of a typical communications network, in which one or more computing systems  115  on a LAN  105  communicate with one or more remote computing systems  125  over a WAN  130  (such as the Internet). One or more routers  120  at each end of the network handle the routing of data packets among the computing systems  115  and  125 . 
         [0014]    A performance enhancing proxy network device  110  is installed at the local and remote sides of the network. Alternatively, a performance enhancing proxy network device  110  may be installed at only one of the ends of the network, although this allows for less functionality. Performance enhancing proxy network devices, such as those described in U.S. application Ser. No. 10/901,952, filed Jul. 28, 2004, which is incorporated by reference in its entirety, are used to enhance the network traffic across a data connection or other characteristics of the connection. 
         [0015]    To avoid a physical inline architecture, the network devices  110  are coupled to the router  120  in a parallel configuration. This allows for easier installation and avoids other problems inherent in inline configurations. As described below, the router  120  is configured to divert or redirect incoming data packets from the WAN  130  to the LAN  105  or outgoing data packets from the LAN  105  to the WAN  130 . The router  120  may be configured to divert all data packets or only certain data packets, according to predefined criteria. The data packets that are diverted by the router  120  are sent to the network device  110 , which may then process the data packets to perform the enhancement processing for which the network devices  110  is designed. After the processing, the network device  110  returns the data packets to the router  120 , which sends the data packets along to their original destination. 
         [0016]    The network device  110  may choose to transform none, some, or all of the packets it receives. Accordingly, the packets that the network device  110  “forwards” to the router  120  may have been transformed in a way that causes the packets to be different from the input packets in some way while maintaining the transparency of the system. For example, compression performed by the network device  110  may cause the transformed packets to be fewer in number and/or smaller in size than the original packets. 
         [0017]    In one embodiment of the invention, the data packets have a destination address that specifies a local or remote computing system  115  or  125 , rather than a network device  110 . When these data packets are received by a router  120 , the router diverts the data packets to a network device  110 . Once the router  120  receives the data packet back from the network device  110 , the router  120  forwards the packet to a destination on the network according to the destination address of the data packet. Because the destination address of each diverted data packet does not have to be changed to accomplish the diversion, the enhanced processing and configuration of the network device is transparent to the network—much like an inline configuration can be. In this way, the configuration of the network device  110  is virtually inline, while being physically connected in parallel. 
         [0018]      FIG. 3  illustrates one embodiment of a router  120  configured to divert data packets to a network device  110 . The router  120  includes a set of rules  140  at its LAN side that apply to outgoing data packets received from the LAN  105 . The LAN-side rules  140  operate on data packets received by the router  120  from the LAN  105 , illustrated by dotted path A passing through the rules  140 . The LAN-side rules  140  may be configured to divert to the network device  110  all of the data packets received, or just some of the data packets based on predetermined criteria. Data packets returned by the network device  110  are then forwarded to their destination over the WAN  130  according to their destination address, illustrated by dotted path B. 
         [0019]    In the inbound direction, incoming data packets are received over a WAN  130  by the router  120 . The router  120  includes a set of rules  145  at its WAN side that apply to incoming data packets received from the WAN  130 . The WAN-side rules  145  operate on data packets received by the router  120  from the WAN  130 , illustrated by dotted path C passing through the rules  145 . The WAN-side rules  145  may be configured to divert to the network device  110  all of the data packets received, or just some of the data packets based on predetermined criteria. Data packets returned by the network device  110  are then forwarded to their destination through the LAN  105  according to their destination address, illustrated by dotted path D. 
         [0020]    By diverting the data packets according to the rules  140  and  145 , instead of by changing their destination addresses, the destination addresses of the data packets can be left unchanged. In this way, diverting the data packets to the network device  110  is transparent to the network. In one embodiment, the rules  140  and  145  used to divert the data packets are policy based routing (PBR) rules, which include a well known set of rules for routing IP packets. The data packets may be IP packets, according to the Internet Protocol (IP). 
         [0021]    As explained above, the router  120  may be configured with PBR rules at each of the local and remote sides to divert incoming and outgoing data packets. The PBR rules at the local (or client) side of the router  120  divert data packets received from the LAN  105  to the network device  110 . The PBR rules at the remote side of the router  120  divert data packets received from the WAN  130  to the network device  110 . 
         [0022]    In one embodiment, the router  120  is configured on the local side using the following configuration: 
         [0000]                                            !           ip cef           !           interface FastEthernet0/0            ip address 10.10.10.5 255.255.255.0            ip policy route-map client_side_map           !           interface FastEthernet0/1            ip address 171.68.1.5 255.255.255.0            ip policy route-map wan_side_map           !           interface FastEthernet1/0            ip address 192.168.1.5 255.255.255.0           !           ip classless           ip route 0.0.0.0 0.0.0.0 171.68.1.1           !           ip access-list extended client_side            permit ip 10.10.10.0 0.0.0.255 20.20.20.0 0.0.0.255           ip access-list extended wan_side            permit ip 20.20.20.0 0.0.0.255 10.10.10.0 0.0.0.255           !           route-map wan_side_map permit 20            match ip address wan_side            set ip next-hop 192.168.1.200           !           route-map client_side_map permit 10            match ip address client_side            set ip next-hop 192.168.1.200           !                        
Similarly, at the remote side, the router  120  is configured using the following configuration:
 
         [0000]                                            !           ip cef           !           interface FastEthernet0/0            ip address 20.20.20.5 255.255.255.0            ip policy route-map client_side_map           !           interface FastEthernet0/1            ip address 171.68.2.5 255.255.255.0            ip policy route-map wan_side_map           !           interface FastEthernet1/0            ip address 192.168.2.5 255.255.255.0           !           ip classless           ip route 0.0.0.0 0.0.0.0 171.68.2.1           !           ip access-list extended client_side            permit ip 20.20.20.0 0.0.0.255 10.10.10.0 0.0.0.255           ip access-list extended wan_side            permit ip 10.10.10.0 0.0.0.255 20.20.20.0 0.0.0.255           !           route-map wan_side_map permit 20            match ip address wan_side            set ip next-hop 192.168.2.200           !           route-map client_side_map permit 10            match ip address client_side            set ip next-hop 192.168.2.200           !                        
These configurations conform to the Cisco IOS CLI, and for other routers from different vendors, a different configuration may be used.
 
         [0023]    In the above examples, an access list is applied to a route-map, which is in turn attached to an appropriate interface. For the client_side access list, all IP packets with source matching 20.20.20.0 0.0.0.255 and destination 10.10.10.0 0.0.0.255 are matched. For the wan_side access list, all IP packets with source matching 10.10.10.0 0.0.0.255 and destination 20.20.20.0 0.0.0.255 are matched. 
         [0024]    In the example above, all matching IP traffic is diverted to the network device. In other embodiments, the router  120  is configured to divert only selected data packets. For example, the router  120  may be configured to divert only TCP traffic to the network device. This can be accomplished, in one embodiment, by changing the access-list configuration to redirect only TCP packets. In the example described above, the configuration of the remote side could be modified as follows to accomplish this (with only the portion modified reproduced): 
         [0000]                                            !           ip access-list extended client_side            permit tcp 20.20.20.0 0.0.0.255 10.10.10.0 0.0.0.255           ip access-list extended wan_side            permit tcp 10.10.10.0 0.0.0.255 20.20.20.0 0.0.0.255           !                        
The local side could also be modified in a corresponding way (i.e., changing “ip” to “tcp”), so that the PBR rules at the local and remote sides remained symmetrical.
 
         [0025]    In another embodiment, the router  120  can be configured to divert only data packets having a source and/or destination address within a defined range. Continuing the example described above, to configured the router  120  to divert IP packets having a source address within the range 10.10.10.0 to 10.10.10.100 and destination address within 20.20.20.0 to 20.20.20.100, the following access list can be used: 
         [0000]                                            !           ip access-list extended test_list            permit ip 10.10.10.0 0.0.0.100 20.20.20.0 0.0.0.100           !                        
These are just a few examples of criteria and techniques for diverting incoming and outgoing data packets received by the router  120  to the network device. For example, data packets may be diverted based on their directions, subnet, and/or service. The PBR rules, as well as other mechanisms for configuring routers, allow for a variety of additional criteria for determining which data packets to divert, as well as different methods of doing so. Preferably, the PBR rules are configured so that the LAN and WAN sides of the router  120  are configured in a way that is symmetric and reverse, as in the example above.
 
         [0026]      FIG. 4  illustrates a local side of a network configuration in which two or more routers  120  share a network device  110 , which is coupled to the routers in a virtual inline configuration. Each router  120  is configured to divert some or all of the incoming and/or outgoing data packets, in accordance with any of the techniques described herein. When the network device  110  is finished processing a diverted data packet, the network device  110  may be configured to send the data packet to either router  120 , for delivery according to the data packet&#39;s destination address. 
         [0027]    In one embodiment, the network device  110  is configured to send all data packets to one of the routers  120 , as long as that pre-selected router  120  is able to receive the data packet. This scheme creates a sort of “master” router that handles all processed data packets unless the router fails or has insufficient resources. In another embodiment, the network device  110  is configured to send each data packet back to the router  120  that originally diverted the data packet. By always returning the data packets to their original routers  120 , this scheme preserves any load balancing that is applied between or among the routers  120 . This scheme is made possible, in part, due to the transparency of the technique, Other systems that change the destination address of the data packets to redirect them may not be able to preserve load balancing applied to the network. 
         [0028]      FIG. 5  illustrates a configuration in which multiple routers  120  share multiple network devices  110 , which are coupled to the routers in a virtual inline configuration. Each router  120  is configured to divert some or all of the incoming and/or outgoing data packets to one or both of the network devices  110 , in accordance with any of the techniques described herein. The network devices  110  may perform different enhancement processing tasks, where data packets are diverted to one or more of the network devices  110  based on the desire to apply the corresponding enhancement processing to each data packet. 
         [0029]    Alternatively, the network devices  110  may perform the same processing, in which multiple network devices  110  are used to handle a larger bandwidth or so that one or more network devices  110  can serve as a backup to the primary network device  110  in case of a failure. In a backup scheme, the routers  120  may be configured to send the data packets to a virtual address, and the designated primary network device  110  is configured to receive network traffic sent to that virtual address. In the event of a failure of that primary device  110 , the network detects the failure and configures the other network device  110  to receive network traffic sent to the virtual address. In this way, the secondary network device  110  performs the enhancement processing upon failure of the primary. Various other configurations for redundancies may be applied with this virtual inline configuration. 
         [0030]    As used herein, the term router is meant broadly to encompass any hardware or software system that routes network traffic, and it may include access points, gateways, servers, and the like. Various alternative configurations other than those shown in the figures may be used with embodiments of the invention, and any number of routers and networks devices (of the same or multiple types) can be added to the system in a virtual inline configuration as described above. 
         [0031]    Accordingly, the foregoing description of the embodiments of the invention has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teachings. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.