Abstract:
A network device includes a virtual router subsystem having potentially numerous virtual routers associated with corresponding different virtual private routed networks (VPRN) and employing generic interface identifiers to identify interfaces at which VPRN traffic is received or transmitted. A virtual interface subsystem couples the virtual router subsystem to physical interfaces of the device. The virtual interface subsystem includes virtual interfaces organized into linked sets, and each set associates a generic identifier of a virtual router with a physical interface to another network device serving the same VPRN. A basic type of set includes two VIs for interfacing a virtual router to a customer access link, and a more complicated set includes multiple pairs of several types of VIs to interface a virtual router to redundant label-switched paths on a channel-oriented backbone link such as an ATM link.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/264,088 filed Jan. 25, 2001.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    The present invention is related to the field of routed networks, and more particularly to routed networks employing virtual private routed network (VPRN) techniques.  
           [0004]    One of the challenges facing designers of data communications networks is to provide improved performance in the face of tremendous growth in network size and complexity. As the number of nodes using distinct network addresses in a network grows, the sizes of routing tables used for routing in the network increase, and more processing power is required to calculate routes and carry out the routing of network traffic. In fact, the processing load associated with routing increases generally as the square of the number of distinct routes. In large networks having a generally flat shared address space, such as the Internet, it may be infeasible for routers to support sufficiently large routing tables, due to constraints in the available processing power.  
           [0005]    It has been known to emulate a private, wide-area routed network within another, generally more public, wide-area network.  
           [0006]    Such an emulated network is referred to as a virtual private routed network (VPRN). Because a VPRN “piggybacks” on a separate and generally shared network, it can be more cost effective than a distinct, dedicated private wide area network. At the same time, there is significant functional separation between the VPRN and the underlying network, so that VPRN largely behaves like a standalone network, with attendant benefits in security, network management, and other aspects of network operation.  
           [0007]    In a common VPRN configuration, the VPRN employs Internet Protocol (IP) technology of the same type used in the Internet, complete with a private instance of a distributed IP routing protocol such as Open Shortest Path First (OSPF) and a private set of network addresses such as IPv 4  addresses. A mesh of “tunnels”, or dedicated virtual channels, are established among a set of private router nodes in the Internet. The router nodes encapsulate VPRN traffic in a format required by the tunnels, transmit encapsulated traffic to other router nodes using the Internet address space and routing protocols, decapsulate received traffic to recover the original VPRN traffic, and then use the VPRN routing protocols and address space to forward the traffic to other nodes in the VPRN outside the Internet.  
           [0008]    As with conventional routers, routers supporting VPRNs contain a large amount of information about physical details of the network. This information takes the form, for example, of physical port identifiers, layer- 2  addresses, etc. It can be difficult to correctly maintain this information in routers. This is especially true of routers supporting VPRNs, because of the greater degree of replication of the information across all active VPRNs. When physical changes to the network are made that might result in the creation of new routes, the deletion of old routes, or the switching of one route for another, it is necessary to update all the relevant information for all the VPRNs in all routers. Such a task becomes increasingly difficult as the size and complexity of networks increase, resulting in sub-optimal network size, performance, or both.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    In accordance with the present invention, a network device is disclosed that employs a collection of virtual interfaces between a virtual router subsystem and physical interfaces of the device. Physical network information is concentrated in the virtual interfaces, so that changes in the physical network can be easily reflected in the network device without requiring re-programming or re-configuring the virtual routers themselves.  
           [0010]    The disclosed network device includes a virtual router subsystem having a number of virtual routers, each virtual router being associated with a corresponding different virtual private routed network (VPRN) and each employing generic interface identifiers to identify interfaces at which routing traffic for the VPRNs is received and transmitted. Also included are a number of physical interfaces to physical network links connecting the network device to other network devices. A virtual interface subsystem couples the virtual router subsystem to the physical interfaces. The virtual interface subsystem includes a number of virtual interfaces of multiple types. The virtual interfaces are organized into linked sets, each set generally including virtual interfaces of different types and being operative to associate a generic identifier used by a given virtual router with a corresponding physical interface to another network device serving the same VPRN.  
           [0011]    The virtual interface represents the connection between virtual routers and the interface&#39;s physical, logical link, and IP layers. In the virtual interface there is an association between commonly shared resources. This simplifies interface management by providing a mechanism to manage interface connections to virtual routers instead individually managing the configuration interface elements.  
           [0012]    The virtual interface is an organized collection of component objects. Each component object could represent an interface element in an interface object model (e.g., a physical port, physical link, a logical link, a protocol instance, etc.). The objects can be linked or layered together in a manner to form an association that defines a traditional interface (e.g., a VLAN, an ATM PVC running NRT-VBR, or an MPLS label stack). In effect, virtual interface allows the configuration of any port with any protocol to any virtual router at any time.  
           [0013]    The virtual interface provides a generic programming framework between the packet forwarding instances of virtual router in the hardware and the configuration information in the management control software. The purpose of that framework is to encapsulate interface information required for packet transport and packet classification. In addition the virtual interface provide a mechanism for link layer backup and load balancing.  
           [0014]    The virtual interface subsystem is highly configurable, enabling the definition of many different types of sets of linked VIs to achieve different operational goals. A basic set contains only two VIs for interfacing a virtual router to a customer access link, whereas a significantly more complicated set includes multiple pairs of several types of VIs to interface a virtual router to redundant label-switched paths on a channel-oriented backbone link such as an ATM link. The use of the virtual interface subsystem provides for desirable decoupling of virtual router operation from the details of the physical channels used for routed traffic in the network.  
           [0015]    Other aspects, features, and advantages of the present invention are disclosed in the detailed description that follows.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0016]    The invention will be more fully understood by reference to the following Detailed Description in conjunction with the Drawing, of which:  
         [0017]    [0017]FIG. 1 is a block diagram of a network including routers employing virtual interfaces in accordance with the present invention;  
         [0018]    [0018]FIG. 2 is a high-level functional block diagram of a router in the network of FIG. 1;  
         [0019]    [0019]FIG. 3 is a more detailed functional block diagram of the router of FIG. 2;  
         [0020]    [0020]FIG. 4 is a high-level block diagram depicting the hardware/software architecture of the router of FIGS. 2 and 3;  
         [0021]    [0021]FIG. 5 is a block diagram of a virtual router subsystem in the router of FIGS.  2 - 4 ;  
         [0022]    [0022]FIG. 6 is a block diagram of a virtual interface subsystem in the router of FIGS.  2 - 4 ; and  
         [0023]    [0023]FIG. 7- 11  are diagrams showing exemplary sets of virtual interfaces in the virtual interface subsystem of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    The disclosure of U.S. Provisional Patent Application No. 60/264,088 filed Jan. 25, 2001, is hereby incorporated by reference herein.  
         [0025]    [0025]FIG. 1 shows a network in which a wide-area routed network  10  is utilized to carry traffic for a number of virtual private routed networks (VPRNs). Each VPRN includes corresponding VPRN subnetworks  12 . In FIG. 1, VPRNs numbered  1  through  3  are shown, with each including corresponding subnetworks  12 - 1 ,  12 - 2  and  12 - 3 . The wide-area routed network  10  includes a number of routers  14 . Each router  14  has connections to access links  16  that connect the router  14  to local VPRN subnetworks  12 , and has connections to backbone links  18  that connect the router  14  to other routers  14  in the wide-area routed network  10 .  
         [0026]    An example of the wide-area routed network  10  is a global network such as the Internet. In general, the wide-area routed network  10  has a given network address space and a defined set of communications protocols, including routing protocols. For example, the wide-area routed network  10  may employ the Internet Protocol (IP) with IP version  4  (IPv 4 ) addressing, and employ routing protocols such as Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), Routing Information Protocol (RIP), etc.  
         [0027]    Each VPRN, which is made up of a corresponding set of VPRN subnetworks  12 , is a routed network having its own network address space and network communications protocols, including a routing protocol. Nodes within a VPRN are generally not assigned addresses in the address space of the wide-area routed network  10 , nor do the routers  14  carry traffic on their specific behalf. Rather, as described in more detail below, the routers  14  utilize the address space and routing protocols of the wide-area routed network  10  on behalf of the VPRN subnetworks  12  as entities. The VPRN subnetworks  12 , in turn, utilize their respective private address spaces and routing protocols for internal routing of data traffic among specific computers or other types of network sources and destinations. Fundamentally, the wide-area routed network  10  and routers  14  serve to provide dedicated virtual connections among the VPRN subnetworks  12  to form the various larger-scale VPRNs.  
         [0028]    [0028]FIG. 2 shows an exemplary organization of a router  14 . Several “virtual access routers” (VARs)  20  are associated with respective customers and connected to the respective customers&#39; access links  16 . These are described in more detail below. A provider “virtual backbone router” (VBR)  22  is connected to the backbone links  18  of the wide area routed network  10  of FIG. 1. The VBR  22  uses IP addresses from the address space of the wide area routed network  10 , which is separate from the address spaces of the VPRNs. The VBR  22  provides a tunneling service to VARs  20  that is used in constructing the VPRNs. A signaling protocol such as the Resource Reservation Protocol (RSVP) is used to set up the tunnels. The VBR  22  may also provide direct access to the wide area routed network  10  for customers desiring such service, such as Customer D in FIG. 2. The VBR  22  participates in the full routing for the wide-area routed network  10 . In the case of the Internet, the VBR  22  generally maintains a full BGP routing table.  
         [0029]    Each VAR  20  has its own routing table and runs its own instances of the routing protocols used in the corresponding VPRN. The network addresses (e.g., IP addresses) of a VAR  20  are taken from the address space of the VPRN to which the VAR belongs. Different VARs  20  can use overlapping sets of addresses, i.e., the same address may appear in different sets, even though the different instances of the address belong to different nodes in different VPRNs. There is generally no direct connection, in the sense of an IP routing adjacency, between different VARs  20  within a router  14  or between a VAR  20  and the VBR  22 .  
         [0030]    As mentioned, RSVP signaling is used to create tunnels within the wide-area routed network  10  to connect VARs  20  residing in different routers  14 . This signaling is accomplished through the use of virtual tunnel adapters (VTAs)  24 . These devices resemble IP hosts residing in the wide-area routed network  10 . Each VTA  24  has a signaling interface via which the VTA  24  is instructed to establish a tunnel connection between a local VAR  20  and a remote VAR  20  residing on another router  14  (not shown in FIG. 2).  
         [0031]    [0031]FIG. 3 shows a more detailed view of a router  14 . The VARs  20  are associated with Virtual Interfaces (VIs)  30 , which in turn are associated with MPLS label switched paths (LSPs) on the backbone links  18  of the wide area routed network  10 . LSPs are established to form the tunnels through the wide area routed network  10  that link the various VPRN subnetworks  12 . As shown, a two-level hierarchy of LSPs is used. An “inner” LSP  32  carries traffic specifically associated with a given VI  30 . An “outer” LSP  34  carries a group of inner LSPs  32 . A different outer LSP  34  is defined between each pair of routers  14  in the wide-area routed network  10 .  
         [0032]    The router  14  also includes various additional functional entities such as a VPN Agent  36 , Quality of Service (QoS) Manager  38 , LSP Manager  40 , MPLS Signaling function  42 , and Line Control Processor (LCP) Interface  44 . The VPN Agent  36  coordinates the configuration of the VPRNs. The VPN Agent  36  instantiates VARs  20  and VIs  30 , interacts with the LSP Manager  40  to coordinate the use of labels, and passes QoS information to the LSP manager  40  for dynamically configured labels. The QoS Manager  38  handles the QoS aspect of the setting up of LSPs, which includes interpreting the QoS parameters of RSVP.  
         [0033]    The LSP Manager  40  coordinates all aspects of LSPs, including the creation and deletion of LSPs and the maintenance of label information. It interfaces with the VPN agent  36  and the MPLS signaling function  42  in the creation, monitoring, and deletion of LSPs.  
         [0034]    The MPLS signaling function  42  implements RSVP signaling for MPLS. At an ingress node for an LSP, the MPLS signaling function  42  signals downstream to obtain a label. At an egress node, the MPLS signaling function  42  passes labels upstream. At a transit node, the MPLS signaling function  42  interfaces with upstream and downstream routers to distribute labels.  
         [0035]    The MPLS signaling function  42  also interfaces with routing code to obtain next hop information, and passes label information to the LSP Manager  40 .  
         [0036]    The LCP interface  44  passes forwarding information from the software-implemented functions of FIG. 3, such as the VARs  20  and VIs  30 , to hardware forwarding engines residing on line cards (not shown) within the router  14 . The forwarding information falls into four categories: next hop routing information, MPLS label information, packet classification information, and QoS information.  
         [0037]    [0037]FIG. 4 shows a high-level software and hardware organization for the routers  14 . A number of physical interfaces (PIs)  50  connect to the access links  16  and backbone links  18  of FIGS.  1 - 3 . Examples of such interfaces include Ethernet interfaces, SONET interfaces, etc. A layer- 2  protocol such as ATM may also be used. Each PI  50  is also connected to a virtual interface (VI) subsystem  52 , which includes all of the VIs in the router  14 , such as the VIs  30  of FIG. 3. The VI subsystem  52  has a number of connections to a virtual router (VR) subsystem  54 , which includes all the virtual routers such as the VARs  20  and VBR  22  of FIG. 3. The PIs  50 , VI subsystem  52 , and VR subsystem  54  are coupled to a collection of other functional elements labeled in FIG. 4 as a management subsystem  56 . The management subsystem  56  includes the VPN agent  36 , QoS Manager  38 , LSP Manager  40 , MPLS Signaling function  42  and LCP interface  44  of FIG. 3.  
         [0038]    The virtual routers (VRs) within the VR subsystem  54  generally consist of processes and associated data that behave as a number of separate, distinct routers. Each VR is associated with a different VPRN. A given router  14  may include a few or many such VRs in accordance with the number of VPRNs having traffic flowing through the router  14 . Subject to hardware constraints of a given platform, such as processing power and memory capacity, a router  14  may be configured with as many as hundreds or potentially thousands of such VRs.  
         [0039]    The VI subsystem  52  provides a special function within the router  14 . A conventional router generally includes a routing subsystem tied directly to physical interfaces, without an intermediate subsystem such as the VI subsystem  52  shown in FIG. 4. Accordingly, changes to the underlying physical network result in the need to change routing tables and other data structures in the routing subsystem. Examples of such changes to the physical network include manual reconfigurations and automatic protection switching. When the routing subsystem has a very large routing data structure, as is the case for the VR subsystem  54 , it is difficult and inefficient to maintain physical-layer information within it. The arrangement of FIG. 4 addresses these problems by “virtualizing” the interfaces from the perspective of the virtual routers in the VR subsystem  54 . Each virtual router employs static, generic interface identifiers, and the VI subsystem  52  handles the translation between these interface identifiers and details of underlying physical interfaces, which in general are subject to dynamic change.  
         [0040]    [0040]FIG. 5 shows the VR subsystem  54 . A collection of routing processes or tasks such as OSPF tasks  60 - 0 , BGP tasks  60 -B, and RIP tasks  60 -R are coupled to a memory  62  via context selection logic  64 . The memory  62  is divided into a number of context areas, shown as CTXT  1 , CTXT  2 , . . . CTXT M, for M distinct VRs. Each context area contains a routing table and other operating state information for a different VR. The tasks  60  are independent processes that are time-shared among the various VRs. The time-sharing is accomplished in part via the context selection logic  64 . As events occur that require action for a given VR (most such events being associated with the sending and receiving of routing protocol messages or packets), the context selection logic  64  couples the appropriate task  60  to the context area CTXT for that VR. The task  60  then executes using the data from that context area CTXT. This processing continues to completion before a subsequent event is permitted to activate another VR, at which time the same or a different task  60  becomes coupled to a context area CTXT for the other VR.  
         [0041]    As an example, let it be assumed that a VR identified as VR #134 is part of a VPRN in which the OSPF routing protocol is used. Context area CTXT  134  of the memory  62  contains the routing table and other operating state for this VR. Upon receipt of a routing protocol packet on a VI associated with VR #134, an OSPF task  60 - 0  is activated, and the context selection logic  64  connects the OSPF task  60 - 0  to context area CTXT  134 . The OSPF task  60 - 0  performs operations in accordance with the received packet, which may include updating the routing table and initiating the transmission of one or more routing protocol packets to other routers in the VPRN. Once the processing associated with the received routing protocol packet is complete, the context selection logic  64  is free to break the connection between the OSPF task  60  and context area CTXT  134  in favor of a new connection, which will generally involve a different context area CTXT of the memory  62  and may involve a different task  60  as well.  
         [0042]    In the illustrated embodiment, the context selection logic  64  employs an inner-LSP label appearing in encapsulated protocol packets to identify which context area  62  to select for processing the packet. A mapping table (not shown) within the context selection logic  64  maps the label to a base address of the associated context area  62 . The inner-LSP label appearing in the encapsulated protocol packets is likewise mapped to the generic interface identifiers used in the routing table that resides in the selected context area  62 .  
         [0043]    The number of tasks  60  can vary in accordance with the routing protocols being used by the active VPRNs and the processing resources available in the router  14 . There must be at least one active task  60  for each different routing protocol used by any of the VPRNs supported by the router  14 . Thus, if all of the active VPRNs are using either OSPF or BGP routing, for example, then the minimum set of tasks  60  is one OSPF task  60 - 0  and one BGP task  60 -B. In general, one task  60  can support a number of VPRNs of the same type (i.e., using the same routing protocol), depending on the processing resources allocated to the task  60  and the demand from the VPRNs. If there are a large number of active VPRNs using a given protocol, it may be desirable that there be multiple tasks  60  of the same type. These tasks may time-share the same physical processor(s), or may be distributed in a parallel fashion among different processors if such hardware processing resources are available in the router  14 .  
         [0044]    Similarly, the memory  62  may be a single memory containing all the context areas CTXT for all VRs of the router  14 , or it may be a system having multiple independent memories, each containing some subset of the context areas CTXT. The context selection logic  64  is generally designed to exploit parallelism in order to maximize performance. If the hardware platform is capable of running multiple tasks  60  simultaneously and accessing multiple context areas CTXT of the memory  62  simultaneously, then preferably the context selection logic  64  looks for opportunities to activate two or more VRs simultaneously.  
         [0045]    The connections  66  shown in FIG. 5 represent logical connections between each VR and the VI subsystem  52  of FIG. 4. In general, there are multiple such logical connections between each VR and the VI subsystem  52 , with each logical connection corresponding to a different interface identifier. Some VRs may have as few as two associated VIs, whereas other VRs may have many.  
         [0046]    [0046]FIG. 6 shows the VI subsystem  52 . As previously indicated, the VIs implement a translation between the VRs and the PIs  50  of FIG. 4. As shown in FIG. 6, this translation is generally multi-layered. A number of MPLS VIs  70  interface to VRs in the VR subsystem  54 . The MPLS VIs define label-switched paths (LSPs) that serve as VPRN-specific tunnels in the wide-area routed network  10 . Channel VIs  72  define abstract channels, some of which are associated with the MPLS VIs and others associated directly with VRs in the VR subsystem  54 . A subset of the channel VIs  72  are associated with automatic protection switching (APS) VIs  74 . The channel VIs  72  and APS VIs  74  are further associated with media VIs  76 , which in turn are associated with corresponding PIs  50  of FIG. 4 via combined logical/physical connections  78 . Each of these classes of VIs is described in turn below.  
         [0047]    A connection between a given PI  50  of FIG. 4 and a given VR is made through a linked set of VIs in the VI subsystem  52 . Such a set generally includes at least one media VI  76  and one channel VI  72 , and may include an MPLS VI  70  or an APS VI  74  as well. Outbound messages generated by a VR that appear on a given connection  66  are processed within the VI subsystem  52  in accordance with information from the associated MPLS VI  70  (if any), channel VI  72 , APS VI  74  (if any), and media VI  76 . Similarly, inbound messages received from the PIs  50  at the connections  78  are processed in accordance with corresponding sets of VIs. The VI subsystem  52  forms a database having a potentially large number of such connected sets of VIs.  
         [0048]    [0048]FIG. 7 shows a first example of a set of linked VIs in the VI subsystem  52 . This set is used to form a transmit interface for a VR on an access link  16 . The interface identifier within the VR points to a channel VI  72 -a, which in turn points to a media VI  76 -a. As indicated, the media VI  76 -a is generally shared with other channel VIs (not shown). The channel VI  72 -a contains information about the individual channel, such as the type of channel (VLAN, MPLS, etc.), the channelization value (e.g. VLAN tag), and channel resources (bandwidth). The Media VI  76 -a contains information about the physical interfaces, such as interface type, encapsulation type, etc.  
         [0049]    [0049]FIG. 8 shows an example set of linked VIs for a backbone link  18 . Here, a channel VI  72 -b is associated with an APS VI  74 -b, which in turn is associated with two media VIs  76 -bl and  76 -b 2 . The APS VI  76 -b contains information indicating which media VI  76 -bl or  76 -b 2  is the “working” instance and which is the “protect” instance, and further includes state information for each media VI such as “factive”, “standby”, “operative”, “inoperative”, etc.  
         [0050]    [0050]FIG. 9 shows an example of a linked set of VIs forming the interface within one VAR  20  via which another VAR  20  of the same VPRN is reached through the wide-area routed network  10 . A first MPLS VI  70 -cl contains the label and other information for an inner LSP, and a second MPLS VI  70 -c 2  contains the label and other information for an outer LSP. Because there are typically multiple inner LSPs for each outer LSP, the outer MPLS VI  70 -c 2  is generally shared with other inner MPLS VIs like MPLS VI  70 -cl. The outer MPLS VI  70 -c 2  points to a channel VI  72 -c, which in turn points to a media VI  76 -c. These MPLS VIs include MPLS path information along with resource and policy information (e.g., set-up priority, hold priority).  
         [0051]    [0051]FIG. 10 shows an example of a set of VIs used when MPLS redundancy is employed. An inner MPLS VI  70 -d 1  points to a “redundancy” MPLS VI  70 -d 2 . The redundancy MPLS VI  70 -d 2  is similar to the APS VI  74 -b of FIG. 8, in that it contains information identifying working and protect paths and associated state information. In contrast to APS, however, each packet is sent over only one of a redundant pair of MPLS paths. The redundancy MPLS VI  70 -d 2  points to two outer MPLS VIs  70 -d 3  and  70 -d 4 . These in turn point to respective channel VIs  72 -d 1  and  72 -d 2 , which point to respective media VIs  76 -d 1  and  76 -d 2 .  
         [0052]    [0052]FIG. 11 shows another example that is used to support load balanced MPLS operation. Inner MPLS VIs  70 -e 1  and  70 -e 2  of different VRs point to respective redundant MPLS VIs  70 -e 3  and  70 -e 4 , both of which point to the same set of outer MPLS VIs  70 -e 5  and  70 -e 6 . The outer MPLS VIs  70 -e 5  and  70 -e 6  point to respective channel VIs  72 -e 1  and  72 -e 2 , which in turn point to respective media VIs  76 -e 1  and  76 -e 2 . This configuration provides for load balancing when both outer LSPs are operational, and also provides for redundant fail-over when one of the outer LSPs fails.  
         [0053]    It will be apparent to those skilled in the art that modifications to and variations of the above-described techniques are possible without departing from the inventive concepts disclosed herein. Accordingly, the invention should be viewed as limited solely by the scope and spirit of the appended claims.