Abstract:
A method and apparatus for interworking between customer edge (CE) devices connected to provider edge (PE) devices via attachment circuits (ACs), the PE devices routing packets across a service provider (SP) network, the CE devices including one or more Ethernet CE devices and a non-Ethernet CE. A virtual switch instance (VSI) is provided on a first PE device coupled to the non-Ethernet CE. The first PE device also including a virtual routing forwarding (VRF) entity interfaced with the VSI such that the SP network appears to offer L 3 VPN service toward the non-Ethernet CE and VPLS toward the one or more Ethernet CE devices. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72( b ).

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to digital computer network technology; more particularly, to methods and apparatus for providing metro Ethernet services.  
       BACKGROUND OF THE INVENTION  
       [0002]     Many enterprises are changing their business processes using advanced information technology (IT) applications to achieve enhanced productivity and operational efficiencies. These advanced applications tend to place increasing importance on peer-to-peer data communications, as compared to traditional client-server data communications. As a result, the underlying network architecture to support these applications is evolving to better accommodate this new model.  
         [0003]     The performance of many peer-to-peer applications benefit from being implemented over service provider networks that support multipoint network services. A multipoint network service is one that allows each customer edge (CE) end point or node to communicate directly and independently with all other CE nodes via a single interface (either virtual or physical). Ethernet switched campus networks are an example of a multipoint service architecture. The multipoint network service contrasts with the hub-and-spoke network service, where the end customer designates one CE node to the hub that multiplexes multiple point-to-point services over a single User-Network Interface (UNI) to reach multiple “spoke” CE nodes. In a hub-and-spoke network architecture, each spoke can reach any other spoke only by communicating through the hub. Traditional wide area networks (WANs) such as Frame Relay (FR) and asynchronous transfer mode (ATM) networks are based on a hub-and-spoke service architecture.  
         [0004]     Virtual Private Network (VPN) services provide secure network connections between different locations. A company, for example, can use a VPN to provide secure connections between geographically dispersed sites that need to access the corporate network. There are three types of VPN that are classified by the network layer used to establish the connection between the customer and provider network. Layer  1  VPNs are simple point-to-point connections such as leased lines, ISDN links, and dial-up connections. In a Layer  2  VPN (L 2 VPN) the provider delivers Layer  2  circuits to the customer (one for each site) and provides switching of the customer data. Customers map their Layer  3  routing to the circuit mesh, with customer routes being transparent to the provider. Many traditional L 2 VPNs are based on Frame Relay or ATM packet technologies. In a Layer  3  VPN (L 3 VPN) the provider router participates in the customer&#39;s Layer  3  routing. That is, the CE routers peer only with attached PEs, advertise their routes to the provider, and the provider router manages the VPN-specific routing tables, as well as distributing routes to remote sites. In a Layer  3  IP VPN, customer sites are connected via IP routers (PEs and P nodes) that can communicate privately over a shared backbone as if they are using their own private network. Multi-protocol label switching (MPLS) Border Gateway Protocol (BGP) networks are one type of L 3 VPN solution. An example of an IP-based Virtual Private Network is disclosed in U.S. Pat. No. 6,693,878. U.S. Pat. No. 6,665,273 describes a MPLS system within a network device for traffic engineering.  
         [0005]     Virtual Private LAN Service (VPLS) has recently emerged to meet the need to connect geographically dispersed locations with a protocol-transparent, any-to-any, full-mesh service. VPLS is an architecture that delivers Layer  2  service that in all respects emulates an Ethernet LAN across a wide area network (WAN) and inherits the scaling characteristics of a LAN. All services in a VPLS appear to be on the same LAN, regardless of location. In other words, with VPLS, customers can communicate as if they were connected via a private Ethernet segment. Basically, VPLS offers a MPLS Layer  2  approach with multipoint connectivity, i.e., multipoint Ethernet LAN services, often referred to as Transparent LAN Service (TLS). VPLS thus supports the connection of multiple sites in a single bridged domain over a managed IP/MPLS network.  
         [0006]      FIG. 1  illustrates an example of a VPLS architecture with an IP or MPLS core. All services are identified by a unique virtual channel label, which is exchanged between each pair of edge routers. Each PE-CE pair is shown connected by an Attachment Circuit (AC). An AC is the customer connection to a service provider network; that is, the connection between a CE and its associated PE. An AC may be a physical interface, or a virtual circuit, and may be any transport technology, i.e., Frame Relay, ATM, Ethernet VLAN, etc. In the context of a VPLS, an AC is typically an Ethernet interface. In the example of  FIG. 1 , each PE includes a Virtual Switch Instance (VSI) that provides an Ethernet bridge (i.e., switch) function that equates to a multi-point L 2 VPN. A Pseudo-Wire (PW) is shown connecting every two VSIs. A PW is a virtual connection that is bi-directional in nature and, in this example, consists of a pair of unidirectional MPLS Virtual Circuits (VCs). Conceptually, VPLS can therefore be thought of as an emulated Ethernet LAN network with each VSI being analogous to a virtual Ethernet switch.  
         [0007]     Virtual channel labels are used by the edge routers to de-multiplex traffic arriving from different VPLS nodes. As traffic arrives on access ports, edge routers learn customer&#39;s Media Access Control (MAC) addresses. Each router enters these learned addresses in a forwarding information base, or table of MAC addresses, it maintains for each VPN instance. Customer traffic is switched according to MAC addresses and forwarded across the service provider network using appropriate PWs.  
         [0008]     There are certain scenarios where a service provider wishes to provide VPLS service to a customer who has sites with disparate Attachment Circuit (AC) types (heterogeneous transport). For instance, a customer may have some sites with ATM ACs, some sites with FR ACs, and still other sites with Ethernet ACs. In situations where the ACs are all of the same technology, i.e., homogeneous, no transport problem exists. However, when a customer site does not use the same homogeneous interface as the other CEs, some sort of interworking function is needed.  
         [0009]     One solution to the problem of providing VPLS to a customer with sites having different AC types is to mandate that the Native Service (NS) be of type Ethernet end-to-end (e.g., among the CE devices). Native Service refers to the common end-to-end service that is carried over the ACs between the two CEs. For example, an AC between a CE and a PE can be ATM or FR, but the NS can be Ethernet (e.g., Ethernet over ATM or Ethernet over FR) As a practical matter, mandating the NS to be Ethernet end-to-end would mean that customers with ATM or FR CEs would have to reconfigure their associated ACs as a bridged interface or as a routed interface with Ethernet encapsulation. The difficulty with this approach is that many service providers are reluctant to adopt such configurations because their customer&#39;s CE devices either do not have such capability, or cannot easily be configured for such operation.  
         [0010]     Another prior art approach for providing interworking between some non-Ethernet sites (e.g., sites with ATM, FR, etc.) and some Ethernet sites is to use L 3 VPN technology, such as RFC2547bis, and for the service providers to participate in the customer&#39;s routing by every PE device connected to its customer&#39;s CE devices. The drawback of this solution, however, is that it fails to address the desire of those service providers who wish to maintain the service offering to their customers at Layer  2 ; that is, service providers who want to offer VPLS service to their customers. This solution is also unacceptable to those customers who want to retain the ability to manage their data packet routes. In other words, although MPLS Layer  3  VPNs provide “any-to-any” connectivity, some enterprises are reluctant to relinquish routing control of their network and desire L 2 VPN services with multipoint connectivity.  
         [0011]     Thus, there is a need for alternative methods and apparatus that would allow a service provider to offer L 2 VPN service such as VPLS to customers having CE devices with disparate interfaces without requiring any configuration changes to a customer&#39;s CE devices.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The present invention will be understood more fully from the detailed description that follows and from the accompanying drawings, which however, should not be taken to limit the invention to the specific embodiments shown, but are for explanation and understanding only.  
         [0013]      FIG. 1  is an example of a typical prior art VPLS system.  
         [0014]      FIG. 2  illustrates an exemplary VPLS system with interworking between a customer&#39;s Ethernet and non-Ethernet sites in accordance with one embodiment of the present invention.  
         [0015]      FIG. 3  is an expanded view of a portion of the VPLS system shown in  FIG. 2 .  
         [0016]      FIG. 4  illustrates a set of Virtual Routing Forwarding tables each of which is associated with a customer site in accordance with one embodiment of the present invention.  
         [0017]      FIG. 5  is an expanded view of a portion of a VPLS system according to an alternative embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0018]     A method and apparatus for providing VPLS service with interworking among a customer&#39;s heterogeneous sites (i.e., sites with Ethernet and non-Ethernet interfaces) without the need for configuration changes in the customer&#39;s CEs is described. In the following description specific details are set forth, such as device types, protocols, configurations, etc., in order to provide a thorough understanding of the present invention. However, persons having ordinary skill in the networking arts will appreciate that these specific details may not be needed to practice the present invention.  
         [0019]      FIG. 2  illustrates an exemplary system  10  providing VPLS service to a customer having three sites/CEs in accordance with one embodiment of the present invention. A Service Provider (SP) network infrastructure  12  includes three Provider Edge devices  13 - 15 , which are shown coupled to three customer sites/CEs  20 - 22  via ACs  23 - 25 , respectively. CE  20  and  21  each have Ethernet interfaces, whereas Site- 3 /CE  22  is connected via ATM with routed interface. In other words, when CE  22  sends data packets to a destination device it transmits across an ATM AC. With routed encapsulation, an IP packet is encapsulated in the ATM frame, but no Ethernet bridge header is included.  
         [0020]     Each PE in  FIG. 2  includes an associated VSI, which functions like a logical Ethernet switch or bridge. That is, PE  13  has an associated VSI  16 , PE  14  has an associated VSI  17 , and PE  15  has an associated VSI  18 . In the latter case, VSI  18  does not connect directly to CE  22  because AC  25  is of an ATM type with routed encapsulation. However, VSI expects to see an Ethernet header attached to data packets it receives from CE  22 . According to the present invention, a Virtual Routing Forwarding (VRF) entity  19  within PE  15  is utilized to provide interworking between the disparate type of AC (i.e., ATM) associated with CE  22  and the Ethernet interfaces of CEs  20  and  21 . Whereas  FIG. 2  illustrates an ATM AC connecting CE  22  with PE  15 , it is appreciated that the present invention may be utilized to provide interworking between sites associated with a variety of disparate AC types (e.g., ATM, FR, etc.)  
         [0021]     As can be seen in the expanded view of  FIG. 3 , VRF  19  is connected between CE  22  and VSI  18 . The SP in system  10  thus provides VPLS service to CE  20  and CE  21 , and L 3 VPN service to CE  22 . Configured in this manner, VRF  19  of PE  15  can be viewed as a virtual router peering with CE  22  at one end, and with CEs  20  and  21  at the other end. Incoming data packets are delivered to CE  22  by VRF  19  with Layer  3  Internet protocol, as indicated by arrow  42  (see  FIG. 3 ). In the other direction, VRF  19  is utilized to generate an Ethernet header for data packets transported from CE  22  to another end device via the SP network infrastructure. To achieve this result, VRF  19  strips the ATM header off the data packet, leaving the encapsulated IP header. VRF  19  then adds an Ethernet header to the packet so that it may be properly transported across the appropriate PW (e.g., either PW  30  or PW  32  in this example) via VSI  18 . This latter operation is depicted in  FIG. 3  by arrow  41 .  
         [0022]     Practitioners in the networking arts will appreciate that the plurality of VSIs  16 - 18  and PWs  30 - 32  connecting the VSIs together can be viewed as collectively comprising a logical LAN segment between VRF  19 , CE  20  and CE  21 . Since VRF  19  is peering with CEs  20 - 22 , it is also involved in the Address Resolution Protocol (ARP) and the required routing protocol with these CEs. Just as each of the VSIs discovers or learns through ARP or other message exchanges among CEs which PW is associated with a particular Ethernet MAC address, VRF  19  also learns through ARP the Ethernet MAC address associated with a particular IP address.  
         [0023]     Autodiscovery and signaling are well-known logical components of a VPLS system that allows PE devices to automatically discover other PE devices that have an association with a particular VPLS instance, and to set up and bind a PW to a particular VSI. Once the PEs have discovered other PEs that have an association with a particular VPLS instance, the PEs can then signal connections to interconnect the PEs associated with a particular VPLS instance. Practitioners will appreciate that there are many mechanisms that can be used to distribute VPLS associations between PE devices.  
         [0024]     The tables of VSI  18  and VRF  19  self learn MAC address to port associations. For example, VSI  18  learns MAC addresses as the result of message exchanges between VRF  19  and CEs  20 - 21 ; whereas VRF  19  learns MAC addresses associated with CEs  20 - 22  as the result of ARP. The VSI will also associate the received frame&#39;s source MAC address with the ingress PW within its forwarding table for future forwarding decisions. In this way, when CE  22  sends data packets with routed encapsulation to another end point CE, VRF  19  looks up the Ethernet MAC address associated with the IP address of the packet and includes that address in the Ethernet header it generates, making it compatible with the connected VSI at Layer  2 . (It should be kept in mind that VRF  19  is already peering with CE  22  at Layer  3 .)  
         [0025]     Thus, in the described example, VRF  19  stores the destination MAC addresses for each of the customer&#39;s sites/CEs (e.g., CE  20  and CE  21 ), so that it may formulate the data packet with the correct Ethernet header.  
         [0026]     According to the interworking scheme of the present invention, it appears as if the SP is offering the L 3 VPN service toward the customer&#39;s CEs with routed interfaces, and offering the VPLS service toward the customer&#39;s CEs with Ethernet interfaces. The interworking between the L 3 VPN and the VPLS services is achieved by having a VSI included on both the PEs providing VPLS functionality and on the PEs providing L 3 VPN functionality. The VSI interfaces with the L 3 VPN forwarding entity, e.g., VRF as defined in RFC2547. In other words, if a customer has one or more non-Ethernet sites, then the VRFs associated with these non-Ethernet sites can be considered as connected to each other through a LAN segment, which is emulated by the VPLS service instance for that customer.  
         [0027]     As a further example, consider a case in which a customer has ten sites, two of which have non-Ethernet connections. The remaining eight have Ethernet connections to their corresponding PE devices. The PE devices that are connected to the non-Ethernet sites may be configured as shown in  FIG. 3  to support both VSI and VRF entities; whereas the PE devices connected to the Ethernet sites only need to support VSIs. The VRF provides IP VPN service (Layer  3 ) toward the non-Ethernet CE devices, and is configured to add an Ethernet header with the appropriate MAC address to packets sent by the non-Ethernet CE to another site via the VSI connected to the VRF. The VPLS service instance for that customer can be considered as providing an emulated bridged LAN segment among the eight customer&#39;s CEs with Ethernet connections and the corresponding VRFs connecting to the two customer&#39;s non-Ethernet CEs.  
         [0028]     The present invention also provides an aggregation mechanism for IP VPN (L 3 VPN). The end-to-end network can be considered as a two-tiered network: The first, aggregation tier consists of VPLS with PE devices that emulate an Ethernet bridged LAN at Layer  2 . The second, core-network tier comprises L 3 VPN PE devices. Persons of skill in the networking arts will appreciate that this aggregation mechanism is efficient; that is, many CEs may be aggregated in to a single interface of a L 3 VPN PE. Instead of using a single interface for each CE, a single VLAN interface can be utilized to provide connectivity to all CEs belonging to the same VPN in a given access network.  
         [0029]     Although PE  15  of  FIGS. 2 &amp; 3  is shown with a single VRF entity, it should be understood that provider edge devices in a Layer  3  VPN may comprise multiple VRF tables. By way of example,  FIG. 4  is a magnified view of a L 3 VPN PE device  45  that shows a set of VRF tables  46  connected to CEs  47 - 49 . In this example, each VRF table is connected to a CE of a different customer. Similarly, multiple VSIs may be present in a single PE, with each VSI being connected to a different customer.  
         [0030]     It should also be understood that although the embodiments described thus far have shown the VSI and VRF entities as separate forwarding tables (one for Layer  2  and the other for Layer  3 ), other implementations may combine the two tables into one single forwarding table function. For example,  FIG. 5  illustrates a portion of a VPLS system according to an alternative embodiment of the present invention in which the separate VSI and VRF entities are combined into a single integrated forwarding table  60  within PE  15 . Forwarding table  60  is shown connected to CE  22  via AC  25 , and to PWs  30  &amp;  32 .  
         [0031]     Persons of skill in the art will appreciate that VSIs  16 - 18  and VRF  19  can be implemented in a variety of ways. For example, any of these entities may be implemented in software, hardware, or firmware that either resides within the PE device, or is accessible by the PE through various media.  
         [0032]     It should also be understood that elements of the present invention may also be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic device) to perform a process. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, elements of the present invention may be downloaded as a computer program product, wherein the program may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection).  
         [0033]     Additionally, although the present invention has been described in conjunction with specific embodiments, numerous modifications and alterations are well within the scope of the present invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.