This disclosure relates generally to the field of digital computer networks and fault detection mechanisms.
Service providers (SPs) are increasingly using Multi-protocol Label Switching (MPLS)/Internet Protocol (IP) networks for delivering various types of services. In SP networks consisting of an MPLS/IP core attached to one or more Ethernet Access Domains, with pseudowires (PWs) utilized for transporting data traffic over the core, occurrence of faults within the core may cause end-to-end service disruption. (A PW is a tunnel established between two provider edge nodes to transport Layer 2 packet data units (PDUs) across a packet switched network (PSN).) Thus, as more legacy networks migrate to the use of MPLS for transport, the role of MPLS Operations, Administration, and Maintenance (OAM) network fault, performance, data, and diagnosis functions, has become increasingly important.
A number of different OAM mechanisms have been developed for fault detection and isolation in MPLS networks. For example, Virtual Circuit Connectivity Verification (VCCV) is a known mechanism for identifying OAM packets at the egress of a PW. VCCV is thus useful in detecting failures in the forwarding plane on the egress of the MPLS PW. Label Distribution Protocol (LDP) status messages and the MPLS Label Switched Path (LSP) Ping tool provide the capability for detecting and isolating failures in the data plane, and for verifying the data plane against the MPLS control plane. Various Ethernet service OAM mechanisms, such as the Ethernet IEEE 802.1ag Connectivity Fault Management (CFM), Link Layer OAM (IEEE 802.3ah OAM), and Ethernet Local Management Interface (E-LMI) (Metro Ethernet Forum Technical Specification 16), also enable a user to detect faults within Ethernet domains.
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.
In the following description specific details are set forth, such as device types, system configurations, communication methods, etc., in order to provide a thorough understanding of the present invention. However, persons having ordinary skill in the relevant arts will appreciate that these specific details may not be needed to practice the embodiments described.
In the context of the present application, a computer network is a geographically distributed collection of interconnected subnetworks for transporting data between nodes, such as intermediate nodes and end nodes (also referred to as endpoints). A local area network (LAN) is an example of such a subnetwork; a plurality of LANs may be further interconnected by an intermediate network node, such as a router, bridge, or switch, to extend the effective “size” of the computer network and increase the number of communicating nodes. Examples of the devices or nodes include servers, mixers, control units, and personal computers. The nodes typically communicate by exchanging discrete frames or packets of data according to predefined protocols.
A customer edge (CE) device, as that term is used in the present disclosure, refers to customer node or device connecting to the service provider. A provider edge (PE) device refers to a device or node that is used to connect CE devices to the service. For example, a user-facing provider edge (u-PE) device is commonly used to connect CE devices to the service. An attachment circuit (AC) is the customer connection to the service provider network. An AC may be a physical port, or a virtual port, and may be any transport technology (e.g., Frame Relay (FR), Asynchronous Transfer Mode (ATM), Ethernet, etc.) A network-facing provider edge (n-PE) is a node or device that acts as a gateway between the SP core (e.g., MPLS) and edge domain, which may be MPLS or Ethernet. Furthermore, it should be understood that for the purposes of OAM protocol interworking, a pseudowire (PW) may comprise either a single hop or a multi-hop spanning several operational domains or network segments.
A “defect”, in the context of the present application, refers to any sort of network failure, which may include anything from a complete loss of connectivity to a intermittent loss of connectivity, or a loss of quality (from partial to complete). A forward defect denotes a type of defect wherein a node or network device is unable to receive packets. Conversely, a reverse defect denotes a type of defect wherein a node or device is unable to send packets. A forward defect may be considered to be a superset of a reverse defect case, since in order to reliably determine whether it has transmitted correctly, a node needs to receive back an acknowledgment from the destination or receiver device. Therefore, an occurrence of a forward defect may be thought of as superseding a reverse defect.
In one embodiment, an interworking mechanism is provided that enables the translation of events and communication of fault information between Ethernet OAM and pseudowire (PW) OAM protocols/tools. The interworking involves mapping remote failure indications for forward defects signaled by targeted LDP (in PW status messages) to Connectivity Fault Management (CFM) Alarm Indication Signal (AIS) messages, and locally detecting forward defects through CFM connectivity check (CC) messages or VCCV-Bidirectional Forwarding Detection (BFD) protocol timeouts and notifying the remote peer device via PW status messages. (BFD is a simple “hello” mechanism that provides short-duration detection of failures in a path between adjacent forwarding engines. BFD can provide failure detection on any kind of path between systems, including virtual circuits and tunnels, and can be used to detect MPLS LSP data plane failures.)
For reverse defects, remote notifications in the form of LDP PW status messages received by the PE device triggers generation of CFM Remote Defect Indication (RDI) messages. In other words, the PE device at the far end of the MPLS core is configured to convert a PW status message to a CFM RDI forwarded to the CE device. Any reverse defects locally detected in the receipt of CFM RDI cause LDP PW status messages to be generated and transmitted to the remote end. Thus, in one embodiment, interworking between Ethernet CFM (IEEE 802.1ag/ITU-T Y.1731) and PW OAM (VCCV-BFD/targeted LDP) is provided.
Although an example for a method of exchanging alarm conditions and reporting service status between an MPLS network (used to deliver Layer 2 Virtual Private Network (L2VPN) services) and an Ethernet bridged access domain is described, it should be understood that other embodiments may include different network topologies, such as MPLS core network connected with other operational domains, e.g., Ethernet access domain on one end and an MPLS access domain on the other, etc. Additionally, although various examples are described that include PWs running across an MPLS core network, it should be understood that in other embodiments PWs may also run over other types of networks, including IP, Layer 2 Tunnel Protocol Version 3 (L2TPv3), etc.), and other technologies which may, in the future, include Ethernet.
In the example embodiment shown, n-PE devices 114 and 115 are configured to map the status of internal core network 111 to the external Ethernet OAM mechanisms, and vice-versa. This operation is represented in
VCCV may run across the MPLS core to provide an in-band OAM mechanism that exercises the data path of each PW. That is, monitoring and troubleshooting of pseudowires is accomplished using VCCV. In general, VCCV may be used to construct an in-band control channel for a specific pseudowire. The control channel traffic is treated and processed by the underlying transport network in the same manner as data traffic. Some VCCV modes—BFD in particular—can be used to convey the operational status of the far-end of the pseudowire (e.g., n-PE 114) to the local-end (e.g., n-PE 115). That is, the BFD with status indication mode of VCCV can be used to convey the up/down status of one or more far-end attachment circuits that utilize the pseudowire associated with the control channel in consideration.
The status of a PW may also be signaled to a PE device using the Status Type-Length-Value (TLV) defined in LDP. (All LDP messages have a common structure that uses a TLV encoding scheme.) The Status TLV (first defined in RFC3036, section 3.4.6) has been extended in RFC4447 to include additional status codes to be used for PWs. In one embodiment, when an attachment circuit to a PE device encounters an error, the PE device uses a PW Notification Message to send a single “wild card” status message, using a PW FEC TLV with only the group ID set, to denote this change in status for all affected PW connections. (The FEC identifies the set of IP packets which may be mapped to a corresponding LSP.) This status message typically contains either the PW FEC TLV with only the group ID set, or the Generalized FEC TLV with only the PW Grouping ID TLV. As discussed above, the Group ID field of the PW FEC element, or the PW Grouping ID TLV used for the Generalized ID FEC element, may be used to send a status notification for all arbitrary sets of PWs.
It should be noted that although the LDP Status Message indicates the TLV based on the FEC/PW, since only one access circuit is associated with a pseudowire, there is a one-to-one mapping, which means that Extended Local Management Interface (E-LMI) or CFM mappings may only receive a single affected circuit to notify.
It should be understood that for the implementations described herein, the status of a PW is conveyed using only one mechanism. For example, if LDP is used to signal the PW, LDP is then also used to convey the far-end access circuits' status. VCCV can be used to augment this by testing the data plane (with status information kept locally). In other words, in the example of
Access circuit status may be signaled to a far-end PE using the VCCV control channel in cases where LDP is not configured for signaling of the pseudowires. In such cases, PW failure or AC status detected locally may be signaled to the remote end using VCCV if the BFD with status messages mode has been signaled. The BFD status bits corresponding to the access circuits may be used to indicate the failure. In this embodiment, LDP Status Messages may not used in conjunction with the BFD with status messages mode.
It is appreciated that other embodiments may have a network topology with a u-PE device is attached directly to MPLS core network 111, with Ethernet being transported across the core via one or more pseudowires.
In this example, dashed line 35 illustrates Directed-LDP (D-LDP) running between PE devices 26 and 27 for defect notification. In addition, defect detection in the MPLS core is provided by VCCV-BFD running between PE devices 26 and 27, as shown by solid line 34. In this embodiment, PE devices 26 and 27 are configured with software (or hardware/firmware) components for communicating defects detected by PW OAM to E-LMI running between the PE devices and their respective CE devices. This interworking function is illustrated by curved arrows 36 and 37 depicted beneath the corresponding PE devices of service layer OAM line 31. For example, arrow 38 represents E-LMI between CE device 25 and PE device 26, whereas arrow 39 represents E-LMI between CE device 28 and PE device 27. (In this example, the service layer is hosting an Ethernet service.)
In the example of
A plurality of intermediate provider nodes 55 are shown providing connectivity over MPLS core 11. Similarly, aggregation PE device 53 (PE-Agg) is shown providing connectivity between u-PE device 52 and n-PE device 54 in Ethernet access network 12. Intermediate node 57 connects u-PE device 58 and n-PE device 56 in MPLS access network 13. Service layer OAM and transport layer OAM mechanisms are illustrated by the horizontal lines extending across the bottom of
The upside-down triangles 71 & 72 represent maintenance endpoints (MEPs) respectively associated with u-PE devices 52 & 58. In accordance with the IEEE 802.1ag standard, a maintenance point at the edge of a domain is called a “maintenance endpoint.” System administrators typically use MEPs to initiate and monitor CFM activity and report the results. A maintenance point inside a domain, and visible to a MEP, is referred to as a “maintenance intermediate point” (MIP). MIPs passively receive and respond to CFM frames initiated by MEPs. In
In the example embodiment of
Forward defects that affect a device's ability to receive traffic may be notified using CFM AIS. Reverse defects that impact the device's ability to transmit traffic may be notified using RDI messages. Ethernet CFM Continuity Check (CC) messages, per IEEE 802.1ag, may be used for proactive connectivity monitoring and defect detection within Ethernet access domains. For purposes of the interworking function, VCCV/BFD may be utilized for PW defect detection and continuity checking.
It is appreciated that OAM status may be measured at the ends of the pseudowire, and also within MPLS core 11. The PW provides the signaling and data encapsulation needed to transport the Ethernet traffic across MPLS core 11. The status of the PW may be determined in a number of ways, but is primarily divided to the control and data plane status. The control plane status may be gathered using the signaling protocol in use, e.g., LDP and the known extensions that facilitate both single and multi-hop PWs. As described above, the data plane of the PW may be verified using VCCV, LSP Ping, or LSP Traceroute, or similar mechanisms.
Practitioners in the art will appreciate that from the perspective of a designated n-PE device, a defect can occur in one of three possible locations: in the local Ethernet access network; within the MPLS core, or in the remote access network. The locality of the defect has implications on the method by which the designated n-PE device detects the defect or is notified of its occurrence. For instance, defects in the local Ethernet access network may be detected by the n-PE device using native Ethernet OAM mechanisms (e.g., CFM or 802.3ah) whereas faults within the remote access network are communicated to the designated n-PE device by the remote n-PE device using some form of MPLS control channel. Defects within the MPLS core can either be detected locally by the n-PE device, or that n-PE device can be notified of their occurrence from the remote n-PE device.
In one embodiment, the interworking function shown by arrows 62 and 65 in
Each of the various states is shown by an ellipse, with the state transitions being shown by the arrows. The Down state designates that the PW is not established, and hence, the services completely down. The Operational state designates that the service is operational, and that no alarm conditions are present. The Forward Defect Local state designates that the device has locally detected a forward defect. Conversely, the Forward Defect Remote state designates that the device has been informed by a remote peer of a forward defect. The Forward Defect state is a superset of the Forward Defect Local and Forward Defect Remote states. An n-PE device enters the Forward Defect state when the combination of events leading to having it enter the above two states occurs in tandem. An n-PE exits this state when those events are cleared, thereby reverting back to one of the initiating two states. An n-PE device also exits this state when the PW is torn down.
The Reverse Defect Local state designates that the device has locally detected a reverse defect. Similarly, the Reverse Defect Remote state designates that the device has been informed by the remote peer of the occurrence of a reverse defect. The Reverse Defect state is a superset of the Reverse Defect Local and Reverse Defect Remote states. An n-PE device enters this state when the combination of events leading to having it enter the above two states occur in tandem. An n-PE exits the Reverse Defect state when those events are cleared, thereby reverting back to one of the initiating two states. An n-PE device also exits this state when the PW is torn down.
In a typical networking application, packets are received from a framer, such as an Ethernet media access control (MAC) controller, of the I/O subsystem attached to the system bus. A DMA engine in the MAC controller is provided a list of addresses (e.g., in the form of a descriptor ring in a system memory) for buffers it may access in the system memory. As each packet is received at the MAC controller, the DMA engine obtains ownership of (“masters”) the system bus to access a next descriptor ring to obtain a next buffer address in the system memory at which it may, e.g., store (“write”) data contained in the packet. The DMA engine may need to issue many write operations over the system bus to transfer all of the packet data.
It should 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 (e.g., a processor or other electronic device) to perform a sequence of operations. Alternatively, the operations may be performed by a combination of hardware and software. 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, or other type of machine-readable medium suitable for storing electronic instructions.
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.
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