WO2017118880A1

WO2017118880A1 - Faster convergence on primary provider edge (pe) failure in a single-active redundancy topology

Info

Publication number: WO2017118880A1
Application number: PCT/IB2016/050093
Authority: WO
Inventors: Prasanna Chalapathy; Raju DUGYALA; Antoni Przygienda
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-01-08
Filing date: 2016-01-08
Publication date: 2017-07-13

Abstract

A method is provided that is implemented by a network device. The method is for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single- active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the network device functions as the backup PE in the Ethernet segment. The method includes detecting a failure of the primary PE via an indication from the CE, changing known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and sending MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

Description

FASTER CONVERGENCE ON PRIMARY PROVIDER EDGE (PE) FAILURE IN A SINGLE-ACTIVE REDUNDANCY TOPOLOGY

FIELD

[0001] Embodiments of the invention relate to the field of Ethernet virtual private networks (EVPNs), and more specifically to improving convergence times in reaction to a failure of a primary provider edge (PE) device.

BACKGROUND

[0002] An Ethernet virtual private network (EVPN) instance is a virtual network encompassing a set of customer edge devices (CEs) that are connected to provider edge devices (PEs), where the PEs are the edge of a provider network that utilizes a multi-protocol label switching (MPLS) infrastructure. The PEs provide virtual layer 2 bridged connectivity between CEs. In a given provider network there may be multiple EVPN instances. CEs may be hosts, routers, switches or similar devices. PEs may be routers or similar devices.

[0003] The infrastructure utilizes media access control (MAC) addresses for routing and multiprotocol border gateway protocol (BGP) over the MPLS/virtual extensible local area network (VxLAN) core for determining the topology of the network. PEs advertise the MAC addresses learned from the CEs that are connected to them, along with an MPLS label to other PEs in the control plane using BGP. Control-plane learning offers greater control over the MAC learning process, such as restricting which devices learn specific information and the ability to apply policies. This enables load balancing of traffic to and from CEs that are multi-homed to multiple PEs. It also improves convergence times in the event of certain network failures.

[0004] A CE that is a host or a router that is multi-homed directly to more than one PE in an EVPN instance on a given Ethernet segment may have one or more Ethernet tags configured on the Ethernet segment. However, only one of the PEs, referred to as a designated forwarder (DF), is responsible for sending broadcast, unknown unicast and multicast (BUM) traffic to this CE. An Ethernet segment is a collection of Ethernet links that connect a customer site to a provider network. A procedure for electing a DF is set forth in the Internet Engineering Task Force (IETF) request for comments (RFC) 7432, entitled "BGP MPLS-Based Ethernet VPN."

[0005] In one embodiment, the process of electing the DF may occur when a PE discovers the Ethernet segment identifier (ESI) of the attached Ethernet segment. The PE advertises an Ethernet Segment route with the associated ES-Import extended community attribute. The PE then starts a timer (default value = 3 seconds) to allow the reception of Ethernet Segment routes from other PEs connected to the same Ethernet segment. This timer value should be the same across all PEs connected to the same Ethernet segment. When the timer expires, each PE builds an ordered list of the IP addresses of all the PEs connected to the Ethernet segment (including itself), in increasing numeric value. Each IP address in this list is extracted from the "Originating Router's IP address" field of an advertised Ethernet Segment route. Every PE is then given an ordinal indicating its position in the ordered list, starting with 0 as the ordinal for the PE with the numerically lowest IP address. The ordinals are used to determine which PE will be the DF for a given EVPN instance on the Ethernet segment, using a rule. The rule assumes a redundancy group of N PEs, for VLAN-based service, where the PE with ordinal i is the DF for an <ES, VLAN V> when (V mod N) = i. In the case of VLAN-(aware) bundle service, then the numerically lowest VLAN value in that bundle on that ES MUST be used in the modulo function.

[0006] Using the "Originating Router's IP address" field in the ES route to get the PE IP address needed for the ordered lists allows for a CE to be multi-homed across different autonomous systems (ASes) if such a need ever arises. The PE that is elected as a DF for a given <ES, VLAN> or <ES, VLAN bundle> will unblock multi-destination traffic for that VLAN or VLAN bundle on the corresponding Ethernet Segment. The DF PE unblocks multi-destination traffic in the egress direction towards the segment. All non-DF PEs continue to drop multi-destination traffic in the egress direction towards that <ES, VLAN> or <ES, VLAN bundle>.

[0007] In the case of link or port failure, the affected PE withdraws its Ethernet Segment route. This will re-trigger the service carving procedures on all the PEs in the redundancy group. For PE node failure or upon PE commissioning or decommissioning, the PEs re-trigger the service carving. When this occurs however it can take some time for remote PEs to detect the node failure and switch to the backup paths. When the Ethernet Segment is operating in single-active redundancy mode and if there is more than one backup PE for the Ethernet Segment, the remote PE uses the DF (also referred to as the primary) PE withdrawal of its set of Ethernet auto- discovery per Ethernet Segment routes as a trigger to start flooding traffic for the associated MAC address (as long as flooding of unknown unicast is administratively allowed) as it is not possible to select a single backup PE due to the fact that any of the backup PEs can become active and the remote PE has no way to detect which backup PE is active until the remote PE receives a MAC/IP route advertisement from the new DF (primary) PE. The time for a new DF PE to learn MAC/IP routes and advertise them is not deterministic. Until this is resolved the remote PEs are unable to forward data traffic to these destination MAC/IP addresses and data traffic is likely to be lost. SUMMARY

[0008] In one embodiment, a method is provided that is implemented by a network device. The method is for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi- homed customer edge (CE), where the network device functions as the backup PE in the Ethernet segment. The method includes detecting a failure of the primary PE via an indication from the CE, changing known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and sending MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

[0009] In another embodiment, a network device is configured to execute a method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the network device functions as the backup PE in the Ethernet segment. The network device includes a non-transitory machine -readable storage medium to store a designated forwarder (DF) manager, and a processor coupled to the non-transitory machine-readable storage medium. The processor is configured to execute the DF manager. The DF manager is configured to detect a failure of the primary PE via an indication from the CE, to change known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and to send MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

[00010] In a further embodiment, a computing device is in communication with a network device in a network with a plurality of network devices. The computing device is configured to execute a plurality of virtual machines for implementing network function virtualization (NFV), wherein a virtual machine from the plurality of virtual machines is configured to implement a method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi- homed customer edge (CE), where the computing device functions as the backup PE in the Ethernet segment. The computing device includes a non-transitory machine -readable storage medium to store a designating forwarder (DF) manager, and a processor coupled to the non- transitory machine-readable storage medium. The processor is configured to execute the virtual machine. The virtual machine is configured to execute the DF manager. The DF manager is configured to detect a failure of the primary PE via an indication from the CE, to change known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and to send MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

[00011] In one embodiment, a control plane device is configured to implement a control plane of a software defined networking (SDN) network. The SDN network includes a plurality of network devices, wherein the control plane device is configured to implement a method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the control plane device functions as the backup PE in the Ethernet segment. The control plane device includes a non-transitory machine-readable storage medium to store a designated forwarder (DF) manager, and a processor coupled to the non-transitory machine- readable storage medium. The processor is configured to execute the DF manager. The DF manager is configured to detect a failure of the primary PE via an indication from the CE, to change known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and to send MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

[00012] The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

[00013] Figure 1 is a diagram of one embodiment of an Ethernet virtual private network

(EVPN) that illustrates the infrastructure related to the embodiments.

[00014] Figure 2 is a flowchart of one embodiment of a process implemented by a provider edge (PE) device in an Ethernet segment to determine a designated forwarder (DF) and notify a remote PE of the new primary PE or DF.

[00015] Figure 3 is a flowchart of one embodiment of a process implemented by a remote

PE to identify a new primary PE or DF for reaching a media access control (MAC) and/or Internet Protocol (IP) address.

[00016] Figures 4A-4E are diagrams that show the state of a set of PEs in an Ethernet segment connected with a multi-homed consumer edge (CE) device.

[00017] Figure 5 is a diagram of one embodiment of an EVPN where a primary PE or DF has failed. [00018] Figures 6A and 6B are diagrams that show the state of the set of PEs in the

Ethernet segment connected with the multi-homed CE device after failure of the primary PE or DF.

[00019] Figure 7A illustrates connectivity between network devices (NDs) within an exemplary network, as well as three exemplary implementations of the NDs, according to some embodiments of the invention.

[00020] Figure 7B illustrates an exemplary way to implement a special-purpose network device according to some embodiments of the invention.

[00021] Figure 7C illustrates various exemplary ways in which virtual network elements

(VNEs) may be coupled according to some embodiments of the invention.

[00022] Figure 7D illustrates a network with a single network element (NE) on each of the NDs, and within this straight forward approach contrasts a traditional distributed approach (commonly used by traditional routers) with a centralized approach for maintaining reachability and forwarding information (also called network control), according to some embodiments of the invention.

[00023] Figure 7E illustrates the simple case of where each of the NDs implements a single NE, but a centralized control plane has abstracted multiple of the NEs in different NDs into (to represent) a single NE in one of the virtual network(s), according to some embodiments of the invention.

[00024] Figure 7F illustrates a case where multiple VNEs are implemented on different

NDs and are coupled to each other, and where a centralized control plane has abstracted these multiple VNEs such that they appear as a single VNE within one of the virtual networks, according to some embodiments of the invention.

[00025] Figure 8 illustrates a general purpose control plane device with centralized control plane (CCP) software, according to some embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

[00026] The following description describes methods and apparatus for reducing the time for a remote provider edge (PE) device to detect a failure of a primary PE, where the primary PE is the designated forwarder (DF) for a customer edge (CE) device, and to determine a backup PE in an Ethernet Segment where the Ethernet Segment connects the CE with multiple PEs such that the CE is multi-homed and the Ethernet Segment is operating in a single-active redundancy mode. In the following description, numerous specific details such as logic implementations, opcodes, means to specify operands, resource partitioning/sharing/duplication implementations, types and interrelationships of system components, and logic partitioning/integration choices are set forth in order to provide a more thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that the invention may be practiced without such specific details. In other instances, control structures, gate level circuits and full software instruction sequences have not been shown in detail in order not to obscure the invention. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation. As used herein PE device and CE device are used interchangeably with PE and CE, respectively.

[00027] References in the specification to "one embodiment," "an embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[00028] Bracketed text and blocks with dashed borders (e.g., large dashes, small dashes, dot-dash, and dots) may be used herein to illustrate optional operations that add additional features to embodiments of the invention. However, such notation should not be taken to mean that these are the only options or optional operations, and/or that blocks with solid borders are not optional in certain embodiments of the invention.

[00029] In the following description and claims, the terms "coupled" and "connected," along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. "Coupled" is used to indicate that two or more elements, which may or may not be in direct physical or electrical contact with each other, co-operate or interact with each other. "Connected" is used to indicate the establishment of communication between two or more elements that are coupled with each other.

[00030] An electronic device stores and transmits (internally and/or with other electronic devices over a network) code (which is composed of software instructions and which is sometimes referred to as computer program code or a computer program) and/or data using machine-readable media (also called computer-readable media), such as machine-readable storage media (e.g., magnetic disks, optical disks, read only memory (ROM), flash memory devices, phase change memory) and machine-readable transmission media (also called a carrier) (e.g., electrical, optical, radio, acoustical or other form of propagated signals - such as carrier waves, infrared signals). Thus, an electronic device (e.g., a computer) includes hardware and software, such as a set of one or more processors coupled to one or more machine-readable storage media to store code for execution on the set of processors and/or to store data. For instance, an electronic device may include non- volatile memory containing the code since the non-volatile memory can persist code/data even when the electronic device is turned off (when power is removed), and while the electronic device is turned on that part of the code that is to be executed by the processor(s) of that electronic device is typically copied from the slower nonvolatile memory into volatile memory (e.g., dynamic random access memory (DRAM), static random access memory (SRAM)) of that electronic device. Typical electronic devices also include a set or one or more physical network interface(s) to establish network connections (to transmit and/or receive code and/or data using propagating signals) with other electronic devices. One or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware.

[00031] A network device (ND) is an electronic device that communicatively

interconnects other electronic devices on the network (e.g., other network devices, end-user devices). Some network devices are "multiple services network devices" that provide support for multiple networking functions (e.g., routing, bridging, switching, Layer 2 aggregation, session border control, Quality of Service, and/or subscriber management), and/or provide support for multiple application services (e.g., data, voice, and video).

[00032] Overview

[00033] IETF RFC 7432 describes border gateway protocol (BGP) multi-protocol label switching (MPLS)-Based Ethernet virtual private network (EVPN) operation and structures. An EVPN is an enhanced Layer-2 service that emulates an Ethernet (virtual) local area network (LAN) across a packet switched network (PSN). EVPN supports load-sharing across multiple connections from a Layer-2 site to an L2VPN service. An EVPN virtual local area network (VLAN) is a VLAN that follows BGP EVPN procedures. EVPNs are instanced and referred to as EVPN instances. An EVPN instance (EVI) spans PEs participating in that EVPN. It can span multiple broadcast domains. Another definition for an EVI is 'a collection of EVPN VLANs.'

[00034] An EVPN comprises a set of provider edge devices (PEs) connected with a set of customer edge devices (CEs) over an Ethernet Segment. An Ethernet Segment (ES) refers to a set of Ethernet links connecting a CE to one or more PEs. An Ethernet Segment Identifier (ESI) refers to a unique non-zero identifier that identifies an Ethernet segment. An EVPN link is an Ethernet link on which EVPN service is provided and is bound to a bridge associating it with one or more EVPN VLANs. A signaled EVPN link is a multi-homed EVPN Link that has a CE side signaling and determining the active/standby links. Examples of signaled EVPN links are pseudo-wires or links that are managed by a link aggregation control protocol (LACP) as part of a link aggregation group (LAG). [00035] When only a single PE, among all the PEs attached to an Ethernet segment, is allowed to forward traffic to/from that Ethernet segment for a given VLAN, then the Ethernet segment is defined to be operating in Single- Active redundancy mode. In contrast, when all PEs attached to an Ethernet segment are allowed to forward known unicast traffic to/from that Ethernet segment for a given VLAN, then the Ethernet segment is defined to be operating in All- Active redundancy mode. In some embodiments, an MPLS label can be used to identify an Ethernet segment of origin for data traffic, which can be referred to as a split horizon label.

[00036] As mentioned above, an EVPN includes a set of CEs connected to a set of PEs, where when a given CE is homed (in communication with as part of an EVI) by more than one PE, then this CE is referred to as a multi-homed device (MHD). However, when a given CE is homed only by a single PE, then the CE is considered a single-homed device (SHD). A PE which learns media access control (MAC) addresses from a SHD or MHD and advertises MAC/Internet Protocol (IP) routes to other PEs is referred to as a primary PE. A MAC/IP route is a route carrying a host MAC and possibly IP address around with it. Processes related to route discovery include Ethernet Auto Discovery routes per Ethernet Segment (Ethernet A-D per ES) and Ethernet Auto Discovery routes per EVPN instance (Ethernet A-D per EVI). In the EVPN infrastructure various labels are utilized with the data traffic, including an alias label and EVPN label. An alias label is a label used to 'alias' an EVI/ESI/<VLAN> carried in an Ethernet A-D per EVI. An EVPN label is a label carried on the MAC/IP route.

[00037] The embodiments described herein below, provide a method and system operating in the environment and with the infrastructure described above. The method and system work in relation to the election of a designated forwarder (DF), and upon failure of a PE or set of PEs in the EVPN, the system re-elects the designated forwarder. As used herein, a DF is a PE (also referred to as the primary PE), which is responsible for sending broadcast, unknown unicast, and multicast (BUM) traffic to the CE which is connected to more than one PE in an EVPN instance on a given Ethernet Segment. In addition, the primary PE or DF is responsible for disseminating reachability information acquired from the CE attached to the EVI to other PEs in the EVPN.

[00038] Figure 1 is a diagram of one embodiment of an EVPN that illustrates the infrastructure related to the embodiments. In the diagram, a CE (CE1) communicates with a set of PEs (PE1-3) over an Ethernet Segment (ES 100). In this example, ES 100 is operating in all- active redundancy mode where all PEs (PE1-3) attached to the ES 100 are allowed to forward known unicast traffic to/from ES 100 for a given VLAN to CE1. In other words, CE1 is multi- homed to PE1, PE2 and PE3. The PEs 1-3 connect the CE1 to a provider MPLS network that enables the CE1 to reach remote devices such as CE2 via PE4. PE4 is a remote PE, relative to CE1, and CE2 is single-homed to PE4. PE4 is a 'remote' PE in the sense that is not a part of the Ethernet Segment and not eligible to be a DF for CE1.

[00039] PEs (e.g., PE1-3, or more specifically the primary PE1 on behalf of the other PEs in the Ethernet Segment) advertise the MAC addresses learned from the CEs (e.g., CE1) that are connected to them, along with an MPLS label to other PEs in the control plane using BGP. Control-plane learning offers greater control over the MAC learning process, such as restricting which other PEs in the EVPN learn specific data items and types and the ability to apply policies. Control-plane learning enables load balancing of traffic to and from CEs that are multi-homed to multiple PEs. Control-plane learning also improves convergence times in the event of certain network failure.

[00040] However, the EVPN configured in this manner has drawbacks that the embodiments are able to overcome. When the primary PE or DF in the Ethernet Segment fails (i.e., in an Ethernet Segment which is operating in single-active redundancy mode), it takes a while for the remote PE (e.g., PE4) to detect the node failure and switch to the use backup paths (e.g., to reach MAC and/or IP addresses via CE2). The embodiments provide a process and system that lets a backup PE in the Ethernet Segment detect the primary PE or DF failure using bi-directional forwarding detection (BFD), signaled EVPN or similar process and subsequently the backup PE forces remote PEs to utilize the new active PE or DF as quickly as possible and thus minimize the loss, referred to as 'black-holing,' of the traffic.

[00041] In the diagram of Figure 1 the example configuration includes a primary PE or

DF at PE1, thus the process and system relate to detecting and recovering in response to failure of the entire PE1 (primary PE). When the Ethernet Segment is operating in single-active redundancy mode and if there is more than one backup PE for a given Ethernet Segment, the remote PE uses the primary PE's withdrawal of its set of Ethernet A-D per ES routes as a trigger to start flooding traffic for the associated MAC addresses (as long as flooding of unknown unicast packets is administratively allowed), as it is not possible to select a single backup PE due to the fact that any of the backup PEs can become active and the remote PE has no way to detect which backup PE is active until the remote PE receives a MAC/IP route advertisement from the new primary PE. Flooding continues until the remote PE learns the MAC/IP routes from the new primary PE. How soon the new primary PE can learn the MAC/IP routes and advertise them is not deterministic.

[00042] In the diagram, this refers to PE1 (i.e., the primary PE) losing connection to

Ethernet Segment 'ES 100.' When the Ethernet Segment is operating in single-active redundancy mode and if there is only one backup, the remote PE starts sending unicast traffic to the backup PE, as soon as it receives Ethernet A-D per ES route withdrawal from the primary PE. However, the remote PE will revert to flooding traffic to MAC address X if the primary PE withdraws the MAC/IP advertisement routes for X even before the new active PE or DF (previously the backup PE) learns and sends the MAC/IP advertisements to the remote PE.

[00043] Alternatively, another way to solve this problem is to flood the traffic only to PEs that are connected to the Ethernet Segment using the Aliasing label advertised by the backup PEs. Also, it is possible to use multi-hop BFD to detect that the primary PE node has failed. The existing or alternative solutions described above minimize the flooding of this traffic to an extent, but these nonetheless have significant limitations. The existing implementations and alternatives have limitations including that (1) multi-hop BFD to detect node failure is expensive in terms of bandwidth utilization, (2) the existing implementations and alternatives depend on how soon the new active PE or DF learns the associated MAC/IP route. The longer it takes for the new active PE or DF to learn the MAC/IP route, the longer that traffic from the remote PE will be flooded. Also, (3) if the primary PE lost connection to the ES and withdraws a MAC/IP route X before the new active PE learns MAC/IP route X from the associated CE, then flooding cannot be limited to only those PEs connected to the ES. This can be prevented by holding withdrawn MAC/IP routes for a certain period of time, but that comes with its own scaling limitations and implementation complexity.

[00044] The novel embodiments disclosed herein overcome these problems of the existing and alternative implementations. The embodiments enable a backup PE or newly selected DF to detect the failure of a primary PE node as quickly as possible. The backup PE makes use of BFD, signaled EVPN (i.e., where the CE elects a new DF or primary PE and signals or indicates that selection to the PEs in the Ethernet Segment) or similar processes to detect failure of the primary PE or DF. In the signaled EVPN embodiment, when the primary PE or DF fails, the EVPN link from the CE to a selected backup PE will become active and the backup PE can treat this as a trigger to become the new primary PE or DF instead of waiting for BGP session failure with the primary PE, as a result of TCP timeout, which typically takes a lot more time for detection of failure.

[00045] The embodiments herein enable a new active PE or DF to send MAC/IP advertisements as quickly as possible, without waiting for actual learning of MACs from the Ethernet Segment. The new active PE or new elected DF starts using the MAC/ESI information that was previously advertised by the previous primary PE or DF. The new primary PE or elected DF uses the 'aliasing label' (which may already be available in the forwarding plane and ready to go) when advertising MAC/IP routes to remote PEs. The new active PE or DF increments the sequence number in MAC/IP advertisements which forces remote PEs to use MAC/IP advertisements from the new active PE or DF immediately. Thus, the embodiments enable remote PEs to determine or identify the new active PE as quickly as possible, so that the remote PEs can stop flooding traffic in the EVPN and send known unicast only to the new active PE.

[00046] The operations in the following flow diagrams will be described with reference to the exemplary embodiments of the other figures. However, it should be understood that the operations of the flow diagrams can be performed by embodiments of the invention other than those discussed with reference to the other figures, and the embodiments of the invention discussed with reference to these other figures can perform operations different than those discussed with reference to the flow diagrams.

[00047] Figure 2 is a flowchart of one embodiment of a process implemented by a provider edge (PE) device in an Ethernet Segment to determine a designated forwarder (DF) and notify a remote PE of the new primary PE or DF. During regular operation of the Ethernet Segment, a primary PE or DF advertises a set of MAC/IP routes that identify the MAC addresses reachable via the CE that is served by the primary PE or DF. In this manner each of the other PEs in the Ethernet Segment learn a set of reachable MAC/IP routes via the advertisements of the DF or primary PE (Block 201). The PEs implementing the process store these MAC/IP routes as they are received.

[00048] A failure of the primary PE may be detected at any time (Block 203). The detection of the failure may be via an indication from the CE, for example by using a signaled EVPN technique or by use of BFD, time out of a TCP session for BGP or using a similar mechanism. Upon detecting a failure of the primary PE or DF the backup PE begins a process for changing the known MAC/IP routes that were previously reachable via the primary PE to be reachable via an alias of the backup PE (Block 205). MAC/IP route advertisements for changed MAC/IP routes with incremented sequence number may then be sent by the newly elected DF or primary PE, which is the implementing PE that was formerly a backup PE (Block 207). Those PEs in the Ethernet segment that do not determine that they are configured to be the primary PE or elected DF remain as backup PEs and may continue to track the MAC/IP route

advertisements in case of further failure in the network.

[00049] Figure 3 is a flowchart of one embodiment of a process implemented by a remote

PE to identify a new primary PE or DF for reaching a media access control (MAC) address. In one embodiment, the process at the remote PE for recovering from a failed PE in the Ethernet Segment of the EVPN begins with the receipt of a MAC/IP route advertisement from the newly elected DF or primary PE (Block 301). The remote PE examines the received MAC/IP route advertisement and identifies the sender PE as a new DF or primary PE at least for the advertised MAC/IP route. To further verify this transition, the remote PE compares the sequence number of the received MAC/IP route advertisement with the last received corresponding MAC/IP route advertisement (i.e., the last MAC/IP route advertisement for the given MAC/IP route X) (Block 303). If the sequence number of the received MAC/IP route advertisement is lower than or equal to the last MAC/IP route advertisement, then the remote PE determines that the received MAC/IP route advertisement is stale and it is ignored and discarded (Block 305).

[00050] However, if the sequence number of the received MAC/IP route advertisement is greater than the last received sequence number then the sender of the MAC/IP route

advertisement is set as the new primary PE for that MAC/IP route X (Block 307). In some embodiments, the new primary PE or DF is set as the primary PE or DF for all MAC/IP routes that were previously handled by the replaced/failed PE or DF (Block 309). In other

embodiments, only the MAC/IP route X that is advertised by the new DF or primary PE is updated at the remote PE to utilize the sender as the DF or primary PE. Once the primary PE or DF has been updated for the given MAC/IP route X then all data traffic destined for that MAC/IP address will be sent to the newly associated primary PE or DF (Block 311).

[00051] Figures 4A-4E are diagrams that show the state of a set of PEs in an Ethernet segment connected with a multi-homed consumer edge (CE) device. The diagrams show the state of the Ethernet AD per EVI routes at each of the PEs as illustrated in the example of Figure 1, namely where PEl is initially a DF or primary PE for a multi-homed CE (i.e., CEl) connected to PE1-3 via the Ethernet Segment (i.e., ES 100) and where PE4 is a remote PE. In Figure 4A PEl advertises Ethernet AD routes that it has discovered to each of the other PEs in the EVPN. In this case PEl advertises the route for the Ethernet Segment with the ESI of ES 100 to all of the other PEs, where the route has a split horizon label (SHL) of PE1_SHL_ES 100 and an alias label of PE1_AL_ES 100. The other PEs similarly advertise the Ethernet A-D routes that they know and each of the other PEs records these including identifying those routes with a SHL and alias label. Figure 4B shows the advertisement by PE2 and Figure 4C shows the advertisement by PE3.

[00052] Figures 4D and 4E show the advertisement by PEl of a set of MAC addresses that it has learned via the CE (i.e., CEl). PEl is the DF or primary PE and is the only PE in the Ethernet segment that will perform this type of advertisement. Each of the other PEs records these MAC addresses Ml-Mm along with the label for PEl (in this case PE1-EVPN_LBL), which is recorded along with the alias labels of the other PEs in the Ethernet Segment. Thus, Figures 4D and 4E would represent the state of the network before a failure of the primary PEl that would trigger the processes described above that select a new DF or primary PE and where the new DF or primary PE advertises MAC/IP routes that were previously learned to effect the changeover to using the new DF or primary PE. [00053] Figure 5 is a diagram of one embodiment of an EVPN where a primary PE or DF has failed. As discussed above, in reference to the example network of Figure 1, Figure 5 shows the failure of the primary PE or DF (i.e., PEl) in this EVPN and as a result the Ethernet segment is reduced to including PE2 and PE3, while PE4 remains a remote PE in this topology. In the example PEl fails, although other similar failures could occur, such as link failures that would similarly require the election of a new DF or primary PE.

[00054] Figures 6A and 6B are diagrams that show the state of the set of PEs in the

Ethernet segment connected with the multi-homed CE device after failure of the primary PE or DF. As illustrated above, PE2 has become the new elected DF and primary PE. In some embodiments, such as signaled Ethernet implementations a link aggregation control protocol (LACP) for the Ethernet Segment which is also a link aggregation group (LAG) status can be utilized to identify the primary PE or elected DF. This would occur when PEl loses connection to Ethernet Segment or the entire PEl fails. PE2 starts owning all the MAC/IP routes advertised by PEl immediately, as if PE2 had learnt these routes on its own from the Ethernet Segment 'ES 100'. PE2 replaces the EVPN label advertised by PEl by its own alias labels, for which the forwarding path is already set and ready to go. This change in the labeling is shown in Figure 6A where PE2 has performed this replacement.

[00055] Figure 6B illustrates the state of PE4, which is the remote PE in this example, after PE2 starts advertising the MAC/IP routes that it has changed over to its ownership. In this way PE4 determines that the new elected DF or primary PE is PE2 in this example as soon as PE4 receives the first MAC/IP route advertisement from PE2. This in turn helps minimize the loss of data traffic destined for these MAC/IP addresses that were previously destined to be forwarded to PEl which is down. With this process, traffic will converge faster when the primary node (PEl in this example) fails or loses connection to an Ethernet Segment in an EVPN.

[00056] Figure 7A illustrates connectivity between network devices (NDs) within an exemplary network, as well as three exemplary implementations of the NDs, according to some embodiments of the invention. Figure 7A shows NDs 700A-H, and their connectivity by way of lines between A-B, B-C, C-D, D-E, E-F, F-G, and A-G, as well as between H and each of A, C, D, and G. These NDs are physical devices, and the connectivity between these NDs can be wireless or wired (often referred to as a link). An additional line extending from NDs 700A, E, and F illustrates that these NDs act as ingress and egress points for the network (and thus, these NDs are sometimes referred to as edge NDs; while the other NDs may be called core NDs).

[00057] Two of the exemplary ND implementations in Figure 7 A are: 1) a special- purpose network device 702 that uses custom application-specific integrated-circuits (ASICs) and a proprietary operating system (OS); and 2) a general purpose network device 704 that uses common off-the-shelf (COTS) processors and a standard OS.

[00058] The special-purpose network device 702 includes networking hardware 710 comprising compute resource(s) 712 (which typically include a set of one or more processors), forwarding resource(s) 714 (which typically include one or more ASICs and/or network processors), and physical network interfaces (NIs) 716 (sometimes called physical ports), as well as non-transitory machine readable storage media 718 having stored therein networking software 720. A physical NI is hardware in a ND through which a network connection (e.g., wirelessly through a wireless network interface controller (WNIC) or through plugging in a cable to a physical port connected to a network interface controller (NIC)) is made, such as those shown by the connectivity between NDs 700A-H. During operation, the networking software 720 may be executed by the networking hardware 710 to instantiate a set of one or more networking software instance(s) 722. Each of the networking software instance(s) 722, and that part of the networking hardware 710 that executes that network software instance (be it hardware dedicated to that networking software instance and/or time slices of hardware temporally shared by that networking software instance with others of the networking software instance(s) 722), form a separate virtual network element 730A-R. Each of the virtual network element(s) (VNEs) 730A-R includes a control communication and configuration module 732A- R (sometimes referred to as a local control module or control communication module) and forwarding table(s) 734A-R, such that a given virtual network element (e.g., 730A) includes the control communication and configuration module (e.g., 732A), a set of one or more forwarding table(s) (e.g., 734A), and that portion of the networking hardware 710 that executes the virtual network element (e.g., 73 OA).

[00059] Software 720 can include code which when executed by networking hardware

710, causes networking hardware 710 to perform operations of one or more embodiments of the present invention as part networking software instances 722. In the embodiments presented herein, the process for implementing the improved convergence times in cases of DF or primary PE failure can be implemented via a DF election module 764.

[00060] The special-purpose network device 702 is often physically and/or logically considered to include: 1) a ND control plane 724 (sometimes referred to as a control plane) comprising the compute resource(s) 712 that execute the control communication and

configuration module(s) 732A-R; and 2) a ND forwarding plane 726 (sometimes referred to as a forwarding plane, a data plane, or a media plane) comprising the forwarding resource(s) 714 that utilize the forwarding table(s) 734A-R and the physical NIs 716. By way of example, where the ND is a router (or is implementing routing functionality), the ND control plane 724 (the compute resource(s) 712 executing the control communication and configuration module(s) 732A-R) is typically responsible for participating in controlling how data (e.g., packets) is to be routed (e.g., the next hop for the data and the outgoing physical NI for that data) and storing that routing information in the forwarding table(s) 734A-R, and the ND forwarding plane 726 is responsible for receiving that data on the physical NIs 716 and forwarding that data out the appropriate ones of the physical NIs 716 based on the forwarding table(s) 734A-R.

[00061] Figure 7B illustrates an exemplary way to implement the special-purpose network device 702 according to some embodiments of the invention. Figure 7B shows a special-purpose network device including cards 738 (typically hot pluggable). While in some embodiments the cards 738 are of two types (one or more that operate as the ND forwarding plane 726 (sometimes called line cards), and one or more that operate to implement the ND control plane 724 (sometimes called control cards)), alternative embodiments may combine functionality onto a single card and/or include additional card types (e.g., one additional type of card is called a service card, resource card, or multi-application card). A service card can provide specialized processing (e.g., Layer 4 to Layer 7 services (e.g., firewall, Internet Protocol Security (IPsec), Secure Sockets Layer (SSL) / Transport Layer Security (TLS), Intrusion Detection System (IDS), peer-to-peer (P2P), Voice over IP (VoIP) Session Border Controller, Mobile Wireless Gateways (Gateway General Packet Radio Service (GPRS) Support Node (GGSN), Evolved Packet Core (EPC) Gateway)). By way of example, a service card may be used to terminate IPsec tunnels and execute the attendant authentication and encryption algorithms. These cards are coupled together through one or more interconnect mechanisms illustrated as backplane 736 (e.g., a first full mesh coupling the line cards and a second full mesh coupling all of the cards).

[00062] Returning to Figure 7A, the general purpose network device 704 includes hardware 740 comprising a set of one or more processor(s) 742 (which are often COTS processors) and network interface controller(s) 744 (NICs; also known as network interface cards) (which include physical NIs 746), as well as non-transitory machine readable storage media 748 having stored therein software 750. During operation, the processor(s) 742 execute the software 750 to instantiate one or more sets of one or more applications 764A-R. While one embodiment does not implement virtualization, alternative embodiments may use different forms of virtualization - represented by a virtualization layer 754 and software containers 762A- R. For example, one such alternative embodiment implements operating system-level virtualization, in which case the virtualization layer 754 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple software containers 762A-R that may each be used to execute one of the sets of applications 764A-R. In this embodiment, the multiple software containers 762A-R (also called virtualization engines, virtual private servers, or jails) are each a user space instance (typically a virtual memory space); these user space instances are separate from each other and separate from the kernel space in which the operating system is run; the set of applications running in a given user space, unless explicitly allowed, cannot access the memory of the other processes. Another such alternative embodiment implements full virtualization, in which case: 1) the virtualization layer 754 represents a hypervisor (sometimes referred to as a virtual machine monitor (VMM)) or a hypervisor executing on top of a host operating system; and 2) the software containers 762A-R each represent a tightly isolated form of software container called a virtual machine that is run by the hypervisor and may include a guest operating system. A virtual machine is a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine; and applications generally do not know they are running on a virtual machine as opposed to running on a "bare metal" host electronic device, though some systems provide para-virtualization which allows an operating system or application to be aware of the presence of virtualization for optimization purposes.

[00063] The instantiation of the one or more sets of one or more applications 764A-R, as well as the virtualization layer 754 and software containers 762A-R if implemented, are collectively referred to as software instance(s) 752. Each set of applications 764A-R, corresponding software container 762A-R if implemented, and that part of the hardware 740 that executes them (be it hardware dedicated to that execution and/or time slices of hardware temporally shared by software containers 762A-R), forms a separate virtual network element(s) 760A-R.

[00064] The virtual network element(s) 760A-R perform similar functionality to the virtual network element(s) 730A-R - e.g., similar to the control communication and

configuration module(s) 732A and forwarding table(s) 734A (this virtualization of the hardware 740 is sometimes referred to as network function virtualization (NFV)). Thus, NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which could be located in Data centers, NDs, and customer premise equipment (CPE). However, different embodiments of the invention may implement one or more of the software container(s) 762A-R differently. For example, while embodiments of the invention are illustrated with each software container 762A-R

corresponding to one VNE 760A-R, alternative embodiments may implement this

correspondence at a finer level granularity (e.g., line card virtual machines virtualize line cards, control card virtual machine virtualize control cards, etc.); it should be understood that the techniques described herein with reference to a correspondence of software containers 762A-R to VNEs also apply to embodiments where such a finer level of granularity is used.

[00065] In certain embodiments, the virtualization layer 754 includes a virtual switch that provides similar forwarding services as a physical Ethernet switch. Specifically, this virtual switch forwards traffic between software containers 762A-R and the NIC(s) 744, as well as optionally between the software containers 762A-R; in addition, this virtual switch may enforce network isolation between the VNEs 760A-R that by policy are not permitted to communicate with each other (e.g., by honoring virtual local area networks (VLANs)).

[00066] Software 750 can include code which when executed by processor(s) 742, cause processor(s) 742 to perform operations of one or more embodiments of the present invention as part software containers 762A-R. This can include the code for the DF election module 764A-R that may be executed by the virtual network elements 760A-R.

[00067] The third exemplary ND implementation in Figure 7A is a hybrid network device

706, which includes both custom ASICs/proprietary OS and COTS processors/standard OS in a single ND or a single card within an ND. In certain embodiments of such a hybrid network device, a platform VM (i.e., a VM that that implements the functionality of the special-purpose network device 702) could provide for para- virtualization to the networking hardware present in the hybrid network device 706.

[00068] Regardless of the above exemplary implementations of an ND, when a single one of multiple VNEs implemented by an ND is being considered (e.g., only one of the VNEs is part of a given virtual network) or where only a single VNE is currently being implemented by an ND, the shortened term network element (NE) is sometimes used to refer to that VNE. Also in all of the above exemplary implementations, each of the VNEs (e.g., VNE(s) 730A-R, VNEs 760A-R, and those in the hybrid network device 706) receives data on the physical NIs (e.g., 716, 746) and forwards that data out the appropriate ones of the physical NIs (e.g., 716, 746). For example, a VNE implementing IP router functionality forwards IP packets on the basis of some of the IP header information in the IP packet; where IP header information includes source IP address, destination IP address, source port, destination port (where "source port" and "destination port" refer herein to protocol ports, as opposed to physical ports of a ND), transport protocol (e.g., user datagram protocol (UDP), Transmission Control Protocol (TCP), and differentiated services (DSCP) values.

[00069] Figure 7C illustrates various exemplary ways in which VNEs may be coupled according to some embodiments of the invention. Figure 7C shows VNEs 770A.1-770A.P (and optionally VNEs 770A.Q-770A.R) implemented in ND 700A and VNE 770H.1 in ND 700H. In Figure 7C, VNEs 770A.1-P are separate from each other in the sense that they can receive packets from outside ND 700A and forward packets outside of ND 700A; VNE 770A.1 is coupled with VNE 770H.1, and thus they communicate packets between their respective NDs; VNE 770A.2-770A.3 may optionally forward packets between themselves without forwarding them outside of the ND 700A; and VNE 770A.P may optionally be the first in a chain of VNEs that includes VNE 770A.Q followed by VNE 770A.R (this is sometimes referred to as dynamic service chaining, where each of the VNEs in the series of VNEs provides a different service - e.g., one or more layer 4-7 network services). While Figure 7C illustrates various exemplary relationships between the VNEs, alternative embodiments may support other relationships (e.g., more/fewer VNEs, more/fewer dynamic service chains, multiple different dynamic service chains with some common VNEs and some different VNEs).

[00070] The NDs of Figure 7A, for example, may form part of the Internet or a private network; and other electronic devices (not shown; such as end user devices including

workstations, laptops, netbooks, tablets, palm tops, mobile phones, smartphones, phablets, multimedia phones, Voice Over Internet Protocol (VOIP) phones, terminals, portable media players, GPS units, wearable devices, gaming systems, set-top boxes, Internet enabled household appliances) may be coupled to the network (directly or through other networks such as access networks) to communicate over the network (e.g., the Internet or virtual private networks (VPNs) overlaid on (e.g., tunneled through) the Internet) with each other (directly or through servers) and/or access content and/or services. Such content and/or services are typically provided by one or more servers (not shown) belonging to a service/content provider or one or more end user devices (not shown) participating in a peer-to-peer (P2P) service, and may include, for example, public webpages (e.g., free content, store fronts, search services), private webpages (e.g., username/password accessed webpages providing email services), and/or corporate networks over VPNs. For instance, end user devices may be coupled (e.g., through customer premise equipment coupled to an access network (wired or wirelessly)) to edge NDs, which are coupled (e.g., through one or more core NDs) to other edge NDs, which are coupled to electronic devices acting as servers. However, through compute and storage virtualization, one or more of the electronic devices operating as the NDs in Figure 7A may also host one or more such servers (e.g., in the case of the general purpose network device 704, one or more of the software containers 762A-R may operate as servers; the same would be true for the hybrid network device 706; in the case of the special-purpose network device 702, one or more such servers could also be run on a virtualization layer executed by the compute resource(s) 712); in which case the servers are said to be co-located with the VNEs of that ND.

[00071] A virtual network is a logical abstraction of a physical network (such as that in

Figure 7A) that provides network services (e.g., L2 and/or L3 services). A virtual network can be implemented as an overlay network (sometimes referred to as a network virtualization overlay) that provides network services (e.g., layer 2 (L2, data link layer) and/or layer 3 (L3, network layer) services) over an underlay network (e.g., an L3 network, such as an Internet Protocol (IP) network that uses tunnels (e.g., generic routing encapsulation (GRE), layer 2 tunneling protocol (L2TP), IPSec) to create the overlay network).

[00072] A network virtualization edge (NVE) sits at the edge of the underlay network and participates in implementing the network virtualization; the network-facing side of the NVE uses the underlay network to tunnel frames to and from other NVEs; the outward-facing side of the NVE sends and receives data to and from systems outside the network. A virtual network instance (VNI) is a specific instance of a virtual network on a NVE (e.g., a NE/VNE on an ND, a part of a NE/VNE on a ND where that NE/VNE is divided into multiple VNEs through emulation); one or more VNIs can be instantiated on an NVE (e.g., as different VNEs on an ND). A virtual access point (VAP) is a logical connection point on the NVE for connecting external systems to a virtual network; a VAP can be physical or virtual ports identified through logical interface identifiers (e.g., a VLAN ID).

[00073] Examples of network services include: 1) an Ethernet LAN emulation service (an

Ethernet-based multipoint service similar to an Internet Engineering Task Force (IETF)

Multiprotocol Label Switching (MPLS) or Ethernet VPN (EVPN) service) in which external systems are interconnected across the network by a LAN environment over the underlay network (e.g., an NVE provides separate L2 VNIs (virtual switching instances) for different such virtual networks, and L3 (e.g., IP/MPLS) tunneling encapsulation across the underlay network); and 2) a virtualized IP forwarding service (similar to IETF IP VPN (e.g., Border Gateway Protocol (BGP)/MPLS IP VPN) from a service definition perspective) in which external systems are interconnected across the network by an L3 environment over the underlay network (e.g., an NVE provides separate L3 VNIs (forwarding and routing instances) for different such virtual networks, and L3 (e.g., IP/MPLS) tunneling encapsulation across the underlay network)). Network services may also include quality of service capabilities (e.g., traffic classification marking, traffic conditioning and scheduling), security capabilities (e.g., filters to protect customer premises from network - originated attacks, to avoid malformed route announcements), and management capabilities (e.g., full detection and processing).

[00074] Fig. 7D illustrates a network with a single network element on each of the NDs of

Figure 7A, and within this straight forward approach contrasts a traditional distributed approach (commonly used by traditional routers) with a centralized approach for maintaining reachability and forwarding information (also called network control), according to some embodiments of the invention. Specifically, Figure 7D illustrates network elements (NEs) 770A-H with the same connectivity as the NDs 700A-H of Figure 7A.

[00075] Figure 7D illustrates that the distributed approach 772 distributes responsibility for generating the reachability and forwarding information across the NEs 770A-H; in other words, the process of neighbor discovery and topology discovery is distributed.

[00076] For example, where the special-purpose network device 702 is used, the control communication and configuration module(s) 732A-R of the ND control plane 724 typically include a reachability and forwarding information module to implement one or more routing protocols (e.g., an exterior gateway protocol such as Border Gateway Protocol (BGP), Interior Gateway Protocol(s) (IGP) (e.g., Open Shortest Path First (OSPF), Intermediate System to Intermediate System (IS -IS), Routing Information Protocol (RIP)), Label Distribution Protocol (LDP), Resource Reservation Protocol (RSVP), as well as RSVP-Traffic Engineering (TE): Extensions to RSVP for LSP Tunnels, Generalized Multi-Protocol Label Switching (GMPLS) Signaling RSVP-TE that communicate with other NEs to exchange routes, and then selects those routes based on one or more routing metrics. Thus, the NEs 770A-H (e.g., the compute resource(s) 712 executing the control communication and configuration module(s) 732A-R) perform their responsibility for participating in controlling how data (e.g., packets) is to be routed (e.g., the next hop for the data and the outgoing physical NI for that data) by

distributively determining the reachability within the network and calculating their respective forwarding information. Routes and adjacencies are stored in one or more routing structures (e.g., Routing Information Base (RIB), Label Information Base (LIB), one or more adjacency structures) on the ND control plane 724. The ND control plane 724 programs the ND forwarding plane 726 with information (e.g., adjacency and route information) based on the routing structure(s). For example, the ND control plane 724 programs the adjacency and route information into one or more forwarding table(s) 734A-R (e.g., Forwarding Information Base (FIB), Label Forwarding Information Base (LFIB), and one or more adjacency structures) on the ND forwarding plane 726. For layer 2 forwarding, the ND can store one or more bridging tables that are used to forward data based on the layer 2 information in that data. While the above example uses the special-purpose network device 702, the same distributed approach 772 can be implemented on the general purpose network device 704 and the hybrid network device 706.

[00077] Figure 7D illustrates that a centralized approach 774 (also known as software defined networking (SDN)) that decouples the system that makes decisions about where traffic is sent from the underlying systems that forwards traffic to the selected destination. The illustrated centralized approach 774 has the responsibility for the generation of reachability and forwarding information in a centralized control plane 776 (sometimes referred to as a SDN control module, controller, network controller, OpenFlow controller, SDN controller, control plane node, network virtualization authority, or management control entity), and thus the process of neighbor discovery and topology discovery is centralized. The centralized control plane 776 has a south bound interface 782 with a data plane 780 (sometime referred to the infrastructure layer, network forwarding plane, or forwarding plane (which should not be confused with a ND forwarding plane)) that includes the NEs 770A-H (sometimes referred to as switches, forwarding elements, data plane elements, or nodes). The centralized control plane 776 includes a network controller 778, which includes a centralized reachability and forwarding information module 779 that determines the reachability within the network and distributes the forwarding information to the NEs 770A-H of the data plane 780 over the south bound interface 782 (which may use the OpenFlow protocol). Thus, the network intelligence is centralized in the centralized control plane 776 executing on electronic devices that are typically separate from the NDs.

[00078] For example, where the special-purpose network device 702 is used in the data plane 780, each of the control communication and configuration module(s) 732A-R of the ND control plane 724 typically include a control agent that provides the VNE side of the south bound interface 782. In this case, the ND control plane 724 (the compute resource(s) 712 executing the control communication and configuration module(s) 732A-R) performs its responsibility for participating in controlling how data (e.g., packets) is to be routed (e.g., the next hop for the data and the outgoing physical NI for that data) through the control agent communicating with the centralized control plane 776 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 779 (it should be understood that in some embodiments of the invention, the control communication and configuration module(s) 732A-R, in addition to communicating with the centralized control plane 776, may also play some role in determining reachability and/or calculating forwarding information - albeit less so than in the case of a distributed approach; such embodiments are generally considered to fall under the centralized approach 774, but may also be considered a hybrid approach).

[00079] In some embodiments, in the centralized approach the process of the

embodiments may be implemented partially or wholly in a DF election module 781 that is executed by the centralized control plane 776 or in the application layer 786.

[00080] While the above example uses the special-purpose network device 702, the same centralized approach 774 can be implemented with the general purpose network device 704 (e.g., each of the VNE 760A-R performs its responsibility for controlling how data (e.g., packets) is to be routed (e.g., the next hop for the data and the outgoing physical NI for that data) by communicating with the centralized control plane 776 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 779; it should be understood that in some embodiments of the invention, the VNEs 760A-R, in addition to communicating with the centralized control plane 776, may also play some role in determining reachability and/or calculating forwarding information - albeit less so than in the case of a distributed approach) and the hybrid network device 706. In fact, the use of SDN techniques can enhance the NFV techniques typically used in the general purpose network device 704 or hybrid network device 706 implementations as NFV is able to support SDN by providing an infrastructure upon which the SDN software can be run, and NFV and SDN both aim to make use of commodity server hardware and physical switches.

[00081] Figure 7D also shows that the centralized control plane 776 has a north bound interface 784 to an application layer 786, in which resides application(s) 788. The centralized control plane 776 has the ability to form virtual networks 792 (sometimes referred to as a logical forwarding plane, network services, or overlay networks (with the NEs 770A-H of the data plane 780 being the underlay network)) for the application(s) 788. Thus, the centralized control plane 776 maintains a global view of all NDs and configured NEs/VNEs, and it maps the virtual networks to the underlying NDs efficiently (including maintaining these mappings as the physical network changes either through hardware (ND, link, or ND component) failure, addition, or removal).

[00082] While Figure 7D shows the distributed approach 772 separate from the centralized approach 774, the effort of network control may be distributed differently or the two combined in certain embodiments of the invention. For example: 1) embodiments may generally use the centralized approach (SDN) 774, but have certain functions delegated to the NEs (e.g., the distributed approach may be used to implement one or more of fault monitoring, performance monitoring, protection switching, and primitives for neighbor and/or topology discovery); or 2) embodiments of the invention may perform neighbor discovery and topology discovery via both the centralized control plane and the distributed protocols, and the results compared to raise exceptions where they do not agree. Such embodiments are generally considered to fall under the centralized approach 774, but may also be considered a hybrid approach.

[00083] While Figure 7D illustrates the simple case where each of the NDs 700A-H implements a single NE 770A-H, it should be understood that the network control approaches described with reference to Figure 7D also work for networks where one or more of the NDs 700A-H implement multiple VNEs (e.g., VNEs 730A-R, VNEs 760A-R, those in the hybrid network device 706). Alternatively or in addition, the network controller 778 may also emulate the implementation of multiple VNEs in a single ND. Specifically, instead of (or in addition to) implementing multiple VNEs in a single ND, the network controller 778 may present the implementation of a VNE/NE in a single ND as multiple VNEs in the virtual networks 792 (all in the same one of the virtual network(s) 792, each in different ones of the virtual network(s) 792, or some combination). For example, the network controller 778 may cause an ND to implement a single VNE (a NE) in the underlay network, and then logically divide up the resources of that NE within the centralized control plane 776 to present different VNEs in the virtual network(s) 792 (where these different VNEs in the overlay networks are sharing the resources of the single VNE/NE implementation on the ND in the underlay network).

[00084] On the other hand, Figures 7E and 7F respectively illustrate exemplary abstractions of NEs and VNEs that the network controller 778 may present as part of different ones of the virtual networks 792. Figure 7E illustrates the simple case of where each of the NDs 700A-H implements a single NE 770A-H (see Figure 7D), but the centralized control plane 776 has abstracted multiple of the NEs in different NDs (the NEs 770A-C and G-H) into (to represent) a single NE 7701 in one of the virtual network(s) 792 of Figure 7D, according to some embodiments of the invention. Figure 7E shows that in this virtual network, the NE 7701 is coupled to NE 770D and 770F, which are both still coupled to NE 770E.

[00085] Figure 7F illustrates a case where multiple VNEs (VNE 770A.1 and VNE

770H.1) are implemented on different NDs (ND 700A and ND 700H) and are coupled to each other, and where the centralized control plane 776 has abstracted these multiple VNEs such that they appear as a single VNE 770T within one of the virtual networks 792 of Figure 7D, according to some embodiments of the invention. Thus, the abstraction of a NE or VNE can span multiple NDs.

[00086] While some embodiments of the invention implement the centralized control plane 776 as a single entity (e.g., a single instance of software running on a single electronic device), alternative embodiments may spread the functionality across multiple entities for redundancy and/or scalability purposes (e.g., multiple instances of software running on different electronic devices).

[00087] Similar to the network device implementations, the electronic device(s) running the centralized control plane 776, and thus the network controller 778 including the centralized reachability and forwarding information module 779, may be implemented a variety of ways (e.g., a special purpose device, a general-purpose (e.g., COTS) device, or hybrid device). These electronic device(s) would similarly include compute resource(s), a set or one or more physical NICs, and a non-transitory machine-readable storage medium having stored thereon the centralized control plane software. For instance, Figure 8 illustrates, a general purpose control plane device 804 including hardware 840 comprising a set of one or more processor(s) 842 (which are often COTS processors) and network interface controller(s) 844 (NICs; also known as network interface cards) (which include physical NIs 846), as well as non-transitory machine readable storage media 848 having stored therein centralized control plane (CCP) software 850.

[00088] In embodiments that use compute virtualization, the processor(s) 842 typically execute software to instantiate a virtualization layer 854 and software container(s) 862A-R (e.g., with operating system-level virtualization, the virtualization layer 854 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple software containers 862A-R (representing separate user space instances and also called virtualization engines, virtual private servers, or jails) that may each be used to execute a set of one or more applications; with full virtualization, the virtualization layer 854 represents a hypervisor (sometimes referred to as a virtual machine monitor (VMM)) or a hypervisor executing on top of a host operating system, and the software containers 862A-R each represent a tightly isolated form of software container called a virtual machine that is run by the hypervisor and may include a guest operating system; with para-virtualization, an operating system or application running with a virtual machine may be aware of the presence of virtualization for optimization purposes). Again, in embodiments where compute virtualization is used, during operation an instance of the CCP software 850 (illustrated as CCP instance 876A) is executed within the software container 862A on the virtualization layer 854. In embodiments where compute virtualization is not used, the CCP instance 876A on top of a host operating system is executed on the "bare metal" general purpose control plane device 804. The instantiation of the CCP instance 876A, as well as the virtualization layer 854 and software containers 862A-R if implemented, are collectively referred to as software instance(s) 852.

[00089] In some embodiments, the CCP instance 876A includes a network controller instance 878. The network controller instance 878 includes a centralized reachability and forwarding information module instance 879 (which is a middleware layer providing the context of the network controller 778 to the operating system and communicating with the various NEs), and an CCP application layer 880 (sometimes referred to as an application layer) over the middleware layer (providing the intelligence required for various network operations such as protocols, network situational awareness, and user - interfaces). At a more abstract level, this CCP application layer 880 within the centralized control plane 776 works with virtual network view(s) (logical view(s) of the network) and the middleware layer provides the conversion from the virtual networks to the physical view.

[00090] The centralized control plane 776 transmits relevant messages to the data plane

780 based on CCP application layer 880 calculations and middleware layer mapping for each flow. A flow may be defined as a set of packets whose headers match a given pattern of bits; in this sense, traditional IP forwarding is also flow-based forwarding where the flows are defined by the destination IP address for example; however, in other implementations, the given pattern of bits used for a flow definition may include more fields (e.g., 10 or more) in the packet headers. Different NDs/NEs/VNEs of the data plane 780 may receive different messages, and thus different forwarding information. The data plane 780 processes these messages and programs the appropriate flow information and corresponding actions in the forwarding tables (sometime referred to as flow tables) of the appropriate NE/VNEs, and then the NEs/VNEs map incoming packets to flows represented in the forwarding tables and forward packets based on the matches in the forwarding tables.

[00091] In some embodiments, the processes of the embodiments in this centralized approach can be implemented by a DF election module 881 in the network controller instance or similar component of the control plane device 804.

[00092] Standards such as OpenFlow define the protocols used for the messages, as well as a model for processing the packets. The model for processing packets includes header parsing, packet classification, and making forwarding decisions. Header parsing describes how to interpret a packet based upon a well-known set of protocols. Some protocol fields are used to build a match structure (or key) that will be used in packet classification (e.g., a first key field could be a source media access control (MAC) address, and a second key field could be a destination MAC address).

[00093] Packet classification involves executing a lookup in memory to classify the packet by determining which entry (also referred to as a forwarding table entry or flow entry) in the forwarding tables best matches the packet based upon the match structure, or key, of the forwarding table entries. It is possible that many flows represented in the forwarding table entries can correspond/match to a packet; in this case the system is typically configured to determine one forwarding table entry from the many according to a defined scheme (e.g., selecting a first forwarding table entry that is matched). Forwarding table entries include both a specific set of match criteria (a set of values or wildcards, or an indication of what portions of a packet should be compared to a particular value/values/wildcards, as defined by the matching capabilities - for specific fields in the packet header, or for some other packet content), and a set of one or more actions for the data plane to take on receiving a matching packet. For example, an action may be to push a header onto the packet, for the packet using a particular port, flood the packet, or simply drop the packet. Thus, a forwarding table entry for IPv4/IPv6 packets with a particular transmission control protocol (TCP) destination port could contain an action specifying that these packets should be dropped. [00094] Making forwarding decisions and performing actions occurs, based upon the forwarding table entry identified during packet classification, by executing the set of actions identified in the matched forwarding table entry on the packet.

[00095] However, when an unknown packet (for example, a "missed packet" or a "match- miss" as used in OpenFlow parlance) arrives at the data plane 780, the packet (or a subset of the packet header and content) is typically forwarded to the centralized control plane 776. The centralized control plane 776 will then program forwarding table entries into the data plane 780 to accommodate packets belonging to the flow of the unknown packet. Once a specific forwarding table entry has been programmed into the data plane 780 by the centralized control plane 776, the next packet with matching credentials will match that forwarding table entry and take the set of actions associated with that matched entry.

[00096] A network interface (NI) may be physical or virtual; and in the context of IP, an interface address is an IP address assigned to a NI, be it a physical NI or virtual NI. A virtual NI may be associated with a physical NI, with another virtual interface, or stand on its own (e.g., a loopback interface, a point-to-point protocol interface). A NI (physical or virtual) may be numbered (a NI with an IP address) or unnumbered (a NI without an IP address). A loopback interface (and its loopback address) is a specific type of virtual NI (and IP address) of a

NE/VNE (physical or virtual) often used for management purposes; where such an IP address is referred to as the nodal loopback address. The IP address(es) assigned to the NI(s) of a ND are referred to as IP addresses of that ND; at a more granular level, the IP address(es) assigned to NI(s) assigned to a NE/VNE implemented on a ND can be referred to as IP addresses of that NE/VNE.

[00097] Some NDs provide support for implementing VPNs (Virtual Private Networks)

(e.g., Layer 2 VPNs and/or Layer 3 VPNs). For example, the NDs where a provider's network and a customer's network are coupled are respectively referred to as PEs (Provider Edge) and CEs (Customer Edge). In a Layer 2 VPN, forwarding typically is performed on the CE(s) on either end of the VPN and traffic is sent across the network (e.g., through one or more PEs coupled by other NDs). Layer 2 circuits are configured between the CEs and PEs (e.g., an Ethernet port, an ATM permanent virtual circuit (PVC), a Frame Relay PVC). In a Layer 3 VPN, routing typically is performed by the PEs. By way of example, an edge ND that supports multiple VNEs may be deployed as a PE; and a VNE may be configured with a VPN protocol, and thus that VNE is referred as a VPN VNE.

[00098] Some NDs provide support for VPLS (Virtual Private LAN Service). For example, in a VPLS network, end user devices access content/services provided through the VPLS network by coupling to CEs, which are coupled through PEs coupled by other NDs. VPLS networks can be used for implementing triple play network applications (e.g., data applications (e.g., high-speed Internet access), video applications (e.g., television service such as IPTV (Internet Protocol Television), VoD (Video-on-Demand) service), and voice applications (e.g., VoIP (Voice over Internet Protocol) service)), VPN services, etc. VPLS is a type of layer 2 VPN that can be used for multi-point connectivity. VPLS networks also allow end use devices that are coupled with CEs at separate geographical locations to communicate with each other across a Wide Area Network (WAN) as if they were directly attached to each other in a Local Area Network (LAN) (referred to as an emulated LAN).

[00099] In VPLS networks, each CE typically attaches, possibly through an access network (wired and/or wireless), to a bridge module of a PE via an attachment circuit (e.g., a virtual link or connection between the CE and the PE). The bridge module of the PE attaches to an emulated LAN through an emulated LAN interface. Each bridge module acts as a "Virtual Switch Instance" (VSI) by maintaining a forwarding table that maps MAC addresses to pseudowires and attachment circuits. PEs forward frames (received from CEs) to destinations (e.g., other CEs, other PEs) based on the MAC destination address field included in those frames.

[000100] Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of transactions on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of transactions leading to a desired result. The transactions are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

[000101] It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

[000102] The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method transactions. The required structure for a variety of these systems will appear from the description above. In addition, embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of embodiments of the invention as described herein.

[000103] In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

[000104] Throughout the description, embodiments of the present invention have been presented through flow diagrams. It will be appreciated that the order of transactions and transactions described in these flow diagrams are only intended for illustrative purposes and not intended as a limitation of the present invention. One having ordinary skill in the art would recognize that variations can be made to the flow diagrams without departing from the broader spirit and scope of the invention as set forth in the following claims.

Claims

CLAIMS What is claimed is:

1. A method implemented by a network device, the method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the network device functions as the backup PE in the Ethernet segment, the method comprising:

detecting a failure of the primary PE via an indication from the CE; changing known media access control (MAC) / internet protocol (IP) routes

previously reachable via the primary PE to be reachable via alias of the backup PE; and

sending MAC/IP route advertisements for the changed MAC/IP routes with

incremented sequence numbers.

2. The method of claim 1, further comprising:

learning the known MAC/IP routes previously reachable via the primary PE from MAC/IP route advertisements of the primary PE.

3. The method of claim 1, wherein the indication from the CE is a signaled Ethernet virtual private network (EVPN) link.

4. The method of claim 1, wherein the incremented sequence numbers are greater than the sequence numbers of MAC/IP route advertisements from the primary PE.

5. The method of claim 1, wherein changing the known MAC/IP routes previously

reachable via the primary PE to be reachable via alias of the backup PE comprises:

overwriting an Ethernet virtual private network (EVPN) label of the primary PE with an alias label of the backup PE.

6. A network device configured to execute a method for expediting convergence to a

backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the network device functions as the backup PE in the Ethernet segment, the network device comprising:

a non-transitory machine-readable storage medium to store a designated forwarder (DF) manager; and

a processor coupled to the non-transitory machine-readable storage medium, the processor configured to execute the DF manager, the DF manager configured to detect a failure of the primary PE via an indication from the CE, to change known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and to send MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

7. The network device of claim 6, wherein the DF manager is further configured to learn the known MAC/IP routes previously reachable via the primary PE from MAC/IP route advertisements of the primary PE.

8. The network device of claim 6, wherein the indication from the CE is a signaled Ethernet virtual private network (EVPN) link.

9. The network device of claim 6, wherein the incremented sequence numbers are greater than the sequence numbers of MAC/IP route advertisements from the primary PE.

10. The network device of claim 6, wherein changing the known MAC/IP routes previously reachable via the primary PE to be reachable via alias of the backup PE comprises overwriting an Ethernet virtual private network (EVPN) label of the primary PE with an alias label of the backup PE.

11. A computing device in communication with a network device in a network with a

plurality of network devices, the computing device to execute a plurality of virtual machines for implementing network function virtualization (NFV), wherein a virtual machine from the plurality of virtual machines is configured to implement a method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the computing device functions as the backup

PE in the Ethernet segment, the computing device comprising:

a non-transitory machine-readable storage medium to store a designating forwarder (DF) manager; and

a processor coupled to the non-transitory machine-readable storage medium, the processor configured to execute the virtual machine, the virtual machine to execute the DF manager, the DF manager to detect a failure of the primary PE via an indication from the CE, to change known media access control (MAC) / internet protocol (IP) routes previously reachable via the primary PE to be reachable via alias of the backup PE, and to send MAC/IP route advertisements for the changed MAC/IP routes with incremented sequence numbers.

12. The computing device of claim 11, wherein the DF manager is further configured to learn the known MAC/IP routes previously reachable via the primary PE from MAC/IP route advertisements of the primary PE.

13. The computing device of claim 11, wherein the indication from the CE is a signaled Ethernet virtual private network (EVPN) link.

14. The computing device of claim 11, wherein the incremented sequence numbers are greater than the sequence numbers of MAC/IP route advertisements from the primary PE.

15. The computing device of claim 11, wherein changing the known MAC/IP routes

previously reachable via the primary PE to be reachable via alias of the backup PE includes overwriting an Ethernet virtual private network (EVPN) label of the primary PE with an alias label of the backup PE.

16. A control plane device configured to implement a control plane of a software defined networking (SDN) network, the SDN network including a plurality of network devices, wherein the control plane device is configured to implement a method for expediting convergence to a backup provider edge (PE) in response to a failure of a primary PE in a single-active redundancy topology of an Ethernet Segment having a multi-homed customer edge (CE), where the control plane device functions as the backup PE in the

Ethernet segment, the control plane device comprising:

17. The control plane device of claim 16, wherein the DF manager is further configured to learn the known MAC/IP routes previously reachable via the primary PE from MAC/IP route advertisements of the primary PE.

18. The control plane device of claim 16, wherein the indication from the CE is a signaled Ethernet virtual private network (EVPN) link.

19. The control plane device of claim 16, wherein the incremented sequence numbers are greater than the sequence numbers of MAC/IP route advertisements from the primary PE.

20. The control plane device of claim 16, wherein changing the known MAC/IP routes

previously reachable via the primary PE to be reachable via alias of the backup PE comprises overwriting an Ethernet virtual private network (EVPN) label of the primary PE with an alias label of the backup PE.