WO2025027375A1

WO2025027375A1 - Methods and systems for a network routing update based on a conditional loopback interface

Info

Publication number: WO2025027375A1
Application number: PCT/IB2023/057807
Authority: WO
Inventors: Davide CARREGA
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-08-01
Filing date: 2023-08-01
Publication date: 2025-02-06
Anticipated expiration: 2026-02-01

Abstract

Methods and systems for enabling a network routing update based on a conditional loopback interface are described. A network node may establish a first routing protocol session with a second network node, wherein the first routing protocol session is based on a loopback interface of the second network node remains up while a condition indicative of a capability of the second network node to forward traffic to a third network node is satisfied. A network node may determine that the first routing protocol session is down as a result of the loopback interface being down when the condition is not satisfied. A network node may, responsive to determining that the first routing protocol session is down, update routing information for reaching the third network node without passing through the second network node.

Description

SPECIFICATION

METHODS AND SYSTEMS FOR A NETWORK ROUTING UPDATE BASED ON A CONDITIONAL LOOPBACK INTERFACE

TECHNICAL FIELD

[0001] Embodiments of the invention relate to the field of networking; and more specifically, to methods and systems for a network routing update based on a conditional loopback interface.

BACKGROUND ART

[0002] A loopback interface is a virtual interface rather than a physical interface that can be configured on a network element such as a router. The loopback interface is not connected to any other physical device but is a purely logical interface. When configured in a network element, any forwarding associated with such a loopback interface is terminated at the network element. Further, the loopback interface is always up. An Internet Protocol (IP) address is assigned to the loopback interface, herein referred to as the loopback IP address.

[0003] The loopback IP address of a network element can be used as the network element’s identifier for Border Gateway Protocol (BGP) peering sessions between network elements. BGP is a routing protocol used to enable exchange of routing information between autonomous systems (ASs). Since the loopback interface is always up, BGP peering sessions have a stable and consistent source and destination IP addresses, even if the physical interfaces on the network elements go down or change. For example, the loopback interface is used in large fully meshed network environments where many network elements (e.g., routers) have multiple BGP peers. Additionally, the loopback interface can be used as a source and destination address for testing network connectivity.

SUMMARY

[0004] In some aspects, the techniques described herein relate to a method in a first network node of updating routing information, the method including: establishing a first routing protocol session with a second network node, where the first routing protocol session is based on a loopback interface of the second network node remains up while a condition indicative of a capability of the second network node to forward traffic to a third network node is satisfied; determining that the first routing protocol session is down as a result of the loopback interface being down when the condition is not satisfied; and responsive to determining that the first routing protocol session is down, updating routing information for reaching the third network node without passing through the second network node.

[0005] In some aspects, the techniques described herein relate to a network device including: a non-transitory machine-readable storage medium that provides instructions that, if executed by a processor, will cause the network device to perform operations. The operations includes: establishing a first routing protocol session between a first network node and a second network node, where the first routing protocol session is based on a loopback interface of the second network node remains up while a condition indicative of a capability of the second network node to forward traffic to a third network node is satisfied, determining that the first routing protocol session is down as a result of the loopback interface being down when the condition is not satisfied, and responsive to determining that the first routing protocol session is down, updating routing information for reaching the third network node without passing through the second network node.

[0006] In some aspects, the techniques described herein relate to a method in a first network node including: establishing a first routing protocol session with a second network node, where the first routing protocol session is based on a loopback interface of the first network node that remains up while a condition indicative of a capability of the first network node to forward traffic to a third network node is satisfied; and responsive to determining that the condition is not satisfied, transitioning the loopback interface down, where the transitioning causes an update, at the second network node, of routing information for reaching the third network node from the second network node.

[0007] In some aspects, the techniques described herein relate to a network device including: a non-transitory machine-readable storage medium that provides instructions that, if executed by a processor, will cause the network device to perform operations. The operations includes: establishing a first routing protocol session between a first network node and a second network node, where the first routing protocol session is based on a loopback interface of the first network node that remains up while a condition indicative of a capability of the first network node to forward traffic to a third network node is satisfied; and responsive to determining that the condition is not satisfied, transitioning the loopback interface down, where the transitioning causes an update, at the second network node, of routing information for reaching the third network node from the second network node. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 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:

[0009] Figure 1 illustrates an exemplary network for enabling routing updates based on a conditional loopback interface, according to some embodiments of the invention.

[0010] Figure 2 illustrates a flow diagram of exemplary operations for enabling routing updates based on conditional loopback interface, according to some embodiments of the invention.

[0011] Figure 3 A illustrates an exemplary configuration of a loopback interface based on a condition, according to some embodiments.

[0012] Figure 3B illustrates an exemplary configuration of a loopback interface based on a condition, according to some embodiments.

[0013] Figure 3C illustrates an exemplary configuration of a loopback interface based on a condition, according to some embodiments.

[0014] Figure 4 illustrates a flow diagram of exemplary operations that can be performed to transition the routing protocol session, according to some embodiments.

[0015] Figure 5 illustrates a flow diagram of exemplary operations for updating routing information as a result of a loopback interface transitioning down, according to some embodiments of the invention.

[0016] Figure 6A 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.

[0017] Figure 6B illustrates an exemplary way to implement a special-purpose network device according to some embodiments of the invention.

[0018] Figure 6C illustrates various exemplary ways in which virtual network elements (VNEs) may be coupled according to some embodiments of the invention.

[0019] Figure 6D illustrates a network with a single network element (NE) on each of the NDs, and within this straightforward 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.

[0020] Figure 6E 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.

[0021] Figure 6F 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.

[0022] Figure 7 illustrates a general purpose control plane device with centralized control plane (CCP) software 750), according to some embodiments of the invention.

DETAILED DESCRIPTION

[0023] The following description describes methods and apparatus for methods and systems for network routing update based on a conditional loopback interface. 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.

[0024] 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.

[0025] Bracketed text and blocks with dashed borders (e.g., large dashes, small dashes, dotdash, 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. [0026] 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.

[0027] Methods and systems for updating routing information based on conditional loopback interface(s) are described. In some embodiments, a first network node establishes a first routing protocol session with a second network node. The first routing protocol session is based on a loopback interface of the second network node that remains up while a condition indicative of a capability of the second network node to forward traffic to a third network node is satisfied. The first network node determines that the first routing protocol session is down as a result of the loopback interface being down when the condition is not satisfied. In response to determining that the first routing protocol session is down, the first network device updates routing information for reaching the third network node without passing through the second network node.

[0028] The present embodiments address disadvantages of prior art rerouting techniques when an intermediary network node is no longer able to forward traffic from an originating network node to a destination network node. In particular, the disadvantages include significant delays in rerouting traffic when the destination node is no longer reachable. According to these techniques most of the delay in rerouting traffic is due to the intermediary network node updating the routing information prior to transmitting a routing update message to the originating network node to indicate that the destination network node is no longer reachable. Thus, the originating network node needs to wait for the routing update to be performed in the intermediary network node and for the receipt of the routing update message before performing its own routing update and rerouting traffic destined to the destination network node. The delay increases proportionately based on the size of the network and/or the complexity of the network topology. The present embodiments of the invention address these significant delays.

[0029] The embodiments of the invention overcome these problems and disadvantages of the prior art through the use of a conditional loopback interface at the intermediary network node based on the ability of this intermediary network node to forward the traffic to the destination node. The use of the conditional loopback interface decreases the delay at the originating network node. The originating node quickly determines that the destination node is no longer reachable through the intermediary network node without waiting for the intermediary node’s routing update message. Further, the use of the conditional loopback interface can be tailored to different types of traffic at the same network device. For example, a routing protocol peer neighbor can be defined for each type of network service and associated with different conditions. These embodiments enable better sharing of the network resources between multiple services using different peering sessions.

[0030] Figure 1 illustrates an exemplary network 100 for enabling routing updates based on a conditional loopback interface, according to some embodiments of the invention.

[0031] Network 100 includes network node 102 A, network node 102B, and network node 102D. Network node 102A and network node 102D are connected through network node 102B. Optionally, network 100 may include one or more additional network nodes, such as network node 102C, that provide an alternate path to reach network node 102D from network node 102A. In some embodiments, a network node from network nodes 102A-D is a network device and/or a virtual network element implemented on a network device. In some embodiments, the network nodes are implemented as described in further details with reference to Figures 6A-F and Figure 7.

[0032] Network node 102A is communicatively coupled with network node 102B.

Additionally or optionally network node 102A is communicatively coupled with network node 102C. In some embodiments, network node 102A is communicatively coupled to network node 102D only through network node 102B and/or network node 102C. In these embodiments, there is no direct communication between network node 102A and network node 102D. In some embodiments, each of network node 102 A, network node 102B, network node 102C, and network node 102D can be part of a respective separate autonomous system. In other embodiments, one or more of the network nodes can be part of the same autonomous system. An autonomous system (AS) is a network or group of networks that has a unified routing policy. Network node 102 A is operative to forward traffic destined to network node 102D through network node 102B. Network node 102B is operative to receive the traffic from network node 102 A to be forwarded to network node 102D. The network traffic can be associated with a respective routing protocol session.

[0033] Routing protocol sessions are established between peer network nodes. For example, routing protocol session 104A is established between network node 102A and network node 102B. Routing protocol session 104B is established between network node 102B and network node 102D. Optionally, routing protocol session 104C is established between network node 102A and network node 102C and routing protocol session 104D is established between network node 102C and network node 102D. A routing protocol session allows each network node to connect to a peer network node for the purpose of sharing routing information. Using the routing information, each network node can properly route outbound traffic received from other network devices. In a non-limiting example, network node 102A, network node 102B, network node 102D, and network node 102C are border gateway routers of four separate autonomous systems (e.g., networks 105A-D). While some embodiments herein are described with respect to the network nodes being BGP peers, the operations described herein can be used in other types of network configurations and deployments (e.g., Mini-link for layer 3 applications, eNodeB for layer 3 applications, virtual network elements with Layer 3 application (server, Cloud BGP, etc.). In one non-limiting example, the nodes herein can be network nodes of a cloud-based environment and allows to provide fast re-route in a redundancy system. Network node 102B and network node 102C can be redundant nodes of a same cloud server.

[0034] In some embodiments, one or more sessions of a network protocol are established to detect faults between the network nodes. For example, a first session can be established between network node 102A and network node 102B and a second session can be established between network node 102B and network node 102D. These sessions are established in addition to routing protocol sessions 104 A and 104B. The sessions provide low-overhead detection of faults even on physical media that doesn't support failure detection of any kind, such as Ethernet, virtual circuits, tunnels and MPLS label-switched paths. In one non-limiting example, the sessions are bidirectional forwarding detection (BFD) sessions. BFD establishes a session between two endpoints over a particular link. If more than one link exists between two network nodes, multiple BFD sessions are established to monitor each one of them.

[0035] Network node 102B is operative to include a conditional loopback interface, loopback interface 106A. Loopback interface 106A is associated with at least one routing protocol session, e.g., routing protocol session 104B. While the embodiments herein are described with a single conditional loopback interface configured in network node 102B for a routing protocol session, in other embodiments, network node 102B can be configured to include several conditional loopback interfaces, each loopback interface associated with a corresponding routing protocol session and/or a corresponding network traffic. Each of the several conditional loopback interfaces can be configured based on an associated condition without departing from the scope of the present embodiments. The multiple loopback interfaces can enable the network node to forward one type of traffic associated with a first conditional loopback interface, while dropping another type of traffic associated with a second conditional loopback interface. In some embodiments, when the network node is a node of the access network (e.g., eNodeB), each one of multiple loopback interfaces can be associated with a different type of traffic (e.g., 3G traffic, 4G traffic, or 5G traffic).

[0036] Network node 102A is operative to establish routing protocol session 104A with network node 102B. Routing protocol session 104A is based on loopback interface 106A of network node 102B that remains up while a condition indicative of a capability of network node 102B to forward traffic to network node 102D is satisfied. Network node 102A determines that routing protocol session 104A is down as a result of loopback interface 106A being down when the condition is not satisfied. In response to determining that routing protocol session 104A is down, network node 102A updates routing information for reaching network node 102D without passing through network node 102B.

[0037] In some embodiments, network node 102 A updates the routing information for reaching the network node 102D prior to receiving from network node 102B, a route update message indicating that network node 102D is not reachable from network node 102B. Thus, if and/or when network node 102A receives a route update message from network node 102B, this message arrives after the routing information update has been initiated. The embodiments herein enable a fast traffic re-route based on conditional loopback interface(s) when network node 102D is no longer reachable through network node 102B.

[0038] The operations in the flow diagrams will be described with reference to the exemplary embodiments of Figure 1, Figure 3A-C, Figures 6A-F, and Figure 7. 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 Figure 1, Figure 3A-C, Figures 6A-F, and Figure 7, and the embodiments of the invention discussed with reference to Figure 1, Figure 3A- C, Figures 6A-F, and Figure 7 can perform operations different than those discussed with reference to the flow diagrams. For example, the operations of the flow diagrams can be performed by a network of network devices that forms a more complex topology than the one illustrated in Figure 1.

[0039] Figure 2 illustrates a flow diagram of exemplary operations performed in network node 102 A for enabling routing updates based on conditional loopback interface, according to some embodiments of the invention. While the operations of Figure 2 are described with reference to network node 102 A, these operations can be performed in network node 102D for updating routing information with respect to traffic destined to network node 102A.

[0040] At operation 210, network node 102A establishes a routing protocol session 104A with network node 102B. Routing protocol session 104A is based on a loopback interface 106A of network node 102B. In a non-limiting example, establishing routing protocol session 104A based on loopback interface 106 A includes using the IP address of the loopback interface 106 A as a destination address for the routing protocol session 104 A. For example, when the routing protocol session 104A is a BGP peering session, establishing the routing protocol session 104A can include establishing a TCP connection followed by the exchange of BGP control packets using the loopback IP address of network node 102B as a BGP identifier of network node 102B for routing protocol session 104 A. The control packets can include OPEN, KEEPALIVE, NOTIFICATION, and UPDATE messages. When the BGP peering session is established, its state is set to Established.

[0041] Loopback interface 106A remains up while a condition indicative of a capability of network node 102B to forward traffic to network node 102D is satisfied. In some embodiments, loopback interface 106 A is configured to be in one of multiple states. The states of loopback interface 106 A include at least an up state and a down state. While in some embodiments loopback interface 106 A can only be set to one of the up and down states, in other embodiments, loopback interface 106 A can be set to more than the two states. In these embodiments, the states can include the up state, the down state, and one or more additional states different from the up and down states. In a non-limiting example, a flag is set to ACTIVE to indicate that loopback interface 106A is up (i.e., in an up state). Additionally, the flag is set to DOWN when loopback interface 106A is down (i.e., in a down state).

[0042] The condition indicative of a capability of network node 102B to forward traffic to network node 102D can be based on a state of a routing protocol session, a state of a port of network node 102B, and/or hardware processing capability for network node 102B (e.g., compute processing availability, storage availability, etc.). In some embodiments, the condition is satisfied when network node 102B is capable of forwarding traffic to network node 102D and the condition is not satisfied when network node 102B is not capable of forwarding traffic to network node 102D. Figures 3A-C illustrate exemplary configurations of loopback interface 106A with one or more conditions, in accordance with some embodiments. Figure 3 A illustrates an exemplary configuration of loopback interface 106 A where an interface of type loopback is configured in network node 102B with an IP address of 100.100.100.140/32 and a condition on BFD session between network node 102B and network node 102D. According to this configuration, the loopback interface of IP 100.100.100.140/32 remains up while the state of the BFD session is up. The loopback interface is down when the state of the BFD session is down. Figure 3B illustrates an exemplary configuration of loopback interface 106 A where an interface of type loopback is configured in network node 102B with an IP address of 100.100.100.140/32 and a condition on Port 1. According to this configuration, the loopback interface of IP address 100.100.100.140/32 remains up while the state of Port 1 is up. The loopback interface is down when the state of the port is down. Figure 3C illustrates another exemplary configuration of loopback interface 106A where an interface of type loopback is configured in network node 102B with the IP address of 100.100.100.140/32 and a condition on Port 1, Port 3, and on a BFD session established between network node 102B and NE102D. According to this configuration, the loopback interface of IP 100.100.100.140/32 remains up while the state of port 1 is up, the state of port 3 is up and the BFD session between network node 102B and network node 102D is up. The loopback interface moves down when the state of port 1 is down, state of port 3 is down, or state of the BFD session moves down. While the embodiments of Figure 3 A-C illustrate some examples of conditions that can be configured for a loopback interface, the embodiments herein are not so limited and different types of conditions or combinations of conditions can be used without departing from the scope of the present embodiments.

[0043] Referring back to Figure 2, network node 102A determines, at operation 220, that the routing protocol session 104A is down as a result of loopback interface 106A being down when the condition is not satisfied. The establishment of the routing protocol session 104A based on loopback interface 106 A being conditional causes routing protocol session 104 A to automatically transition down at network node 102B when loopback interface 106A is down. In some embodiments, determining whether the condition is satisfied is performed by network node 102B and causes loopback interface 106 A to be set down resulting in routing protocol session 104 A to be set down. In some embodiments, transitioning the routing protocol session 104A down is performed in response to determining that a reply message was not received before expiration of a time interval from network node 102B because routing protocol session 104A is down on network node 102B. In a non-limiting example, when a BFD session is established between network node 102A and network node 102B, transitioning routing protocol session 104A down is performed in response to determining that a BFD reply message has not been received by network node 102 A before expiration of a time interval and in response to a BFD hello message sent to network node 102B.

[0044] Referring back to Figure 2, at operation 230, responsive to determining that the routing protocol session 104A is down, network node 102 A updates routing information for reaching network node 102D. The update of the routing information can include determining a path for traffic destined to network node 102D without passing through network node 102B. For example, network node 102 A can determine that an alternate path through network node 102C exists and update the routing information to forward the traffic through network node 102C toward network node 102B. In another example, network node 102 A may determine that no other path exists and may update the routing information to drop the traffic received destined to network node 102D. In some embodiments, the update of the routing information can include transmitting routing protocol update messages to one or more network devices to indicate that network node 102D is no longer reachable. In a non-limiting embodiment, the update of the routing information can include updating one or more routing information databases (e.g., routing information base, forwarding information base, etc.). In some embodiments, network node 102 A updates the routing information for reaching the network node 102D prior to receiving, network node 102B, a route update message indicating that network node 102D is not reachable from network node 102B. In these embodiments, in addition to automatically transitioning routing protocol session 104A down when the loopback interface’s condition is no longer satisfied, network node 102B may update routing information when network node 102D is no longer reachable. In response to the update of the routing information, network node 102B may transmit a route update message to network node 102 A indicating that network node 102D is no longer reachable. The route update message reaches network node 102A after network node 102 A has initiated the update of the routing information due to routing protocol session 104A transitioning down enabling a faster re-route of traffic when network node 102D is no longer reachable through network node 102B. In a non-limiting example, the route update message is a BGP UPDATE message advertising routing information indicating that network node 102D is not reachable. In a non-limiting example, if network nodes 102A, 102B, 102C, and 102D are operative to forward Synchronous Digital Hierarchy (SDH) and/or Plesiochronous Digital Hierarchy (PDH) traffic, based on the conditional loopback interface network node 102A is operative to determine an updated route for the traffic (e.g., when 102D is no longer reachable through 102B) within a time period that is shorter than 50 ms.

[0045] In some embodiments, when the condition is satisfied and routing protocol session 104A is still up, network traffic received at network node 102 A and destined to network node 102D is transmitted to network node 102B to be forwarded to network node 102D. In other embodiments, following the update of the routing information for reaching network node 102D, network node 102 A transmits network traffic destined to network node 102D without forwarding it to network node 102B. In some embodiments, when the alternate path through network node 102C is identified, the traffic is forwarded to network node 102C to be forwarded to network node 102D.

[0046] Figure 4 illustrates a flow diagram of exemplary operations performed in network node 102B for updating routing information as a result of a loopback interface transitioning down, according to some embodiments of the invention. At operation 410, network node 102B establishes the routing protocol session with network node 102A. Routing protocol session 104A is based on loopback interface 106A of network node 102B. Loopback interface 106A remains up while a condition indicative of a capability of network node 102B to forward traffic to network node 102D is satisfied. In response to determining that the condition is not satisfied, network node 102B transitions loopback interface 106A down, at operation 420. The transition causes an update at network node 102 A of routing information for reaching network node 102D from network node 102A. In some embodiments, operation 420 is performed as described with reference to Figure 5.

[0047] Figure 5 illustrates a flow diagram of exemplary operations that can be performed to automatically transition the routing protocol session down when the condition is no longer satisfied, in accordance to some embodiments. At operation 510, network node 102B determines whether the condition is satisfied. In some embodiments, determining whether the condition is satisfied can include detecting or not an interrupt indicative of a port, a connection, and/or a routing session being down. When the interrupt is detected, the condition is not satisfied. When the interrupt is not detected, the condition is satisfied. Alternatively or additionally, determining whether the condition is satisfied can include detecting whether a message was received from network node 102D. In a non-limiting example, when a BFD session is established between network node 102B and network node 102D, determining whether the condition is satisfied can include determining whether a BFD reply message has been received by network node 102B in response to a BFD hello message sent to network node 102D. Determining that the condition is not satisfied includes detecting that the BFD reply message was not received by network node 102B within a determined interval of time in response to a BFD hello message sent to network node 102D. Alternatively, determining that the condition is satisfied includes detecting that the BFD reply message was received by network node 102B within a determined interval of time in response to a BFD hello message sent to network node 102D.

[0048] At operation 520, in response to determining that the condition is not satisfied, network node 102B transition loopback interface 106A down. Alternatively, when the condition is satisfied, network node 102B does not update the state of loopback interface 106A and loopback interface 106 A remains up.

[0049] At operation 530, in response to loopback interface 106A being down, the routing protocol session 104 A transitions down. In some embodiments, transitioning the routing protocol session 104 A down includes setting a flag indicative of the state of routing protocol session 104 A to a down state. In a non-limiting example, transitioning the routing protocol session 104A includes setting the state of a BGP peering session between network node 102A and network node 102B to the IDLE state. In some alternative embodiments, transitioning the routing protocol session 104A includes setting the state of one or more routing protocol sessions different from BGP to a down state. In some embodiments, routing protocol session 104A between network node 102A and network node 102B transitions down as a result of network node 102D no longer being reachable from 102B (i.e., as indicated by the condition no longer being satisfied). [0050] In some embodiments, transitioning the routing protocol session 104 A down causes network node 102B to not send a reply message to network node 102 A when a hello or keepalive message is received from network node 102A for routing protocol session 104A. In a non-limiting example, when a BFD session is established between network node 102A and network node 102B and routing protocol session 104 A transitions down, network node 102B can received a BFD hello message and does not response as routing protocol session 104A is down. This causes network node 102A to transitions routing protocol session 104A down on network node 102 A.

[0051] The embodiments herein describe methods and systems for enabling routing update based on a conditional loopback interface. A first network device establishes a first routing protocol session with a second network device. The first routing protocol session is based on a loopback interface of the second network device that remains up while a condition indicative of a capability of the second network device to forward traffic to a third network device is satisfied. The first network device may determine that the first routing protocol session is down as a result of the loopback interface being down when the condition is not satisfied. Responsive to determining that the first routing protocol session is down, the first network device updates routing information for reaching the third network device.

[0052] System

[0053] 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, solid state drives, 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 (e.g., where a processor is a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, other electronic circuitry, a combination of one or more of the preceding) 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 non- volatile 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) (NI(s)) to establish network connections (to transmit and/or receive code and/or data using propagating signals) with other electronic devices. For example, the set of physical NIs (or the set of physical NI(s) in combination with the set of processors executing code) may perform any formatting, coding, or translating to allow the electronic device to send and receive data whether over a wired and/or a wireless connection. In some embodiments, a physical NI may comprise radio circuitry capable of receiving data from other electronic devices over a wireless connection and/or sending data out to other devices via a wireless connection. This radio circuitry may include transmitted s), received s), and/or transceiver(s) suitable for radiofrequency communication. The radio circuitry may convert digital data into a radio signal having the appropriate parameters (e.g., frequency, timing, channel, bandwidth, etc.). The radio signal may then be transmitted via antennas to the appropriate recipient(s). In some embodiments, the set of physical NI(s) may comprise network interface controlled s) (NICs), also known as a network interface card, network adapter, or local area network (LAN) adapter. The NIC(s) may facilitate in connecting the electronic device to other electronic devices allowing them to communicate via wire through plugging in a cable to a physical port connected to a NIC. One or more parts of an embodiment of the invention may be implemented using different combinations of software, firmware, and/or hardware.

[0054] 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).

[0055] Figure 6A 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 6A shows NDs 600A-H, and their connectivity by way of lines between 600A-600B, 600B-600C, 600C-600D, 600D-600E, 600E-600F, 600F-600G, and 600A-600G, as well as between 600H and each of 600A, 600C, 600D, and 600G. 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 600A, 600E, and 600F 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). In some embodiments, network nodes 102A-D can be an ND from NDs 600 A-H. Alternatively or additionally, one or more of network nodes 102A-D can a VNE from VNEs 660 A-R.

[0056] Two of the exemplary ND implementations in Figure 6A are: 1) a special-purpose network device 602 that uses custom application-specific integrated-circuits (ASICs) and a special-purpose operating system (OS); and 2) a general purpose network device 604 that uses common off-the-shelf (COTS) processors and a standard OS.

[0057] The special -purpose network device 602 includes networking hardware 610 comprising a set of one or more processor(s) 612, forwarding resource(s) 614 (which typically include one or more ASICs and/or network processors), and physical network interfaces (NIs) 616 (through which network connections are made, such as those shown by the connectivity between NDs 600 A-H), as well as non-transitory machine readable storage media 618 having stored therein networking software 620. During operation, the networking software 620 may be executed by the networking hardware 610 to instantiate a set of one or more networking software instance(s) 622. Each of the networking software instance(s) 622, and that part of the networking hardware 610 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) 622), form a separate virtual network element 630 A-R. Each of the virtual network element(s) (VNEs) 630A- R includes a control communication and configuration module 632A-R (sometimes referred to as a local control module or control communication module) and forwarding table(s) 634A-R, such that a given virtual network element (e.g., 630 A) includes the control communication and configuration module (e.g., 632A), a set of one or more forwarding table(s) (e.g., 634A), and that portion of the networking hardware 610 that executes the virtual network element (e.g., 630A).

[0058] The special-purpose network device 602 is often physically and/or logically considered to include: 1) a ND control plane 624 (sometimes referred to as a control plane) comprising the processor(s) 612 that execute the control communication and configuration module(s) 632A-R; and 2) a ND forwarding plane 626 (sometimes referred to as a forwarding plane, a data plane, or a media plane) comprising the forwarding resource(s) 614 that utilize the forwarding table(s) 634A-R and the physical NIs 616. By way of example, where the ND is a router (or is implementing routing functionality), the ND control plane 624 (the processor(s) 612 executing the control communication and configuration module(s) 632A-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) 634A-R, and the ND forwarding plane 626 is responsible for receiving that data on the physical NIs 616 and forwarding that data out the appropriate ones of the physical NIs 616 based on the forwarding table(s) 634A-R.

[0059] Figure 6B illustrates an exemplary way to implement the special-purpose network device 602 according to some embodiments of the invention. Figure 6B shows a special-purpose network device including cards 638 (typically hot pluggable). While in some embodiments the cards 638 are of two types (one or more that operate as the ND forwarding plane 626 (sometimes called line cards), and one or more that operate to implement the ND control plane 624 (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 636 (e.g., a first full mesh coupling the line cards and a second full mesh coupling all of the cards).

[0060] Returning to Figure 6A, the general purpose network device 604 includes hardware 640 comprising a set of one or more processor(s) 642 (which are often COTS processors) and physical NIs 646, as well as non-transitory machine readable storage media 648 having stored therein software 650. During operation, the processor(s) 642 execute the software 650 to instantiate one or more sets of one or more applications 664A-R. While one embodiment does not implement virtualization, alternative embodiments may use different forms of virtualization. For example, in one such alternative embodiment the virtualization layer 654 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple instances 662A-R called software containers that may each be used to execute one (or more) of the sets of applications 664A-R; where the multiple software containers (also called virtualization engines, virtual private servers, or jails) are user spaces (typically a virtual memory space) that are separate from each other and separate from the kernel space in which the operating system is run; and where the set of applications running in a given user space, unless explicitly allowed, cannot access the memory of the other processes. In another such alternative embodiment the virtualization layer 654 represents a hypervisor (sometimes referred to as a virtual machine monitor (VMM)) or a hypervisor executing on top of a host operating system, and each of the sets of applications 664A-R is run on top of a guest operating system within an instance 662A-R called a virtual machine (which may in some cases be considered a tightly isolated form of software container) that is run on top of the hypervisor - the guest operating system and application may not know they are running on a virtual machine as opposed to running on a “bare metal” host electronic device, or through para-virtualization the operating system and/or application may be aware of the presence of virtualization for optimization purposes. In yet other alternative embodiments, one, some or all of the applications are implemented as unikemel(s), which can be generated by compiling directly with an application only a limited set of libraries (e.g., from a library operating system (LibOS) including drivers/libraries of OS services) that provide the particular OS services needed by the application. As a unikernel can be implemented to run directly on hardware 640, directly on a hypervisor (in which case the unikernel is sometimes described as running within a LibOS virtual machine), or in a software container, embodiments can be implemented fully with unikemels running directly on a hypervisor represented by virtualization layer 654, unikemels running within software containers represented by instances 662A-R, or as a combination of unikemels and the above-described techniques (e.g., unikemels and virtual machines both run directly on a hypervisor, unikemels and sets of applications that are run in different software containers).

[0061] The instantiation of the one or more sets of one or more applications 664A-R, as well as virtualization if implemented, are collectively referred to as software instance(s) 652. Each set of applications 664 A-R, corresponding virtualization construct (e.g., instance 662 A-R) if implemented, and that part of the hardware 640 that executes them (be it hardware dedicated to that execution and/or time slices of hardware temporally shared), forms a separate virtual network element(s) 660A-R.

[0062] The virtual network element(s) 660A-R perform similar functionality to the virtual network element(s) 630 A-R - e.g., similar to the control communication and configuration module(s) 632A and forwarding table(s) 634A (this virtualization of the hardware 640 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). While embodiments of the invention are illustrated with each instance 662A-R corresponding to one VNE 660A-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 instances 662A-R to VNEs also apply to embodiments where such a finer level of granularity and/or unikemels are used.

[0063] In certain embodiments, the virtualization layer 654 includes a virtual switch that provides similar forwarding services as a physical Ethernet switch. Specifically, this virtual switch forwards traffic between instances 662A-R and the physical NI(s) 646, as well as optionally between the instances 662A-R; in addition, this virtual switch may enforce network isolation between the VNEs 660A-R that by policy are not permitted to communicate with each other (e.g., by honoring virtual local area networks (VLANs)).

[0064] The third exemplary ND implementation in Figure 6A is a hybrid network device 606, which includes both custom ASICs/ special-purpose 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 602) could provide for para-virtualization to the networking hardware present in the hybrid network device 606.

[0065] 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) 630A-R, VNEs 660 A-R, and those in the hybrid network device 606) receives data on the physical NIs (e.g., 616, 646) and forwards that data out the appropriate ones of the physical NIs (e.g., 616, 646). 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 code point (DSCP) values.

[0066] Figure 6C illustrates various exemplary ways in which VNEs may be coupled according to some embodiments of the invention. Figure 6C shows VNEs 670A.1-670A.P (and optionally VNEs 670A.Q-670A.R) implemented in ND 600A and VNE 670H.1 in ND 600H. In Figure 6C, VNEs 670A.1-P are separate from each other in the sense that they can receive packets from outside ND 600A and forward packets outside of ND 600A; VNE 670A.1 is coupled with VNE 670H.1, and thus they communicate packets between their respective NDs; VNE 670A.2-670A.3 may optionally forward packets between themselves without forwarding them outside of the ND 600A; and VNE 670A.P may optionally be the first in a chain of VNEs that includes VNE 670A.Q followed by VNE 670A.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 6C 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).

[0067] The NDs of Figure 6A, 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 6A may also host one or more such servers (e.g., in the case of the general purpose network device 604, one or more of the software instances 662A-R may operate as servers; the same would be true for the hybrid network device 606; in the case of the special-purpose network device 602, one or more such servers could also be run on a virtualization layer executed by the processor(s) 612); in which case the servers are said to be co-located with the VNEs of that ND.

[0068] A virtual network is a logical abstraction of a physical network (such as that in Figure 6A) 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).

[0069] 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).

[0070] 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 IPVPN) 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).

[0071] Fig. 6D illustrates a network with a single network element on each of the NDs of Figure 6A, 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 6D illustrates network elements (NEs) 670A-H with the same connectivity as the NDs 600A-H of Figure 6A. [0072] Figure 6D illustrates that the distributed approach 672 distributes responsibility for generating the reachability and forwarding information across the NEs 670A-H; in other words, the process of neighbor discovery and topology discovery is distributed.

[0073] For example, where the special-purpose network device 602 is used, the control communication and configuration module(s) 632A-R of the ND control plane 624 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) (including RSVP-Traffic Engineering (TE): Extensions to RSVP for LSP Tunnels and 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 670A-H (e.g., the processor(s) 612 executing the control communication and configuration module(s) 632A-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 624. The ND control plane 624 programs the ND forwarding plane 626 with information (e.g., adjacency and route information) based on the routing structure(s). For example, the ND control plane 624 programs the adjacency and route information into one or more forwarding table(s) 634A-R (e.g., Forwarding Information Base (FIB), Label Forwarding Information Base (LFIB), and one or more adjacency structures) on the ND forwarding plane 626. 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 602, the same distributed approach 672 can be implemented on the general purpose network device 604 and the hybrid network device 606.

[0074] Figure 6D illustrates that a centralized approach 674 (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 674 has the responsibility for the generation of reachability and forwarding information in a centralized control plane 676 (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 676 has a south bound interface 682 with a data plane 680 (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 670A-H (sometimes referred to as switches, forwarding elements, data plane elements, or nodes). The centralized control plane 676 includes a network controller 678, which includes a centralized reachability and forwarding information module 679 that determines the reachability within the network and distributes the forwarding information to the NEs 670A-H of the data plane 680 over the south bound interface 682 (which may use the OpenFlow protocol). Thus, the network intelligence is centralized in the centralized control plane 676 executing on electronic devices that are typically separate from the NDs. [0075] For example, where the special-purpose network device 602 is used in the data plane 680, each of the control communication and configuration module(s) 632A-R of the ND control plane 624 typically include a control agent that provides the VNE side of the south bound interface 682. In this case, the ND control plane 624 (the processor(s) 612 executing the control communication and configuration module(s) 632A-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 676 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 679 (it should be understood that in some embodiments of the invention, the control communication and configuration module(s) 632A-R, in addition to communicating with the centralized control plane 676, 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 674, but may also be considered a hybrid approach).

[0076] While the above example uses the special-purpose network device 602, the same centralized approach 674 can be implemented with the general purpose network device 604 (e.g., each of the VNE 660A-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 676 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 679; it should be understood that in some embodiments of the invention, the VNEs 660A-R, in addition to communicating with the centralized control plane 676, 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 606. In fact, the use of SDN techniques can enhance the NFV techniques typically used in the general purpose network device 604 or hybrid network device 606 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.

[0077] Figure 6D also shows that the centralized control plane 676 has a north bound interface 684 to an application layer 686, in which resides application(s) 688. The centralized control plane 676 has the ability to form virtual networks 692 (sometimes referred to as a logical forwarding plane, network services, or overlay networks (with the NEs 670A-H of the data plane 680 being the underlay network)) for the application(s) 688. Thus, the centralized control plane 676 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).

[0078] While Figure 6D shows the distributed approach 672 separate from the centralized approach 674, 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) 674, 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 674, but may also be considered a hybrid approach.

[0079] While Figure 6D illustrates the simple case where each of the NDs 600A-H implements a single NE 670A-H, it should be understood that the network control approaches described with reference to Figure 6D also work for networks where one or more of the NDs 600A-H implement multiple VNEs (e.g., VNEs 630A-R, VNEs 660A-R, those in the hybrid network device 606). Alternatively or in addition, the network controller 678 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 678 may present the implementation of a VNE/NE in a single ND as multiple VNEs in the virtual networks 692 (all in the same one of the virtual network(s) 692, each in different ones of the virtual network(s) 692, or some combination). For example, the network controller 678 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 676 to present different VNEs in the virtual network(s) 692 (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).

[0080] On the other hand, Figures 6E and 6F respectively illustrate exemplary abstractions of NEs and VNEs that the network controller 678 may present as part of different ones of the virtual networks 692. Figure 6E illustrates the simple case of where each of the NDs 600A-H implements a single NE 670A-H (see Figure 6D), but the centralized control plane 676 has abstracted multiple of the NEs in different NDs (the NEs 670A-C and G-H) into (to represent) a single NE 6701 in one of the virtual network(s) 692 of Figure 6D, according to some embodiments of the invention. Figure 6E shows that in this virtual network, the NE 6701 is coupled to NE 670D and 670F, which are both still coupled to NE 670E.

[0081] Figure 6F illustrates a case where multiple VNEs (VNE 670A.1 and VNE 670H.1) are implemented on different NDs (ND 600A and ND 600H) and are coupled to each other, and where the centralized control plane 676 has abstracted these multiple VNEs such that they appear as a single VNE 670T within one of the virtual networks 692 of Figure 6D, according to some embodiments of the invention. Thus, the abstraction of a NE or VNE can span multiple NDs.

[0082] While some embodiments of the invention implement the centralized control plane 676 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).

[0083] Similar to the network device implementations, the electronic device(s) running the centralized control plane 676, and thus the network controller 678 including the centralized reachability and forwarding information module 679, 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 processor(s), a set or one or more physical NIs, and a non-transitory machine-readable storage medium having stored thereon the centralized control plane software. For instance, Figure 7 illustrates, a general purpose control plane device 704 including hardware 740 comprising a set of one or more processor(s) 742 (which are often COTS processors) and physical NIs 746, as well as non-transitory machine readable storage media 748 having stored therein centralized control plane (CCP) software 750.

[0084] In embodiments that use compute virtualization, the processor(s) 742 typically execute software to instantiate a virtualization layer 754 (e.g., in one embodiment 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 instances 762A-R called software containers (representing separate user spaces and also called virtualization engines, virtual private servers, or jails) that may each be used to execute a set of one or more applications; in another embodiment 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 an application is run on top of a guest operating system within an instance 762A-R called a virtual machine (which in some cases may be considered a tightly isolated form of software container) that is run by the hypervisor ; in another embodiment, an application is implemented as a unikernel, which can be generated by compiling directly with an application only a limited set of libraries (e.g., from a library operating system (LibOS) including drivers/libraries of OS services) that provide the particular OS services needed by the application, and the unikemel can run directly on hardware 740, directly on a hypervisor represented by virtualization layer 754 (in which case the unikernel is sometimes described as running within a LibOS virtual machine), or in a software container represented by one of instances 762A-R). Again, in embodiments where compute virtualization is used, during operation an instance of the CCP software 750 (illustrated as CCP instance 776A) is executed (e.g., within the instance 762A) on the virtualization layer 754. In embodiments where compute virtualization is not used, the CCP instance 776A is executed, as a unikernel or on top of a host operating system, on the “bare metal” general purpose control plane device 704. The instantiation of the CCP instance 776A, as well as the virtualization layer 754 and instances 762A-R if implemented, are collectively referred to as software instance(s) 752.

[0085] In some embodiments, the CCP instance 776A includes a network controller instance 778. The network controller instance 778 includes a centralized reachability and forwarding information module instance 779 (which is a middleware layer providing the context of the network controller 678 to the operating system and communicating with the various NEs), and an CCP application layer 780 (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 780 within the centralized control plane 676 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.

[0086] The centralized control plane 676 transmits relevant messages to the data plane 680 based on CCP application layer 780 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 680 may receive different messages, and thus different forwarding information. The data plane 680 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.

[0087] 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. In embodiments of the present invention, a loopback interface can be a conditional loopback interface. A conditional loopback interface is set to an up state when the condition is satisfied. Alternatively, the loopback interface is set to a down state when the condition is not satisfied. 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.

[0088] Each VNE (e.g., a virtual router, a virtual bridge (which may act as a virtual switch instance in a Virtual Private LAN Service (VPLS) is typically independently administrable. For example, in the case of multiple virtual routers, each of the virtual routers may share system resources but is separate from the other virtual routers regarding its management domain, AAA (authentication, authorization, and accounting) name space, IP address, and routing database(s). Multiple VNEs may be employed in an edge ND to provide direct network access and/or different classes of services for subscribers of service and/or content providers.

[0089] Within certain NDs, “interfaces” that are independent of physical NIs may be configured as part of the VNEs to provide higher-layer protocol and service information (e.g., Layer 3 addressing). The subscriber records in the AAA server identify, in addition to the other subscriber configuration requirements, to which context (e.g., which of the VNEs/NEs) the corresponding subscribers should be bound within the ND. As used herein, a binding forms an association between a physical entity (e.g., physical NI, channel) or a logical entity (e.g., circuit such as a subscriber circuit or logical circuit (a set of one or more subscriber circuits)) and a context’s interface over which network protocols (e.g., routing protocols, bridging protocols) are configured for that context. Subscriber data flows on the physical entity when some higher-layer protocol interface is configured and associated with that physical entity.

[0090] While the flow diagrams in the figures show a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.).

[0091] While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.

Claims

CLAIMS What is claimed is:

1. A method in a first network node (102 A) of updating routing information, the method comprising: establishing (210) a first routing protocol session (104A) with a second network node (102B), wherein the first routing protocol session (104A) is based on a loopback interface of the second network node (102B) remains up while a condition indicative of a capability of the second network node (102B) to forward traffic to a third network node (102D) is satisfied; determining (220) that the first routing protocol session (104A) is down as a result of the loopback interface being down when the condition is not satisfied; and responsive to determining that the first routing protocol session (104A) is down, updating (230) routing information for reaching the third network node (102D) without passing through the second network node (102B).

2. The method of claim 1, wherein the updating (230) the routing information for reaching the third network node (102D) is performed prior to receiving, from the second network node (102B), a route update message indicating that the third network node (102D) is not reachable from the second network node (102B).

3. The method of any of claims 1-2 further comprising: receiving network traffic destined to the third network node (102D); and following the updating the routing information for reaching the third network node (102D), transmitting the network traffic toward the third network node (102D) without forwarding the network traffic to the second network node (102B).

4. The method of claim 3 further comprising: responsive to determining that the first routing protocol session (104A) is up, transmitting the network traffic to the second network node (102B) to be forwarded to the third network node (102D).

5. The method of any of claims 1-4, wherein the determining (220) that the first routing protocol session (104A) is down includes: determining that a reply message was not received from the second network node (102B) before expiration of a time interval.

6. The method of any of claims 1-5, wherein the determining (220) that the first routing protocol session (104A) is down is based on bidirectional forwarding detection (BFD) protocol.

7. The method of any of claims 1-6, wherein the first routing protocol session (104A) is a border gateway protocol (BGP) session.

8. A machine-readable medium comprising computer program code which when executed by a computer carries out the method steps of any of claims 1-7.

9. A network devi ce compri sing : a non-transitory machine-readable storage medium that provides instructions that, if executed by a processor, will cause the network device to perform operations including, establishing (210) a first routing protocol session (104A) between a first network node (102 A) and a second network node (102B), wherein the first routing protocol session (104A) is based on a loopback interface of the second network node (102B) remains up while a condition indicative of a capability of the second network node (102B) to forward traffic to a third network node (102D) is satisfied, determining (220) that the first routing protocol session (104A) is down as a result of the loopback interface being down when the condition is not satisfied, and responsive to determining that the first routing protocol session (104A) is down, updating (230) routing information for reaching the third network node (102D) without passing through the second network node (102B).

10. The network device of claim 9, wherein the updating (230) the routing information for reaching the third network node (102D) is performed prior to receiving, from the second network node (102B), a route update message indicating that the third network node (102D) is not reachable from the second network node (102B).

11. The network device of claim 10, wherein the operations further comprise: receiving network traffic destined to the third network node (102D); and following the updating the routing information for reaching the third network node (102D), transmitting the network traffic toward the third network node (102D) without forwarding the network traffic to the second network node (102B).

12. The network device of claim 11, wherein the operations further comprise: responsive to determining that the first routing protocol session (104A) is up, transmitting the network traffic to the second network node (102B) to be forwarded to the third network node (102D).

13. The network device of any of claims 9-12, wherein the determining (220) that the first routing protocol session (104A) is down includes: determining that a reply message was not received from the second network node (102B) before expiration of a time interval.

14. The network device of any of claims 9-13, wherein the determining (220) that the first routing protocol session (104A) is down is based on bidirectional forwarding detection (BFD) protocol.

15. The network device of any of claims 9-14, wherein the first routing protocol session (104A) is a border gateway protocol (BGP) session.

16. A method in a first network node (102B) comprising: establishing (410) a first routing protocol session (104A) with a second network node (102A), wherein the first routing protocol session (104A) is based on a loopback interface of the first network node (102B) that remains up while a condition indicative of a capability of the first network node (102B) to forward traffic to a third network node (102D) is satisfied; and responsive to determining that the condition is not satisfied, transitioning (420) the loopback interface down, wherein the transitioning causes an update, at the second network node (102 A), of routing information for reaching the third network node (102D) from the second network node (102A).

17. The method of claim 16, wherein the update, at the second network node (102A), of routing information for reaching the third network node (102D) from the second network node (102A) is caused prior to transmitting, to the second network node (102A), a route update message indicating that the third network node (102D) is not reachable from the first network node (102B).

18. The method of any of claims 16-17, wherein the first routing protocol session (104A) is a border gateway protocol (BGP) sessions.

19. A machine-readable medium comprising computer program code which when executed by a computer carries out the method steps of any of claims 16-18.

20. A network device comprising: a non-transitory machine-readable storage medium that provides instructions that, if executed by a processor, will cause the network device (102A) to perform operations including, establishing (410) a first routing protocol session (104A) between a first network node (102B) and a second network node (102 A), wherein the first routing protocol session (104A) is based on a loopback interface of the first network node (102B) that remains up while a condition indicative of a capability of the first network node (102B) to forward traffic to a third network node (102D) is satisfied; and responsive to determining that the condition is not satisfied, transitioning (420) the loopback interface down, wherein the transitioning causes an update, at the second network node (102A), of routing information for reaching the third network node (102D) from the second network node (102A).

21. The network device of claim 20, wherein the update, at the second network node (102 A), of routing information for reaching the third network node (102D) from the second network node (102A) is caused prior to transmitting, to the second network node (102A), a route update message indicating that the third network node (102D) is not reachable from the first network node (102B).

22. The network device of any of claims 20-21, wherein the first routing protocol session (104A) is a border gateway protocol (BGP) sessions.