WO2018065813A1

WO2018065813A1 - Method and system for distribution of virtual layer 2 traffic towards multiple access network devices

Info

Publication number: WO2018065813A1
Application number: PCT/IB2016/056358
Authority: WO
Inventors: V.S. Jagannadham JONNALAGADDA (Jack); Sajjad Ahmed
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-10-05
Filing date: 2016-10-21
Publication date: 2018-04-12

Abstract

A method and system for enabling load balancing of traffic across a plurality of access network devices are described. A first access network device is one of the plurality of access network devices which are coupled with a destination network device through a plurality of access links. A first access link capacity (ALC) indicator is advertised to one or more remote network devices. The first ALC indicator is representative of the forwarding capacities of a first access link coupling the first access network device with the destination network device. The one or more remote network devices are caused to forward traffic to the destination network device through the first access network device by load balancing the traffic across the access network devices according to the first ALC indicator and to other ALC indicators of other access network devices from the plurality of access network devices.

Description

METHOD AND SYSTEM FOR DISTRIBUTION OF VIRTUAL LAYER 2 TRAFFIC TOWARDS MULTIPLE ACCESS NETWORK DEVICES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 62/404,459, filed October 5, 2016, which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] Embodiments of the invention relate to the field of packet networks; and more specifically, to multi-destination traffic in a multi-homed Ethernet Virtual Private Network (EVPN).

BACKGROUND

[0003] An Ethernet Virtual Private Network (EVPN) is a type of VPN technology which introduces routing Media Access Control (MAC) addresses using Multiprotocol Border Gateway Protocol (MP-BGP) over Multiprotocol Label Switching (MPLS). As with other types of VPNs, an EVPN is comprised of customer edge (CE) devices connected to provider edge (PE) devices that form the edge of an MPLS infrastructure. A CE may be a host, a router, or a switch. The PEs provide virtual Layer 2 bridged connectivity between the CEs. There may be multiple EVPN instances in a provider's network. The PEs may be connected by an MPLS Label Switched Path (LSP) infrastructure, which provides the benefits of MPLS technology, such as fast reroute, resiliency, etc. The PEs may also be connected by an IP infrastructure, in which case IP/GRE (Generic Routing Encapsulation) tunneling or other IP tunneling can be used between the PEs. The CEs can connect to multiple active points of attachment (i.e., to multiple PEs).

[0004] In EVPN, PEs advertise the MAC addresses learned from the CEs that are connected to them, along with an MPLS label (e.g., an aliasing label) to other PEs in the control plane using BGP. Control-plane route learning through MP-BGP offers greater control over a MAC route learning process, and enables the introduction of restriction on which device learns which information as well as the ability to apply policies. It further enables load balancing of traffic to and from CEs that are multi-homed to multiple PEs and improves convergence times in the event of certain network failures. [0005] In EVPN, aliasing labels indicate whether the network device (e.g., PE) is coupled with a group of access links (e.g., an Ethernet Segment (ES)) and may be used for forwarding packets of the group of access links. With the existing aliasing concept in EVPN, traffic originating from a remote PE is load shared to all the multi-homed PEs coupled with a CE. Such load sharing utilizes all the multi-homed access links (e.g., all the Ethernet Segments connecting the multi- homed PEs to the CE) without regard for the capacity of each access link resulting in the inefficient use of access link resources (bandwidth and speed). In particular, inefficiencies are more prominent when the bandwidth and link-speed of the access links connecting the multi- homed PEs to the CE differ (i.e., when these access links are heterogeneous).

SUMMARY

[0006] A method in a first access network device that is one of a plurality of access network devices coupled with a destination network device through a plurality of access links, of load balancing traffic across the plurality of access network devices is described. The method comprises: advertising a first access link capacity indicator to one or more remote network devices, where the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling the first access network device with the destination network device; and causing the one or more remote network devices to forward traffic to the destination network device through the first access network device by load balancing the traffic across the plurality of access network devices according to the first access link capacity indicator and to other access link capacity indicators of other access network devices from the plurality of access network devices.

[0007] A method in a network device for enabling load balancing of traffic across a plurality of access network devices coupled with a destination network device through a plurality of access links is described. The method comprises: receiving a first access link capacity indicator, where the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling a first access network device with the destination network device; receiving a second access link capacity indicator, where the second access link capacity indicator is representative of forwarding capacities of a second access link from the plurality of access links, the second access link coupling a second access network device with the destination network device; and load balancing traffic across first and second paths based on the first and the second access link capacity indicators, where the load balancing traffic across the first and the second paths includes forwarding a first portion of the traffic across the first path towards the destination network device through the first access network device, and forwarding a second portion of the traffic across the second path towards the destination network device through the second access network device.

[0008] A first access network device that is one of a plurality of access network devices coupled with a destination network device through a plurality of access links, for enabling load balancing traffic across the plurality of access network devices is described. The first access network device comprises: a non-transitory computer readable medium to store instructions; and a processor coupled with the non-transitory computer readable medium to process the stored instructions to: advertise a first access link capacity indicator to one or more remote network devices, where the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling the first access network device with the destination network device; and cause the one or more remote network devices to forward traffic to the destination network device through the first access network device by load balancing the traffic across the plurality of access network devices according to the first access link capacity indicator and to other access link capacity indicators of other access network devices from the plurality of access network devices.

[0009] A network device for enabling load balancing of traffic across a plurality of access network devices coupled with a destination network device through a plurality of access links is described. The remote network device comprises: a non-transitory computer readable medium to store instructions; and a processor coupled with the non-transitory computer readable medium to process the stored instructions to: receive a first access link capacity indicator, where the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling a first access network device with the destination network device; receive a second access link capacity indicator, where the second access link capacity indicator is representative of forwarding capacities of a second access link from the plurality of access links, the second access link coupling a second access network device with the destination network device; and load balance traffic across first and second paths based on the first and the second access link capacity indicators, where the load balancing traffic across the first and the second paths includes forwarding a first portion of the traffic across the first path towards the destination network device through the first access network device, and forwarding a second portion of the traffic across the second path towards the destination network device through the second access network device.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] 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:

[0011] Figure 1 illustrates a block diagram of an exemplary network for load balancing traffic received from a remote PE across multiple network elements, according to some embodiments.

[0012] Figure 2 illustrates a block diagram of an exemplary autonomous network in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic across multiple access network devices in accordance with some embodiments.

[0013] Figure 3 illustrates a block diagram of an exemplary scenario in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic forwarded across autonomous systems in accordance with some embodiments.

[0014] Figure 4 illustrates a block diagram of an exemplary scenario in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic forwarded across autonomous systems in accordance with some embodiments.

[0015] Figure 5 illustrates a flow diagram of operations for advertising an access link capacity indicator of an access link causing the load balancing of traffic across multiple access links in accordance with some embodiments.

[0016] Figure 6 illustrates a flow diagram of operations for load balancing traffic across access network devices in accordance with some embodiments.

[0017] 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.

[0018] Figure 7B illustrates an exemplary way to implement a special-purpose network device according to some embodiments of the invention.

[0019] Figure 7C illustrates various exemplary ways in which virtual network elements (VNEs) may be coupled according to some embodiments of the invention.

[0020] 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.

[0021] 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. [0022] 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.

[0023] Figure 8 illustrates a general purpose control plane device with centralized control plane (CCP) software 850), according to some embodiments of the invention.

DETAILED DESCRIPTION

[0024] The following description describes methods and apparatuses for load balancing of virtual Layer 2 traffic across multiple network elements. 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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 a PE (Provider Edge) and a CE (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. An Ethernet Virtual Private Network (EVPN) is a type of VPN technology developed to address the limitations of Virtual Private LAN Service (VPLS) by providing multi-homing and redundancy, multicast optimization, provisioning simplicity, flow- based load balancing, and multipathing. IETF RFC 7432: "BGP MPLS-Based Ethernet VPN," February 2015, describes procedures for BGP MPLS based EVPN, which introduces routing MAC addresses using control plane routing protocol (e.g., Multiprotocol Border Gateway Protocol (MP-BGP)) over Multiprotocol Label Switching (MPLS). While the embodiments below will be described with reference to Ethernet and MP-BGP, other access technologies and routing and reachability technologies can respectively be used without departing from the scope and spirit of the present invention.

[0030] A method and first network device for enabling load balancing of traffic across a plurality of access network devices are described. The first access network device is one of the plurality of access network devices which are coupled with a destination network device through a plurality of access links. A first access link capacity indicator is advertised to one or more remote network devices. The first access link capacity indicator is representative of the forwarding capacities of a first access link from the plurality of access links coupling the first network device with the destination network device. The one or more remote network devices are caused to forward traffic to the destination network device through the first network device by load balancing the traffic across the access network devices according to the first access link capacity indicator and to other access link capacity indicators of other network devices from the plurality of access network devices.

[0031] In one embodiment, the techniques described herein enable efficient use of access link resources (bandwidth and speed) in a VPN instance. For example, the techniques enable efficient use of access link resources in an EVPN instance when forwarding traffic from a remote ND (e.g., a remote PE) to a multi-homed destination ND (e.g., multi-homed CE). An EVPN instance includes a set of network devices acting as provider edges (PEs) and a set of network devices acting as customer edges (CEs) coupled with the PEs. In one embodiment, each access link from a group of links (e.g., Ethernet Segment) which coupled an access PE with the multi-homed CE is configured with an associated attribute referred to herein as an access link capacity (ALC) indicator. The ALC indicator is a dynamic indication of the capacity of the access link (e.g., speed and/or bandwidth capacity). The proposed solution provides a mechanism to optimally load share aliased Layer 2 (L2) Destination EVPN traffic across the destination PEs multi-homing a CE.

[0032] The embodiments of the present invention enable efficient and dynamic load share of traffic received from a remote ND among access NDs that are multi-homed to a destination ND. This enables the optimal utilization of the access links between access NDs and destination ND as the load share is performed based on the respective capacity of each access link and is adapted dynamically based on the changes that occur in the links' respective capacities.

[0033] Figure 1 illustrates a block diagram of an exemplary network for load balancing traffic received from a remote ND across multiple network devices, according to some embodiments. The network includes a set of access NDs 111, 112, 113 and 114 coupled with a set of destination NDs 101-103. In some embodiments, the destination NDs 101, 102, 103 are customer edge (CEs) network devices coupled with Provider Edge network devices NDs 111, 112, 113 and 114. These NDs represent connection points in the network in which a customer's site (e.g., a data center, customer's network, computing device, etc.) connects with a provider's network. One of ordinary skill in the art would understand that the number of NDs in network 100 are exemplary only and not intended to be limiting. A network 100 may include any number of network devices. In some embodiments, Figure 1 illustrates an exemplary EVPN instance including the set of NDs 101-103 and 111-114. Each one of the NDs 111-114 and 101-103 can be implemented as described in further details with reference to Figures 7A-F.

[0034] Each one of the NDs 101-103 may be a host, a router, or a switch coupled with one or more customer sites (not shown in Figure 1). The NDs 111-114 provide virtual Layer 2 bridged connectivity between NDs 101-103. The NDs 111-114 are coupled through a network 105. For example, the NDs can be coupled through an MPLS Label Switched Path (LSP) infrastructure, which provides the benefits of MPLS technology, such as fast reroute, resiliency, etc. In other embodiments, the NDs 111-114 may be connected by an IP infrastructure, in which case IP/GRE (Generic Routing Encapsulation) tunneling or other IP tunneling can be used between the NDs.

[0035] Each one of the destination NDs 101-103 can connect to one or more active points of attachment (i.e., to multiple access NDs). For example, ND 101 is coupled with access ND 111, access ND 112, and access ND 113 through a group of access links 125. The group of access links includes access link 121 coupling ND 101 with ND 111, access link 122 coupling ND 101 with ND 112, and access link 123 coupling ND 101 with ND 113. The group of access links is associated with a unique non-zero identifier. In some embodiments, the group of access links is an Ethernet segment and is associated with an Ethernet Segment Identifier (ESI). The group of access links can operate in a "Single-Active Redundancy Mode," where only a single ND from the NEs 111-113 is allowed to forward traffic to/from that Ethernet segment for a given broadcast domain. Alternatively the group of access links 125 may operate in an "All-Active Redundancy Mode," where all NEs 111-113 attached to the group of access links are allowed to forward known unicast traffic to/from that group of access links. In another example, ND 103 is coupled to a single ND 113 through the access link 124 that is not part of the group of access links 125. ND 102 is coupled to a single ND 114 through the link 126 that is not part of the group of access links 125.

[0036] During a route learning mechanism, each one of NEs 111-114 learns the MAC addresses of the CEs coupled with it. In one embodiment, each one of the CEs (e.g., ND 101, 102, and 103) advertises a MAC address to an associated PE (e.g., NDs 111-114) to which it is coupled. For example, ND 101 advertises its MAC address to ND 111, 112 and 113; ND 102 advertises its MAC address to ND 114; and ND 103 advertises its MAC address to ND 113. Further, each one of the PEs (e.g., ND 111, ND 112, ND 113 and ND 114) learns the MAC addresses of the CEs to which other PEs are coupled as well as routing labels enabling a PE to forward traffic to the other PEs. For example, a routing protocol may be used to distribute in the control plane routing topology (e.g., through the distribution of routing labels) within the EVPN instance (e.g., MP-BGP may be used).

[0037] Each one of access NDs 111-114 is assigned a respective aliasing label that is communicated to the other network devices to enable the other network devices to forward packets towards the access ND. The aliasing label indicates whether the network device is coupled with a group of access links (e.g., 125) and may be used for forwarding packets of the group of access links. Each one of the NDs 111-113 has an associated aliasing label AL11, AL12, AL13 indicating that the respective device is coupled with a group of access links (125). In one non-limiting example, the aliasing label is carried as part of Ethernet Auto-discovery Route (EAD) (e.g., the aliasing label is the MPLS label part of the EAD) advertised by an access network device for a given Ethernet Segment.

[0038] Each one of the access links 121-123, which are part of the group of links 125, is associated with an attribute indicative of the forwarding characteristics and capacity of the link. The attribute, which is referred to herein as an access link capacity (ALC) indicator, is representative of the capacity (in terms of bandwidth and/or speed) of a respective access link from the group of links for processing traffic from a remote network device (e.g., ND 102) towards the destination network device (e.g., ND 101). In one embodiment, the ALC indicator of an access link from the group of links 125 is a normalized representation of speed, bandwidth and/or of any other parameter that characterizes forwarding attributes of an associated access link. In some embodiments, the parameter that characterized the forwarding attribute of an associated access link is determined by an administrator of the network 100.

[0039] The determination and assignment of an ALC indicator to each access link from the group of access links is performed based on similar link characteristics. In one embodiment, each ALC indicator is representative of the speed (i.e., forwarding rate) of its associated access link. In another embodiment, each ALC indicator is representative of the bandwidth of its associated link. In other embodiments, each ALC indicator is representative of the speed and bandwidth of its associated link. Other parameters representative of the forwarding

characteristics of an access link can be used to determine the ALC indicator for each link that is part of the same group of links.

[0040] The ALC indicator is configured at each associated ND for a given access link. For example, as illustrated in the exemplary scenario of Figure 1 , ND 111 is configured with respective ALC1 indicator (that is associated with the access link 121 and has a value X), ND 112 is configured with respective ALC2 indicator (that is associated with the access link 122 and has a value Y), and ND 113 is configured with respective ALC3 indicator (that is associated with the access link 123 and has a value Z). In some embodiments, the ALC indicator of each link is determined relative to other ALC indicators of the other access links that are part of the same group of links. For example, each one of the values assigned to the indicators ALC1, ALC2 and ALC3 respectively can be determined respective to one another based on the forwarding characteristics of each link. As illustrated in the example of Figure 1, ALC1 indicator is assigned a value 20%, ALC2 indicator is assigned a value 30%, and ALC3 indicator is assigned a value 50%, which are determined with respect to the capacity and forwarding characteristics of one another.

[0041] In other embodiments, the ALC indicator of each link is assigned a value

independently of the other ALC indicators. For example, ALC1 indicator can be assigned a value 4, ALC2 indicator is assigned a value 4, and ALC3 indicator is assigned a value 8. In these embodiments, the following operation of distributing the traffic across the access network devices is performed based on the ALC indicator of each link relative to the ALC indicators of the other access links forming the group of links 125. For example, it is determined that 25% (i.e., 4/(4+4+8)) of traffic should go on the link 121 coupling ND 111 to ND 101; that 25% (i.e., 4/(4+4+8)) of traffic should go on link 122 coupling ND 112 to ND 101; and that 50% (i.e., 8/(4+4+8)) of traffic should go on link 123 coupling ND 113 to ND 101. While Figure 1 shows that each of NDs 111-113 is coupled to ND 101 with a single access link associated with a respective ALC indicator, in other embodiments, one or more of NDs 111-113 may be coupled to ND 101 with more than one access link, where each access link is associated with a respective ALC indicator.

[0042] At operation 1, each one of NDs 111-113 is operative to advertise the ALC indicator associated with the access link towards a remote ND 114. Each ALC indicator, ALC1, ALC2, and ALC3 can be advertised independently of one another from a respective ND. The ALC indicator associated with an access link is propagated to all distinct remote NDs for enabling load-balancing of traffic destined to the destination network device ND 101. While Figure 1 illustrates a single remote ND 114 forwarding traffic (received from ND 102) towards destination ND 101, this scenario is intended to be exemplary only. In other scenarios, multiple remote NDs receive the advertised ALC indicator. For example, the access capacity indicator is propagated by a respective ND to all distinct remote NDs (e.g., all remote PEs that originates traffic destined to the destination ND) enabling optimal load-balancing of the aliased Layer 2 traffic.

[0043] In some embodiments, the ALC indicator is advertised to the ND 114 via a routing and reachability protocol. For example, the ALC indicator can be advertised as part of a route/path advertised for a given EVPN instance (including the NDs 101-103, and NDs 111-114) and a given Ethernet Segment instance (e.g., the group of links 125) to all NDs which are peers of the network device with respect to the routing and reachability protocol. Upon association of an EVPN instance (EVI) with an Ethernet Segment Instance (ESI), a route update is propagated to all the neighbors (i.e., peers) of a respective access ND within the EVI. In some

embodiments, the access NDs propagate the ALC indicators to the remote ND using a new generic BGP path attribute Type propagated as part of an update message (e.g., EAD message) for the given EVPN instance and Ethernet Segment. The new BGP path attribute is a transitive Type Length Value (TLV) attribute. In one non-limiting embodiment, the type may be a 2 Byte field identifying the field as an ALC indicator, the length may be a 1 Byte field indicating the length of the value field of the ALC indicator, and a 4 Byte value including a number (e.g., a normalized number) representing the ALC indicator value.

[0044] The provisioning of the ALC indicator though the BGP path attribute provides an automatic mapping between the EVI/ESI route towards an access link and the ALC indicator associated with the access link.

[0045] In some embodiments, the ALC indicator is propagated through the EAD message updates through the network 100. As will described in further details below, the ALC indicator associated with an access link is propagated within an autonomous system or across autonomous systems. For example, the ALC indicator can be propagated through Internal BGP (iBGP) within an autonomous system or through External BGP (eBGP) from a first autonomous system to another autonomous system. Thus contrary to existing load balancing attributes (e.g., Local preference, or Multi Exit Discriminator (MED), which are respectively limited to iBGP or eBGP respectively), the access link capacity indicator can be used in various topology scenarios.

[0046] While the propagation/advertisement of the ALC indicator has been described with reference to a BGP path attribute, the embodiments are not so limited. In other embodiments, the ALC indicator can be provisioned to remote NDs through other technologies such as Software- Defined Networking (SDN), Network Configuration Protocol (NETCONF), Command Line Interface (CLI), etc. Further, in some embodiments, the access NDs may be operative to enable that a ALC indicator be removed from a route.

[0047] The ALC indicators cause the remote ND 114 to forward traffic, at operation 2, to the ND 101 by load balancing the traffic through the NDs 111, 112 and 113 based on their respective ALC indicators. The receipt of the ALC indicators cause the updates of control and communication information (e.g., routing tables) and forwarding tables at the ND 114 for forwarding traffic towards the destination ND 101 through the access NDs 111-113. In one embodiment, when the ALC indicator is propagated through a BGP path attribute, upon receipt of the ALC indicator, the aliasing label forwarding construct (e.g., an aliasing label forwarding table) is programmed with a load distribution algorithm that is based on the received ALC indicators and their respective associated EAD/EVI/ESI route. The ND 114 efficiently distributes traffic in proportion to the received ALC indicators among the access NDs when forwarding aliased traffic. Referring back to the example of Figure 1 , when forwarding aliased Layer 2 destination traffic from ND 102, 20% of traffic is forwarded via aliased packets (AL1) trough ND 111 ; 30% of traffic is forwarded via aliased packets (AL2) through ND 112; and 50% of traffic is forwarded via aliased packets (AL3) through ND 113.

[0048] The load balancing of traffic can be performed based on various load balancing mechanisms without departing from the scope of the present invention. As will be described in further details, the load balancing algorithms are adapted based on the received ALC indicator for each ND. For example, a weighted round robin can be used. In some embodiments, upon receipt of the ALC indicator, the remote ND 114 provides the ALC indicator as an input to a load balancing mechanism that is selected based on a 'user policy' . The 'user policy' provides a configuration mechanism for an administrator/operator of the network 100 to select a forwarding load balancing/distribution algorithm that will distribute traffic towards the access NDs 111-113.

[0049] After an initial setup of the topology of the network 100 (e.g., an initial configuration of the EVPN instance), any change to an ALC indicator value at one or more access links of a group of links is automatically reflected by recalculating, at the remote ND 114, the load share distribution of aliased unicast traffic associated with all the access links of the group of links. That is, a change in any one or more of ALC1, ALC2, and ALC3 indicator values results in recalculation of the load share distribution of the traffic to all of access links 121, 122, and 123 of the group of links 125. The new value of an ALC indicator value (a new value assigned to any of ALC1, ALC2, or ALC3 indicators) can be distributed through an update message of a routing and reachability protocol (e.g., through a BGP message update).

[0050] In one embodiment, the techniques described herein enable efficient use of access link resources (bandwidth and speed) in an EVPN instance when forwarding traffic from a remote ND (e.g., a remote PE) to a multi-homed destination ND (e.g., multi-homed CE). When the ALC indicator is advertised through BGP, any application dependent on BGP to make control plane or forwarding plane decisions can use the ALC indicator to provide efficient and optimal forwarding in a network. While the embodiments are described with respect to EVPN, in other embodiments, the techniques described herein apply to other types of virtual Layer 2 networks, in which a destination ND is multi-homed to multiple access NDs.

[0051] Exemplary Deployment Scenarios:

[0052] The ALC indicator can be used in various topology scenarios as will be described in further details below. Figure 2 illustrates a block diagram of an exemplary autonomous system in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic across multiple access network devices in accordance with some embodiments. Figure 2 illustrates the use case of this solution as part of an intra-Autonomous System (AS) deployment in which iBGP is used as a routing and reachability exchange protocol. In the exemplary scenario, an Autonomous system 205 is deployed including the access NDs 211-214. The access NDs 211 and 212 are coupled with the destination ND 201. The access ND 213 is coupled with the ND 202 and the access ND 214 is coupled with the ND 203. The access link bandwidth from ND 211 to ND 201 is 400Gigabits/s, and from ND 212 to ND 201 is 600Gigabits/s for the same Ethernet Segment 225.

[0053] The Ethernet Segment bandwidths (400G and 600G) of ND 211 and ND 212 are normalized (40% and 60%) and then advertised in ALC indicators (ALC21 and ALC22) as part of a path attribute of EAD/ESI route towards ND 213 and ND 214. Upon receipt of the aliased information (i.e., the aliasing labels (AL21 and AL22) associated with each access ND (ND 211 and ND 212 respectively)) from EAD/EVI/ESI route and the ALC indicator for each access link, each of the NDs 213 and 214 is operative to program the forwarding plane aliasing label forwarding table. ALC indicators (ALC21 and ALC22) are respectively used to calculate and program the aliasing label forwarding table. The aliasing label forwarding table is used to forward aliased traffic towards the ND 201. Referring to the illustrated example of Error! Reference source not found.2, the aliased traffic from the remote ND 213 is load balanced with 40% and 60% ratios towards ND 211 and ND 212 respectively. Similarly the aliased traffic from the remote ND 214 is load balanced with 40% and 60% ratios towards ND 211 and ND 212 respectively.

[0054] In some embodiments, an access link capacity indicator provides a mechanism for a network device part of a local autonomous system to convey to an adjacent autonomous system the optimal entry point into an access link of the local AS. Figure 3 illustrates a block diagram of an exemplary scenario in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic forwarded across autonomous systems in accordance with some embodiments. The exemplary scenario of Figure 3 presents an example of Inter- AS Option B or 2547bis option B, as described in IETF RFC 4364: "BGP/MPLS IP Virtual Private Networks (VPNs)", February 2006. Inter-AS Option uses BGP to signal VPN labels (e.g., aliasing labels) between the AS boundary network devices. The base MPLS tunnels are local to each AS.

Stacked tunnels run from end to end between PE routers on the different ASs.

[0055] In the illustrated example of Figure 3, a first AS 305 is coupled with a second AS 306. The first AS 305 includes edge NDs, ND 311, ND 312 and ND 314. The ND 311 and ND 312 are coupled to a destination ND 301 through access links of an Ethernet Segment 325. The second AS 306 includes edge NDs, ND 315 and ND 316. ND 316 is coupled with ND 302 and forwards traffic 340 destined to ND 301, which can be reached through AS 306 and AS 305 and the Ethernet Segment 325. The ALC indicators associated with each one of the access links of the Ethernet Segment 325, respectively coupling ND 311 with ND 301 and ND 312 with ND 301, are propagated to the BGP peers of the NDs without modification. [0056] Upon receipt of the EAD/EVI/ESI route updates and ALC indicator from each of the NDs 311 and 312, ND 314 is operative to program the forwarding plane aliasing label forwarding table. Each of the ALC indicators is used to calculate and program the aliasing label forwarding table. The traffic received at the ND 314 and destined to destination ND 301 is forwarded towards ND 311 based on an aliasing Label AL31 , and it is forwarded towards ND 312 based on an aliasing label AL32. While the forwarding of the traffic and selection of the routes is performed based on the aliasing labels, the ALC indicator influences the distribution of the load across the different routes. The ND 315 and ND 314 are Autonomous System Boundary Routers (ASBR) operating in Option B. Thus while there is a single path connecting the two AS (and the two ASBRs ND 315 and ND 314), the aliased traffic originating from ND 316 is divided in proportion to the capacity of the access links (i.e., 40% towards ND 311 with AL59 from ND 316 to ND 315, and with AL19 between ND 315 and ND 314, and with AL31 from ND314 to ND 311; and 60% towards ND 312 with AL69 from ND 316 to ND 315, and with AL29 between ND 315 and ND 314, and with AL32 from ND 314 to ND 312).

[0057] Figure 4 illustrates a block diagram of an exemplary scenario in which access link capacity indicators are used to enable load balancing of Layer 2 destination traffic forwarded across autonomous systems in accordance with some embodiments. Figure 4 illustrates a deployment scenario in which VPN Option C (as described in IETF RFC 4364: "BGP/MPLS IP Virtual Private Networks (VPNs)", February 2006) is used. Option C introduces multihop eBGP redistribution of labeled routes between source and destination autonomous systems.

[0058] In the illustrated example, there is a first Multi-Hop eBGP session between ND 411 and ND 416 and a second Multi-Hop eBGP session between ND 412 and ND 416. The Ethernet Segment bandwidths of ND 411 and ND 412 (400G and 600G) are normalized (40% and 60% respectively) and then advertised in ALC indicator path attributes of EAD/ESI routes towards ND 416. Upon receipt of the EAD/EVI/ESI route and ALC indicator from each of the NDs 411 and 412, ND 416 is operative to program the forwarding plane aliasing label forwarding table. Each of the ALC indicators (ALC41 and ALC42) is used to calculate and program the aliasing label forwarding table. The aliased traffic originating from ND 416 and destined to ND 401 is divided in proportion to the bandwidth capacity of each access link (i.e., 40% towards ND 411 and 60% towards ND 412).

[0059] The operations in the 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.

[0060] Figure 5 illustrates a flow diagram of operations for advertising an access link capacity indicator of an access link causing the load balancing of traffic across multiple access links in accordance with some embodiments. At operation (502), a first access link capacity indicator (e.g., ALC1) is advertised to one or more remote network devices (e.g., ND 114). The first access link capacity indicator is representative of forwarding capacities of a first access link coupling a first access network device with a destination network device. The first access link is one of a plurality of access links coupling the destination network device with a plurality of access network devices including the first access network device. The access link capacity indicator can be representative of bandwidth and/or speed capacity of the access link. Flow then moves to operation 504, at which, following receipt of the access link capacity indicator, the one or more remote network devices are caused to forward traffic to the destination network device through the first access network device by load balancing the traffic across the plurality of access network devices according to the first access link capacity indicator and to other access link capacity indicators of other access network devices from the plurality of access network devices. In some embodiments, the operations 502 and 504 are performed at an access network device (e.g., ND 111, 211, 311, or 411) coupled with the destination ND through the access link.

[0061] Figure 6 illustrates a flow diagram of operations for load balancing traffic across access network devices in accordance with some embodiments. At operation (602), a first access link capacity indicator is received. The first access link capacity indicator is representative of forwarding capacities of a first access link coupling a first access network device with a destination network device. The first access link is one of a plurality of access links coupling the destination network device with a plurality of access network devices including the first access network device. At operation (604), a second access link capacity indicator is received. The second access link capacity indicator is representative of forwarding capacities of a second access link coupling a second access network device with the destination network device. The plurality of access links includes the second access link, and the plurality of access network devices includes the second access network device. Flow then moves to operation (606) at which, the traffic is load balanced across first and second paths based on the first and the second access link capacity indicators. The load balancing of the traffic across the first and the second paths includes forwarding a first portion of the traffic across the first path towards the destination network device through the first access network device, and forwarding a second portion of the traffic across the second path towards the destination network device through the second access network device. In some embodiments, the operations 602, 604 and 606 are performed at network devices such as remote network device (e.g., ND 114, 214, 314, or 414) coupled with the destination ND through the first and second access links and the first and second access network devices. In other embodiments, the operations 602 and 604 may be performed at a centralized network controller (e.g., an SDN controller) and causes the load balancing of the traffic, at a remote network device (e.g., ND 114, 214, 314, or 414) as described with reference to operation 606 and the exemplary scenarios described with reference to Figures 1-4.

[0062] The operations described with reference to the flow diagrams of Figures 5 and 6 can be performed at an initial setup stage, where topology of the network 100 is initialized (e.g., an initial configuration of the EVPN instance). Alternatively or additionally these operations can be performed at subsequent stages, following the initialization stage, such as any change to an ALC indicator value at one or more access links of a group of links is automatically reflected by recalculating, at the remote NDs, the load share distribution of aliased unicast traffic associated with all the access links of the group of links. A new value of an ALC indicator value can be distributed through an update message of a routing and reachability protocol (e.g., through a BGP message update) and result in an optimal update of the forwarding capabilities of the access NDs in a network.

[0063] Architecture

[0064] 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.

[0065] 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).

[0066] 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 700A-700B, 700B-700C, 700C-700D, 700D-700E, 700E-700F, 700F-700G, and 700A-700G, as well as between 700H and each of 700A, 700C, 700D, and 700G. 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, 700E, and 700F 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).

[0067] 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 special-purpose operating system (OS); and 2) a general purpose network device 704 that uses common off-the-shelf (COTS) processors and a standard OS.

[0068] 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., 730A).

[0069] 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.

[0070] 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).

[0071] 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. For example, in one such alternative 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 that may each be used to execute one (or more) of the sets of applications 764A-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 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 each of the sets of applications 764A-R is run on top of a guest operating system within an instance 762A-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 unikernel(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 740, 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 unikernels running directly on a hypervisor represented by virtualization layer 754, unikernels running within software containers represented by instances 762A-R, or as a combination of unikernels and the above-described techniques (e.g. , unikernels and virtual machines both run directly on a hypervisor, unikernels and sets of applications that are run in different software containers).

[0072] The instantiation of the one or more sets of one or more applications 764A-R, as well as virtualization if implemented, are collectively referred to as software instance(s) 752. Each set of applications 764A-R, corresponding virtualization construct (e.g., instance 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), forms a separate virtual network element(s) 760A-R.

[0073] 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). While embodiments of the invention are illustrated with each instance 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 instances 762A-R to VNEs also apply to embodiments where such a finer level of granularity and/or unikernels are used.

[0074] 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 instances 762A-R and the NIC(s) 744, as well as optionally between the instances 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)).

[0075] The third exemplary ND implementation in Figure 7A is a hybrid network device 706, 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 702) could provide for para-virtualization to the networking hardware present in the hybrid network device 706. [0076] 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 code point (DSCP) values.

[0077] 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 700 A and forward packets outside of ND 700 A; VNE 770 A.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 700 A; and VNE 770 A. 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).

[0078] 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 instances 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.

[0079] 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).

[0080] 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).

[0081] 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).

[0082] 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.

[0083] 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.

[0084] 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) (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 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.

[0085] 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.

[0086] 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).

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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 700 A-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).

[0091] 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.

[0092] 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. [0093] 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).

[0094] 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.

[0095] In embodiments that use compute virtualization, the processor(s) 842 typically execute software to instantiate a virtualization layer 854 (e.g., in one embodiment 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 instances 862A-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 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 an application is run on top of a guest operating system within an instance 862A-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 unikernel can run directly on hardware 840, directly on a hypervisor represented by virtualization layer 854 (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 862A-R). Again, in embodiments where compute virtualization is used, during operation an instance of the CCP software 850 (illustrated as CCP instance 876A) is executed (e.g., within the instance 862A) on the virtualization layer 854. In embodiments where compute virtualization is not used, the CCP instance 876A is executed, as a unikernel or on top of a host operating system, 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 instances 862A-R if implemented, are collectively referred to as software instance(s) 852.

[0096] 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.

[0097] 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.

[0098] 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). [0099] 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.

[00100] 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.

[00101] 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.

[00102] 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.

[00103] Certain NDs (e.g., certain edge NDs) internally represent end user devices (or sometimes customer premise equipment (CPE) such as a residential gateway (e.g., a router, modem)) using subscriber circuits. A subscriber circuit uniquely identifies within the ND a subscriber session and typically exists for the lifetime of the session. Thus, a ND typically allocates a subscriber circuit when the subscriber connects to that ND, and correspondingly deallocates that subscriber circuit when that subscriber disconnects. Each subscriber session represents a distinguishable flow of packets communicated between the ND and an end user device (or sometimes CPE such as a residential gateway or modem) using a protocol, such as the point-to-point protocol over another protocol (PPPoX) (e.g., where X is Ethernet or

Asynchronous Transfer Mode (ATM)), Ethernet, 802.1Q Virtual LAN (VLAN), Internet Protocol, or ATM). A subscriber session can be initiated using a variety of mechanisms (e.g., manual provisioning a dynamic host configuration protocol (DHCP), DHCP/client-less internet protocol service (CLIPS) or Media Access Control (MAC) address tracking). For example, the point-to-point protocol (PPP) is commonly used for digital subscriber line (DSL) services and requires installation of a PPP client that enables the subscriber to enter a username and a password, which in turn may be used to select a subscriber record. When DHCP is used (e.g., for cable modem services), a username typically is not provided; but in such situations other information (e.g., information that includes the MAC address of the hardware in the end user device (or CPE)) is provided. The use of DHCP and CLIPS on the ND captures the MAC addresses and uses these addresses to distinguish subscribers and access their subscriber records.

[00104] 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.

[00105] 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.

[00106] For example, 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.).

[00107] 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 access network device that is one of a plurality of access network devices coupled with a destination network device through a plurality of access links, of load balancing traffic across the plurality of access network devices, the method comprising:

advertising (502) a first access link capacity indicator to one or more remote network devices, wherein the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling the first access network device with the destination network device; and

causing (504) the one or more remote network devices to forward traffic to the

destination network device through the first access network device by load balancing the traffic across the plurality of access network devices according to the first access link capacity indicator and to other access link capacity indicators of other access network devices from the plurality of access network devices.

2. The method of claim 1 , wherein the forwarding capacities include at least one of a speed and a bandwidth capacity of the access link.

3. The method of claim 1, wherein advertising the first access link capacity indicator is performed by transmitting the access link capacity indicator as a path attribute part of a route propagation mechanism.

4. The method of claim 3, wherein the route propagation mechanism is Multiprotocol Border Gateway Protocol (MP-BGP) and the access link capacity indicator is advertised as part of an Ethernet Auto-discovery Route (EAD) message.

5. The method of claim 1, wherein the plurality of access network devices is part of an Ethernet Virtual Private Network (EVPN) instance.

6. A method in a network device for enabling load balancing of traffic across a plurality of access network devices coupled with a destination network device through a plurality of access links, the method comprising:

receiving (602) a first access link capacity indicator, wherein the first access link

capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling a first access network device with the destination network device;

receiving (604) a second access link capacity indicator, wherein the second access link capacity indicator is representative of forwarding capacities of a second access link from the plurality of access links, the second access link coupling a second access network device with the destination network device; and

load balancing (606) traffic across first and second paths based on the first and the

second access link capacity indicators, wherein the load balancing traffic across the first and the second paths includes forwarding a first portion of the traffic across the first path towards the destination network device through the first access network device, and forwarding a second portion of the traffic across the second path towards the destination network device through the second access network device.

7. The method of claim 6, wherein the forwarding capacities include at least one of a speed and a bandwidth capacity of a respective access link.

8. The method of claim 6, wherein the first access link capacity indicator and the second access link capacity indicator are received as a first and a second path attribute part of a route propagation mechanism.

9. The method of claim 8, wherein the route propagation mechanism is Multiprotocol Border Gateway Protocol (MP-BGP) and the first access link capacity indicator and the second access link capacity indicator are received as part of Ethernet Auto-discovery Route (EAD) messages.

10. The method of claim 6, wherein the plurality of access network devices is part of an Ethernet Virtual Private Network (EVPN) instance.

11. A first access network device that is one of a plurality of access network devices coupled with a destination network device through a plurality of access links, for enabling load balancing traffic across the plurality of access network devices, the first access network device comprising: a non-transitory computer readable medium to store instructions; and

a processor coupled with the non-transitory computer readable medium to process the stored instructions to:

advertise (502) a first access link capacity indicator to one or more remote

network devices, wherein the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling the first access network device with the destination network device; and

cause (504) the one or more remote network devices to forward traffic to the destination network device through the first access network device by load balancing the traffic across the plurality of access network devices according to the first access link capacity indicator and to other access link capacity indicators of other access network devices from the plurality of access network devices.

12. The first access network device of claim 11, wherein the forwarding capacities include at least one of a speed and a bandwidth capacity of the access link.

13. The first access network device of claim 11, wherein to advertise the first access link capacity indicator is performed by transmitting the access link capacity indicator as a path attribute part of a route propagation mechanism.

14. The first access network device of claim 13, wherein the route propagation mechanism is Multiprotocol Border Gateway Protocol (MP-BGP) and the access link capacity indicator is advertised as part of an Ethernet Auto-discovery Route (EAD) message.

15. The first access network device of claim 11, wherein the plurality of access network devices is part of an Ethernet Virtual Private Network (EVPN) instance.

16. A network device for enabling load balancing of traffic across a plurality of access network devices coupled with a destination network device through a plurality of access links, the network device comprising:

a non-transitory computer readable medium to store instructions; and

receive (602) a first access link capacity indicator, wherein the first access link capacity indicator is representative of forwarding capacities of a first access link from the plurality of access links, the first access link coupling a first access network device with the destination network device;

receive (604) a second access link capacity indicator, wherein the second access link capacity indicator is representative of forwarding capacities of a second access link from the plurality of access links, the second access link coupling a second access network device with the destination network device; and

load balance (606) traffic across first and second paths based on the first and the second access link capacity indicators, wherein the load balancing traffic across the first and the second paths includes forwarding a first portion of the traffic across the first path towards the destination network device through the first access network device, and forwarding a second portion of the traffic across the second path towards the destination network device through the second access network device.

17. The network device of claim 16, wherein the forwarding capacities include at least one of a speed and a bandwidth capacity of a respective access link.

18. The network device of claim 16, wherein the first access link capacity indicator and the second access link capacity indicator are received as a first and a second path attribute part of a route propagation mechanism.

19. The network device of claim 18, wherein the route propagation mechanism is

Multiprotocol Border Gateway Protocol (MP-BGP) and the first access link capacity indicator and the second access link capacity indicator are received as part of Ethernet Auto-discovery Route (EAD) messages.

20. The network device of claim 16, wherein the plurality of access network devices is part of an Ethernet Virtual Private Network (EVPN) instance.