WO2017144945A1

WO2017144945A1 - Method and apparatus for multicast in multi-area spring network

Info

Publication number: WO2017144945A1
Application number: PCT/IB2016/050983
Authority: WO
Inventors: David Ian Allan
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2016-02-23
Filing date: 2016-02-23
Publication date: 2017-08-31
Anticipated expiration: 2018-08-23

Abstract

A method is implemented by a network device that functions as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (L1) network and the second area is a level 2 (L2) network. The method supports the interworking of areas in the hierarchical computed SPRING network.

Description

METHOD AND APPARATUS FOR MULTICAST IN MULTI-AREA

SPRING NETWORK

FIELD

[0001] Embodiments of the invention relate to the field of interworking of communication networks; and more specifically, to multi-area configurations that support multicast for source packet in routing (SPRING) networks.

BACKGROUND

[0002] Shortest path bridging (SPB) is a protocol related to computer networking for the configuration of computer networks that enables multipath routing. In one embodiment, the protocol is specified by the Institute of Electrical and Electronics Engineers (IEEE) 802. laq standard. This protocol replaces prior standards such as spanning tree protocols. SPB enables all paths in the computing network to be active with multiple equal costs paths being utilized through load sharing and similar technologies. The standard enables the implementation of logical Ethernet networks in Ethernet infrastructures using a link state protocol to advertise the topology and logical network memberships of the nodes in the network. SPB implements large scale multicast as part of implementing virtualized broadcast domains. A key distinguishing feature of the SPB standard is that the MDTs are computed from the information in the routing system's link state database via an all-pairs- shortest-path algorithm, which minimizes the amount of control messaging to converge multicast.

[0003] SPRING is an exemplary profile of the use of MPLS technology whereby global identifiers are used in the form of a global label assigned per label switched route (LSR) used for forwarding to that LSR. A full mesh of unicast tunnels is constructed via every node in the network computing the shortest path to every other node and installing the associated global labels accordingly. In the case of SPRING, this also allows explicit paths to be set up via the application of label stacks at the network ingress. Encompassed with this approach is the concept of a strict (every hop specified) or loose (some waypoints specified) route dependent on how exhaustively the ingress applied label stack specifies the path.

[0004] Proposals have been made to use global identifiers in the dataplane combined with the IEEE 802. laq technique of advertising multicast registrations in the interior gateway protocol (IGP) and replicating the "all pairs shortest path" approach of IEEE 802. laq to compute MDTs without the additional handshaking. Such an approach would inherit a lot of desirable properties embodied in the IEEE 802. laq approach, primarily in the simplification of the amount of control plane exchange required to converge the network. Further proposals have been made to combine the IEEE 802. laq approach with SPRING tunneling such that multicast distribution tree construction is a hybrid of sparsely deployed multicast state and unicast tunnels.

[0005] Given the above context, a node in the SPRING network could compute its role in implementing any given multicast (S, G) tree in a scenario where it had complete visibility of the network topology. An algorithm that starts with all pairs shortest path computation augmented with algorithms to identify the nodes with specific roles of source, leave or replication point may be employed by each node. Existing unicast tunnels may be used between sources, replication points and leaves of an MDT such that the overall amount of state in the network is minimized. However, these advantages of SPRING networks do not work across administrative boundaries where topology is obscured or abstracted such that multicast can take advantage of these efficiencies.

SUMMARY

[0006] In one embodiment, a first method is implemented by a network device. The network device functions as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network. The method includes receiving an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, advertising the logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, determining whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, advertising a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and advertising a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

[0007] In one embodiment, another method is implemented by a network device. The network device functions as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in second area are represented as virtual nodes a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network. The method includes receiving an advertisement of a send/receive interest from the L2 network for a multicast group with a source in the L2 network, advertising a logical OR of send/receive interest in the multicast group into the L2 network using a global label for the multicast group and proxying a send/receive interest for the virtual node into the LI network, in response to the border node being on the shortest path, advertising a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network, and advertising a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network.

[0008] In a further embodiment, a network device functions as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network. The network device includes a non-transitory machine readable storage device having stored therein a multi-area multicast manager, and a processor configured to execute the multi-area multicast manager. The multi-area multicast manager is configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise the logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

[0009] A computing device is in communication with a network device in a network implementing multicast using unicast tunneling. The computing device executes a plurality of virtual machines for implementing network function virtualization (NFV). The network device functioning as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network. The computing device includes a non-transitory machine readable storage device having stored therein a multi-area multicast manager, and a processor configured to execute a virtual machine from the plurality of virtual machines. The virtual machine to execute the multi-area multicast manager. The multi- area multicast manager is configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise the logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

[0010] A control plane device is configured to implement a control plane of a software defined networking (SDN) network including a network device in a network with a plurality of network devices, wherein the control plane device is configured to configure the network device. The network device implements multicast using unicast tunneling. The network device functions on a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network. The control plane device includes a non- transitory machine readable storage device having stored therein a multi-area multicast manager, and a processor configured to execute the multi-area multicast manager. The multi-area multicast manager is configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise the logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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:

[0012] Figure 1 is a flowchart of one embodiment of process for an operation of a border node between two source packet in routing (SPRING) networks.

[0013] Figure 2 is a flowchart of one embodiment of process for an operation of a border node between two source packet in routing (SPRING) networks.

[0014] Figure 3A is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0015] Figure 3B is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0016] Figure 3C is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0017] Figure 3D is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0018] Figure 3E is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0019] Figure 3F is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0020] Figure 3G is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network.

[0021] Figure 4A 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.

[0022] Figure 4B illustrates an exemplary way to implement a special-purpose network device according to some embodiments of the invention.

[0023] Figure 4C illustrates various exemplary ways in which virtual network elements (VNEs) may be coupled according to some embodiments of the invention.

[0024] Figure 4D 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.

[0025] Figure 4E 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.

[0026] Figure 4F 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.

[0027] Figure 5 illustrates a general purpose control plane device with centralized control plane (CCP) software 550), according to some embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

[0028] The following description describes methods and apparatus for providing a multi-area implementation of multicast in a source in packet routing (SPRING) domains. The multi-area SPRING domain may have a hierarchical organization. A second level area in a pairwise relationship is represented into the adjacent first level area as a single virtual node by the border nodes. The border nodes proxy the interworking of interior gateway protocol (IGP) announcements and dataplane forwarding between the areas in order to condense state and facilitate topology abstraction. The technique is designed such that the second level area is abstracted to a single virtual node that is represented into the first level area, and the first level area's topology is collapsed onto the border nodes in the second level area. Therefore no topology information about peer areas is shared outside the border nodes, such that the scaling properties of the multi-area solution are not compromised. Multi-area capability enhances the scalability of the network, not least in response to the fact that computed multicast' s

computational complexity is exponentially in proportion to network size. The embodiments provide a multi-area solution that makes scale a divisible problem.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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).

[0035] 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.

[0036] Next hop selection by the routing system for a given destination may resolve to one path (that is, a routing protocol may generate one next hop on a shortest path); but if the routing system determines there are multiple viable next hops (that is, the routing protocol generated forwarding solution offers more than one next hop on a shortest path - multiple equal cost next hops), some additional criteria is used - for instance, in a connectionless network, Equal Cost Multi Path (ECMP) (also known as Equal Cost Multi Pathing, multipath forwarding and IP multipath) may be used (e.g., typical implementations use as the criteria particular header fields to ensure that the packets of a particular packet flow are always forwarded on the same next hop to preserve packet flow ordering). For purposes of multipath forwarding, a packet flow is defined as a set of packets that share an ordering constraint. As an example, the set of packets in a particular TCP transfer sequence need to arrive in order, else the TCP logic will interpret the out of order delivery as congestion and slow the TCP transfer rate down.

[0037] SPRING Networks

[0038] The embodiments utilize the computations of multicast distribution trees (MDTs) and the exemplary information available in shortest path bridging (SPB) implementations such as IEEE 802. laq adapted to other technologies. In IEEE 802. laq multicast registrations are advertised in the interior gateway protocol (IGP), thus all nodes in the network have multicast group membership information about the other nodes in the network and are explicitly delegated with the task of determining their role in each MDT on the basis of information in the IGP.

[0039] In one embodiment for a SPRING network multicast registrations would identify both the multicast group and the global label or "multicast segment identifier" a given source intended to use for the MDT.

[0040] IEEE 802. laq performs an all-pairs shortest path computation that determines a path from all nodes in a network to all other nodes in the network that selects a shortest path to each node from a source node. When combined with the tie breaking algorithms specified in IEEE 802. laq the result is an acyclic shortest path tree. Multicast distribution trees can also be computed in a similar manner as they can be derived from the shortest path trees using the notion of reverse path forwarding. With the use of multicast protocol label switching (MPLS) a global multicast label is assigned by the management system and used on a per (S, G) multicast distribution tree basis. The (S, G) notation indicates an S - source and G - multicast group relation where the multicast tree has a single source and a group of listeners in a network, and more than one source may send traffic to the group implying multiple (S,G) trees may be employed as part of the overall construction of a multicast group. The multicast labels in the network are globally unique and carried end to end (E2E). This is inherent to the operation of SPRING. A multicast implementation MPLS could also be envisioned that combined IGP registrations and an LDP signaled unicast tunnel mesh could also be adapted to carry the labels E2E.

[0041] The example embodiments utilize SPRING for unicast tunneling. As a consequence of SPRING operation, upon nodal convergence to align with the view of the network available via the IGP, the local forwarding information base (LFIB) of each network device in the network will have at least one unicast SPRING-label switched route to each other LSR. It is not necessary, but assumed that the network will also utilize penultimate-hop popping (PHP) on SPRING based LSPs where the outermost label is removed before being forwarded to the last hop to a destination. [0042] After a shortest path first (SPF) tree (i.e., an (S, *) tree where S indicates the node is the source and * indicates the tree reaches all nodes) is computed for a given node that node can then determine whether it is a source, a leaf or a replication node for each possible (S, G) MDT. If the node has one of these three roles in a given MDT it will then install the appropriate state for each, whereas if the node does not participate in the MDT in any of the three roles then no state needs to be installed for that MDT. The installed state where the node is a source or a replicating node utilizes established a priori unicast tunnels to deliver multicast packets to downstream non-adjacent leaves or replicating nodes. Tunnels do not need to be established for downstream immediately adjacent nodes that have a role in the MDT as they will have installed state for the MDT. Knowledge of the role of each node in the network in relation to a given MDT is an artifact of the all-pairs shortest path computation.

[0043] Overview

[0044] The computational complexity of the computed with tunnels approach to SPRING multicast is exponentially proportional to network size. The embodiments permit the benefits of the computed with tunnels approach to be extended to larger networks by dividing the size of the individual computational domains to mitigate the exponential nature of the computed solution. The multi-area SPRING multicast embodiments carry forward many of the properties of other multi-area solutions. The topology of each area is abstracted between the areas, such that with the exception of the border nodes, the areas are not aware of the details of the topology of other areas. The multi-area SPRING networks of the embodiments maintain the characteristics of single area SPRING networks in terms of bandwidth efficiency and the use of minimal state in the forwarding plane.

[0045] Generally, designated router election schemes have a number of undesirable properties. An ordinal ranking scheme of designated routers (as per EVPN for IEEE 802. laq as defined in RFC 7734) can result in significant network churn when an elected border router fails. The assignment of traffic to border routers on the basis of hashing can offer greater stability when a border router fails (as only the displaced (S,G) trees are shifted), but this may not result in an even or useful distribution of load. Neither ordinal ranking nor hashing will guarantee that the shortest path is utilized or that minimum bandwidth is consumed in any area.

[0046] For the embodiments, it is a design feature that a border router can also be a leaf of a multicast tree. The computed solution of the MDTs for multicast groups in each area should still have the property of being almost minimum cost. In addition, the embodiments are consistent with multi-area unicast SPRING functionality.

[0047] As discussed above, the embodiments work in a context where multicast membership is advertised in the IGP. A domain global label is associated with each (S,G) multicast instance where domain is defined as a routing area (e.g., a first level area (LI) or second level area (L2)). As per IEEE 802. laq there are send/receive attributes associated with each node that participates in a multicast group. A node in the multi-area SPRING network can register sender, receiver, or send/receive interest in a multicast group. MDTs for each S,G multicast group instance are computed using a combination of all pairs shortest path, and pruning. One skilled in the art would understand methods and structures by which border nodes sharing a common area know that each other exist and will not create inter-area loops.

[0048] In some embodiments, a two layer hierarchy is utilized to organize the multi-area SPRING network. The organization may be similar to or work in combination with

Intermediate System - Intermediate System (IS-IS) layer one/ layer two (L1/L2) organization. In one embodiment, all interworking is achieved via processing of knowledge of state visible to the border routers such that they have knowledge of the state in both the local LI and L2 areas. In this embodiment, the second layer (L2) is represented by the border routers between the first layer (LI) and L2 as a single node in L2 "behind" the border routers that is equal cost from all border routers connected to the two areas. This places an additional requirement on the set of border nodes between a given L2 and LI area in that the advertisements representing L2 into the LI IGP need to be synchronized between the border nodes so logically they appear to have come from a single entity; the virtual node in L2. In the following description, a specific border node will originate advertisements into L2 as an artifact of the area interworking function, but all advertisements into LI by any one border router will be mirrored by the other border routers on the area boundary.

[0049] The L2 representation of a virtual node into subtending LI areas, has available a full set of multicast group G labels for all groups G in the network that will be used for multicast traffic originating in L2 and presented into LI as if the source was the virtual node. These labels may be pre -provisioning or derived by other means. These labels are unique within their areas, i.e., labels in LI are unique to LI and labels in L2 are unique to L2. In the embodiments, the labels are multicast segment identifiers (IDs) as mentioned herein above. Similarly each border node has a full set of multicast group labels for traffic originating in the subtending LI and presented into L2 as if the border node was the source.

[0050] Any multicast groups with at least one node registering multicast interest in any LI area is advertised into L2 with the logical OR of the attributes (send or receive interest) by the border node on the shortest path between those nodes registering interest and L2.

[0051] A border node that detects an intersection of interest between LI and L2 (either send interest in LI and receive interest in L2 or vice versa) will in synchronization with the other border routers between the LI and L2 of interest, advertise the L2 interest into LI as if the advertisement originated with the L2 virtual node, and using a globally unique multicast label.

[0052] IGP advertisements in L2 will be required to indicate the LI of origin such that sufficient information exists in the IGP for computing nodes to prevent inter-area multicast loops (i.e., LI multicast traffic looping back into LI via L2).

[0053] The embodiments offer advantages over the prior art. The advantages include improved stability. Losing a border node only disrupts traffic that transits that border node, in contrast, in the prior art a failure in an ordinal ranked system required rearranging the designated routers of all multicast groups not just the handling of the multicast groups transiting the failed border router. The embodiments also offer an improvement in bandwidth efficiency. A path from a node in LI to a node in L2 in the same multicast group is an actual shortest path in the embodiments. However, in the prior art due to the arbitrary selection of a border node as a designated router for a multicast group, the route between nodes is not a shortest path. The embodiments also provide a completely computed solution, which permits a minimum cost/minimum state approach to the management of MDTs to be employed. However, MDTs that transit area boundaries do require state to be maintained at the boundaries (i.e., at the boundary routers). The embodiments may also require overprovisioning of multicast labels or a comparable solution such that each border router has a label per G in L2. Also, the combined L1/L2/L1 path is not necessarily shortest path, but the overall route is likely to be better than where ordinal or hashing based selection mechanisms for designated routers are utilized. Finally, the embodiments permit state summarization at area boundaries in that all multicast traffic for a given group originated in all other areas is condensed to a single MDT in any given LI area.

[0054] While a network with these characteristics is described herein with relation to the embodiments, one skilled in the art would understand that this description is provided by way of example and not limitation. Other technologies, protocols and architectures can be utilized in place or in combination with those described herein where the other technologies function in a similar manner or with similar purpose.

[0055] Figure 1 is a flowchart of one embodiment of process for an operation of a border node between two source packet in routing (SPRING) networks. In the embodiments, the border node begins participation in multi-area SPRING network when receiving an advertisement of a send/receive interest from a LI network node for a multicast group via the LI network interior gateway protocol (IGP) (Block 101). This advertisement may originate from a source in the multicast group in the LI area. The border node may be pre -provisioned with labels for all multicast groups within the SPRING network hierarchy or may have some other mechanism to ensure label uniqueness in L2 for the (Border Router, Group) MDT. The process advertises a logical OR of the send/receive interest for the multicast group from nodes in the LI network for which the border node is on the shortest path into the L2 network via the IGP and specifies a unique global label for the multicast group (Block 103). The unique global label is unique to the border node and the multicast group. The shortest path is determined relative to other border nodes at the L1/L2 boundary.

[0056] A check is made to determine whether a new intersection (i.e., matches that did not exist prior to the received advertisement) exists between advertised send/receive interests from the L2 network and send/receive interests of nodes in the LI network that are on the shortest path to the border node (Block 105) If no such intersections are found, then the process is complete. However, if it is determined that there is an intersection of a send interest in the LI network and a receive interest in the L2 network (Block 109), then the process advertises a receive interest of a virtual node into the LI network (Block 107). If it is determined that there is an intersection of a send interest in the L2 network and a receive interest in the LI network (Block 113), then the process advertises a send interest of the virtual node into the LI network (Block 111). All multicast segments in the multicast group in L2 may be aggregated onto the single segment rooted on the virtual node that are determined to transit the border node into the multicast segment advertised in LI. The border node may track the set of nodes that have sent a send or receive interest and for which it is on the shortest path such that it can remove the interests in the multicast group when there are not interested nodes in LI. If the border node is not on the shortest path for the sending node, then the process advertises a send interest in the multicast group into the L2 network using a unique global label for the multicast group and proxy send/receive interest for a virtual node representing the multicast group into LI network (Block 111).

[0057] Figure 2 is a flowchart of one embodiment of process for an operation of a border node between two source packet in routing (SPRING) networks. In this case a border node is receiving an advertisement from the L2 network (Block 201). This advertisement may be for a source located in the L2 network, or a border node aggregating the set of sources in a subtending LI network. The border node advertises the logical OR of send/receive interest in the multicast group advertised in LI by nodes on the shortest path to L2 into the L2 network using a unique global label for the multicast group and in synchronization with the other border (Block 203).

[0058] A check is made to determine whether there is an intersection of a send interest in the LI network and a receive interest in the L2 network (Block 209), then the process advertises a receive interest of a virtual node into the LI network (Block 207). If it is determined that there is an intersection of a send interest in the L2 network and a receive interest in the LI network (Block 213), then the process advertises a send interest of a virtual node into the LI network (Block 211).

[0059] All multicast segments in the multicast group in L2 may be aggregated that are determined to transit the border node into the multicast segment advertised in LI. Multicast traffic is received from the L2 network having a plurality of segment IDs for the multicast group, and the plurality of multicast group segment IDs is replaced with a segment ID for the virtual node as a source for the multicast group in LI, before forwarding the multicast traffic to the LI network.

[0060] Figure 3A is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. In this example, there is a two layer network (L1/L2) with three areas. Two border nodes are on the boundary of each area. A virtual node VI is advertised into the LI IGP by the border nodes to represent multicast groups in L2. In the example, a node in the LI 1 network advertises an interest in a multicast group G into area LI 1 via IGP. This interest is broadcast via the IGP in LI 1 and reaches the border nodes B 1 and B2.

[0061] Figure 3B is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. In the next stage of the process, the border nodes B l and B2 process the received interest as discussed in regard to Figure 1 herein above. The border nodes B l and B2 register node NTs interest in multicast group G, then both make a determination as to which is on the shortest path between Nl and VI. The border node on the shortest path (in this case B l) advertises the logical OR of all send/receive interests for multicast group Gl by nodes on LI on the shortest path to VI along with a unique global label for the multicast group G into L2. In this example, no nodes have previously registered and receive interest in multicast group Gl in L2 (or LI), so there is no intersection of interest and thus no state is installed at the border nodes.

[0062] Figure 3C is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. Further to the example, a second node N2 may advertise a send/receive interest in the same multicast group Gl into L12. In L12 the multicast group will be known by another label. The advertised interest in the multicast group Gl will be received by the border nodes B3 and B4.

[0063] Figure 3D is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. After the border nodes B3 and B4 received the advertisement of the node N2 in the L12 area, these border nodes will each process the advertisement. Border nodes B3 and B4 both may determine that any advertisement of node N2 relates to the multicast group Gl and its global label by looking up the relationship with any local label to L12. Border nodes B3 and B4 have previously received advertised interests in multicast group Gl from border nodes B l and B2. Border node B3 also determines that it is not on a shortest path from L2/V1 to the node N2. Thus, B3 will not advertise interest in Gl into L2 on N2's behalf. Border node B4, however, determines that it is on the shortest path from the node N2 to the L2 area, thus it advertises send/receive interest into L2 and as it has determined an intersection of interest between L12 and L2, proxies the logical or of send/receive interest for all other areas in Gl the virtual node VI into the L12 area, which in the example is only the send/receive interest advertised by Nl.

[0064] Subsequently, border nodes B 1 and B2 see the registrations of interests from border nodes B3 and B4 through the L2 area. Both border nodes B l and B2 also establish there is an intersection of interest, and do a proxy advertisement registering send/receive interest in Gl for node VI into area LI 1. This occurs, because this is the first instance of a node in another area than LI 1 advertising an interest.

[0065] Figure 3E is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. As a result of the advertisements in the hierarchical multi-area SPRING network a set of paths are determined by the constituent nodes of each area. Each intermediate node in each area has seen the advertisements of the

send/receive interests in multicast group Gl and makes the computation independently of the respective nodes role in a MDT or path for the multicast group Gl in the area. Intermediate nodes in Ll l, L12 and L2 independently determine the connectivity and forwarding illustrated in Figure 3E. Node Nl and the intermediate nodes determine connectivity with border node B l. Node N2 and the intermediate nodes determine connectivity with border node B4. In L2 the border nodes and intermediate nodes determine connectivity between the border nodes. If any actual (non-virtual) node had advertised an interest in L2, then it would be connected as well. Send and receive connectivity is established between B 1 and B4, whereas send only

connectivity is established by border nodes B2 and B3.

[0066] Label translation occurs at border nodes B 1 and B4 as traffic traverses the boundary to use the local or global labels. In one example, for all sources S for multicast group G in LI 1, a common label in L2 and L12 may be used. Border nodes B 1-B4 may all use a common label for virtual node VI and multicast group G in all LI areas.

[0067] Figure 3F is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. Figure 3F furthers the example, such that another node N3 in area LI 1 advertises send/receive interest in the multicast group Gl. Border nodes B 1 and B2 receive the advertisement. Border nodes B 1 has already advertised an interest in multicast group Gl. However, border node B2 determines that it lays on a shortest path for node N3 to the virtual node VI. Thus, B2 advertises into the L2 area to indicate send/receive interest.

[0068] Figure 3G is a diagram of one example of the process for a border node between two SPRING networks in a hierarchical SPRING network. As a result of the advertisements by node N3 and border node B2. The intermediate nodes in LI 1 and L2 update their forwarding to support a set of paths for a MDT that now includes node N3. In LI 1 paths are established between node Nl and node N3, as well as between node N3 and border node B2. Border node B2 now also has a send and receive interest in L2, thus the intermediate nodes there establish receive paths from border nodes B3 and B4 to border node B2 that are in addition to the previously established send paths. Border node B3 still remains in a scenario where it is not on a shortest path with any node in L12, thus traffic does not transit this border node.

[0069] These examples illustrate the function of border nodes to help establish multi-area support. Border nodes also terminate unicast labels for the L2 virtual node (e.g., virtual node VI) received from LI nodes. The L2 virtual node has a unicast label assigned that is advertised in all LI areas. In some embodiments, application of penultimate hop popping on paths to border nodes in L2 may utilize the use of an 'anycast' forwarding equivalence class (FEC) for virtual node VI. Otherwise, the border nodes may need to pop and swap labels to access the multicast labels instead of a standard swap. Multicast labels are both summarized and translated at border nodes. For example, all S, G multicast instances in LI that transit L2 use the border node G label. So in the example, border nodes B 1-B4 and virtual node VI each need to have pre-provisioned label for multicast group Gl, as virtual node VI is border nodes B 1-B4 proxying VI, thus all of the border nodes need to be provisioned with common information for virtual node VI.

[0070] Architecture

[0071] Figure 4A 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 4A shows NDs 400A-H, and their connectivity by way of lines between 400A-400B, 400B-400C, 400C-400D, 400D-400E, 400E-400F, 400F-400G, and 400A-400G, as well as between 400H and each of 400A, 400C, 400D, and 400G. 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 400A, 400E, and 400F 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).

[0072] Two of the exemplary ND implementations in Figure 4A are: 1) a special-purpose network device 402 that uses custom application-specific integrated-circuits (ASICs) and a special-purpose operating system (OS); and 2) a general purpose network device 404 that uses common off-the-shelf (COTS) processors and a standard OS.

[0073] The special-purpose network device 402 includes networking hardware 410 comprising compute resource(s) 412 (which typically include a set of one or more processors), forwarding resource(s) 414 (which typically include one or more ASICs and/or network processors), and physical network interfaces (NIs) 416 (sometimes called physical ports), as well as non- transitory machine readable storage media 418 having stored therein networking software 420. 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 400A-H. During operation, the networking software 420 may be executed by the networking hardware 410 to instantiate a set of one or more networking software instance(s) 422. Each of the networking software instance(s) 422, and that part of the networking hardware 410 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) 422), form a separate virtual network element 430A-R. Each of the virtual network element(s)

(VNEs) 430A-R includes a control communication and configuration module 432A-R

(sometimes referred to as a local control module or control communication module) and forwarding table(s) 434A-R, such that a given virtual network element (e.g., 430A) includes the control communication and configuration module (e.g., 432A), a set of one or more forwarding table(s) (e.g., 434A), and that portion of the networking hardware 410 that executes the virtual network element (e.g., 430A).

[0074] The special-purpose network device 401 can implement a multi-area multicast manager 464. The multi-area multicast manager 464 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-3 that provide multi-area forwarding of multicast frames in a SPRING network. The multi-area multicast manager 464 can be stored by the non-transitory machine readable storage media 418 and executed by the compute resources 412.

[0075] The special-purpose network device 402 is often physically and/or logically considered to include: 1) a ND control plane 424 (sometimes referred to as a control plane) comprising the compute resource(s) 412 that execute the control communication and configuration

module(s) 432A-R; and 2) a ND forwarding plane 426 (sometimes referred to as a forwarding plane, a data plane, or a media plane) comprising the forwarding resource(s) 414 that utilize the forwarding table(s) 434A-R and the physical NIs 416. By way of example, where the ND is a router (or is implementing routing functionality), the ND control plane 424 (the compute resource(s) 412 executing the control communication and configuration module(s) 432A-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) 434A-R, and the ND forwarding plane 426 is responsible for receiving that data on the physical NIs 416 and forwarding that data out the appropriate ones of the physical NIs 416 based on the forwarding table(s) 434A-R.

[0076] Figure 4B illustrates an exemplary way to implement the special-purpose network device 402 according to some embodiments of the invention. Figure 4B shows a special- purpose network device including cards 438 (typically hot pluggable). While in some embodiments the cards 438 are of two types (one or more that operate as the ND forwarding plane 426 (sometimes called line cards), and one or more that operate to implement the ND control plane 424 (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 436 (e.g., a first full mesh coupling the line cards and a second full mesh coupling all of the cards).

[0077] Returning to Figure 4A, the general purpose network device 404 includes hardware 440 comprising a set of one or more processor(s) 442 (which are often COTS processors) and network interface controller(s) 444 (NICs; also known as network interface cards) (which include physical NIs 446), as well as non-transitory machine readable storage media 448 having stored therein software 450. During operation, the processor(s) 442 execute the software 450 to instantiate one or more sets of one or more applications 464A-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 454 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple instances 462A-R called software containers that may each be used to execute one (or more) of the sets of applications 464A-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 454 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 464A-R is run on top of a guest operating system within an instance 462A-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 440, 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 454, unikernels running within software containers represented by instances 462A-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).

[0078] The instantiation of the one or more sets of one or more applications 464A-R, as well as virtualization if implemented, are collectively referred to as software instance(s) 452. Each set of applications 464 A-R, corresponding virtualization construct (e.g., instance 462A-R) if implemented, and that part of the hardware 440 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) 460A-R.

[0079] The virtual network element(s) 460A-R perform similar functionality to the virtual network element(s) 430A-R - e.g., similar to the control communication and configuration module(s) 432A and forwarding table(s) 434A (this virtualization of the hardware 440 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 462A-R corresponding to one VNE 460A-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 462A-R to VNEs also apply to embodiments where such a finer level of granularity and/or unikernels are used.

[0080] In certain embodiments, the virtualization layer 454 includes a virtual switch that provides similar forwarding services as a physical Ethernet switch. Specifically, this virtual switch forwards traffic between instances 462A-R and the NIC(s) 444, as well as optionally between the instances 462A-R; in addition, this virtual switch may enforce network isolation between the VNEs 460A-R that by policy are not permitted to communicate with each other (e.g., by honoring virtual local area networks (VLANs)).

[0081] The general purpose network device 404 can implement a multi-area multicast manager 464A-R. The multi-area multicast manager 464A-R can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-3 that provide multi-area forwarding of multicast frames in a SPRING network. The multi-area multicast manager 464A-R can be stored by the non-transitory machine readable storage media 448 and executed by the software instances 452 and processors 442.

[0082] The third exemplary ND implementation in Figure 4A is a hybrid network device 406, 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 402) could provide for para-virtualization to the networking hardware present in the hybrid network device 406.

[0083] 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) 430A-R, VNEs 460A-R, and those in the hybrid network device 406) receives data on the physical NIs (e.g., 416, 446) and forwards that data out the appropriate ones of the physical NIs (e.g., 416, 446). For example, a VNE implementing IP router functionality forwards IP packets on the basis of some of the IP header information in the IP packet; where IP header information includes source IP address, destination IP address, source port, destination port (where "source port" and "destination port" refer herein to protocol ports, as opposed to physical ports of a ND), transport protocol (e.g., user datagram protocol (UDP), Transmission Control Protocol (TCP), and differentiated services (DSCP) values.

[0084] Figure 4C illustrates various exemplary ways in which VNEs may be coupled according to some embodiments of the invention. Figure 4C shows VNEs 470A.1-470A.P (and optionally VNEs 470A.Q-470A.R) implemented in ND 400A and VNE 470H.1 in ND 400H. In Figure 4C, VNEs 470A.1-P are separate from each other in the sense that they can receive packets from outside ND 400A and forward packets outside of ND 400A; VNE 470A.1 is coupled with VNE 470H.1, and thus they communicate packets between their respective NDs; VNE 470A.2-470A.3 may optionally forward packets between themselves without forwarding them outside of the ND 400A; and VNE 470A.P may optionally be the first in a chain of VNEs that includes VNE 470A.Q followed by VNE 470A.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 4C 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).

[0085] The NDs of Figure 4A, 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 4A may also host one or more such servers (e.g., in the case of the general purpose network device 404, one or more of the software instances 462A-R may operate as servers; the same would be true for the hybrid network device 406; in the case of the special-purpose network device 402, one or more such servers could also be run on a virtualization layer executed by the compute resource(s) 412); in which case the servers are said to be co-located with the VNEs of that ND.

[0086] A virtual network is a logical abstraction of a physical network (such as that in Figure 4A) 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).

[0087] 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).

[0088] 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).

[0089] Fig. 4D illustrates a network with a single network element on each of the NDs of Figure 4A, 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 4D illustrates network elements (NEs) 470A-H with the same connectivity as the NDs 400A-H of Figure 4A.

[0090] Figure 4D illustrates that the distributed approach 472 distributes responsibility for generating the reachability and forwarding information across the NEs 470A-H; in other words, the process of neighbor discovery and topology discovery is distributed.

[0091] For example, where the special-purpose network device 402 is used, the control communication and configuration module(s) 432A-R of the ND control plane 424 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 RS VP-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 470A-H (e.g., the compute resource(s) 412 executing the control communication and configuration

module(s) 432A-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 424. The ND control plane 424 programs the ND forwarding plane 426 with information (e.g., adjacency and route information) based on the routing structure(s). For example, the ND control plane 424 programs the adjacency and route information into one or more forwarding table(s) 434A-R (e.g., Forwarding Information Base (FIB), Label Forwarding Information Base (LFIB), and one or more adjacency structures) on the ND forwarding plane 426. 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 402, the same distributed approach 472 can be implemented on the general purpose network device 404 and the hybrid network device 406.

[0092] Figure 4D illustrates that a centralized approach 474 (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 474 has the responsibility for the generation of reachability and forwarding information in a centralized control plane 476 (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 476 has a south bound interface 482 with a data plane 480 (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 470A-H (sometimes referred to as switches, forwarding elements, data plane elements, or nodes). The centralized control plane 476 includes a network controller 478, which includes a centralized reachability and forwarding information module 479 that determines the reachability within the network and distributes the forwarding information to the NEs 470A-H of the data plane 480 over the south bound interface 482 (which may use the OpenFlow protocol). Thus, the network intelligence is centralized in the centralized control plane 476 executing on electronic devices that are typically separate from the NDs.

[0093] For example, where the special-purpose network device 402 is used in the data plane 480, each of the control communication and configuration module(s) 432A-R of the ND control plane 424 typically include a control agent that provides the VNE side of the south bound interface 482. In this case, the ND control plane 424 (the compute resource(s) 412 executing the control communication and configuration module(s) 432A-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 476 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 479 (it should be understood that in some embodiments of the invention, the control communication and configuration module(s) 432A-R, in addition to communicating with the centralized control plane 476, 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 474, but may also be considered a hybrid approach). [0094] While the above example uses the special-purpose network device 402, the same centralized approach 474 can be implemented with the general purpose network device 404 (e.g., each of the VNE 460A-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 476 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 479; it should be understood that in some embodiments of the invention, the VNEs 460A-R, in addition to communicating with the centralized control plane 476, 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 406. In fact, the use of SDN techniques can enhance the NFV techniques typically used in the general purpose network device 404 or hybrid network device 406 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.

[0095] Figure 4D also shows that the centralized control plane 476 has a north bound interface 484 to an application layer 486, in which resides application(s) 488. The centralized control plane 476 has the ability to form virtual networks 492 (sometimes referred to as a logical forwarding plane, network services, or overlay networks (with the NEs 470A-H of the data plane 480 being the underlay network)) for the application(s) 488. Thus, the centralized control plane 476 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).

[0096] While Figure 4D shows the distributed approach 472 separate from the centralized approach 474, 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) 474, 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 474, but may also be considered a hybrid approach. [0097] While Figure 4D illustrates the simple case where each of the NDs 400A-H implements a single NE 470A-H, it should be understood that the network control approaches described with reference to Figure 4D also work for networks where one or more of the NDs 400A-H implement multiple VNEs (e.g., VNEs 430A-R, VNEs 460A-R, those in the hybrid network device 406). Alternatively or in addition, the network controller 478 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 478 may present the implementation of a VNE/NE in a single ND as multiple VNEs in the virtual networks 492 (all in the same one of the virtual network(s) 492, each in different ones of the virtual

network(s) 492, or some combination). For example, the network controller 478 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 476 to present different VNEs in the virtual network(s) 492 (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).

[0098] The centralized control plane 476 can implement a multi-area multicast manager 481. The multi-area multicast manager 481 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-3 that provide multi- area forwarding of multicast frames in a SPRING network.

[0099] On the other hand, Figures 4E and 4F respectively illustrate exemplary abstractions of NEs and VNEs that the network controller 478 may present as part of different ones of the virtual networks 492. Figure 4E illustrates the simple case of where each of the NDs 400A-H implements a single NE 470A-H (see Figure 4D), but the centralized control plane 476 has abstracted multiple of the NEs in different NDs (the NEs 470A-C and G-H) into (to represent) a single NE 4701 in one of the virtual network(s) 492 of Figure 4D, according to some

embodiments of the invention. Figure 4E shows that in this virtual network, the NE 4701 is coupled to NE 470D and 470F, which are both still coupled to NE 470E.

[00100] Figure 4F illustrates a case where multiple VNEs (VNE 470A.1 and VNE 470H.1) are implemented on different NDs (ND 400 A and ND 400H) and are coupled to each other, and where the centralized control plane 476 has abstracted these multiple VNEs such that they appear as a single VNE 470T within one of the virtual networks 492 of Figure 4D, according to some embodiments of the invention. Thus, the abstraction of a NE or VNE can span multiple NDs.

[00101] While some embodiments of the invention implement the centralized control plane 476 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).

[00102] Similar to the network device implementations, the electronic device(s) running the centralized control plane 476, and thus the network controller 478 including the centralized reachability and forwarding information module 479, 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 5 illustrates, a general purpose control plane device 504 including hardware 540 comprising a set of one or more processor(s) 542 (which are often COTS processors) and network interface controller(s) 544 (NICs; also known as network interface cards) (which include physical NIs 546), as well as non-transitory machine readable storage media 548 having stored therein centralized control plane (CCP) software 550.

[00103] In embodiments that use compute virtualization, the processor(s) 542 typically execute software to instantiate a virtualization layer 554 (e.g., in one embodiment the virtualization layer 554 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple instances 562A-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 554 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 562A-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 540, directly on a hypervisor represented by virtualization layer 554 (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 562A-R). Again, in embodiments where compute virtualization is used, during operation an instance of the CCP software 550 (illustrated as CCP instance 576A) is executed (e.g., within the instance 562A) on the virtualization layer 554. In embodiments where compute virtualization is not used, the CCP instance 576A is executed, as a unikernel or on top of a host operating system, on the "bare metal" general purpose control plane device 504. The instantiation of the CCP instance 576A, as well as the virtualization layer 554 and instances 562A-R if implemented, are collectively referred to as software instance(s) 552.

[00104] In some embodiments, the CCP instance 576A includes a network controller instance 578. The network controller instance 578 includes a centralized reachability and forwarding information module instance 579 (which is a middleware layer providing the context of the network controller 478 to the operating system and communicating with the various NEs), and an CCP application layer 580 (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 580 within the centralized control plane 476 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.

[00105] The centralized control plane 476 transmits relevant messages to the data plane 480 based on CCP application layer 580 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 480 may receive different messages, and thus different forwarding information. The data plane 480 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.

[00106] The general purpose control plane device 504 can implement a multi-area multicast manager 581. The multi-area multicast manager 581 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-3 that provide multi-area forwarding of multicast frames in a SPRING network. The multi-area multicast manager 581 can be stored by the non-transitory machine readable storage media 548 and executed by the software instances 552 and processors 542.

[00107] 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).

[00108] 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.

[00109] 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.

[00110] However, when an unknown packet (for example, a "missed packet" or a "match- miss" as used in OpenFlow parlance) arrives at the data plane 480, the packet (or a subset of the packet header and content) is typically forwarded to the centralized control plane 476. The centralized control plane 476 will then program forwarding table entries into the data plane 480 to accommodate packets belonging to the flow of the unknown packet. Once a specific forwarding table entry has been programmed into the data plane 480 by the centralized control plane 476, the next packet with matching credentials will match that forwarding table entry and take the set of actions associated with that matched entry.

[00111] 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 implemented by a network device, the network device functioning as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network, the method comprising:

receiving (101) an advertisement of a send/receive interest from a node in the LI

network via an interior gateway protocol (IGP) for a multicast group;

advertising (103) a logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on a shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group;

determining (105) whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node;

advertising (107) a receive interest of a virtual node into the LI network and a send

interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network; and advertising (111) a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

2. The method of claim 1, wherein the method further comprises:

aggregating all multicast segments in the multicast group in the LI network that are determined to transit the border node into the multicast segment advertised into L2; and

aggregating all multicast segments in the multicast group in L2 that are determined to transit the border node into the multicast segment advertised in LI.

3. The method of claim 1, wherein the method further comprises:

receiving multicast traffic from the LI network having a plurality of segment IDs

corresponding to a set of sources for a multicast group in the LI network; and replacing the plurality of segment ID with a global multicast segment ID, before forwarding the multicast traffic to the L2 network.

The method of claim 1, wherein the method further comprises:

receiving multicast traffic from the L2 network having a plurality of segment IDs for the border nodes that are sources for the multicast group in L2; and

replacing a common multicast group segment ID with a segment ID for the virtual node, before forwarding the multicast traffic to the LI network.

The method of claim 1, wherein the border node is pre-provisioned with segment IDs to utilize for the virtual node that represents a multicast tree in the L2 network.

A method implemented by a network device, the network device functioning as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in second area are represented as virtual nodes a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network, the method comprising: receiving (201) an advertisement of a send/receive interest from the L2 network for a multicast group with a source in the L2 network;

advertising (205) a logical OR of send/receive interest in the multicast group into the L2 network using a global label for the multicast group and proxying a send/receive interest for a virtual node into the LI network, in response to the border node being on a shortest path;

advertising (207) a receive interest of a virtual node into the LI network and a send

interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network; and

advertising (211) a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network.

The method of claim 5, wherein the method further comprises:

receiving multicast traffic from the LI network having a common LI label for the virtual node; and

replacing a virtual node label with a label for a global multicast group label, before

forwarding the multicast traffic to the L2 network.

8. The method of claim 5, wherein the method further comprises:

receiving multicast traffic from the L2 network having a common L2 label for the

multicast group; and

replacing a common multicast group label with a label for the virtual node, before

forwarding the multicast traffic to the LI network.

9. The method of claim 5, wherein the border node is pre-provisioned with labels to utilize for the virtual node that represents a multicast tree in the L2 network.

10. A network device functioning as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network, the network device comprising:

a non-transitory machine readable storage device (618) having stored therein a multi-area multicast manager (664); and

a processor (612) configured to execute the multi-area multicast manager, the multi-area multicast manager configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise a logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on a shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

11. The network device of claim 10, wherein the multi-area multicast manager is further configured to aggregate all multicast segments in the multicast group in the LI network that are determined to transit the border node into the multicast segment advertised into L2, and to aggregate all multicast segments in the multicast group in L2 that are determined to transit the border node into the multicast segment advertised in LI.

12. The network device of claim 10, wherein the multi-area multicast manager is further configured to receive multicast traffic from the LI network having a plurality of segment IDs corresponding to a set of sources for a multicast group in the LI network, and to replace the plurality of segment ID with a global multicast segment ID, before forwarding the multicast traffic to the L2 network.

13. The network device of claim 10, wherein the multi-area multicast manager is further configure to receive multicast traffic from the L2 network having a plurality of segment IDs for the border nodes that are sources for the multicast group in L2, and to replace a common multicast group segment ID with a segment ID for the virtual node, before forwarding the multicast traffic to the LI network.

14. The network device of claim 10, wherein the border node is pre-provisioned with

segment IDs to utilize for the virtual node that represents a multicast tree in the L2 network.

15. A computing device in communication with a network device in a network implementing multicast using unicast tunneling, the computing device to execute a plurality of virtual machines for implementing network function virtualization (NFV), the network device functioning as a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network, the computing device comprising:

a non-transitory machine readable storage device (648) having stored therein a multi-area multicast manager (664 A); and

a processor (642) configured to execute a virtual machine from the plurality of virtual machines, the virtual machine to execute the multi-area multicast manager, the multi-area multicast manager configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise a logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

16. The computing device of claim 15, wherein the multi-area multicast manager is further configured to aggregate all multicast segments in the multicast group in the LI network that are determined to transit the border node into the multicast segment advertised into L2, and to aggregate all multicast segments in the multicast group in L2 that are determined to transit the border node into the multicast segment advertised in LI.

17. The computing device of claim 15, wherein the multi-area multicast manager is further configured to receive multicast traffic from the LI network having a plurality of segment IDs corresponding to a set of sources for a multicast group in the LI network, and to replace the plurality of segment ID with a global multicast segment ID, before forwarding the multicast traffic to the L2 network.

18. A control plane device is configured to implement a control plane of a software defined networking (SDN) network including a network device in a network with a plurality of network devices, wherein the control plane device is configured to configure the network device, the network device implementing multicast using unicast tunneling, the network device functioning a border node of a first area and a second area of a multi-area hierarchical computed source packet in routing (SPRING) network, where sources for multicast groups with sources in a second area are represented as virtual nodes in a first area, where the first area is a level 1 (LI) network and the second area is a level 2 (L2) network, the control plane device comprising:

a processor (612) configured to execute the multi-area multicast manager, the multi-area multicast manager configured to receive an advertisement of a send/receive interest from a node in the LI network via an interior gateway protocol (IGP) for a multicast group, to advertise a logical OR of send/receive interest in the multicast group from nodes in the LI network for which the border node is on the shortest path to L2 into the L2 network using a global multicast segment identifier (ID) unique to the border node and the multicast group, to determine whether a new intersection exists between advertised send/receive interest from the L2 network and send/receive interests of nodes in LI network that are on shortest path to the border node, to advertise a receive interest of a virtual node into the LI network and a send interest of the border node into the L2 network, in response to an intersection of a send interest in the LI network and a receive interest in the L2 network, and to advertise a send interest of the virtual node into the LI network and a receive interest of the border node into the L2 network, in response to an intersection of a receive interest in the LI network and a send interest in the L2 network.

19. The control plane device of claim 18, wherein the multi-area multicast manager is further configured to aggregate all multicast segments in the multicast group in the LI network that are determined to transit the border node into the multicast segment advertised into L2, and to aggregate all multicast segments in the multicast group in L2 that are determined to transit the border node into the multicast segment advertised in LI.

20. The control plane device of claim 18, wherein the multi-area multicast manager is further configured to receive multicast traffic from the LI network having a plurality of segment IDs corresponding to a set of sources for a multicast group in the LI network, and to replace the plurality of segment ID with a global multicast segment ID, before forwarding the multicast traffic to the L2 network.