WO2017144946A1

WO2017144946A1 - Method and apparatus for legacy network support for computed spring multicast

Info

Publication number: WO2017144946A1
Application number: PCT/IB2016/050984
Authority: WO
Inventors: David Ian Allan
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-02-23
Filing date: 2016-02-23
Publication date: 2017-08-31

Abstract

A method is implemented by a network device, where the network device functions as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain is represented as a virtual node of the CSD. The method includes receiving an advertisement of a multicast group having a source in the CSD, advertising the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, receiving a join addressed to the border node as a source of the multicast group from the legacy domain, and declaring a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

Description

METHOD AND APPARATUS FOR LEGACY NETWORK SUPPORT FOR

COMPUTED SPRING MULTICAST

TECHNICAL FIELD

[0001] Embodiments of the invention relate to the field of interworking of communication networks; and more specifically, to the interworking of multicast in source packet in routing (SPRING) networks with multicast in legacy networks.

BACKGROUND

[0002] Numerous techniques and protocols exist for configuring networks to handle multicast traffic. For Internet Protocol (IP) and/or multiprotocol label switching (MPLS) implementations the existing solutions for multicast are based on multicast label distribution protocol (mLDP) or protocol independent multicast (PIM). These are all techniques that depend on a unicast shortest path first (SPF) computation followed by handshaking between peers to sort out a loop free multicast distribution tree (MDT) for each multicast source. In these approaches, a

comprehensive view of multicast connectivity does not exist at the node level, all decisions are entirely local and driven by the combination of the unicast forwarding solution derived from routing information and peer interactions.

[0003] 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; the only real time peer interaction being advertisement of topology changes to the IGP database.

[0004] 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.

[0005] 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 associated with legacy approaches to multicast. 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 significantly reducing the overall amount of multicast state in the network.

[0006] Given the above context, a node in the SPRING network could compute its role in implementing any given multicast (S, G) tree purely from information in the IGP. An algorithm that starts with all pairs shortest path computation augmented with algorithms to identify the nodes with specific roles of source, leaf and/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 are inconsistent with the operation of many existing networks. Therefore multicast services that spans a SPRING network and one of these existing legacy networks is not currently possible. Existing multicast solutions utilized in legacy networks such as PIM or mLDP use dataplane transactions to construct multicast trees that follow the unicast shortest path.

SUMMARY

[0007] In one embodiment, a method is implemented by a network device, where the network device functions as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain is represented as a virtual node of the CSD. The method includes receiving an advertisement of a multicast group having a source in the CSD, to advertising the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, receiving a join addressed to the border node as a source of the multicast group from the legacy domain, and declaring a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

[0008] In one embodiment, another method is implemented by a network device, where the network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain represented as a virtual node in the CSD. The method includes receiving an advertisement of a multicast group having a source in the legacy domain via a discovery mechanism of the legacy domain, receiving a join addressed to a virtual node representing the legacy domain as a source of the multicast group from the CSD, forwarding the join toward the source in the legacy domain, and advertising the multicast group having a source in the legacy domain into the CSD.

[0009] In one embodiment, a network device functions as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain is represented as a virtual node of the CSD. The network device a non-statutory machine-readable storage medium having stored therein a legacy network interworking manager, and a processor coupled to the non- statutory machine-readable storage medium. The processor is configured to execute the legacy network interworking manager. The legacy network interworking manager is configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

[0010] In one embodiment, a computing device is configured to execute a plurality of virtual machines. The plurality of virtual machines implement network function virtualization (NFV). The computing device is in communication with a network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain is represented as a virtual node of the CSD. The computing device includes a non-statutory machine-readable storage medium having stored therein a legacy network interworking manager, and a processor coupled to the non-statutory machine-readable storage medium. The processor is configured to execute a virtual machine from the plurality of virtual machines. The virtual machine is configured to execute a legacy network interworking manager. The legacy network interworking manager is configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

[0011] In a further embodiment, a control plane device is configured to implement a control plane of a software defined networking (SDN) network including a network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain. The legacy domain is represented as a virtual node of the CSD, wherein the control plane device is configured to configure the network device. The control plane device includes a non-statutory machine-readable storage medium having stored therein a legacy network interworking manager, and a processor coupled to the non-statutory machine-readable storage medium, the processor configured to execute the legacy network interworking manager, the legacy network interworking manager configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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:

[0013] Figure 1 is a flowchart of one embodiment of process for an operation of a border node between a legacy network and a source packet in routing (SPRING) network that supports forwarding packets received from the SPRING network into the legacy network.

[0014] Figure 2 is a flowchart of one embodiment of process for an operation of a border node between a legacy network and a source packet in routing (SPRING) network that supports forwarding packets received from the SPRING network into the legacy network.

[0015] Figure 3A is a diagram of one example of the process for a node in the in a computed

SPRING domain (CSD) advertising into the legacy domain. [0016] Figure 3B is a diagram of one example of the process for a node in the in a computed SPRING domain (CSD) advertising into the legacy domain as assisted by the border node.

[0017] Figure 3C is a diagram of one example of the process for a node in the in a legacy domain advertising into the CSD.

[0018] Figure 3D is a diagram of one example of the process for a node in the in legacy domain advertising into the CSD with assistance from the border nodes.

[0019] Figure 3E is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0020] Figure 3F is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0021] Figure 3G is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0022] Figure 4A is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0023] Figure 4B is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0024] Figure 4C is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

[0025] Figure 5A 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.

[0026] Figure 5B illustrates an exemplary way to implement a special-purpose network device according to some embodiments of the invention.

[0027] Figure 5C illustrates various exemplary ways in which virtual network elements (VNEs) may be coupled according to some embodiments of the invention.

[0028] Figure 5D 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.

[0029] Figure 5E 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. [0030] Figure 5F 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.

[0031] Figure 6 illustrates a general purpose control plane device with centralized control plane (CCP) software 650), according to some embodiments of the invention.

DESCRIPTION OF EMBODIMENTS

[0032] The following description describes methods and apparatus for providing interworking for multicast services between source in packet routing (SPRING) domains and legacy domains. The legacy domain in such a pairwise relationship is represented into the SPRING domain's interior gateway protocol (IGP) as a single virtual node by the border nodes. The border nodes proxy the interworking between the domains. The proxy nodes and the other nodes in the SPRING domain compute multicast trees from an IGP topology view inclusive of the virtual node that represents the adjacent domain.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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). [0039] 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.

[0040] SPRING Networks and Multicast

[0041] These embodiments work in combination with, but are not limited to other methods of utilizing unicast tunnels within a network to minimize multicast related state. 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 both membership and topology information in the IGP.

[0042] 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. The multicast labels in the network are carried end to end (E2E) unmodified. This is inherent to the operation of SPRING. A multicast implementation MPLS could also be envisioned that combined IGP registrations, globally administered multicast labels and an LDP signaled unicast tunnel mesh. [0043] The example embodiments utilize SPRING for unicast tunneling as a component of MDT construction. 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.

[0044] 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 via further processing of the resulting solution whether it is a source, a leaf and/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 MDT determination.

Further, a source has knowledge of the set of leaves and is aware of leaf interest in a multicast group independently of the establishment of dataplane state.

[0045] Overview

[0046] Existing multicast solutions such as protocol independent multicast (PIM) or multicast label distribution protocol (mLDP) use dataplane transactions to construct multicast trees that follow the unicast shortest path. It would be useful to be able to interwork such legacy technologies and networks with computed multicast for SPRING to expand the scope of services that a carrier could offer. The concept of a designated router is utilized in broadcast/multicast domains to provide a single point of interworking that is selected to minimize the probability of packet duplication and cyclic loops for multicast trees that span network domains. The selection and management of a designated router (DR) for multicast as the point of interworking the networks is the focus of the embodiments. Examples of existing election schemes include ordinal ranking where the multicast groups are placed in an ordered list, as well as the potential set of DRs. The assignment of a multicast group to a DR is on the basis of a multicast group ordinal modulo the maximum number of DRs to select a DR ordinal ranking. This is a source of major network churn in any failure scenarios as the addition or removal of a single DR from the set will re-arrange the traffic distribution of all DRs. Other techniques such as using the multicast group number modulo the number of DRs can be a source of bandwidth/load spreading inefficiency when the number of multicast groups to be interworked is small. It would be desirable to overcome these issues and be able to interwork SPRING computed multicast with existing networks.

[0047] In some embodiments, the domains are not integrated. Thus, topology abstraction is utilized between the two domains. That is, the full topology of the peer domain is not known and a simplification or abstraction of that topology is utilized in order to permit the control plane to scale. The embodiments are both bandwidth efficient and require minimal state information to be exchanged between nodes in the respective networks.

[0048] Interworking two domains has similar properties to communications between interworking multi-areas. The chief difference is that interworking domains involves the interworking of dissimilar control plane interactions. Both PIM and mLDP support point to multi-point (p2mp) and multi-point to multi-point (mp2mp trees), thus interworking with the SPRING domain can also support both p2mp and mp2mp trees where the mp2mp tree is rooted in the non-SPRING domain.

[0049] As mentioned above, multicast membership is advertised in IGP within the SPRING domain. A domain global label is associated with each (S,G) multicast group instance. As per IEEE 802. laq there are send/receive attributes associated with each node that participates in a multicast group advertised in the IGP. A node can register sender, receiver, or send/receive interest in a multicast group. MDTs for each S,G are computed using a combination of all pairs shortest path, and pruning. The embodiments model a peer legacy domain as a single node in the computed SPRING domain IGP.

[0050] In the legacy domain, PIM and mLDP use "leaf initiated joins," where nodes that seek to join a multicast group issue a join request and are treated as leaves. This requires that the leaf have knowledge of both the source or root and the shortest path to the source in order to properly direct join transactions. A source does not have knowledge of the set of leaves that has "joined" the tree, only the local interfaces that multicast traffic should be sent on to serve tat set. A node knows it is a leaf node via means outside RFC 6388. In the embodiments, this means of obtaining knowledge of the role of nodes in the legacy domain is genericized to refer to it as a "discovery system."

[0051] In the computed SPRING domain (CSD), the embodiments uses a computation technique combined with the representing of the legacy network in the IGP as a single node into the computed SPRING domain that is equidistant from the border nodes. Therefore, it is possible to perform the actual interworking node selection per (S,G) multicast tree and upon the basis of both shortest path and minimal overall cost of the MDT in the CSD from the source S to the legacy domain. This model of domain representation has to be asymmetrical (i.e., the CSD domain cannot also be represented as a single node into the legacy domain as well), because the technique uses the shortest path in one domain as the selection criteria, something that is not guaranteed to be simultaneously true in both domains.

[0052] In the embodiments, the border nodes have a mechanism to generate domain unique labels to proxy for the virtual node that represents the legacy domain in the CSD. This may be via pre-provisioning or some other method. That is to say they will both originate IGP information and modify traffic transiting the domains as if the virtual node existed, and was a single unique source of multicast traffic simply relayed by the border nodes. The border nodes have knowledge of the other border nodes and their availability. This knowledge may be via advertisement of the virtual node or other means that would be understood by one skilled in the art. Thus, in the organization of MDTs across the domains, there are two general scenarios, where the MDT has sources in the CSD and leaves in the legacy domain, or the opposite, where the sources are in the legacy domain and leaves in the CSD.

[0053] In the scenario where the sources are in the CSD, and leaves in the legacy domain, a border node will advertise itself into the legacy domain via the legacy domain discovery mechanism as the source for all multicast groups that have sources in the CSD and where the border node has determined it is on the shortest path between at least one source in the CSD and the virtual node representing the legacy domain. A border node that receives a join addressed to itself as a source from the legacy domain for a multicast group that has been advertised in the CSD IGP will declare itself as a group member with a receive interest in the CSD IGP. The border node will translate all S, G labels received from the CSD into its mLDP labels for the multicast group G in the legacy domain. A border node may optionally translate the source address in a multicast IP packets to its own IP address so that it appears as the source in the legacy domain.

[0054] In the scenario where the sources are in legacy domain, and the leaves in the CSD for given MDTs, nodes in the legacy domain that are sources for any group advertise themselves into the legacy domain discovery system. A border node that learns of a source in the legacy domain for which there are leaves in the CSD and where that border node is on the shortest path between any of those leaves and the virtual node representing the legacy domain will issue joins upstream in the legacy domain, and it will advertise a virtual node (VI in the examples herein below) as a source for the group in the CSD IGP. The border node will translate all mLDP S,G labels received from the legacy domain to the VI, G label to be used in the CSD. The border node may translate the source address in multicast IP packets to its own IP address such that nodes in the CSD see the border node as the source of the MDT. A border node will not issue join requests for any multicast trees it becomes aware of via the discovery mechanism that are rooted on a peer border node. This avoids creating inter domain multicast loops.

[0055] The embodiments provide advantages over the prior art in that the embodiments provide minimum disruption of the network upon failure or return to service of a border node. The embodiments provide bandwidth efficiency, since CSD uses entirely minimum cost shortest paths from each source into the legacy domain. Load is spread on the basis of shortest path (vs. ordinal ranking or hashing approaches). Modeling the legacy domain as a single node provides a mechanisms for both doing minimum cost shortest path, and interworking mp2mp legacy with p2mp CSD. State is condensed at domain boundaries. Because all sources in one domain are represented a single source (into the CSD) or a small number (into the legacy domain), summarization of multicast sources at the interworking boundary becomes possible. A synchronization mechanism is required between the border nodes to ensure a consistent view of the virtual nodes (e.g., VI) group memberships is advertised into the CSD. Employing a model where the legacy domain is represented by a virtual node into the CSD does bias the replication load towards the legacy domain, however this is an unavoidable artifact of using shortest path as a selection criteria, which is a mode of operation not used in the legacy domain.

[0056] Figure 1 is a flowchart of one embodiment of process for an operation of a border node between a legacy network and a source packet in routing (SPRING) network that supports forwarding packets received from the SPRING network into the legacy network. The process begins with the border node receiving an advertisement of a multicast group having a source in the CSD (Block 101). The advertisement may be received via IGP and be generated by a source in the multicast group. The border node determines if it is on the shortest path between the node advertising interest and the virtual node representing the legacy domain (Block 102), and if it is then advertising the multicast group into the legacy domain via a discovery mechanism of the legacy domain (Block 103) such that potential receivers in the legacy domain know of it. The discovery mechanism can be the Border Gateway Protocol (e.g., BGP - RFC 6514). When the multicast group is advertised into the legacy domain, the border node is advertised as a source for the multicast group for the legacy domain. Once the multicast group has thereafter been advertised into each domain, the border node may subsequently receive a join addressed to the border node as a source for the multicast group from any node within the legacy domain (Block 105).

[0057] In response to the join request being received any of the border nodes, the borders node will in turn advertise virtual node VI as a member of the multicast group with a receive interest into the CSD (Block 107) in coordination with the other border nodes on the domain boundary. If the border nodes have already made such a declaration or was already a part of the multicast group, then it does not need to perform this step. The border node may track each of the nodes that have joined from the legacy domain for which it is the designated forwarder. When there are no legacy nodes that remain as subscribers, then the border nodes will unsubscribe from the multicast group by removing the multicast registration proxied for node VI from the IGP advertisements into the CSD.

[0058] As a consequence of both SPRING and legacy domain convergence multicast connectivity will be established from the source in the CSD domain to the border node, and from the border node to the node with receive interest in the legacy domain.

[0059] Subsequently, the border node receives multicast traffic from the CSD having a source S, group G (S, G) label of a multicast group where the border node has advertised a receive interest (Block 109). The border node may then translate the (S, G) labels of the multicast traffic that has been received into group labels for the legacy domain before forwarding the multicast traffic to the legacy domain. In some embodiments, translation of the received multicast traffic where the multicast traffic from the CSD has a source IP address that is then replaced with IP address of the border node before forwarding into the legacy domain. In some embodiments, the mapping may be of a SPRING multicast segment identifier (SID) to an mLDP label. Thus, other identifiers can be utilized rather than labels. Thus, identifiers can be utilized to identify multicast groups in each domain where identifiers can be labels or similar formats. Also, there are variations of the encapsulation of such labels in each domain.

[0060] Figure 2 is a flowchart of one embodiment of process for an operation of a border node between a legacy network and a source packet in routing (SPRING) network that supports forwarding packets received from the SPRING network into the legacy network. In this case, the border node receives an advertisement of a multicast group having a source in the legacy domain via a discovery mechanism of the legacy domain (Block 201). The multicast group with one or more sources in the legacy domain will be represented in the CSD as a virtual node that is a reachable via the border nodes. The advertisement of the virtual node and multicast group may be via IGP or similar protocol. Because the border node will be aware of receive interest in the multicast group in the CSD via IGP, it does not need to immediately advertise the source in the legacy domain into the CSD IGP and can defer this advertisement until a receive interest is actually advertised.

[0061] After the advertisement of the multicast group source in the legacy domain, the border nodes may receive a membership advertisement (i.e., a join) in the IGP from a node in the CSD that indicates a receive interest in the multicast group (Block 203). The border node that determines it is on the shortest path between the CSD node and the peer domain originates a legacy join transaction toward the source in the legacy domain (Block 205). The border node summarizes receive and send interests on behalf of the nodes in the CSD as joins in the legacy domain. As long as there are CSD nodes that have a receive or send interest in a multicast group that has senders or receivers in the legacy domain, the border node will maintain a receive or send interest in the legacy domain via joins for the multicast group from the CSD domain. At the same time the border node in coordination with the other border nodes will advertise the virtual node as a source for the multicast group into the CSD (Block 207).

[0062] The combination of receive interest by a node in the CSD and source interest advertised by the border nodes will result in the CSD establishing multicast connectivity from the receiver to the border node, similarly the join proxied by the border node towards the source in the legacy domain will result in connectivity from the source in the legacy domain and the border node being established.

[0063] Subsequently, the border node will receive multicast traffic from the legacy domain having a source S and group G (S, G) labels (Block 209). The border node translates the (S, G) labels of the multicast traffic into group labels for the CSD before forwarding the multicast traffic to the CSD. In one embodiment, the border node receives multicast traffic from the legacy domain having source IP address that is replaced with the source IP address of the border node before being forwarded into the CSD. In some embodiments, the legacy domain format of header may be encapsulated by SPRING, in which case there is no translation (e.g., in combination with PIM) or we may map the SPRING multicast SID to an mLDP label. Thus, identifiers can be utilized to identify multicast groups in each domain where identifiers can be labels or similar formats. Also, there are variations of the encapsulation of such labels in each domain. It should be noted that although the embodiments have split the roles out such that each node is uniquely a source or receiver, a node can have both roles simultaneously.

[0064] Figures 3A-3E are diagrams of an example of the operation of the interworking of a computed SPRING domain and legacy domain. Figure 3A is a diagram of one example of the process for a node in the in a computed SPRING domain (CSD) advertising into the legacy domain. In this diagram, the example shows a scenario where a source for a multicast group is in the CSD and where leaves of the multicast group exist in the legacy domain. The example shows the two networks sharing two border nodes (B l and B2). A node Nl in the CSD is advertising an interest, in this case an interest as a source, in a multicast group Gl via IGP in the CSD.

[0065] The legacy domain is a PIM or mLDP domain. The legacy domain includes a discovery mechanism such as BGP. The legacy network and CSD can include any number of network devices and only those network devices playing a role in the interworking operations are illustrated for sake of clarity. In an initial state of this example, there are no members of the multicast group Gl before node Nl in the CSD advertises a send interest.

[0066] Figure 3B is a diagram of one example of the process for a node in the in a computed SPRING domain (CSD) advertising into the legacy domain as assisted by the border node. The send interest sent by the node Nl is received by each of the border nodes (B l and B2) via IGP in the CSD. B l receives the advertisement and using the known topology of the SPRING network determines it is on a shortest path between node Nl and to a virtual node VI that represents the legacy domain in the CSD. In response, B l advertises itself as a source for Gl to the discovery mechanism of the legacy domain. In this way, the node Nl and the rest of the CSD is abstracted out at the network boundary and the nodes of the legacy domain are not aware of the specific nodes of the CSD. B2 also receives the advertisement, but determines it is not on the shortest path to VI and therefore does nothing with the advertisement. In some embodiments, a tie breaking mechanism is required for the scenario whereby node Nl is equidistant from border nodes B 1 and B2 to ensure a unique selection of a node on the shortest path.

[0067] Figure 3C is a diagram of one example of the process for a node in the in a legacy domain advertising into the CSD. In the ongoing example, a node N2 in the legacy domain issues a join for the multicast group Gl. The node N2 has learned of the multicast group and the border node as a source via the discovery mechanism and sends a legacy join towards the border node (B l) which eventually propagates across the legacy network to B l.

[0068] Figure 3D is a diagram of one example of the process for a node in the in legacy domain advertising into the CSD with assistance from the border nodes. B l receives the join from node N2. Border node B l then advertises the virtual node VI as a leaf for the multicast group Gl into the CSD, while tracking that node N2 has joined the multicast group Gl. B2 synchronizes with B l to duplicate this tracking and similar state associated with virtual node VI. Border node B2 also then advertises the multicast group Gl and VI into the CSD, such that the nodes of the CSD know that VI is reachable through both border nodes (B l and B2).

[0069] Figure 3E is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains. With the constituent nodes of the multicast group Gl thus advertised through the CSD, the nodes of the CSD independently determine their role in the MDT and fill in the path from Nl to B l. Border node B 1 then begins to perform the appropriate identifier/label translation between the domains to enable the exchange of data between multicast group members. For the legacy domain local labels are utilized for the multicast group. For example, mLDP translates the Nl/Gl global label into a B l/Gl local label or similar label translation is performed. [0070] Figure 3F is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains. The example can be furthered to illustrate the process of adding a node N3 as a source for the multicast group Gl. The node advertises this via IGP in the CSD. Border nodes B l and B2 receive this notification. The border node B l has already advertised the virtual node VI as a leaf in the multicast group Gl. The border node B l already serves the leaves of the multicast group Gl in the legacy domain.

[0071] Figure 3G is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains. The border node B l receives the advertisement of the source node at node N3 and adds the N3/G1 as a label to be translated into B l/Gl in the legacy domain. No further actions are needed to advertise, since the multicast group Gl is already established in each domain. The nodes in the CSD converge in response to the advertisement to connect node N3 with border node B 1. The border node will translate the SPRING labels for both sources (Nl and N3) into the identifier used B l/G.

[0072] Figures 4A-C provide a contrasting example where a source of a multicast group is in the legacy domain. Figure 4A is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains. In the initial state of this example, the multicast group Gl has no participants. The node N2 advertises an interest as a source in the multicast group Gl via the discovery mechanism of the legacy domain. In turn, the border nodes B 1 and B2 receive and note this interest.

[0073] Figure 4B is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains.

Subsequently, a node Nl in the CSD advertises receive interest in group Gl into the IGP.

[0074] Figure 4C is a diagram of one example of the process for a border node between a CSD and a legacy domain supporting multicast traffic forwarding between the domains. The border nodes B l and B2 then receive registration from Nl of its receive interest in Gl. Both nodes B l & B2 are aware there is at least one source for the multicast group Gl in the legacy domain. B l determines that it is on the shortest path between node Nl and virtual node VI, therefor it issues a join to the multicast group S, Gl in the legacy domain. Both border nodes B l and B2 originate source interest into the CSD IGP on behalf of virtual node VI such that upon network convergence, connectivity will exist between border node B l and node Nl for multicast traffic sourced in the legacy domain. Similarly, the join issued towards node N2 by border node B l in the legacy domain will cause connectivity to be established. When both networks have converged data traffic can be exchanged via the border node for the multicast group Gl and the border node may take part in translating the labels and forwarding multicast traffic for Gl to enable the interworking of the two domains.

[0075] A key distinction to note in the operation of the two domains, is that a join in the legacy domain is a join to a specific source, while an advertisement of receive interest in the CSD domain, is a "join all sources," therefore, knowledge of individual sources is not required.

Therefore, a border node can defer advertising legacy sources into the CSD until such time as interest has been registered in the IGP.

[0076] Architecture

[0077] Figure 5A 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 5A shows NDs 500A-H, and their connectivity by way of lines between 500A-500B, 500B-500C, 500C-500D, 500D-500E, 500E-500F, 500F-500G, and 500A-500G, as well as between 500H and each of 500A, 500C, 500D, and 500G. 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 500A, 500E, and 500F 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).

[0078] Two of the exemplary ND implementations in Figure 5 A are: 1) a special-purpose network device 502 that uses custom application-specific integrated-circuits (ASICs) and a special-purpose operating system (OS); and 2) a general purpose network device 504 that uses common off-the-shelf (COTS) processors and a standard OS.

[0079] The special-purpose network device 502 includes networking hardware 510 comprising compute resource(s) 512 (which typically include a set of one or more processors), forwarding resource(s) 514 (which typically include one or more ASICs and/or network processors), and physical network interfaces (NIs) 516 (sometimes called physical ports), as well as non- transitory machine readable storage media 518 having stored therein networking software 520. 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 500A-H. During operation, the networking software 520 may be executed by the networking hardware 510 to instantiate a set of one or more networking software instance(s) 522. Each of the networking software instance(s) 522, and that part of the networking hardware 510 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) 522), form a separate virtual network element 530A-R. Each of the virtual network element(s)

(VNEs) 530A-R includes a control communication and configuration module 532A-R

(sometimes referred to as a local control module or control communication module) and forwarding table(s) 534A-R, such that a given virtual network element (e.g., 530A) includes the control communication and configuration module (e.g., 532A), a set of one or more forwarding table(s) (e.g., 534A), and that portion of the networking hardware 510 that executes the virtual network element (e.g., 53 OA).

[0080] The special-purpose network device 501 can implement a congruent multicast manager 364. The legacy network interworking manager 564 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-4 that provide support for interworking of SPRING networks with legacy networks. The legacy network interworking manager 564 can be stored by the non-transitory machine readable storage media 518 and executed by the compute resources 512.

[0081] The special-purpose network device 502 is often physically and/or logically considered to include: 1) a ND control plane 524 (sometimes referred to as a control plane) comprising the compute resource(s) 512 that execute the control communication and configuration

module(s) 532A-R; and 2) a ND forwarding plane 526 (sometimes referred to as a forwarding plane, a data plane, or a media plane) comprising the forwarding resource(s) 514 that utilize the forwarding table(s) 534A-R and the physical NIs 516. By way of example, where the ND is a router (or is implementing routing functionality), the ND control plane 524 (the compute resource(s) 512 executing the control communication and configuration module(s) 532A-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) 534A-R, and the ND forwarding plane 526 is responsible for receiving that data on the physical NIs 516 and forwarding that data out the appropriate ones of the physical NIs 516 based on the forwarding table(s) 534A-R.

[0082] Figure 5B illustrates an exemplary way to implement the special-purpose network device 502 according to some embodiments of the invention. Figure 5B shows a special- purpose network device including cards 538 (typically hot pluggable). While in some embodiments the cards 538 are of two types (one or more that operate as the ND forwarding plane 526 (sometimes called line cards), and one or more that operate to implement the ND control plane 524 (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 536 (e.g., a first full mesh coupling the line cards and a second full mesh coupling all of the cards).

[0083] Returning to Figure 5A, the general purpose network device 504 includes 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 software 550. During operation, the processor(s) 542 execute the software 550 to instantiate one or more sets of one or more applications 564A-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 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 that may each be used to execute one (or more) of the sets of applications 564A-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 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 each of the sets of applications 564A-R is run on top of a guest operating system within an instance 562A-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 540, 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 554, unikernels running within software containers represented by instances 562A-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).

[0084] The instantiation of the one or more sets of one or more applications 564A-R, as well as virtualization if implemented, are collectively referred to as software instance(s) 552. Each set of applications 564 A-R, corresponding virtualization construct (e.g., instance 562A-R) if implemented, and that part of the hardware 540 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) 560A-R.

[0085] The virtual network element(s) 560A-R perform similar functionality to the virtual network element(s) 530A-R - e.g., similar to the control communication and configuration module(s) 532A and forwarding table(s) 534A (this virtualization of the hardware 540 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 562A-R corresponding to one VNE 560A-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 562A-R to VNEs also apply to embodiments where such a finer level of granularity and/or unikernels are used.

[0086] In certain embodiments, the virtualization layer 554 includes a virtual switch that provides similar forwarding services as a physical Ethernet switch. Specifically, this virtual switch forwards traffic between instances 562A-R and the NIC(s) 544, as well as optionally between the instances 562A-R; in addition, this virtual switch may enforce network isolation between the VNEs 560A-R that by policy are not permitted to communicate with each other (e.g., by honoring virtual local area networks (VLANs)). [0087] The general purpose network device 504 can implement a legacy network interworking manager 568. The legacy network interworking manager 568 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-4 that provide support for interworking legacy networks with SPRING networks. The legacy network interworking manager 568 can be stored by the non-transitory machine readable storage media 548 and executed by the software instances 552 and processors 542.

[0088] The third exemplary ND implementation in Figure 5A is a hybrid network device 506, 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 502) could provide for para-virtualization to the networking hardware present in the hybrid network device 506.

[0089] 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) 530A-R, VNEs 560A-R, and those in the hybrid network device 506) receives data on the physical NIs (e.g., 516, 546) and forwards that data out the appropriate ones of the physical NIs (e.g., 516, 546). 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.

[0090] Figure 5C illustrates various exemplary ways in which VNEs may be coupled according to some embodiments of the invention. Figure 5C shows VNEs 570A.1-570A.P (and optionally VNEs 570A.Q-570A.R) implemented in ND 500A and VNE 570H.1 in ND 500H. In Figure 5C, VNEs 570A.1-P are separate from each other in the sense that they can receive packets from outside ND 500A and forward packets outside of ND 500A; VNE 570A.1 is coupled with VNE 570H.1, and thus they communicate packets between their respective NDs; VNE 570A.2-570A.3 may optionally forward packets between themselves without forwarding them outside of the ND 500A; and VNE 570A.P may optionally be the first in a chain of VNEs that includes VNE 570A.Q followed by VNE 570A.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 5C 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).

[0091] The NDs of Figure 5A, 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 5A may also host one or more such servers (e.g., in the case of the general purpose network device 504, one or more of the software instances 562A-R may operate as servers; the same would be true for the hybrid network device 506; in the case of the special-purpose network device 502, one or more such servers could also be run on a virtualization layer executed by the compute resource(s) 512); in which case the servers are said to be co-located with the VNEs of that ND.

[0092] A virtual network is a logical abstraction of a physical network (such as that in

Figure 5A) 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). [0093] 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).

[0094] 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).

[0095] Fig. 5D illustrates a network with a single network element on each of the NDs of Figure 5A, 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 5D illustrates network elements (NEs) 570A-H with the same connectivity as the NDs 500A-H of Figure 5A.

[0096] Figure 5D illustrates that the distributed approach 572 distributes responsibility for generating the reachability and forwarding information across the NEs 570A-H; in other words, the process of neighbor discovery and topology discovery is distributed. [0097] For example, where the special-purpose network device 502 is used, the control communication and configuration module(s) 532A-R of the ND control plane 524 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 570A-H (e.g., the compute resource(s) 512 executing the control communication and configuration

module(s) 532A-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 524. The ND control plane 524 programs the ND forwarding plane 526 with information (e.g., adjacency and route information) based on the routing structure(s). For example, the ND control plane 524 programs the adjacency and route information into one or more forwarding table(s) 534A-R (e.g., Forwarding Information Base (FIB), Label Forwarding Information Base (LFIB), and one or more adjacency structures) on the ND forwarding plane 526. 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 502, the same distributed approach 572 can be implemented on the general purpose network device 504 and the hybrid network device 506.

[0098] Figure 5D illustrates that a centralized approach 574 (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 574 has the responsibility for the generation of reachability and forwarding information in a centralized control plane 576 (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 576 has a south bound interface 582 with a data plane 580 (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 570A-H (sometimes referred to as switches, forwarding elements, data plane elements, or nodes). The centralized control plane 576 includes a network controller 578, which includes a centralized reachability and forwarding information module 579 that determines the reachability within the network and distributes the forwarding information to the NEs 570A-H of the data plane 580 over the south bound interface 582 (which may use the OpenFlow protocol). Thus, the network intelligence is centralized in the centralized control plane 576 executing on electronic devices that are typically separate from the NDs.

[0099] For example, where the special-purpose network device 502 is used in the data plane 580, each of the control communication and configuration module(s) 532A-R of the ND control plane 524 typically include a control agent that provides the VNE side of the south bound interface 582. In this case, the ND control plane 524 (the compute resource(s) 512 executing the control communication and configuration module(s) 532A-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 576 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 579 (it should be understood that in some embodiments of the invention, the control communication and configuration module(s) 532A-R, in addition to communicating with the centralized control plane 576, 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 574, but may also be considered a hybrid approach).

[00100] While the above example uses the special-purpose network device 502, the same centralized approach 574 can be implemented with the general purpose network device 504 (e.g., each of the VNE 560A-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 576 to receive the forwarding information (and in some cases, the reachability information) from the centralized reachability and forwarding information module 579; it should be understood that in some embodiments of the invention, the VNEs 560A-R, in addition to communicating with the centralized control plane 576, 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 506. In fact, the use of SDN techniques can enhance the NFV techniques typically used in the general purpose network device 504 or hybrid network device 506 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.

[00101] Figure 5D also shows that the centralized control plane 576 has a north bound interface 584 to an application layer 586, in which resides application(s) 588. The centralized control plane 576 has the ability to form virtual networks 592 (sometimes referred to as a logical forwarding plane, network services, or overlay networks (with the NEs 570A-H of the data plane 580 being the underlay network)) for the application(s) 588. Thus, the centralized control plane 576 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).

[00102] While Figure 5D shows the distributed approach 572 separate from the centralized approach 574, 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) 574, 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 574, but may also be considered a hybrid approach.

[00103] While Figure 5D illustrates the simple case where each of the NDs 500A-H implements a single NE 570A-H, it should be understood that the network control approaches described with reference to Figure 5D also work for networks where one or more of the

NDs 500A-H implement multiple VNEs (e.g., VNEs 530A-R, VNEs 560A-R, those in the hybrid network device 506). Alternatively or in addition, the network controller 578 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 578 may present the implementation of a VNE/NE in a single ND as multiple VNEs in the virtual networks 592 (all in the same one of the virtual network(s) 592, each in different ones of the virtual network(s) 592, or some combination). For example, the network controller 578 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 576 to present different VNEs in the virtual network(s) 592 (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).

[00104] The centralized control plane 576 can implement a legacy networking interworking manager 581. The legacy networking interworking manager 581 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-4 that provide interworking between legacy networks and SPRING networks.

[00105] On the other hand, Figures 5E and 5F respectively illustrate exemplary abstractions of NEs and VNEs that the network controller 578 may present as part of different ones of the virtual networks 592. Figure 5E illustrates the simple case of where each of the NDs 500A-H implements a single NE 570A-H (see Figure 5D), but the centralized control plane 576 has abstracted multiple of the NEs in different NDs (the NEs 570A-C and G-H) into (to represent) a single NE 5701 in one of the virtual network(s) 592 of Figure 5D, according to some

embodiments of the invention. Figure 5E shows that in this virtual network, the NE 5701 is coupled to NE 570D and 570F, which are both still coupled to NE 570E.

[00106] Figure 5F illustrates a case where multiple VNEs (VNE 570A.1 and VNE 570H.1) are implemented on different NDs (ND 500A and ND 500H) and are coupled to each other, and where the centralized control plane 576 has abstracted these multiple VNEs such that they appear as a single VNE 570T within one of the virtual networks 592 of Figure 5D, according to some embodiments of the invention. Thus, the abstraction of a NE or VNE can span multiple NDs.

[00107] While some embodiments of the invention implement the centralized control plane 576 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).

[00108] Similar to the network device implementations, the electronic device(s) running the centralized control plane 576, and thus the network controller 578 including the centralized reachability and forwarding information module 579, 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 6 illustrates, a general purpose control plane device 604 including hardware 640 comprising a set of one or more processor(s) 642 (which are often COTS processors) and network interface controller(s) 644 (NICs; also known as network interface cards) (which include physical NIs 646), as well as non-transitory machine readable storage media 648 having stored therein centralized control plane (CCP) software 650.

[00109] In embodiments that use compute virtualization, the processor(s) 642 typically execute software to instantiate a virtualization layer 654 (e.g., in one embodiment the virtualization layer 654 represents the kernel of an operating system (or a shim executing on a base operating system) that allows for the creation of multiple instances 662A-R called software containers (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 654 represents a hypervisor (sometimes referred to as a virtual machine monitor (VMM)) or a hypervisor executing on top of a host operating system, and an application is run on top of a guest operating system within an instance 662A-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 640, directly on a hypervisor represented by virtualization layer 654 (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 662A-R). Again, in embodiments where compute virtualization is used, during operation an instance of the CCP software 650 (illustrated as CCP instance 676A) is executed (e.g., within the instance 662A) on the virtualization layer 654. In embodiments where compute virtualization is not used, the CCP instance 676A is executed, as a unikernel or on top of a host operating system, on the "bare metal" general purpose control plane device 604. The instantiation of the CCP instance 676A, as well as the virtualization layer 654 and

instances 662A-R if implemented, are collectively referred to as software instance(s) 652.

[00110] In some embodiments, the CCP instance 676A includes a network controller instance 678. The network controller instance 678 includes a centralized reachability and forwarding information module instance 679 (which is a middleware layer providing the context of the network controller 578 to the operating system and communicating with the various NEs), and an CCP application layer 680 (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 680 within the centralized control plane 576 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.

[00111] The centralized control plane 576 transmits relevant messages to the data plane 580 based on CCP application layer 680 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 580 may receive different messages, and thus different forwarding information. The data plane 580 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.

[00112] The general purpose control plane device 604 can implement a legacy networking interworking manager 681. The legacy networking interworking manager 681 can be a program or similar set of instructions that implement the methods described herein above in reference to Figures 1-4 that provide interworking between legacy networks and SPRING networks.

[00113] 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).

[00114] 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.

[00115] 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.

[00116] However, when an unknown packet (for example, a "missed packet" or a "match- miss" as used in OpenFlow parlance) arrives at the data plane 580, the packet (or a subset of the packet header and content) is typically forwarded to the centralized control plane 576. The centralized control plane 576 will then program forwarding table entries into the data plane 580 to accommodate packets belonging to the flow of the unknown packet. Once a specific forwarding table entry has been programmed into the data plane 580 by the centralized control plane 576, the next packet with matching credentials will match that forwarding table entry and take the set of actions associated with that matched entry.

[00117] 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 computed source packet in routing (SPRING) domain (CSD) and a legacy domain, the legacy domain represented as a virtual node of the CSD, the method comprising:

receiving (101) an advertisement of a multicast group having a source in the CSD;

advertising (103) the multicast group having a source in the CSD to a discovery

mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain;

receiving (105) a join addressed to the border node as a source of the multicast group from the legacy domain; and

declaring (107) a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

2. The method of claim 1, further comprising:

receiving (109) multicast traffic from the CSD having source S, group G (S, G)

identifiers of the CSD; and

updating (111) the (S, G) identifiers of the multicast traffic into group identifiers for the legacy domain before forwarding the multicast traffic to the legacy domain.

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

receiving multicast traffic from the CSD having a source Internet Protocol (IP) address; and

replacing the source IP address with an IP address of the border node, before forwarding the multicast traffic to the legacy domain.

4. The method of claim 1, wherein the legacy domain implements multicast label

distribution protocol (mLDP) or protocol independent multicast (PIM).

5. The method of claim 1, wherein the legacy domain implements point to multipoint

(P2MP) or multi-point to multi-point (MP2MP) multicast distribution trees (MDTs).

6. The method of claim 1, wherein the border node is pre-provisioned with segment identifiers (IDs) to utilize for a virtual node that represents a multicast tree in the legacy domain.

7. A method implemented by a network device, the network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain, the legacy domain represented as a virtual node of the CSD, the method comprising:

receiving (201) an advertisement of a multicast group having a source in the legacy

domain via a discovery mechanism of the legacy domain;

receiving (203) a join addressed to a virtual node representing the legacy domain as a source of the multicast group from the CSD;

forwarding (205) the join toward the source in the legacy domain; and

advertising (207) the multicast group having a source in the legacy domain into the CSD.

8. The method of claim 7, wherein the method further comprises:

receiving (209) multicast traffic from the legacy domain having source S, group G (S, G) identifiers; and

updating (211) the (S, G) labels of the multicast traffic into group identifiers for the CSD before forwarding the multicast traffic to the CSD.

9. The method of claim 7, wherein the method further comprises:

receiving multicast traffic from the legacy domain having a source Internet Protocol IP address; and

replacing the source IP address with an IP address of the border node, before forwarding the multicast traffic to the CSD.

10. The method of claim 7, wherein the legacy domain implements multicast label

distribution protocol (mLDP) or protocol independent multicast (PIM).

11. The method of claim 7, wherein the border node is pre-provisioned with labels to utilize for a virtual node that represents a multicast tree in the legacy domain.

12. A network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain, the legacy domain represented as a virtual node of the CSD, the network device comprising:

a non-statutory machine -readable storage medium (518) having stored therein a legacy network interworking manager (564); and

a processor (512) coupled to the non-statutory machine-readable storage medium, the processor configured to execute the legacy network interworking manager, the legacy network interworking manager configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

13. The network device of claim 12, wherein the legacy network interworking manager is further configured to receive multicast traffic from the CSD having source S, group G (S, G) identifiers of the CSD, and updating the (S, G) identifiers of multicast traffic into group identifiers for the legacy domain before forwarding the multicast traffic to the legacy domain.

14. The network device of claim 12, wherein the legacy network interworking manager is further configured to receive another advertisement of the multicast group having a source in the legacy domain via a discovery mechanism of the legacy domain, advertise the multicast group having the source in the legacy domain into the CSD, receive a join addressed to a virtual node representing the legacy domain as a source of the multicast group from the CSD, and to forward the join toward the source in the legacy domain.

15. A computing device configured to execute a plurality of virtual machines, the plurality of virtual machines implementing network function virtualization (NFV), the computing device in communication with a network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain, the legacy domain represented as a virtual node of the CSD, the computing device comprising:

a non-statutory machine -readable storage medium (548) having stored therein a legacy network interworking manager (568); and

a processor (542) coupled to the non-statutory machine-readable storage medium, the processor configured to execute a virtual machine from the plurality of virtual machines, the virtual machine configured to execute a legacy network interworking manager, the legacy network interworking manager configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

16. The computing device of claim 15, wherein the legacy network interworking manager is further configured to receive multicast traffic from the CSD having source S, group G (S, G) identifiers of the CSD, and updating the (S, G) identifiers of multicast traffic into group identifiers for the legacy domain before forwarding the multicast traffic to the legacy domain.

17. The computing device of claim 15, wherein the legacy network interworking manager is further configured to receive another advertisement of the multicast group having a source in the legacy domain via a discovery mechanism of the legacy domain, advertise the multicast group having the source in the legacy domain into the CSD, receive a join addressed to a virtual node representing the legacy domain as a source of the multicast group from the CSD, and to forward the join toward the source in the legacy domain.

18. A control plane device is configured to implement a control plane of a software defined networking (SDN) network including a network device functioning as a border node of a computed source packet in routing (SPRING) domain (CSD) and a legacy domain, the legacy domain represented as a virtual node of the CSD, wherein the control plane device is configured to configure the network device, the control plane device comprising:

a non-statutory machine -readable storage medium (648) having stored therein a legacy network interworking manager (681); and

a processor (642) coupled to the non-statutory machine-readable storage medium, the processor configured to execute the legacy network interworking manager, the legacy network interworking manager configured to receive an advertisement of a multicast group having a source in the CSD, to advertise the multicast group having a source in the CSD to a discovery mechanism of the legacy domain, as though a source of the MDT was the border node, in response to the border node being on a shortest path between a sender of the advertisement and a virtual node representing the legacy domain, to receive a join addressed to the border node as a source of the multicast group from the legacy domain, and to declare a virtual node as if it were attached to the border node as a member of the multicast group with a receive interest into the CSD.

19. The control plane device of claim 18, wherein the legacy network interworking manager is further configured to receive multicast traffic from the CSD having source S, group G (S, G) identifiers of the CSD, and updating the (S, G) identifiers of multicast traffic into group identifiers for the legacy domain before forwarding the multicast traffic to the legacy domain.

20. The control plane device of claim 18, wherein the legacy network interworking manager is further configured to receive another advertisement of the multicast group having a source in the legacy domain via a discovery mechanism of the legacy domain, advertise the multicast group having the source in the legacy domain into the CSD, receive a join addressed to a virtual node representing the legacy domain as a source of the multicast group from the CSD, and to forward the join toward the source in the legacy domain.