Discovery of a multicast router topology

Abstract

Network device for determining the topology of a multicast router, comprising: A processing resource (240); and a memory resource (242) coupled to the processing resource, the memory resource (242) storing instructions executable by the processing resource (240) to: send a Connected Multicast Router Discovery Request, CMRDR, (108-1) from an initial router (104-1) having multiple interfaces executing a Multicast Routing Protocol, MRP; receive a first number of responses (110-1, 110-2) from a first number of routers (104-2, 104-3), wherein the first number of routers (104-2, 104-3) have a network connection with the initial router (104-1), have received the CMRDR (108-1), and have a plurality of interfaces executing an MRP, and wherein the first number of responses (110-1, 110-2) include the address and subnet of each of the plurality of interfaces of the first number of routers (110-1, 110-2) that have a network connection with the initial router (104-1), have received the CMRDR (108-1), and have a plurality of interfaces executing an MRP; receive a second number of responses (110-3) from a second number of routers (104-4), the second number of routers (104-4) having a network connection with the first number of routers (104-2, 104-3), having received a forwarded CMRDR (108-4, 108-7) from the first number of routers (104-2, 104-3), and having a plurality of interfaces executing an MRP; to create a multicast router topology of the initial router (104-1), the first number of routers (104-2, 104-3), and the second number of routers (104-4) by determining at the initial router (104-1) the initial routers (104-1), the first number of routers (104-2, 104-3), and the second number of routers (104-4) connected to one another via a number of network connections that execute the MRP on the series of interfaces on the interconnected initial routers (104-1), the first number of routers (104-2, 104-3), and the second number of routers (104-4); and Specifying a node count and time limit in the CMRDR (108-1), wherein the time limit is a time in which the initial router (104-1) waits for the first number of responses (110-1, 110-2) and the second number of responses (110-3) before aggregating the multicast router topology, wherein CMRDRs are sent with increasing node count and / or time limit until the same multicast router topology is repeatedly generated.

Description

background

[0001] Computer networks can contain multiple devices, including network devices such as routers, switches and hubs, computing devices such as servers, desktop computers, laptops, workstations and peripherals such as printers, fax machines and scanners, which are interconnected via a LAN (Local Area Network), a WLAN (Wireless Local Area Network) and / or WAN (Wide Area Network).

[0002] Multicasting can be used in a network when the same information is required by multiple devices. Multicasting can reduce the amount of network resources consumed when transmitting multicast data to multiple devices by delivering the data to all devices that need it at once. Multicasting can involve logically routing multicast data across a network to avoid redundancy and route data efficiently across the network. The topology of the devices on the network used for multicasting the routed data can be useful in logically routing multicast data across a network. For large networks, the topology of the devices on the network used for multicasting can be difficult to determine.

[0003] Waitzman, D., et al.: Distance Vector Multicast Routing Protocol, RFC-1075 (1988) and Pusateri, T.: Distance Vector Multicast Routing Protocol, Internet-Draft (1996) disclose a receiver-based routing protocol with a distance vector algorithm that determines the shortest path to the data source. However, a method for determining a multicast router topology is known from US 2011 / 0134797.

[0004] However, it cannot be ruled out that the method does not provide a complete picture of the router topology. The invention therefore aims to at least mitigate these disadvantages. Short description of the drawings Fig. 1A- Fig. 1D show an example of a computer network according to the invention for determining a multicast router topology. Fig. 2 is a block diagram of a processing resource, a storage resource, and a machine-readable medium according to the invention. Fig. 3 is a flowchart of an example of a method for determining a multicast router topology according to the invention. Detailed description

[0005] The above object is achieved by the invention specified in the independent claims. Advantageous further developments can be found in the subclaims. Embodiments according to the invention can comprise network devices, systems and methods, in particular also executable instructions and logic located thereon, for determining a topology of a multicast router. A network device comprises a processing resource coupled to a memory. The memory comprises program instructions that can be executed by the processing resource for determining a

[0006] Topology of a multicast router can be performed by determining a number of routers connected to each other via a number of network links that run an MRP (Multicast Routing Protocol) on a number of interfaces on the interconnected routers.

[0007] In the following detailed description of the present invention, reference is made to the accompanying drawings, which form a part of the present invention and are presented to illustrate the practice of examples of the invention. These examples are described in sufficient detail to enable those skilled in the art to practice the embodiments of the invention; it is understood that other examples may be used, and that procedural, electrical, and / or structural changes are possible without departing from the scope of the present invention.

[0008] These drawings correspond to a numbering system in which the first number(s) of the drawing number, and the remaining numbers, identify an element or component of the drawing. Similar elements or components of different drawings may be assigned similar numbers. For example, 108 may represent element "08" of the Fig. 1B, and a similar element can be found in the Fig. 2 as 208. The elements illustrated in the various drawings may be added, interchanged, and / or omitted to provide various further examples of the present invention. Furthermore, the proportions and scale of the elements illustrated in the drawings are intended to be illustrative of the present invention and are not to be construed as limiting.

[0009] Fig. 1A - 1D show an example of a computer network 100 for determining a multicast router topology. The Fig. The computer network 100 illustrated in Figure 1A includes multiple routers. In some examples, a computer network may include multiple devices interconnected in a LAN and / or WAN via routers, hubs, switches, etc. As used herein, a "network device" refers to a switch, router, hub, bridge, access point, etc., e.g., a router connected to a network 100 with processor and memory resources.

[0010] In some examples, devices may be connected to each other and / or to other networks using, for example, routers, hubs, and / or switches. As mentioned above, these devices may include a processor communicating with a memory, and may also include network chips with hardware logic, e.g., in the form of ASICs (Application-Specific Integrated Circuits), associated with the corresponding number of network interfaces. As used herein, the term "network" is not limited to the number, type, and / or configuration of the Fig. 1 shown devices.

[0011] In this sense, a network can provide a communications system that connects two or more devices, gives users access to resources on other devices, and enables them to exchange messages with other users. A network enables users to share resources on their own systems with other network users and to access data on centrally located systems or systems in decentralized offices. It can provide connections to the Internet or the networks of other organizations. Users can interact with network-enabled, machine-readable instructions, e.g., software and / or firmware, applications, to make a network request, e.g., for a file. Applications can also communicate with machine-readable network management instructions, which in turn can communicate with the network's hardware to transfer data between devices on the network.

[0012] The computer network 100 of Fig. 1A includes Router A (104-1), Router B (104-2), Router C (104-3), Router D (104-4), Router E (104-5), Router F (104-6), and Router G (104-7). Each of the routers can include multiple interfaces, where the interfaces are named depending on the router they are located on and the specific interface on the router. For example, interface b on Router C is called interface Cb. The multiple interfaces can execute an MRP, as indicated by the MRP name at the interfaces in the Fig. 1 shown routers. In the Fig. 1, router 104-1 includes four interfaces referred to as interfaces Aa, Ab, Ac, and Ad. Router 104-2 includes four interfaces referred to as interfaces Ba, Bb, Bc, and Bd. Router 104-3 includes four interfaces referred to as interfaces Ca, Cb, Cc, and Cd. Router 104-4 includes four interfaces referred to as interfaces Da, Db, Dc, and Dd. Router 104-5 includes two interfaces referred to as interfaces Ea and Eb. Router 104-6 includes four interfaces referred to as interfaces Fa, Fb, Fc, and Fd. Router 104-7 includes two interfaces referred to as interfaces Ga and Gb.

[0013] The Fig. The routers shown in Figure 1A can have multiple network connections. With multiple network connections and routers, one router can be connected to another router. Fig. 1A, network connection 106-1 connects interface Ac of router 104-1 to interface Ba of router 104-2. Network connection 106-2 connects interface Ad of router 104-1 to interface Ca of router 104-3. Network connection 106-3 connects interface Bc of router 104-2 to interface Cb of router 104-3. Network connection 106-4 connects interface Cd of router 104-2 to interface Da of router 104-4. Network connection 106-5 connects interface Bd of router 104-3 to interface Db of router 104-4. Network connection 106-6 connects interface Dc of router 104-4 to interface Eb of router 104-5. Network connection 106-7 connects interface Dd of router 104-4 to interface Ga of router 104-7.Network connections 106-1, 106-2, 106-3, 106-4, 106-5, 106-6, and 106-7 can be used to transfer data between multiple routers. The network connections can be used to transfer data from one interface of one router to another interface of another router, provided a network connection exists between the two routers. For example, router 104-1 can be connected to router 104-4 via network connection 106-1, router 104-2, and network connection 106-4.

[0014] Fig. Figure 1B shows an example of a computer network 100 for determining a multicast router topology. Fig. 1B, router 104-1 is chosen as the initial router. Once router 104-1 is chosen as the initial router, router 104-1 is examined for interfaces executing an MRP. Router 104-1 has four interfaces (Aa, Ab, Ac, and Ad) executing an MRP. Router 104-1 can send a CMRDR (Connected Multicast Router Discovery Request) associated with each interface on the router executing an MRP. For example, router 104-1 can send a CMRDR for interface Aa, a CMRDR for Ab, a CMRDR for Ac, and a CMRDR for Ad. The CMRDRs can be sent as individual multicast packets on the network links connecting router 104-1 to the other routers in the network. A CMRDR can specify the interface on which the CMRDR was initiated as well as the interface from which the CMRDR was sent. For example, CMRDR 108-1 may indicate that it is being sent from interface Ab (in the Fig. 1B shown as i=Ab) and from the interface Ad (in the Fig. 1B, represented as S=Ad). A CMRDR can also specify a node count and a wait time. A node count can specify the number of forwarding options for the CMRDR in the computer network. The wait time specifies how long the initial router will wait for responses from routers in the computer network.

[0015] Router 104-1 may send the CMRDR 108-1 via a single multicast packet to router 104-2 on network link 106-1 and to router 104-3 on network link 106-2. The CMRDR 108-1 indicates that the CMRDR was initiated by interface Ab and sent by interface Ad. The CMRDR 108-1 may be received by router 104-2 on interface Ba and by router 104-3 on interface Ca. Routers 104-2 and 104-3 may determine whether to send a response to the initial router 104-1 or to discard the CMRDR 108-1. A response may be sent to the initial router 104-1 provided the receiving router has a direct network connection to the initial router and / or the router received the CMRDR on the interface corresponding to the interface initiating the CMRDR.

[0016] In the Fig. 1B, responses 110-1 and 110-2 are sent to router 104-1, since routers 104-2 and 104-3 each have a direct network connection to router 104-1. In the example of Fig. 1B, response 110-1 may be sent from router 104-2 to router 104-1 on network link 106-1, and response 110-1 may be sent upon receipt of CMRDR 108-1 from router 104-1 on network link 106-1. Response 110-1 may indicate that router 104-2 is sending the response (in response 110-1 of the Fig. 1B as B) and that the response 110-1 is to be assigned to the request from the interface Ab of the router 104-1 (In the response 110-1 of the Fig. 1B as i=Ab). The response 110-2 may indicate that the router 104-3 sends the response (in the response 110-2 of the Fig. 1B as C) and that the response 110-1 is to be assigned to the request from the interface Ab of the router 104.1 (in the response 110-2 of the Fig. 1B as i=Ab). Responses 110-1 and 110-2 may be sent as a unicast packet to router 104-1. A response to a CMRDR may include the addresses of the interfaces of the responding router that are executing an MRP, as well as the subnet data of each of the interfaces, etc. For example, response 110-1 may include the addresses of the interfaces of router 104-2 that are executing an MRP, as well as the subnet data of each of the interfaces. Response 110-2 may include the addresses of the interfaces of router 104-3 that are executing an MRP, as well as the subnet data of each of the interfaces.

[0017] Fig. Figure 1C shows an example of a computer network 100 for determining a multicast router topology. Fig. 1C, routers 104-2 and 104-3 forward the CMRDR from router 104-1 to other routers of computer network 100. In some examples, the routers that receive a CMRDR and respond to the initial router sending the CMRDR may forward the CMRDR on their MRP-executing interfaces that have a network connection to another router. Fig. 1C, router 104-2 can forward the CMRDR 108-1 received from router 104-1 because router 104-2 sent the response 110-1 to router 104-1. Router 104-3 can forward the CMRDR 108-1 received from router 104-1 because router 104-3 sent the response 110-2 to router 104-1.

[0018] Router 104-2 has three interfaces that run an MRP and have network connections to another router, so router 104-2 can forward the CMRDR from these three interfaces. When forwarding a CMRDR, the router forwarding the CMRDR can update the CMRDR to specify the router and interface from which the CMRDR is forwarded. For example, router 104-2 can forward the updated CMRDR 108-2 from interface Ba to interface Ac of router 104-1. The CMRDR 108-2 can specify that it is from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Ba (in the Fig. 1C as S=Ba). Router 104-2 may forward the updated CMRDR 108-3 from interface Bc to interface Cb of router 104-2. The CMRDR 108-3 may indicate that it was sent from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Bc (in the Fig. 1C as S=Bc). Router 104-2 may forward the updated CMRDR 108-4 from interface Bd to interface Da of router 104-4. The CMRDR 108-4 may indicate that it is being sent from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Bd (in the Fig. 1C shown as S=Bd).

[0019] If CMRDRs 108-2, 108-3, and 108-4 are each received once by routers 104-1, 104-3, and 104-4, the routers can decide whether to send a response to the initial router 104-1 or discard the CMRDR. Router 104-1 can discard CMRDR 108-2 because an RPF (Reverse Path Forwarding) check failed, as interface Cb is not the correct path to reach interface Ab in router 104-1. An RPF check is used to verify whether the interface that received a CMRDR is also the one through which the source of the CMRDR could be reached. Router 104-4 may discard CMRDR 108-4 because an RPF check failed because interface Da is not the correct path to reach interface Ab in router 104-1.

[0020] Router 104-3 has three interfaces running an MRP and having network connections to another router, so router 104-3 can forward the CMRDR from these three interfaces. For example, router 104-3 can forward the updated CMRDR 108-5 from interface Ca to interface Ad of router 104-1. The CMRDR 108-5 can indicate that it is coming from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Ca (in the Fig. 1C as S=Ca). Router 104-3 may forward the updated CMRDR 108-6 from interface Cb to interface Bc of router 104-2. The CMRDR 108-6 may indicate that it was sent from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Cb (in the Fig. 1C as S=Cb). Router 104-3 may forward the updated CMRDR 108-7 from interface Cd to interface Db of router 104-4. The CMRDR 108-7 may indicate that it was sent from interface Ab (in the Fig. 1C shown as i=Ab) and from the interface Cd (in the Fig. 1C represented as S=Cd).

[0021] If CMRDRs 108-5, 108-6, and 108-7 are each received once by routers 104-1, 104-2, and 104-4, the routers can decide whether to send a response to initial router 104-1 or discard the CMRDR. Router 104-1 can discard CMRDR 108-5 because router 104-1 is the initial router. Router 104-3 can discard CMRDR 108-3 because an RPF check failed, as interface Cb is not the correct path to reach interface Ab on router 104-1. Router 104-4 can send a response because the CMRDR 108-4 is received by interface Db of router 104-4 and an RPF check is passed, because interface Db is the correct path to reach interface Ab in router 104-1. In the example of Fig. 1C, response 110-3 may be sent from router 104-4 to router 104-1 as a unicast packet. Response 110-3 may indicate that router 104-4 is sending the response and that response 110-3 is associated with the request from interface Ab of router 104-1. Response 110-3 may include the addresses of the interfaces of router 104-4 that are running an MRP, as well as the subnet information for each of the interfaces.

[0022] Fig. Figure 1D shows an example of a computer network 100 for determining a topology of a multicast router. Fig. 1D, router 104-4 forwards the CMRDR from router 104-1 to the other routers in computer network 100. In some examples, the routers that receive a CMRDR and respond to the initial router sending the CMRDR may forward the CMRDR on their interfaces running an MRP that have a network connection to another router. Fig. 1D, router 104-4 can forward the CMRDR 108-7 received from router 104-3 because the CMRDR 108-7 was accepted and processed by router 104-4.

[0023] Router 104-4 has three interfaces running an MRP and having network connections to another router, so router 104-4 can forward the CMRDR from the three interfaces. When forwarding a CMRDR, the router forwarding the CMRDR can update the CMRDR to specify the router and interface from which the CMRDR is forwarded. For example, router 104-4 can forward the updated CMRDR 108-8 from interface Da to interface Bd of router 104-2. The CMRDR 108-8 can specify that it is from interface Ab (in the Fig. 1D shown as i=Ab) and from the interface Da (in the Fig. 1D as S=Da). Router 104-4 may forward the updated CMRDR 108-9 from interface Dc to interface Eb of router 104-5. The CMRDR 108-9 may indicate that it was sent from interface Ab (in the Fig. 1D shown as i=Ab) and from the interface Dc (in the Fig. 1D as S=Dc). Router 104-4 may forward the updated CMRDR 108-10 from interface Db to interface Cd of router 104-3. The CMRDR 108-10 may indicate that it was sent from interface Ab (in the Fig. 1D shown as i=Ab) and from the interface Db (in the Fig. 1D represented as S=Db).

[0024] If CMRDRs 108-8, 108-9, and 108-10 are each received once by routers 104-2, 104-5, and 104-3, the routers can decide whether to send a response to the initial router 104-1 or discard the CMRDR. Router 104-2 can discard CMRDR 108-8 because an RPF check failed, as interface Bd is not the correct path to reach interface Ab in router 104-1. Router 104-5 can discard CMRDR 108-9 because interface Eb of router 104-5, which received CMRDR 108-9, is not executing MRP. Router 104-3 may discard CMRDR 108.10 because an RPF check failed because interface Cd is not the correct path to reach interface Ab in router 104-1.

[0025] As soon as in the example the Fig. 1D Router 104-4 forwarded the CMRDR, the CMRDR is not forwarded to or by any other router, because the CMRDR was forwarded to interfaces on routers that failed an RPF check or the CMRDR was forwarded to interfaces that do not perform MPR, such as interface Eb on router 104-5. Fig. 1D, the CMRDR is not forwarded to router 104-6 because there is no network connection between router 104-6 and another router in the network of the Fig. 1D exists. The CMRDR is not forwarded to router 104-7 because interface Dd on router 104-4 is not running MRP, so the CMRDR cannot be forwarded to interface Ga on router 104-7 via network connection 106-7. Therefore, the CMRDR is not forwarded by initial router 104-1 to any other router on computer network 100, and initial router 104-1 does not receive any further responses from routers on computer network 100. Initial router 104-1 can use the data received in responses 110-1, 110-2, and 110-3 to determine a multicast router topology. The data in responses 110-1, 110-2, and 110-3 can be stored in router 104-1 according to the settings.Once the router has received all responses from the routers in the computer network and / or the wait time has been exceeded, the data from responses 110-1, 110-2, and 110-3 can be combined to determine the multicast router topology of network 100.

[0026] Fig. 2 is a block diagram of a processing resource 240, a storage resource 242, and a machine-readable medium 244 according to the invention. The processing resource 240 and storage resource 242 may be local resources of a computer network, e.g., located on a router. The machine-readable medium 244 (e.g., a tangible, non-transitory medium) and / or the storage resource 242 may store a set of instructions (e.g., software, firmware, etc.) executable by the processing resource 240. The machine-readable medium may be local to a router or distributed. For examples where the machine-readable medium is remote from the router, the instructions may be loaded into the router's storage resource 242.

[0027] The instructions stored in medium 244 can be executed as a programmable alternative of the router. For example, a network administrator can enable the functions provided by parts of the instructions or all of the instructions as appropriate for the programmable alternative. Providing the instructions as a programmable alternative can be advantageous because various examples of the invention may not conform to various wireless transmission standards (e.g., IEEE 802.11). In some examples, the function provided by the instructions may be disabled by default and only enabled by the programmable alternative; however, the examples are not limited to this.

[0028] The commands can be executed to transmit a CMRDR 208 as a multicast packet from an initial router. The CMRDR 208 can be received by various routers on a computer network. Upon receipt of the CMRDR, the command can be executed by any of the routers on the computer network receiving the CMRDR 208 to send a response 210 to the initial router or to discard the CMRDR 208. The commands can be executed to send a response 210 to the initial router if the router receiving the CMRDR 208 has a network connection to the initial router or if the CMRDR 208 is received by an interface that corresponds to the interface initiating the CMRDR 208.The commands can be executed to discard the CMRDR 208 if the CMRDR is received from an interface on a router that fails an RPF check, if the CMRDR is received from an interface that does not correspond to the interface initiating the CMRDR 208, or if the CMRDR is received from an interface that is not executing an MRP. The commands can be executed to forward the CMRDR 208 from a router that has received the CMRDR 208 and sent a response 210. The CMRDR can be forwarded to routers on the computer network that have a network connection to an interface executing an MRP.

[0029] The commands can be executed to aggregate the data from responses 210 to determine a multicast router topology. The multicast router topology can include data about the routers on a computer network that are running an MRP and have network connections to each other. The multicast router topology can include the addresses and subnets of each interface that is running an MRP and has network connections. The multicast router topology can be transferred to another computing device on the computer network and can be used to determine how to send multicast packets on the computer network.

[0030] Fig.3 is a flowchart of an example method for determining a multicast router topology. In step 360, a CMRDR may be sent from an initial router having multiple interfaces executing an MRP. A CMRDR may be sent as a single multicast packet from the interfaces on the initial router executing an MRP. A CMRDR may include data indicating the router and interface that initiated the CMRDR or is sending the CMRDR, a node count, or a time limit to be associated with the CMRDR. The node count associated with the CMRDR may indicate the number of forwarding opportunities for the CMRDR on the computer network. For example, a CMRDR may be forwarded by a router that has responded to the initial router.Each CMRDR is forwarded; the node count can be reduced, and the CMRDR can be forwarded by routers that have sent a response to the initial router until the node count is zero. The time limit associated with the CMRDR can limit the time the initial router waits for responses from routers in a computer network before aggregating the multicast router topology. For example, CMRDRs can be sent repeatedly with increasing node count and / or time limit until the same multicast router topology is generated repeatedly, indicating that the generated multicast router topology is complete.

[0031] In step 362, multiple responses may be received from multiple routers that have a network connection to the initial router, that received the CMRDR, and that have multiple interfaces executing an MRP, wherein the multiple responses include the address and subnet of each of the multiple interfaces of the multiple routers that have a network connection to the initial router, that received the CMRDR, and that have multiple interfaces executing an MRP. The responses may be sent to the initial router as a unicast packet. A response may be sent from a router receiving a CMRDR, provided the router has a direct network connection to the initial router and has not yet sent a response to the initial router, or the CMRDR was received on the interface corresponding to the interface initiating the CMRDR.

[0032] It should be understood that the foregoing description is for illustrative purposes only and should not be construed as limiting the invention. Although specific examples have been described and illustrated herein, other component arrangements and device logic may be substituted for the illustrated examples. Accordingly, the present invention is not limited to the use of more than one signal stream.

[0033] The present invention is also not limited to the use of more than one antenna for a particular device.

Claims

[1] Network device for determining the topology of a multicast router, comprising: A processing resource (240); and a memory resource (242) coupled to the processing resource, wherein the memory resource (242) stores instructions that can be executed by the processing resource (240) to: to send a Connected Multicast Router Discovery Request, CMRDR, (108-1) from an initial router (104-1) with multiple interfaces running a Multicast Routing Protocol, MRP; to receive an initial number of responses (110-1, 110-2) from an initial number of routers (104-2, 104-3), wherein the initial number of routers (104-2, 104-3) have a network connection to the initial router (104-1) that have received the CMRDR (108-1) and have multiple interfaces executing an MRP, and wherein the initial number of responses (110-1, 110-2) contain the address and subnet of each of the multiple interfaces of the initial number of routers (110-1, 110-2) that have a network connection to the initial router (104-1) that have received the CMRDR (108-1) and that have multiple interfaces executing an MRP; to receive a second set of responses (110-3) from a second set of routers (104-4), wherein the second set of routers (104-4) have a network connection with the first set of routers (104-2, 104-3), have received a forwarded CMRDR (108-4, 108-7) from the first set of routers (104-2, 104-3), and have several interfaces executing an MRP; to create a multicast router topology of the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) by identifying, at the initial router (104-1), the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) interconnected via a number of network connections, which execute the MRP on the set of interfaces on the interconnected initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4); and Specifying a node count and time limit in the CMRDR (108-1), where the time limit is a time in which the initial router (104-1) waits for the first number of responses (110-1, 110-2) and the second number of responses (110-3) before aggregating the multicast router topology, with CMRDRs being sent with increasing node count and / or time limit until the same multicast router topology is repeatedly generated. [2] Device according to claim 1, wherein the multicast router topology includes an address and a subnet of each of the multiple interfaces to the initial router (104-1), the first number of routers (104-2, 104-3), and the second number of routers (104-4) that are connected and execute an MRP. [3] Device according to claim 1, wherein the multicast router topology is determined by initiating the CMRDR (108-1) from an interface on the initial router (104-1). [4] Device according to claim 3, wherein a first response (110-1) of the first number of responses (110-1, 110-2) to the initial router (104-1) is sent by a router of the first number of routers (104-2, 104-3) which receives the CMRDR (108-1) on an interface corresponding to the interface on the initial router (104-1) which initiated the CMRDR (108-1). [5] Device according to claim 4, wherein the first response (110-1) is a unicast packet containing the address and subnet of the router that the CMRDR received on an interface corresponding to the interface on the initial router (104-1) that initiated the CMRDR (108-1). [6] Device according to claim 3, wherein the CMRDR (108-1) is a single multicast packet. [7] Method for determining the topology of a multicast router, comprising: Sending (360) a CMRDR (108-1) from an initial router (104-1) with multiple interfaces running an MRP; Receiving (362) a first number of replies (110-1, 110-2) from a first number of routers (104-2, 104-3) that have a network connection with the initial router (104-1) that received the CMRDR (108-1) and have multiple interfaces executing an MRP, wherein the first number of replies (110-1, 110-2) contain the address and subnet of each of the multiple interfaces of the first number of routers (104-1, 104-2) that have a network connection with the initial router (104-1) that received the CMRDR (108-1) and have multiple interfaces executing an MRP; Forwarding the CMRDR (108-4, 108-7) from the first set of routers (104-1, 104-3) to a second set of routers (104-4); and Receiving a second set of responses (110-3) from the second set of routers (104-4) that have a network connection with the first set of routers (104-2, 104-3) that received the forwarded CMRDR (108-4, 108-7) from the first set of routers (104-2, 104-3) and have multiple interfaces executing an MRP; Creating a multicast router topology of the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) by determining, at the initial router (104-1), the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) connected to each other via a number of network connections, that execute the MRP on the set of interfaces on the interconnected initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4); and Specifying a node count and time limit in the CMRDR (108-1), where the time limit is a time in which the initial router (104-1) waits for the first number of responses (110-1, 110-2) and the second number of responses (110-3) before aggregating the multicast router topology, with CMRDRs being sent with increasing node count and / or time limit until the same multicast router topology is repeatedly generated. [8] Method according to claim 7, wherein the reception of the first number of responses (110-1, 110-2) is the reception of unicast responses from the first number of routers (104-2, 104-3) that have received the CMRDR (108-1) on an interface corresponding to the interface on the initial router (104-1) that initiated the CMRDR (108-1). [9] Method according to claim 7, wherein the method comprises discarding the CMRDR (108-1) when the CMRDR (108-1) is received at an interface where multicast routing is not enabled. [10] Method according to claim 7, wherein the method comprises discarding the CMRDR (108-1) when the CMRDR (108-1) is sent to an interface from a router of the first number of routers (104-2, 104-3) that corresponds to an interface other than an interface on the initial router (104-1) initiating the CMRDR (108-1). [11] Non-volatile, computer-readable medium (244) that stores a set of instructions executable by a processor, the instruction set being executed by the processor to: to send a Connected Multicast Router Discovery Request, CMRDR, (108-1) from an initial router (104-1) with multiple interfaces running a Multicast Routing Protocol, MRP; to receive an initial number of responses (110-1, 110-2) from an initial number of routers (104-2, 104-3), wherein the initial number of routers (104-2, 104-3) have a network connection to the initial router (104-1) that received the CMRDR (108-1) and have multiple interfaces executing an MRP, and wherein the initial number of responses (110-1, 110-3) contain the address and subnet of each of the multiple interfaces of the initial number of routers (104-2, 104-3) that have a network connection to the initial router (104-1) that received the CMRDR and that have multiple interfaces executing an MRP; to receive a second set of responses (110-3) from a second set of routers (104-4), wherein the second set of routers (104-4) have a network connection with the first set of routers (104-2, 104-3), have received a forwarded CMRDR from the first set of routers (104-2, 104-3), and have several interfaces executing an MRP; and to create a multicast routing topology of the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) by determining at the initial router (104-1) the initial router (104-1), the first set of routers (104-2, 104-3), and the second set of routers (104-4) connected to each other via a number of network connections, which execute the MRP on the set of interfaces on the interconnected initial router (104-4), the first set of routers (104-2, 104-3), and the second set of routers (104-4); and Specifying a node count and time limit in the CMRDR (108-1), where the time limit is a time in which the initial router (104-1) waits for the first number of responses (110-1, 110-2) and the second number of responses (110-3) before aggregating the multicast router topology, with CMRDRs being sent with increasing node count and / or time limit until the same multicast router topology is repeatedly generated. [12] Medium according to claim 11, wherein the multicast router topology is created based on data in the first number of responses (110-1, 110-2) and the second number of responses (110-3).

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