Point-to-multipoint layer-2 network extension over layer-3 network

1. A method comprising:

receiving, by an ingress router of a plurality of routers via a first Open Systems Interconnection (OSI) Model Layer-2 (L2) network, a multipoint L2 frame specifying receiver devices, wherein the plurality of routers form an OSI Model Layer-3 (L3) network;

determining, by the ingress router and based at least in part on the receiver devices specified by the multipoint L2 frame, one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices via one or more second L2 networks;

determining, by the ingress router and based on the determined one or more egress routers, one or more paths from the ingress router to the determined one or more egress routers;

generating, by the ingress router and for each egress router of the determined one or more egress routers, a respective unicast L3 packet comprising:

an L3 header specifying a source address that is an address of the ingress router and a destination address that is an address of an intermediate router of the plurality of routers, the intermediate router being a next router along a path of the one or more paths toward the respective egress router of the determined one or more egress routers; and

a session identifier for the unicast L3 packet, the session identifier identifying a corresponding session between the ingress router and the respective egress router of the determined one or more egress routers; and

forwarding, by the ingress router, the respective unicast L3 packet for each egress router of the determined one or more egress routers.

2. The method of claim 1 ,

wherein the multipoint L2 frame comprises a Media Access Control (MAC) address for an unknown receiver device of the receiver devices,

wherein determining the one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices comprises performing MAC learning to learn the MAC address for the unknown receiver device of the receiver devices, and

wherein the method further comprises storing, by the ingress router, the MAC address for the unknown receiver device.

3. The method of claim 1 , wherein each respective unicast L3 packet further comprises:

a first portion of metadata comprising a source Media Access Control (MAC) address of a source device originating the multipoint L2 frame and a multipoint destination MAC address of the receiver devices;

a second portion of metadata comprising the session identifier for the respective unicast L3 packet; and

an L3 payload comprising an L2 payload of the multipoint L2 frame.

4. The method of claim 1 ,

wherein the session identifier for the unicast L3 packet comprises a placeholder session identifier for the multipoint L2 frame, wherein the placeholder session identifier comprises a 5-tuple specifying placeholder L3 address information, and

wherein each respective unicast L3 packet further comprises an L3 payload comprising an L2 payload of the multipoint L2 frame.

5. The method of claim 1 ,

wherein determining the one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices comprises determining that a first egress router of the plurality of routers is connected to two or more first receiver devices of the receiver devices and a second egress router of the plurality of routers is connected to two or more second receiver devices of the receiver devices,

wherein generating the respective unicast L3 packet comprises generating, for the first egress router, a respective first unicast L3 packet and generating, for the second egress router, a respective second unicast L3 packet, and

wherein forwarding the respective unicast L3 packet comprises forwarding the first unicast L3 packet toward the first egress router and forwarding the second unicast L3 packet toward the second egress router.

6. The method of claim 1 ,

wherein determining the one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices comprises determining that each of a first egress router and a second egress router of the plurality of routers are connected to at least one of the receiver devices;

wherein generating the respective unicast L3 packet comprises:

generating, for the first egress router, a first unicast L3 packet comprising:

a first L3 header; and

a first session identifier identifying a first session between the ingress router and the first egress router; and

generating, for the second egress router, a second unicast L3 packet comprising:

a second L3 header; and

a second session identifier identifying a second session between the ingress router and the second egress router; and

wherein the forwarding comprises:

forwarding the first unicast L3 packet toward the first egress router; and

forwarding the second unicast L3 packet toward the second egress router.

7. The method of claim 1 ,

wherein the multipoint L2 frame comprises a multipoint Ethernet frame, and

wherein the respective unicast L3 packet for each egress router of the determined one or more egress routers comprises one of a unicast User Datagram Protocol (UDP) packet or a unicast Transmission Control Protocol (TCP) packet.

8. The method of claim 1 , wherein the multipoint L2 frame comprises a multicast Ethernet frame.

9. The method of claim 1 , wherein the multipoint L2 frame comprises a broadcast Ethernet frame.

10. The method of claim 1 , wherein the multipoint L2 frame comprises an unknown unicast Ethernet frame.

11. An ingress router configured to:

receive, via a first Open Systems Interconnection (OSI) Model Layer-2 (L2) network, a multipoint L2 frame specifying receiver devices, wherein a plurality of routers include the ingress router, and wherein the plurality of routers form an OSI Model Layer-3 (L3) network;

determine, based at least in part on the receiver devices specified by the multipoint L2 frame, one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices via one or more second L2 networks;

determine, based on the determined one or more egress routers, one or more paths from the ingress router to the determined one or more egress routers;

generate, for each egress router of the determined one or more egress routers, a respective unicast L3 packet comprising:

an L3 header specifying a source address that is an address of the ingress router and a destination address that is an address of an intermediate router of the plurality of routers, the intermediate router being a next router along a path of the one or more paths toward the respective egress router of the determined one or more egress routers; and

a session identifier for the unicast L3 packet, the session identifier identifying a corresponding session between the ingress router and the respective egress router of the determined one or more egress routers; and

forward the respective unicast L3 packet for each egress router of the determined one or more egress routers.

12. The ingress router of claim 11 ,

wherein the multipoint L2 frame comprises a Media Access Control (MAC) address for an unknown receiver device of the receiver devices,

wherein to determine the one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices, the ingress router is configured to perform MAC learning to learn the MAC address for the unknown receiver device of the receiver devices, and

wherein the ingress router is further configured to store the MAC address for the unknown receiver device.

13. The ingress router of claim 11 , wherein each respective unicast L3 packet further comprises:

a first portion of metadata comprising a source Media Access Control (MAC) address of a source device originating the multipoint L2 frame and a multipoint destination MAC address of the receiver devices;

a second portion of metadata comprising the session identifier for the respective unicast L3 packet; and

an L3 payload comprising an L2 payload of the multipoint L2 frame.

14. The ingress router of claim 11 ,

wherein the session identifier for the unicast L3 packet comprises a placeholder session identifier for the multipoint L2 frame, wherein the placeholder session identifier comprises a 5-tuple specifying placeholder L3 address information, and

wherein each respective unicast L3 packet further comprises an L3 payload comprising an L2 payload of the multipoint L2 frame.

15. The ingress router of claim 11 ,

wherein to determine the one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices, the ingress router is configured to determine that a first egress router of the plurality of routers is connected to two or more first receiver devices of the receiver devices and a second egress router of the plurality of routers is connected to two or more second receiver devices of the receiver devices,

wherein to generate the respective unicast L3 packet, the ingress router is configured to generate, for the first egress router, a respective first unicast L3 packet and generate, for the second egress router, a respective second unicast L3 packet, and

wherein to forward the respective unicast L3 packet, the ingress router is configured to forward the first unicast L3 packet toward the first egress router and forward the second unicast L3 packet toward the second egress router.

16. The ingress router of claim 11 ,

wherein the multipoint L2 frame comprises a multipoint Ethernet frame, and

wherein the respective unicast L3 packet for each egress router of the determined one or more egress routers comprises one of a unicast User Datagram Protocol (UDP) packet or a unicast Transmission Control Protocol (TCP) packet.

17. The ingress router of claim 11 , wherein the multipoint L2 frame comprises a multicast Ethernet frame.

18. The ingress router of claim 11 , wherein the multipoint L2 frame comprises a broadcast Ethernet frame.

19. The ingress router of claim 11 , wherein the multipoint L2 frame comprises an unknown unicast Ethernet frame.

20. A non-transitory, computer-readable medium comprising instructions that, when executed, are configured to cause processing circuitry of an ingress router to:

receive, via a first Open Systems Interconnection (OSI) Model Layer-2 (L2) network, a multipoint L2 frame specifying receiver devices, wherein a plurality of routers include the ingress router, and wherein the plurality of routers form an OSI Model Layer-3 (L3) network;

determine, based at least in part on the receiver devices specified by the multipoint L2 frame, one or more egress routers of the plurality of routers that are connected to at least one of the receiver devices via one or more second L2 networks;

determine, based on the determined one or more egress routers, one or more paths from the ingress router to the determined one or more egress routers;

generate, for each egress router of the determined one or more egress routers, a respective unicast L3 packet comprising:

an L3 header specifying a source address that is an address of the ingress router and a destination address that is an address of an intermediate router of the plurality of routers, the intermediate router being a next router along a path of the one or more paths toward the respective egress router of the determined one or more egress routers; and

a session identifier for the unicast L3 packet, the session identifier identifying a corresponding session between the ingress router and the respective egress router of the determined one or more egress routers; and

forward the respective unicast L3 packet for each egress router of the determined one or more egress routers.