Scalable overlay multicast routing in multi-tier edge gateways

1. A method comprising:

at a first host computer of a plurality of host computers:

receiving a multicast packet having an overlay multicast group identifier, wherein each of the plurality of host computers executes at least one edge router through which packets pass through to enter or exit an overlay network;

mapping the overlay multicast group identifier to an underlay multicast group identifier;

encapsulating the multicast packet with an encapsulation header that includes the underlay multicast group identifier to create an encapsulated multicast packet; and

forwarding the encapsulated multicast packet to a physical switch that sends copies of the encapsulated multicast packet to ports of a set of edge routers that are implemented at a set of other host computers and that are determined to be interested in the underlay multicast group identifier, the encapsulated multicast packet being replicated to the ports.

2. The method of claim 1 , wherein each host computer is addressable by a unique virtual tunnel endpoint (VTEP), wherein a particular edge router implemented on the first host computer is a multicast querier of a first network segment associated with the multicast packet, and the physical switch is a physical switch of the first network segment.

3. The method of claim 1 , wherein the multicast packet is received from an overlay network and the first host computer hosts an edge router that serves data traffic to and from the overlay network.

4. The method of claim 1 , wherein:

a particular edge router executing on the first host computer serves data traffic to and from an external network,

the multicast packet is received from the external network.

5. The method of claim 4 , wherein the particular edge router is a first-tier edge router that actively serves data traffic to and from the external network and other first-tier edge routers executing on other host computers are standing by and not actively serving data traffic to and from the external network.

6. The method of claim 4 , wherein the particular edge router

(i) receives a multicast packet having an overlay multicast group identifier from the external network;

(ii) maps the overlay multicast group identifier to the underlay multicast group identifier;

(iii) encapsulates the multicast packet with an encapsulation header that includes the underlay multicast group identifier; and

(iv) forwards the encapsulated multicast packet to the physical switch to forward copies of the encapsulated multicast packet at one or more ports to host computers having other edge routers that are determined to be interested in the underlay multicast group identifier.

7. The method of claim 4 , wherein the particular edge router receives a copy of the encapsulated multicast packet from the physical switch and forwards a decapsulated copy of the multicast packet to the external network without the underlay multicast group identifier.

8. The method of claim 1 , wherein an edge router receiving a copy of the encapsulated multicast packet decapsulates the multicast packet to remove the underlay multicast group identifier and forwards the decapsulated multicast packet to an overlay network by multicast based on the overlay multicast group identifier.

9. The method of claim 1 , wherein a network controller sends multicast grouping information associating an overlay multicast group identifier with (i) a corresponding underlay multicast group identifier and (ii) a list of VTEPs that are interested in the multicast group to each edge routers.

10. The method of claim 9 , wherein the network controller receives multicast reports associating VTEPs with overlay multicast group identifiers and generates the multicast grouping information based on the received multicast reports.

11. A first host computer that is part of a plurality of host computers, the first host computer comprising:

one or more processors; and

a computer-readable storage medium storing a program for execution by at least one processing unit, the program comprising sets of instructions for:

receiving a multicast packet having an overlay multicast group identifier, wherein each of the plurality of host computers executes at least one edge router through which packets pass through to enter or exit an overlay network;

mapping the overlay multicast group identifier to an underlay multicast group identifier;

encapsulating the multicast packet with an encapsulation header that includes the underlay multicast group identifier to create an encapsulated multicast packet; and

forwarding the encapsulated multicast packet to a physical switch that sends copies of the encapsulated multicast packet to ports a set of edge routers that are implemented at a set of other host computers and that are determined to be interested in the underlay multicast group identifier, the encapsulated multicast packet being replicated to the ports.

12. The first host computer of claim 11 , wherein each host computer is addressable by a unique virtual tunnel endpoint (VTEP), wherein a particular edge router implemented on the first host computer is a multicast querier of a first network segment associated with the multicast packet, and the physical switch is a physical switch of the first network segment.

13. The first host computer of claim 11 , wherein the multicast packet is received from an overlay network and the first host computer hosts an edge router that serves data traffic to and from the overlay network.

14. The first host computer of claim 11 , wherein:

a particular edge router executing on the first host computer serves data traffic to and from an external network,

the multicast packet is received from the external network.

15. The first host computer of claim 14 , wherein the particular edge router is a first-tier edge router that actively serves data traffic to and from the external network and other first-tier edge routers executing on other host computers are standing by and not actively serving data traffic to and from the external network.

16. The first host computer of claim 14 , wherein the particular edge router

(i) receives a multicast packet having an overlay multicast group identifier from the external network;

(ii) maps the overlay multicast group identifier to the underlay multicast group identifier;

(iii) encapsulates the multicast packet with an encapsulation header that includes the underlay multicast group identifier; and

(iv) forwards the encapsulated multicast packet to the physical switch to forward copies of the encapsulated multicast packet at one or more ports to host computers having other edge routers that are determined to be interested in the underlay multicast group identifier.

17. The first host computer of claim 14 , wherein the particular edge router receives a copy of the encapsulated multicast packet from the physical switch and forwards a decapsulated copy of the multicast packet to the external network without the underlay multicast group identifier.

18. The first host computer of claim 11 , wherein an edge router receiving a copy of the encapsulated multicast packet decapsulates the multicast packet to remove the underlay multicast group identifier and forwards the decapsulated multicast packet to an overlay network by multicast based on the overlay multicast group identifier.

19. The first host computer of claim 11 , wherein a network controller sends multicast grouping information associating an overlay multicast group identifier with (i) a corresponding underlay multicast group identifier and (ii) a list of VTEPs that are interested in the multicast group to each edge routers.

20. The first host computer of claim 19 , wherein the network controller receives multicast reports associating VTEPs with overlay multicast group identifiers and generates the multicast grouping information based on the received multicast reports.