Logical router

1. A system comprising:

a plurality of host machines for hosting a plurality of virtual machines, each host machine comprising:

a managed physical switching element (MPSE) comprising a plurality of ports for performing link layer forwarding of packets to and from a set of virtual machines running on the host machine, each port associated with a unique media access control (MAC) address; and

a managed physical routing element (MPRE) for receiving a data packet from a port of the MPSE and performing network layer routing in order to forward the received data packet from a first virtual machine of a first network segment to a second virtual machine of a second network segment, wherein the MPRE comprises a plurality of logical interfaces, each logical interface for receiving data packets from a different segment of the logical network; and

a physical network for interconnecting the plurality of host machines,

wherein each of the logical interfaces on the MPREs of the plurality of host machines is addressable by an identical link layer address, and

wherein, for each MPRE of each host machine, each logical interface for receiving data packets from the first network segment of the logical network has a same network layer address that is different from a network layer address used by each logical interface for receiving data packets from the second network segment of the logical network.

2. The system of claim 1 , wherein a network segment is one of an IP (internet protocol) subnet and an encapsulation overlay network.

3. The system of claim 1 , wherein at least one of the network segments is an encapsulation overlay network.

4. The system of claim 1 , wherein the first and second network segments are different encapsulation overlay networks with different network identifiers.

5. The system of claim 1 , wherein the port from which the MPRE receives the data packet is associated with a virtual MAC (VMAC) address that is common to all MPREs of all host machines in the plurality of host machines.

6. The system of claim 5 , wherein each host machine's MPRE is assigned a unique physical MAC (PMAC) address for addressing the MPRE from other host machines, wherein different host machine's MPREs are assigned different PMACs.

7. The system of claim 6 , wherein each host machine converts the PMAC address to the VMAC address in an incoming data packet from the physical network before the incoming data packet reaches the MPSE.

8. The system of claim 6 , wherein each host machine converts the VMAC address to the PMAC address in an outgoing data packet to the physical network after the outgoing data packet leaves the MPSE.

9. A computing device in a set of computing devices serving as host machines in a logical network, the computing device executing a computer program comprising sets of instructions for:

executing a plurality of virtual machines that are in a plurality of different segments of the logical network; and

operating a managed physical routing element (MPRE) for routing data packets between different segments of the logical network, the MPRE comprising a plurality of logical interfaces, each logical interface for receiving data packets from a different segment of the logical network,

wherein each of the logical interfaces is addressable by an identical link layer address, and

wherein, for each MPRE operating on the set of computing devices, each logical interface for receiving data packets from a first segment of the logical network has a same network layer address different from a network layer address used by each logical interface for receiving data packets from a second segment of the logical network.

10. The computing device of claim 9 , wherein a network segment is one of an IP (internet protocol) subnet and an encapsulation overlay network.

11. The computing device of claim 9 , wherein the computer program further comprises a set of instructions for operating a managed physical switching element (MPSE) for performing link layer forwarding of packets to and from the plurality of virtual machines and the MPRE.

12. The computing device of claim 11 , wherein the identical link layer address is a virtual MAC (VMAC) address that is common to all host machines in the logical network.

13. The computing device of claim 12 , wherein the host machine's MPRE is associated with a unique physical MAC (PMAC) address that is different from other host machine's MPREs in the logical network.

14. The computing device of claim 13 further comprising a set of instructions for converting the PMAC address to the VMAC address in an incoming data packet from a physical network before the incoming data packet reaches the MPRE.

15. The computing device of claim 13 further comprising a set of instructions for converting the VMAC address to the PMAC address in an outgoing data packet to a physical network after the outgoing data packet leaves the MPRE.

16. A system comprising:

a plurality of host machines for hosting a plurality of virtual machines in a logical network, each host machine operating a managed physical routing element (MPRE) for routing data packet between virtual machines that are in different segments of the logical network, wherein each MPRE comprises a plurality of logical interfaces, each logical interface for receiving data packets from a different segment of the logical network, wherein each logical interface of the MPRE is addressed by virtual machines in the logical network by an identical generic link layer address, wherein each MPRE's logical interface for a first network segment shares a network layer address different from a network layer address shared by each MPRE's logical interface for a second network segment; and

a physical network for interconnecting the plurality of host machines.

17. The system of claim 16 , wherein a network segment is one of an IP (internet protocol) subnet and an encapsulation overlay network.

18. The system of claim 16 , wherein each host machine further operates a managed physical switching element(MPSE) for performing link layer forwarding of packets to and from the plurality of virtual machines and the MPRE operating in the host machine.

19. The system of claim 18 , wherein each host machine addresses each MPRE operated by another host machine by a unique link layer address, and wherein each host machine converts the unique link layer address to the generic link layer address in an incoming data packet from the physical network before the incoming data packet reaches the MPSE.

20. The system of claim 18 , wherein each host machine addresses each MPRE operated by another host machine by a unique link layer address, and wherein each host machine converts the generic link layer address to the unique link layer address in an outgoing data packet to the physical network after the outgoing data packet leaves the MPSE.