Deploying secure neighbor discovery in EVPN

1. A method comprising:

receiving, by a first network device that implements Ethernet Virtual Private Network (EVPN), a neighbor discovery response message including a nonce originated by a second network device, wherein the first network device and second network device are coupled to a host device by a multi-homed intermediate network device by an Ethernet segment;

determining, by the first network device, whether the nonce of the neighbor discovery response message matches a nonce stored in the first network device; and

in response to determining that the nonce of the neighbor discovery response message does not match a nonce stored in the first network device, determining, by the first network device, whether the neighbor discovery response message was received on an Ethernet segment identifier (ESI) interface of the Ethernet segment; and

in response to determining that the neighbor discovery response message was received on the ESI interface of the Ethernet segment, dropping the nonce from the neighbor discovery response message to learn a link layer address from the neighbor discovery response message.

2. The method of claim 1 , wherein the first network device and the second network device operate as both a layer 2 gateway and a layer 3 gateway.

3. The method of claim 1 , wherein the neighbor discovery response message comprises a neighbor advertisement message configured using a Neighbor Discovery Protocol (NDP).

4. The method of claim 3 , wherein the Neighbor Discovery Protocol is extended to include security extensions including SEcure Neighbor Discovery (SEND).

5. The method of claim 1 , wherein the neighbor discovery response message comprises a first neighbor discovery response message including a first nonce originated by the second network device, further comprising:

receiving, by the first network device, a second neighbor discovery response message including a second nonce originated by the second network device,

determining, by the first network device, whether the second nonce of the second neighbor discovery response message matches a nonce stored in the first network device;

in response to a determining that the second nonce of the second neighbor discovery message does not match the nonce stored in the first network device, determining that a destination address of the second neighbor discovery response message is a physical IP address of the second network device; and

in response to determining that the destination address of the second neighbor discovery response message is the physical IP address of the second network device, sending, by the first network device, the second neighbor discovery response message to the second network device via an overlay network.

6. A first network device that implements Ethernet Virtual Private Network (EVPN), comprising:

one or more processors coupled to a memory, wherein the one or more processors are configured to:

receive a neighbor discovery response message including a nonce originated by a second network device, wherein the first network device and the second network device are coupled to a host device by a multi-homed intermediate network device by an Ethernet segment;

determine whether the nonce of the neighbor discovery response message matches a nonce stored in the first network device; and

in response to a determination that the nonce of the neighbor discovery message does not match a nonce stored in the first network device, determining that a destination address of the neighbor discovery response message is a physical IP address of the second network device; and

in response to determining that the destination address of the neighbor discovery response message is the physical IP address of the second network device, sending, by the first network device, the neighbor discovery response message to the second network device via an overlay network.

7. The first network device of claim 6 , wherein the neighbor discovery response message comprises a neighbor advertisement message configured using a Neighbor Discovery Protocol (NDP).

8. The first network device of claim 6 , wherein the Neighbor Discovery Protocol is extended to include security extensions including SEcure Neighbor Discovery (SEND).

9. The first network device of claim 6 ,

wherein the first network device and the second network device operate as a layer 2 gateway.

10. A non-transitory computer-readable storage medium comprising instructions for causing one or more programmable processors of a first network device to:

intercept, from a local host device coupled to the first network device, a first neighbor discovery response message including a nonce, wherein the first neighbor discovery response message is generated by the local host device in response to a first neighbor discovery request message, wherein the first neighbor discovery response message is destined for a remote host device;

determine whether the nonce of the neighbor discovery response message matches a nonce stored in the first network device; and

in response to a determination that the nonce of the neighbor discovery response message does not match a nonce stored in the first network device, store the nonce;

drop the first neighbor discovery response message;

send a second neighbor discovery request message to the local host device, wherein the second neighbor discovery request message includes the nonce;

receive, from the local host device, a second neighbor discovery response message including the nonce; and

in response to determining that the nonce is stored in the first network device, store one or more link layer addresses learned from the second neighbor discovery response message.

11. The non-transitory computer-readable storage medium of claim 10 , wherein the instructions further cause one or more programmable processors of the first network device to:

receive a third neighbor discovery request message from a second local host device and destined for the remote host device; and

send, by the first network device and using the one or more link layer addresses stored in the first network device, a third neighbor discovery response message rather than sending the third neighbor discovery request message over an EVPN core.

12. The non-transitory computer-readable storage medium of claim 10 , wherein the first neighbor discovery response message comprises a neighbor advertisement message configured using a Neighbor Discovery Protocol (NDP).

13. The non-transitory computer-readable storage medium of claim 12 , wherein the Neighbor Discovery Protocol is extended to include security extensions including SEcure Neighbor Discovery (SEND).