Method and system for efficient address resolution in extended subnets
One embodiment of the present invention facilitates address resolution protocol (ARP) resolution in an extended subnet. A gateway of a first segment of the extended subnet can determine that a layer-2 address corresponding to a layer-3 destination address of a packet is locally unavailable. The gateway can then determine whether a respective egress interface of an ARP request for the layer-3 destination address is associated with a layer-2 subnet extension from the first segment to a second segment of the extended subnet. The extension can provide a common layer-2 broadcast domain comprising the first and second segments with a same default gateway layer-3 address. If the egress interface is associated with the extension, the gateway can insert a layer-3 address of a first endpoint associated with the extension as a source protocol address in the ARP request. The gateway can send the modified ARP request via the egress interface.
1. A method for facilitating address resolution protocol (ARP) in an extended subnet across two network segments sharing a common gateway Internet Protocol (IP) address, the method comprising:
generating, by a local gateway of a local network segment, an ARP request to be broadcast via a local network interface on the local gateway to the local network segment, wherein the ARP request includes a target protocol address (TPA) and a source protocol address (SPA), and wherein the SPA includes the common gateway IP address;
modifying, by the local gateway, the ARP request by replacing the common gateway IP address with an interface IP address in the SPA to generate a modified ARP request comprising the same TPA and a modified SPA, wherein the interface IP address is different from the common gateway IP address and assigned to an external network interface of the local gateway coupled to a remote gateway of a remote network segment via a tunnel, and wherein the common gateway IP address is allocated to both the local gateway and the remote gateway;
forwarding, via the tunnel, the modified ARP request to the remote gateway for broadcasting the modified ARP request to the remote network segment; and
receiving, by the local gateway, an ARP response corresponding to the modified ARP request based on the interface IP address.
2. The method of claim 1 , wherein the two network segments are at separate sites.
3. The method of claim 2 , wherein the sites are located on customer premises or in a public cloud.
4. The method of claim 1 , wherein the ARP response's TPA includes the interface IP address assigned to the external network interface of the local gateway.
5. The method of claim 1 , wherein the tunnel is a virtual extensible local area network (VXLAN) tunnel; and
wherein the external network interface of the local gateway serves as a VXLAN Tunnel End Point (VTEP) for the tunnel.
6. The method of claim 1 , further comprising storing an IP-to-MAC address mapping in a local data structure based on the ARP response.
7. The method of claim 1 , wherein the ARP response is received via the external network interface based on the interface IP address.
8. A non-transitory computer-readable storage medium storing instructions that when executed by a computer cause the computer to perform a method for facilitating address resolution protocol (ARP) in an extended subnet across two network segments sharing a common gateway Internet Protocol (IP) address, the method comprising:
generating, by a local gateway of a local network segment, an ARP request to be broadcast via a local network interface on the local gateway to the local network segment, wherein the ARP request includes a target protocol address (TPA) and a source protocol address (SPA), and wherein the SPA includes the common gateway IP address;
modifying, by the local gateway, the ARP request by replacing the common gateway IP address with an interface IP address in the SPA to generate a modified ARP request comprising the same TPA and a modified SPA, wherein the interface IP address is different from the common gateway IP address and assigned to an external network interface of the local gateway coupled to a remote gateway of a remote network segment via a tunnel, and wherein the common gateway IP address is allocated to both the local gateway and the remote gateway; and
forwarding, via the tunnel, the modified ARP request to the remote gateway for broadcasting the modified ARP request to the remote network segment; and
receiving, by the local gateway, an ARP response corresponding to the modified ARP request based on the interface IP address.
9. The non-transitory computer-readable storage medium of claim 8 , wherein the two network segments are at separate sites.
10. The non-transitory computer-readable storage medium of claim 9 , wherein the sites are located on customer premises and in a public cloud.
11. The non-transitory computer-readable storage medium of claim 8 , wherein the ARP response's TPA includes the interface IP address assigned to the external network interface of the local gateway.
12. The non-transitory computer-readable storage medium of claim 8 , wherein the tunnel is a virtual extensible local area network (VXLAN) tunnel; and
wherein the external network interface of the local gateway serves as a VXLAN Tunnel End Point (VTEP) for the tunnel.
13. The non-transitory computer-readable storage medium of claim 8 , wherein the method further comprises storing an IP-to-MAC address mapping in a local data structure based on the ARP response.
14. The non-transitory computer-readable storage medium of claim 8 , wherein the ARP response is received via the external network interface based on the interface IP address.
15. A computer system, comprising:
a processor; and
a non-transitory computer-readable storage medium storing instructions that when executed by the processor cause the computer system to perform a method for facilitating address resolution protocol (ARP) in an extended subnet across two network segments sharing a common gateway Internet Protocol (IP) address, the method comprising:
generating, by a local gateway of a local network segment, an ARP request to be broadcast via a local network interface on the local gateway to the local network segment, wherein the ARP request includes a target protocol address (TPA) and a source protocol address (SPA), and wherein the SPA includes the common gateway IP address;
modifying, by the local gateway, the ARP request by replacing the common gateway IP address with an interface IP address in the SPA to generate a modified ARP request comprising the same TPA and a modified SPA, wherein the interface IP address is different from the common gateway IP address and assigned to an external network interface of the local gateway coupled to a remote gateway of a remote network segment via a tunnel, and wherein the common gateway IP address is allocated to both the local gateway and the remote gateway;
forwarding, via the tunnel, the modified ARP request to the remote gateway for broadcasting the modified ARP request to the remote network segment; and
receiving, by the local gateway, an ARP response corresponding to the modified ARP request based on the interface IP address.
16. The computer system of claim 15 , wherein the two network segments are at separate sites, and wherein the sites are located on customer premises or in a public cloud.
17. The computer system of claim 15 , wherein the ARP response's TPA is-includes the interface IP address assigned to the external network interface of the local gateway.
18. The computer system of claim 15 , wherein the tunnel is a virtual extensible local area network (VXLAN) tunnel; and
wherein the external network interface of the local gateway serves as a VXLAN Tunnel End Point (VTEP) for the tunnel.
19. The computer system of claim 15 , wherein the method further comprises storing an IP-to-MAC address mapping in a local data structure based on the ARP response.
20. The computer system of claim 15 , wherein the ARP response is received via the external network interface based on the interface IP address.