METHOD FOR THE PROVISION OF GATEWAY ANYCAST VIRTUAL MAC REACHABILITY IN EXTENDED SUBNETS

• US 20110116509A1
• Filed: 11/16/2009
• Published: 05/19/2011
• Est. Priority Date: 11/16/2009
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Sane, Sanjay, MORENO, VICTOR M., Starmer, Robert
• Granted Patent: US 8,848,508 B2
• Time in Patent Office: Days
• US Class Current: 370/401
• CPC Class Codes: H04L 12/4625 Single bridge functionality, e.g. connection of two networks over a single bridge
• CPC Class Codes: H04L 45/28 using route fault recovery
• CPC Class Codes: H04L 45/66 Layer 2 routing, e.g. in Ethernet based MAN's
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches

Abstract

A method and apparatus is disclosed for providing gateway anycast virtual MAC reachability in extended subnets. When an extended L2 subnet spans more than one geographical location, it is desirable that the gateway MAC addresses learned in each location be the same across all IP hosts. Accordingly, the gateway MAC address may be preserved (i.e., programmed) in more than one port on a bridge, such as both a local port and a LAN extension port. The bridge may forward traffic having the anycast MAC address to the closest instance of the MAC address, rather than replicating the traffic to the multiple ports on which the anycast MAC address is programmed. If the gateway reachable on the local port goes down, the frame may be forwarded to the local gateway in the second layer 2 subnet over the LAN extension port.

Claims

1. A computer implemented method for providing anycast virtual media access control (MAC) reachability in extended subnets, comprising:

identifying, in an extended subnet, a gateway MAC address that is reachable over both a LAN extension port and a local port, wherein the extended subnet includes a first layer 2 subnet and a second layer 2 subnet connected through a respective bridge on the first layer 2 subnet and the second layer 2 subnet, and wherein each layer 2 subnet has at least one local gateway connecting the respective layer 2 subnet to an IP network; and

preserving the identified gateway MAC address by programming the identified gateway MAC address on both the local port and the LAN extension port.

2. The method of claim 1, further comprising:

receiving, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

forwarding the network frame only towards the local gateway of the first layer 2 subnet over the local port of the first layer 2 subnet on which the destination MAC address is programmed.

3. The method of claim 1, further comprising:

receiving, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

in response to determining that the local gateway of the first layer 2 subnet is unreachable, forwarding the network frame to the local gateway in the second layer 2 subnet over the LAN extension port.

4. The method of claim 1, wherein the LAN extension port is one of a physical port and a logical port.

5. The method of claim 1, further comprising:

synchronizing members of a First Hop Resiliency Protocol (FHRP) group to inform all the members of the identified MAC address.

6. The method of claim 1, wherein the first layer 2 subnet and the second layer 2 subnet are disjoint.

7. The method of claim 1, wherein the respective bridge in the first layer 2 subnet and the second layer 2 subnet each includes a set of local ports and the LAN extension port connecting one of the first layer 2 subnet and the second layer 2 subnet to the other layer 2 subnet.

8. The method of claim 1, further comprising:

determining that the IP network is unreachable over the local gateway in the first layer 2 subnet; and

removing the MAC address entry programmed for the local gateway in the first layer 2 subnet.

9. A switch, comprising:

a processor; and

a memory containing a program configured to forward layer 2 network traffic, which, when executed on the processor performs an operation, comprising;

identifying, in an extended subnet, a gateway MAC address that is reachable over both a LAN extension port on the switching device and a local port on the switching device, wherein the switching device connects a first layer 2 subnet to a second layer 2 subnet, and wherein each layer 2 subnet has at least one local gateway connecting the respective layer 2 subnet to an IP network, and

preserving the identified gateway MAC address by programming the identified gateway MAC address on both the local port and the LAN extension port.

10. The switching device of claim 9, wherein the operation further comprises:

receiving, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

forwarding the network frame only towards the local gateway of the first layer 2 subnet over the local port of the first layer 2 subnet on which the destination MAC address is programmed.

11. The switching device of claim 9, wherein the operation further comprises:

receiving, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

in response to determining that the local gateway of the first layer 2 subnet is unreachable, forwarding the network frame to the local gateway in the second layer 2 subnet over the LAN extension port.

12. The switching device of claim 9, wherein the LAN extension port is one of a physical port and a logical port.

13. The switching device of claim 9, wherein the operation further comprises:

synchronizing members of a First Hop Resiliency Protocol (FHRP) group to inform all the members of the identified MAC address.

14. The switching device of claim 9, wherein the first layer 2 subnet and the second layer 2 subnet are disjoint.

15. The switching device of claim 9, wherein the switching device includes a set of local ports and the LAN extension port connecting the first layer 2 subnet to the second layer 2 subnet.

16. The switching device of claim 9, wherein the operation further comprises:

determining that the IP network is unreachable over the local gateway in the first layer 2 subnet; and

removing the MAC address entry programmed for the local port for the local gateway in the first layer 2 subnet.

17. A computer-readable storage medium, containing a program, which, when executed on a processor is operable to:

identify, in an extended subnet, a gateway MAC address that is reachable over both a LAN extension port and a local port, wherein the extended subnet includes a first layer 2 subnet and a second layer 2 subnet connected through a respective bridge on the first layer 2 subnet and the second layer 2 subnet, and wherein each layer 2 subnet has at least one local gateway connecting the respective layer 2 subnet to an IP network; and

preserve the identified gateway MAC address by programming the identified gateway MAC address on both the local port and the LAN extension port.

18. The computer-readable storage medium of claim 17, further operable to:

receive, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

forward the network frame only towards the local gateway of the first layer 2 subnet over the local port of the first layer 2 subnet on which the destination MAC address is programmed.

19. The computer-readable storage medium of claim 17, further operable to:

receive, from a host in the first layer 2 subnet, a network frame having a destination address of the identified gateway MAC address; and

in response to determining that the local gateway of the first layer 2 subnet is unreachable, forward the network frame to the local gateway in the second layer 2 subnet over the LAN extension port.

20. The computer-readable storage medium of claim 17, further operable to:

determine that the IP network is unreachable over the local gateway in the first layer 2 subnet; and

remove the MAC address entry programmed on a local port of the local gateway in the first layer 2 subnet.