Method and system for subnetting in a switched IP network

• US 6,262,988 B1
• Filed: 05/12/2000
• Issued: 07/17/2001
• Est. Priority Date: 03/11/1998
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Vig, Deepak
• Primary Examiner(s): Olms, Douglas
• Assistant Examiner(s): VANDERPUYE, KENNETH N
• Application Number:
  US09/569,682
• Time in Patent Office: 431 Days
• Field of Search: 370/401, 370/469, 370/400, 370/402, 370/390, 370/432
• US Class Current: 370/401
• CPC Class Codes: H04L 2101/604 Address structures or formats
• CPC Class Codes: H04L 49/201 Multicast operation; Broadcast operation
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches
• CPC Class Codes: H04L 49/602 Multilayer or multiprotocol switching, e.g. IP switching
• CPC Class Codes: H04L 61/00 Network arrangements, protocols or services for addressing or naming

Abstract

A large flat IP network is created in a switched layer-2 network by adjusting the subnet masks of hosts such that these hosts can communicate directly with other hosts without the use of an intermediate router. The layer-2 switches are configured with user-selected IP subnets and monitor and analyze multicast packets to learn the mapping between IP subnets and switch ports. The layer-2 switches selectively forward the mulitcast packets based on the learned mappings between IP subnets and ports. After the destination host responds to the forwarded multicast, a direct connection is established between the source and destination hosts using the media access control addresses of both hosts.

Claims

1. A switch for providing a data link layer switching function between distinct subnetworks of a data communications system having a plurality of interconnected subnetworks for enabling end stations on the distinct subnetworks to communicate directly without the use of router devices, the switch comprising:

a subnet mask and a plurality of subnets specified by a user via a user interface, the subnet mask being larger in value than a subnet mask of a source end station on a first distinct subnetwork, said source end station having a network layer address, and a data link layer address, the subnet mask of the switch also being larger in value than a subnet mask of a destination end station on a second distinct subnetwork, said destination end station having a network layer address, and a data link address;

packet analysis and forwarding programming code, operating on a processing unit in said switch, for analyzing a multicast packet, having both network layer information and a medium access control (MAC) address, received from said source end station, and selectively forwarding said multicast packet to all ports associated with a destination subnet; and

a subnet to port mapping table for storing a mapping of said plurality of subnets to a plurality of ports associated with each said subnet;

the packet analysis and programming code also analyzing the MAC address of the multicast packet to make a determination of whether the packet is an all stations multicast message, and if the code determines that the multicast packet is an all stations multicast message, the code then analyzes the network layer information to determine whether the multicast packet is an address resolution protocol packet, and if the code determines that the multicast packet is an address resolution protocol packet, the code then makes a forwarding decision for the multicast packet based upon subnet information derived from the network layer information.

2. A switch according to claim 1, further comprising a data link layer address to port mapping table for storing a mapping of data link layer addresses to ports based on address information in a reply packet received from said destination end station in response to said forwarded multicast packet.

3. A switch according to claim 2, wherein the switch conveys packets from said source end station to said destination end station using said data link layer address to port mapping table.

4. A switch according to claim 1, wherein said subnet to port mapping table is built by said packet analysis and forwarding programming code by logically combining said switch subnet mask with the source network layer address in each multicast packet received from a source end station attached to one of said switch ports to determine the subnet corresponding to said source end station.

5. A switch according to claim 1, wherein said plurality of subnetworks communicate using the Internet Protocol (IP).

6. A switch according to claim 1, wherein said data link layer addresses of said source end station and said destination end station are media access control (MAC) addresses.

7. A switch according to claim 1, wherein said distinct subnetworks are each Ethernet local area networks.

8. A switch according to claim 1, wherein said distinct subnetworks are each token ring networks.

9. A switch according to claim 1, wherein each multicast packet received is automatically forwarded to said switch processing unit for packet analysis and forwarding.

10. A method implemented by a switch for enabling source and destination end stations to communicate directly, without the use of router devices, in a data communication system having a plurality of interconnected subnetworks, the switch providing a data link layer switching function between a source end station on a first subnetwork and a destination end station on a second subnetwork, the method comprising:

specifying in the switch a plurality of subnets for said data communication system and a subnet mask, the subnet mask being larger in value than a subnet mask specified at the source end station, the subnet mask in the switch also being larger in value than a subnet mask specified in the destination end station;

determining each port of the switch associated with each of said plurality of subnets in said data communication system;

analyzing at the switch a multicast packet, having both network layer information and a Medium Access Control (MAC) address, received from said source end station to determine the ports associated with a destination subnet; and

selectively forwarding at the switch said multicast packet to said ports associated with said destination subnet;

analysis of the multicast packet including determining whether the MAC address indicates that the multicast packet is an all stations multicast message, and if the multicast packet is an all stations multicast message, the method also includes analyzing the network layer information to determine whether the multicast packet is an address resolution protocol packet, and if the multicast packet is an address resolution protocol packet, a forwarding decision is made for the multicast packet based upon subnet information derived from the network layer information.

11. A method according to claim 10, further comprising building a subnet to port mapping table in the switch which maps said plurality of subnets to a plurality of ports associated with each said subnet.

12. A method according to claim 10, wherein said determining each port step includes logically combining said switch subnet mask with a source network layer address in each multicast packet received from said source end station attached to one of said switch ports to determine the subnet corresponding to said source end station.

13. A method according to claim 10, further comprising building a data link layer address to port mapping table in said switch which maps data link layer addresses to ports based on address information in a reply packet received from said destination end station in response to said forwarded multicast packet.

14. A method according to claim 10, wherein said plurality of subnetworks are local area networks with said source end station communicating with said destination end station using the Internet Protocol (IP).

15. A method according to claim 10, wherein said analyzing and selectively forwarding steps are performed by packet analysis and forwarding code operating on a processing unit in said switch.

16. A switch for providing a data link layer switching function in a communication system having a plurality of interconnected subnetworks, the system including a source end station on a first subnetwork and a destination end station on a second subnetwork, the switch comprising:

means for specifying a plurality of subnets for said data communication system and a subnet mask in said switch, the subnet mask being larger in value than a subnet mask specified in the source end station;

means for determining each port associated with each of said plurality of subnets in said data communication system;

means for analyzing a multicast packet, having both network layer information and a medium access control (MAC) address, received from said source end station to determine the ports associated with a destination subnet; and

means for selectively forwarding said multicast packet to said ports associated with said destination subnet;

the means for analyzing including means for determining if the multicast packet is an all stations multicast message, and means for analyzing the network layer information to determine whether the multicast packet is an address resolution protocol packet, and means for making a forwarding decision, if the multicast packet is an address resolution protocol packet, for the multicast packet based upon subnet information derived from the network layer information.

17. A switch according to claim 16, further comprising means for building a subnet to port mapping table in said switch which maps said plurality of subnets to a plurality of ports associated with each said subnet.

18. A switch according to claim 16, wherein said means for determining each port steps includes means for logically combining said switch subnet mask with a source network layer address in each multicast packet received from said source end station attached to one of said switch ports to determine the subnet corresponding to said source end station.

19. A switch according to claim 16, further comprising means for building a data link layer address to port mapping table in said switch which maps data link layer addresses to ports based on address information in a reply packet received from said destination end station in response to said forwarded multicast packet.

20. A switch according to claim 16, further comprising means for automatically forwarding each multicast packet from said source end station to a processing unit in said switch for packet analysis and forwarding.