Fault tolerant lane system

• US 5,835,481 A
• Filed: 08/28/1996
• Issued: 11/10/1998
• Est. Priority Date: 08/28/1996
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Finn, Norman W., Akyol, Cihangir M., Benson, Bradley A., Jay, Steven H.
• Primary Examiner(s): TON, DANG T
• Application Number:
  US08/703,938
• Time in Patent Office: 804 Days
• Field of Search: 370/389, 370/404, 370/257, 370/396, 370/469, 370/408, 370/395, 370/216, 370/217, 370/218, 370/225, 370/401, 370/403, 370/407, 370/406, 370/827, 370/825.01, 395/180, 395/181, 379/221
• US Class Current: 370/395.53
• CPC Class Codes: H04L 12/4608 LAN interconnection over ATM networks
• CPC Class Codes: H04L 2012/5617 Virtual LANs; Emulation of LANs
• CPC Class Codes: H04L 2012/5627 Fault tolerance and recovery
• CPC Class Codes: H04Q 11/0478 Provisions for broadband connections

Abstract

A system and method are disclosed for providing a redundancy scheme in an ATM network providing a LAN emulation. The ATM network includes a set of LAN Emulation Connection Servers (LECS'"'"'s) which connect with each other to determine which servers are operational and to automatically select an operational master LECS. The master LECS maintains a back end verification circuit with a set of operational LAN Emulation Servers (LES'"'"'s), determines which operational LES will be the master LES, and directs LAN Emulation Clients (LEC'"'"'s) to that LES. LEC'"'"'s which lose their LES connection are directed to the proper LECS by a table stored in the ATM switch.

Claims

1. In an Lan Emulation Configuration Server configured for use in an ATM network implementing a LAN emulation, a method of selecting a master Lan Emulation Configuration Server from among a plurality of Lan Emulation Configuration Servers in the ATM network, the method comprising:

determining a relative hierarchical position among said plurality of Lan Emulation Configuration Servers said relative hierarchical position specifying that a given Lan Emulation Configuration Server is a higher Lan Emulation Configuration Server with respect to other Lan Emulation Configuration Servers lower hierarchical positions and said given Lan Emulation Configuration Server is a lower Lan Emulation Configuration Server with respect to other Lan Emulation Configuration Servers in higher hierarchical positions;

establishing a connection from said Lan Emulation Configuration Server to any other Lan Emulation Configuration Servers which are lower Lan Emulation Configuration Servers with respect to said Lan Emulation Configuration Server;

detecting any connections made by higher Lan Emulation Configuration Servers; and

if a connection is detected from a higher Lan Emulation Configuration Server, assuming the state of slave Lan Emulation Configuration Server, otherwise assuming the state of master Lan Emulation Configuration Server.

2. The method of claim 1 further comprising

assuming the state of master Lan Emulation Configuration Server until said Lan Emulation Configuration Server receives a connection from a higher Lan Emulation Configuration Server.

3. The method of claim 1 further comprising

while in the state of slave Lan Emulation Configuration Server detecting the loss of a connection from a higher Lan Emulation Configuration Server;

determining if said loss of a connection was a last connection from a higher level Lan Emulation Configuration Server; and

if said loss of a connection was the last connection from a higher Lan Emulation Configuration Server, assuming the state of the master Lan Emulation Configuration Server.

4. The method of claim 1 further comprising:

while in the state of master Lan Emulation Configuration Server, receiving a connection from a higher Lan Emulation Configuration Server;

transitioning to the state of slave Lan Emulation Configuration Server; and

closing any non-Lan Emulation Configuration Server connections.

5. The method of claim 1 wherein assuming the state of master Lan Emulation Configuration Server further comprises registering a well known Lan Emulation Configuration Server address at an ATM switch.

6. The method of claim 1 wherein assuming the state of slave Lan Emulation Configuration Server further comprises de-registering a well known Lan Emulation Configuration Server address at an ATM switch.

7. In a device configured for use in an ATM network implementing a LAN emulation, a method of establishing and maintaining a connection to a master Lan Emulation Configuration Server the method comprising:

evaluating a hierarchical list having an order ranking a plurality of Lan Emulation Configuration Servers;

attempting connections from said device to each said Lan Emulation Configuration Servers according to the order of said hierarchical list;

establishing a connection between said device and a first Lan Emulation Configuration Server for which an attempted connection is successful, said first Lan Emulation Configuration Server being a master Lan Emulation Configuration Server; and

if said first Lan Emulation Configuration Server is redesignated as a slave Lan Emulation Configuration Server, breaking said connection.

8. The method of claim 7 wherein said device is an Lan Emulation Client.

9. The method of claim 7 wherein said device is an Lan Emulation Server.

10. The method of claim 7, wherein in said step of reviewing, said hierarchical list is provided on an ATM switch, and wherein the hierarchical list provides, for each listed Lan Emulation Configuration Server, a respected ATM address.

11. An Lan Emulation Configuration Server having a determinable state and being configured for use in an ATM network implementing a LAN emulation, said Lan Emulation Configuration Server comprising:

means for determining a hierarchical position of said Lan Emulation Configuration Server among a plurality of Lan Emulation Configuration Servers;

means for establishing a connection from said Lan Emulation Configuration Server to each lower Lan Emulation Configuration Server of said plurality of Lan Emulation Configuration Servers, said each lower Lan Emulation Configuration Server being in a lower hierarchical position relative to said Lan Emulation Configuration Server;

means for detecting connections made to said Lan Emulation Configuration Server by a higher Lan Emulation Configuration Server of said plurality of Lan Emulation Configuration Servers said higher Lan Emulation Configuration Server being in a higher hierarchical position relative to said Lan Emulation Configuration Server; and

means for switching said determinable state between a master state and slave state consistent with said hierarchical position and said connections made to said Lan Emulation Configuration Server.

12. The Lan Emulation Configuration Server of claim 11, further comprising:

means for setting said determinable state to be a slave state upon the detection of a connection from a higher Lan Emulation Configuration Server.

13. The Lan Emulation Configuration Server of claim 11, wherein said means for switching said determinable state initially sets said determinable state to the master state upon power up by said Lan Emulation Configuration Server.

14. The Lan Emulation Configuration Server of 11 wherein said means for switching said determinable state switches said determinable state from the slave state to the master state upon the loss of a connection from a last remaining connected higher Lan Emulation Configuration Server.

15. A device configured for connection to a master Lan Emulation Configuration Server in an ATM network implementing a LAN emulation, the device comprising:

means for evaluating a hierarchical list having an order which ranks a plurality of Lan Emulation Configuration Servers and their respective ATM addresses from an ATM switch;

means for atttempting connections to said Lan Emulation Configuration Servers according to the order of said hierarchical list; and

means for establishing a connection between said device and a first Lan Emulation Configuration Server for which attempted connection is successful, said first Lan Emulation Configuration Server being a master Lan Emulation Configuration Server.

16. The device of claim 15 wherein said device is an Lan Emulation Client.

17. The device of claim 15 wherein said device is an Lan Emulation Server.

18. The device of claim 17 wherein said Lan Emulation Server further includes means for verifying a connected Lan Emulation Client with said first Lan Emulation Configuration Server.

19. The device of claim 15 further comprising means for maintaining said connection as long as said first Lan Emulation Configuration Server is a master Lan Emulation Configuration Server.

20. In an Lan Emulation Configuration Server configured for use in an ATM network implementing a LAN emulation, a method for designating a master Lan Emulation Server comprising:

for each Lan Emulation Server within a set of Lan Emulation Servers associated with said Lan Emulation Configuration Server, specifying a hierarchical position such that said each Lan Emulation Server is a higher Lan Emulation Server with respect to all other Lan Emulation Servers in an lower hierarchical position and said each Lan Emulation Server is a lower Lan Emulation Server with respect to all other Lan Emulation Servers in a higher hierarchical position;

establishing a verification connection from each of said Lan Emulation Servers which is operational to said Lan Emulation Configuration Server;

maintaining data indicating which members of the set of Lan Emulation Servers is connected to said master Lan Emulation Configuration Server;

determining the highest Lan Emulation Server which is connected to said Lan Emulation Configuration Server; and

designating said highest Lan Emulation Server as the master Lan Emulation Server.

21. The method of claim 20 further including:

detecting the nonoperational status of a previously operational master Lan Emulation Server;

determining a next hightest operational Lan Emulation Server in said set of Lan Emulation Servers; and

designating said next highest operational Lan Emulation Server in said set of Lan Emulation Servers as the master Lan Emulation Server.

22. The method of claim 20 further including:

receiving a new connection from a newly operational Lan Emulation Server which has a hierarchical position that is higher than said master Lan Emulation Server;

dropping said verification connection with said master Lan Emulation Server;

redesignating said master Lan Emulation Server as a slave Lan Emulation Server; and

designating said newly operational Lan Emulation Server as the master Lan Emulation Server.

24. The method of claim 20 wherein a verification connection with an Lan Emulation Server which is operational is detected by said Lan Emulation Configuration Server and is detected by said Lan Emulation Server.

25. The method of claim 20 wherein a verification connection with an Lan Emulation Server which is operational is automatically broken when said Lan Emulation Server becomes non-operational.

26. The method of claim 20 wherein verification connection with an Lan Emulation Server which is operational may be selectively broken by said Lan Emulation Configuration Server.

23. The method of 22 further including:

breaking a verification connection with said slave Lan Emulation Server;

rejecting verification requests from said slave Lan Emulation Server for Lan Emulation Configuration Servers connected to said slave Lan Emulation Server; and

directing said Lan Emulation Configuration Servers connected to said slave Lan Emulation Server to said master Lan Emulation Server;

whereby said each Lan Emulation Client is disconnected from said slave Lan Emulation Server and said each Lan Emulation Client is connected to said new current master Lan Emulation Server.

27. An Lan Emulation Configuration Server comprising:

means for assigning to each Lan Emulation Server within a set of Lan Emulation Servers a hierarchical position such that said each Lan Emulation Server is a higher Lan Emulation Server with respect to all other Lan Emulation Servers in a lower hierarchical position and said each Lan Emulation Server is a lower Lan Emulation Server with respect to all other Lan Emulation Servers in a higher hierarchical position;

means for establishing a verification connection with each of said Lan Emulation Servers which is operational;

means for determining which members of said set of Lan Emulation Servers are connected to said Lan Emulation Configuration Server;

means for redesignating a current master Lan Emulation Server as a slave Lan Emulation Server and dropping said verification connection with said slave Lan Emulation Server;

means for rejecting all verification requests from said slave Lan Emulation Server; and

means for directing an Lan Emulation Client previously connected to said slave Lan Emulation Server to a new master Lan Emulation Server;

whereby said Lan Emulation Configuration Servers is configured to redirect an Lan Emulation Client to a new master Lan Emulation Server.

28. The Lan Emulation Configuration Servers of claim 27 further comprising:

means for detecting said verification connection with each of said Lan Emulation Servers which is operational.

29. The Lan Emulation Configuration Server of claim 27 further comprising:

means for selectively breaking a verification connection with an operational Lan Emulation Server.

30. An Lan Emulation Server comprising:

means for establishing a verification connection with an Lan Emulation Configuration Server;

means for sending a verification request to a master Lan Emulation Configuration Server for each Lan Emulation Client connected to said Lan Emulation Server; and

means for tearing down all connections between said Lan Emulation Server and said each Lan Emulation Client connected to said Lan Emulation Server upon the rejection of a verification request associated with said each Lan Emulation Client connected to said Lan Emulation Server;

whereby said Lan Emulation Server either verifies or drops all Lan Emulation Client connections upon connection to the master Lan Emulation Configuration Servers.

31. THE Lan Emulation Server of claim 30, further comprising means for locating the master Lan Emulation Configuration Server upon the loss of said verification connection.