Establishing and maintaining master and standby LAN...

Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability

Reexamination Certificate

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Details

C370S395530

Reexamination Certificate

active

06701448

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to LAN emulation. More specifically, a system for establishing and maintaining master and standby LAN emulation server connections to provide a fault tolerant LAN without creating excess traffic or load on an LECS is disclosed.
BACKGROUND OF THE INVENTION
Purpose of LAN Emulation
In general, the purpose of Asynchronous Transfer Mode (ATM) LAN Emulation (LANE) is to emulate a multiple-access, broadcast media (e.g., Etheniet) over a point-to-point, virtual circuit oriented media (ATM). The specification for LAN Emulation over an ATM may be found in the LANE ATM specification, “LAN emulation over ATM” version 1.0 Document No. AF-LANE-0021 which is herein incorporated by reference, “LAN emulation over ATM Version 1.0 Addendum” Document No. AF-LANE-0050.000 which is herein incorporated by reference (collectively, the “LANE specification version 1”), and in version 2 of the LANE ATM specification, “LAN emulation over ATM Version 2 LUNI Specification Documnent No. AF-LANE-0084.000 which is herein incorporated by reference (the “LANE specification version 2”). It is necessary to emulate the services available over the LAN so that the existing base of software can take advantage of the ATM network. LANE provides an easy way to connect existing LAN applications into the ATM environment by supporting “unmodified” interaction amongst legacy applications on the ATM network, and by supporting the interconnection of ATM networks with legacy LAN's. This provides interoperability between applications on the ATM network and those on legacy LANs.
LAN Emulation Components
FIG. 1A
shows the components of an emulated LAN (ELAN) implemented over an ATM network
100
. The ELAN components include at least one LEC
102
. LEC
102
may include end stations (e.g., hosts), routers or bridges and each LEC
102
is responsible for setting up the association with the ELAN assets to provide LANE services to a local host or router. Two other components of the LANE service are a LAN Emulation Server (LES)
104
and a Broadcast and Unknown Server (BUS)
106
. LES
104
provides a registration facility to allow clients to register unicast and multicast media access control (MAC) addresses and/or ring route descriptors, and a forwarding service for control frames. BUS
106
receives frames from LEC
102
and retransmits them to other LEC's on the ELAN. The LANE Service may use more than one BUS, and the BUS
106
may be distributed over multiple physical entities or collocated on a single box. In certain implementations, a single LES/BUS is collocated on one router. Another ELAN component, an LECS
108
, enables LEC
102
to find and to connect to LES
104
for the proper ELAN over the ATM network
100
.
LES
104
and LECS
108
are referred to as “edge devices” on the ELAN because they are not required for the operation of the ATM network itself, but are required in order for the ATM network to emulate a LAN. The functions and protocols implemented for these devices are further described in the LANE specification.
The LECS, LES and BUS may be implemented on various network devices including switches, hosts, routers or bridges. Any device which includes an ATM interface and can support virtual circuits may function as the LECS or LES, including a PC with an ATM interface. Such devices include a processor capable of executing logic operations and memory, along with an ATM interface. Based on the operations executed by the processor, the device is able to process outside events, record those events in memory, and also to determine states and store those states in memory.
FIG. 1B
shows how LEC
102
connects to the LANE service so that LEC
102
may perform data forwarding, address resolution and registration of MAC addresses with LES
104
. When LEC
102
wishes to connect to an ELAN, it locates LECS
108
on ATM network
100
at a well-known address, and then sets up a point to point configure direct connection
112
with LECS
108
. LECS
108
services configuration requests from LEC
102
and tells LEC
102
which ELAN it should join and the address of the LES that it should use. LEC
102
then sets up a control direct connection
114
with LES
104
. LES
104
establishes a point to multipoint connection
116
with LEC
102
, as well as with any other LEC
110
on the ELAN. Finally, LEC
102
establishes a multicast send point to point connection
118
with BUS
106
and a point to multipoint multicast forwvard connection
120
is set up between BUS
106
and LEC
102
and any other LEC
110
.
Once LEC
102
registers with LES
104
, it receives address resolution requests for unregistered destinations from LES
104
. LES
104
provides a registration facility to allow clients to register unicast and multicast MAC addresses and/or token ring route descriptors, and a forwarding service for control frames. Optionally, it may generate control frames. Bridges may register with LES
104
any MAC addresses that they are capable of foraarding. BUS
106
receives frames from clients or other multicast servers, and retransmits them to other clients. There is at least one BUS in an emulated LAN which handles broadcast and multicast addresses.
In order for the ELAN to function, the servers that function as LES
104
and LECS
108
must remain operational. Wien LEC
102
wants to participate in the ELAN, it must first ask LECS
108
for the address of LES
104
and then execute a joining procedure with the LES. When this transaction is completed, LEC
102
connects to LES
104
. This completes the joining of LEC
102
to the ELAN. LEC
102
must maintain a control direct connection with LES
104
as long as it continues to be connected to the ELAN. LES
104
and LECS
108
therefore represent potential single points of failure for the ELAN. Although the LANE specification details the operation of the LECS's and the LES's as described above, there is no provision for a system of redundant or backup servers.
What is needed is a redundancy scheme that provides a way for backup or slave servers to automatically and transparently take over the tasks of a failed master server so that the LANE service may continue to operate without significant disruption. Because LES
104
and LECS
108
may be interconnected to a numerous and changing group of LEC's, a way is needed to both detect failure of these edge devices and redesignate a slave or backup device as the master device and also to reconnect the LEC's to the new master devices with minimum disruption to the LEC's.
In addition, in a system where a large number of LEC's may be connected to an LES, a method is needed to direct LEC's to a backup LES upon failure of a master LES that does not require all of the LEC's to contact the LECS. Also, it would be desirable if a method of determining a master LES from among a group of available LES's could be devised that would minimize switching among LES's while a system is being brought on line. Finally, it is important that such a system be able to accommodate older LECS's, LES's and LEC's that have not been modified to operate in the system as well as LECS's, LES's and LEC's that have been designed to operate in the system. Thus, a robust redundancy scheme compatible with the LANE specification that reduces backend traffic between LES's and the master LECS and that also reduces the need for clients to contact an LECS when an LES fails is needed.
SUMMARY OF THE INVENTION
A redundancy scheme that reduces backend traffic between LES's and the master LECS and that also reduces the need for clients to contact an LECS when an LES fails is disclosed. The master LECS broadcasts configuration information to all LES's that includes a list of the master LES and any available backup LES's. This information is relayed by the LES's to modified LEC's that keep track of the available LES's. The LEC's use such information instead of contacting the LECS to deter

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