U.S. patent application number 10/867212 was filed with the patent office on 2005-12-15 for network relay system and control method thereof.
Invention is credited to Kimoto, Atsushi, Kitani, Makoto, Watanuki, Tatsuya, Yamate, Keiichiro.
Application Number | 20050276215 10/867212 |
Document ID | / |
Family ID | 35460429 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050276215 |
Kind Code |
A1 |
Kitani, Makoto ; et
al. |
December 15, 2005 |
Network relay system and control method thereof
Abstract
The network relay device of the invention makes a pair with at
least a specific network device to relay data in a network. The
network relay device includes: a control module that sends and
receives a control frame signal to and from the specific network
device, selects either of a master mode and a backup mode based on
at least the control frame signal sent from the specific network
device, and changes a working state according to a result of the
selection; and a communication module that is under control of the
control module to open a port and enable data transmission via a
line linked to the port in the case of setting a master state to
the working state, and to block off the port and disconnect the
line linked to the port in the case of setting a backup state or
another non-master state to the working state. The control module
changes the working state from the backup state to a first
intermediate state in response to selection of the master mode,
determines whether the specific network device is in the backup
state, based on the control frame signal sent from the specific
network device, and changes the working state from the first
intermediate state to the master state after confirmation that the
specific network is in the backup state.
Inventors: |
Kitani, Makoto; (Atsugi,
JP) ; Watanuki, Tatsuya; (Ebina, JP) ; Yamate,
Keiichiro; (Hadano, JP) ; Kimoto, Atsushi;
(Atsugi, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13th Street
Washington
DC
20005-3096
US
|
Family ID: |
35460429 |
Appl. No.: |
10/867212 |
Filed: |
June 15, 2004 |
Current U.S.
Class: |
370/217 |
Current CPC
Class: |
H04L 49/1523 20130101;
H04L 49/55 20130101 |
Class at
Publication: |
370/217 |
International
Class: |
H04L 012/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2004 |
JP |
2004-172451(P) |
Claims
What is claimed is:
1. A network relay device that makes a pair with at least a
specific network device to relay data in a network, the network
relay device comprising: a control module that sends and receives a
control frame signal to and from the specific network device,
selects either of a master mode and a backup mode based on at least
the control frame signal sent from the specific network device, and
changes a working state according to a result of the selection; and
a communication module that is under control of the control module
to open a port and enable data transmission via a line linked to
the port in the case of setting a master state to the working
state, and to block off the port and disconnect the line linked to
the port in the case of setting a backup state or another
non-master state to the working state, the control module changing
the working state from the backup state to a first intermediate
state in response to selection of the master mode, determining
whether the specific network device is in the backup state, based
on the control frame signal sent from the specific network device,
and changing the working state from the first intermediate state to
the master state after confirmation that the specific network is in
the backup state.
2. A network relay device in accordance with claim 1, wherein the
control module changes the working state from either of the backup
state and the first intermediate state to a second intermediate
state in the event of failed reception of the control frame signal
from the specific network device for a preset time period, in the
case of subsequent resuming reception of the control frame signal
from the specific network device, the control module selecting
either of the master mode and the backup mode and changing the
working state from the second intermediate state to the first
intermediate state in response to selection of the master mode,
while changing the working state from the second intermediate state
to the backup state in response to selection of the backup
mode.
3. A network relay device in accordance with claim 2, wherein the
control module changes the working state from the second
intermediate state to the master state, in response to an
externally given transition instruction to the master state.
4. A network relay device in accordance with claim 3, wherein the
network includes a large number of virtual LANs, which are divided
into multiple groups, the control module carries out selection of
either of the master mode and the backup mode and management of the
working state with regard to each of the multiple groups, and the
communication module under control opens and blocks off the port
with regard to each of the multiple groups.
5. A network relay device in accordance with claim 1, wherein the
network includes a large number of virtual LANs, which are divided
into multiple groups, the control module carries out selection of
either of the master mode and the backup mode and management of the
working state with regard to each of the multiple groups, and the
communication module under control opens and blocks off the port
with regard to each of the multiple groups.
6. A network relay device in accordance with claim 2, wherein the
network includes a large number of virtual LANs, which are divided
into multiple groups, the control module carries out selection of
either of the master mode and the backup mode and management of the
working state with regard to each of the multiple groups, and the
communication module under control opens and blocks off the port
with regard to each of the multiple groups.
7. A control method of controlling a network relay device that
makes a pair with at least a specific network device to relay data
in a network, the control method comprising the steps of: (a)
sending and receiving a control frame signal to and from the
specific network device, selecting either of a master mode and a
backup mode based on at least the control frame signal sent from
the specific network device, and changing a working state according
to a result of the selection; and (b) opening a port and enabling
data transmission via a line linked to the port in the case of
setting a master state to the working state, while blocking off the
port and disconnecting the line linked to the port in the case of
setting a backup state or another non-master state to the working
state, the step (a) comprising the steps of: (a-1) changing the
working state from the backup state to a first intermediate state
in response to selection of the master mode, and determining
whether the specific network device is in the backup state, based
on the control frame signal sent from the specific network device;
and (a-2) changing the working state from the first intermediate
state to the master state after confirmation that the specific
network is in the backup state.
8. A control method in accordance with claim 7, wherein the step
(a) further comprises the steps of: (a-3) changing the working
state from either of the backup state and the first intermediate
state to a second intermediate state in the event of failed
reception of the control frame signal from the specific network
device for a preset time period, (a-4) in the case of subsequent
resuming reception of the control frame signal from the specific
network device after the step (a-3), selecting either of the master
mode and the backup mode and changing the working state from the
second intermediate state to the first intermediate state in
response to selection of the master mode, while changing the
working state from the second intermediate state to the backup
state in response to selection of the backup mode.
9. A control method in accordance with claim 8, wherein the step
(a) further comprises the step of: (a-5) changing the working state
from the second intermediate state to the master state, in response
to an externally given transition instruction to the master state.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a network relay device that
relays data in a network.
[0003] 2. Description of the Related Art
[0004] The network generally adopts the redundant structure, in
order to prevent the shutdown of the entire network due to the
occurrence of some trouble or failure in a line or a device
included in the network.
[0005] A layer 2 (data link layer) and a layer 3 (network layer) in
the OSI reference model have different network characteristics. In
the case of an internet protocol (IP) as a typical example of the
layer 3, simple connection of two devices by a physical line does
not establish intercommunication between the connected devices
unless IP addresses are set in the respective devices. In the case
of Ethernet (registered trademark) as a typical example of the
layer 2, on the other hand, simple connection of two devices by a
physical line establishes intercommunication between the connected
devices.
[0006] An L2 switch is one example of layer 2 (L2)-compliant
network relay devices. Interconnection of multiple L2 switches by
two or a greater number of physical lines or establishment of the
redundant structure by multiple L2 switches undesirably causes a
loop in the network as shown in FIG. 7. In the illustration of FIG.
7, SW represents an L2 switch.
[0007] The occurrence of the loop in the network may lead to a
significant problem. In the process of transmission of packets via
the Ethernet (registered trademark), for example, in the case of an
unknown destination (MAC address) of the packets, the L2 switch
uses a broadcast address and sends broadcast packets. The L2 switch
sends the broadcast packets to a line other than the
packet-receiving line and does not memorize the packets transmitted
previously. In the presence of a loop in the network, the broadcast
packets infinitely multiply and endlessly circulate in the loop.
This applies significant loading to the packet transfer of the L2
switch and affects other networks to occupy the available
bandwidth.
[0008] A known measure against this potential problem divides the
multiple lines and multiple L2 switches constituting the loop into
an active system and a standby system. This technique blocks off
the packet transfer from the L2 switches in the standby system and
disconnects the lines in the standby system, while establishing
communication only by the L2 switches and the lines in the active
system. This prevents the occurrence of a loop in the network.
[0009] In the case of virtual LANs (VLANs), setting of the active
system or the standby system is carried out with regard to each
group of a single or multiple virtual LANs. Namely the L2 switches
and the lines working as the active system in one group may be
specified as the standby system in another group, and vice
versa.
[0010] A prior art system may use a pair of the L2 switches, which
are interlocked to effect a switchover between a master mode and a
backup mode as shown in FIG. 8. This structure enables a smooth
switchover from the active system to the standby system, in the
event of any trouble or failure arising in the current active
system.
[0011] In the system using the paired L2 switches, one of the L2
switches is set to the master L2 switch and is used in the active
system, whereas the other of the L2 switches is set to the backup
L2 switch and is used in the standby system. The master L2 switch
opens a port to establish communication via a line linked to the
port, while the backup L2 switch blocks off the port to disconnect
the line linked to the port. During operations, the master L2
switch and the backup L2 switch send and receive the control frame
signals to and from each other at regular intervals for mutual
confirmation of the effective presence. In the event of any trouble
or failure arising in the master L2 switch or in the line
connecting with the master L2 switch, the backup L2 switch detects
the occurrence of the trouble or failure and takes over the master
mode in place of the current master L2 switch to open the blocked
port and establish communication via the line linked to the port.
This leads to a switchover of the entire network from the active
system to the standby system.
[0012] The network-related technique described above is disclosed,
for example, in U.S. Pat. No. 5,473,599.
[0013] As mentioned above, the master L2 switch and the backup L2
switch send and receive the control frame signals to and from each
other at regular intervals for mutual confirmation of the effective
presence. A control module in each of the L2 switches manages the
control frame signals. The control module in the master L2 switch
may fall into some busy status. The communication module generally
carries out the hardware processing and thus attains normal
transfer of packets even in the busy status. The control module in
the busy status may, however, fail to send the control frame signal
to the backup L2 switch. In response to failed reception of the
control frame signal from the master L2 switch, the control module
in the backup L2 switch wrongly detects the occurrence of a failure
or trouble in the master L2 switch and takes over the master mode
in place of the current master L2 switch to open the blocked port
and establish communication via the line linked to the port. This
causes both the paired L2 switches to work in the master mode and
fall into a double master situation. Communication is established
individually via the paired L2 switches in the master mode. This
undesirably causes a loop in the network.
SUMMARY OF THE INVENTION
[0014] The object of the present invention is thus to eliminate the
drawbacks of the prior art discussed above and to provide a
technique that effectively prevents the double master situation and
restrains the occurrence of a loop in a network.
[0015] In order to attain at least part of the above and the other
related objects, the present invention is directed to a network
relay device that makes a pair with at least a specific network
device to relay data in a network. The network relay device
includes: a control module that sends and receives a control frame
signal to and from the specific network device, selects either of a
master mode and a backup mode based on at least the control frame
signal sent from the specific network device, and changes a working
state according to a result of the selection; and a communication
module that is under control of the control module to open a port
and enable data transmission via a line linked to the port in the
case of setting a master state to the working state, and to block
off the port and disconnect the line linked to the port in the case
of setting a backup state or another non-master state to the
working state.
[0016] The control module changes the working state from the backup
state to a first intermediate state in response to selection of the
master mode, determines whether the specific network device is in
the backup state, based on the control frame signal sent from the
specific network device, and changes the working state from the
first intermediate state to the master state after confirmation
that the specific network is in the backup state.
[0017] The network relay device of the invention does not
immediately change the working state from the backup state to the
master state in response to selection of the master mode but
temporarily changes the working state to the first intermediate
state. After confirmation that the specific network device is in
the backup state based on the control frame signal sent from the
specific network device, the network relay device changes the
working state from the first intermediate state to the master
state.
[0018] The network relay device of the invention changes the
working state from the backup state to the master state after
confirmation that the working state of the pairing specific network
device is in the backup state. This arrangement effectively
prevents both the network relay device and the pairing specific
network device from being simultaneously set in the master state
(double master situation) and thereby restrains the occurrence of a
loop in the network.
[0019] In one preferable embodiment of the network relay device of
the invention, the control module changes the working state from
either of the backup state and the first intermediate state to a
second intermediate state in the event of failed reception of the
control frame signal from the specific network device for a preset
time period.
[0020] In the case of subsequent resuming reception of the control
frame signal from the specific network device, the control module
selects either of the master mode and the backup mode and changes
the working state from the second intermediate state to the first
intermediate state in response to selection of the master mode,
while changing the working state from the second intermediate state
to the backup state in response to selection of the backup
mode.
[0021] In the event of failed transmission of the control frame
signal from the specific network device that is in some busy
status, the control module in the network relay device of the
invention changes the working state to the second intermediate
state on the condition that the control frame signal has not been
received for the preset time period. Namely the network relay
device of the invention does not immediately change its working
state to the master state. When the specific network device resumes
transmission of the control frame signal in response to
cancellation of the busy status, the control module in the network
relay device of the invention resumes reception of the control
frame signal and selects either the master mode or the backup mode.
The working state is changed to the first intermediate state in
response to selection of the master mode, while being changed to
the backup state in response to selection of the backup mode. This
arrangement effectively prevents the double master situation.
[0022] In the network relay device of the invention having the
above arrangement, it is preferable that the control module changes
the working state from the second intermediate state to the master
state, in response to an externally given transition instruction to
the master state.
[0023] In the event of failed transmission of the control frame
signal due to the occurrence of some trouble or failure in the
specific network device, the network relay device of the invention
changes the working state to the second intermediate state after
elapse of the preset time period. In the case of the occurrence of
some trouble or failure, it is expected that failed reception of
the control frame signal from the specific network device
continues. The working state is directly changed to the master
state, in response to input of externally given transition
instruction to the master state. The network relay device of the
invention thus takes over the master mode in place of the specific
network device. This attains a changeover from the active system to
the standby system in the network and thereby ensures the
redundancy of the network.
[0024] In another preferable embodiment of the network relay device
of the invention, the network includes a large number of virtual
LANs, which are divided into multiple groups. The control module
carries out selection of either of the master mode and the backup
mode and management of the working state with regard to each of the
multiple groups. The communication module under control opens and
blocks off the port with regard to each of the multiple groups.
[0025] In the network including a large number of virtual LANs, it
is preferable to carry out the control and management discussed
above with regard to each group of a single or multiple virtual
LANs. This arrangement effectively prevents the double master
situation and restrains the occurrence of a loop in each virtual
LAN.
[0026] The technique of the invention is not restricted to the
network relay device described above but is also applicable to a
control method of such a network relay device. The invention may be
actualized by diversity of other applications, for example,
computer programs to attain the network relay device and its
control method, recording media in which such computer programs are
recorded, and data signals that include such computer programs and
are embodied in carrier waves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a block diagram showing the configuration of an L2
switch 100 in one embodiment of the invention;
[0028] FIG. 2 shows a connection of the L2 switch 100 shown in FIG.
1;
[0029] FIG. 3 is a state transition diagram showing a transition of
the working state in the L2 switch 100 shown in FIG. 1;
[0030] FIG. 4 shows a transition of the working state of the L2
switch 100 on a start-up and transmission of control frame
signals;
[0031] FIG. 5 shows a transition of the working state of the L2
switch 100 and transmission of control frame signals in the case of
failed reception of the control frame signal;
[0032] FIG. 6 shows a transition of the working state of the L2
switch 100 and transmission of control frame signals in the case of
failed reception of the control frame signal;
[0033] FIG. 7 shows occurrence of a loop in a network; and
[0034] FIG. 8 shows paired L2 switches.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] One mode of carrying out the invention is discussed below in
the following sequence:
[0036] A. Configuration of Embodiment
[0037] B. Connection
[0038] C. Operations of Embodiment
[0039] D. Modifications
[0040] A. Configuration of Embodiment
[0041] FIG. 1 is a block diagram showing the configuration of an L2
switch 100 in one embodiment of the invention. As shown in FIG. 1,
the L2 switch 100 of the embodiment mainly includes a control
module 110 and a communication module 120. The control module 110
has a CPU 112 and a memory 114. The CPU 112 executes programs
stored in the memory 114 to manage the whole system, process
control packets, and send and receive control frame signals. The
communication module 120 includes network interfaces 122 and relays
packets on a layer 2 (data link layer) of the OSI reference model.
The network interfaces 122 are respectively connected to physical
lines (for example, twisted pair cables or optical fibers) of
Ethernet (registered trademark) or another adequate network via
corresponding ports (not shown).
[0042] B. Connection
[0043] FIG. 2 shows a connection of the L2 switch 100 shown in FIG.
1. The L2 switch 100 of the embodiment and another L2 switch 200
make a pair and are interconnected via physical lines as shown in
FIG. 2. The L2 switch 200 has the same configuration as that of the
L2 switch 100 shown in FIG. 1.
[0044] The paired L2 switches 100 and 200 are individually linked
to other four L2 switches 300 through 600 by physical lines.
Connection of the L2 switches 100 and 200 with the four other L2
switches ensures the redundancy of the network. Interconnection
between the L2 switches 100 and 200 by the two physical lines also
ensures the redundancy.
[0045] C. Operations of Embodiment
[0046] The paired L2 switches 100 and 200 are interlocked to allow
for a switchover between a master mode and a backup mode. One of
the L2 switches is set to the master L2 switch and is used in the
active system, whereas the other of the L2 switches is set to the
backup L2 switch and is used in the standby system.
[0047] The number of effective ports, the priority value, and the
MAC address determine which of the L2 switches 100 and 200 works as
the master L2 switch or as the backup L2 switch. The number of
effective ports represents the number of communicable ports. The
priority value is allocated in advance to each L2 switch.
[0048] More specifically the L2 switch having the greater number of
effective ports, the higher priority value, and the smaller MAC
address works as the master L2 switch. The general procedure sets
the order of precedence between the number of effective ports and
the priority value. For example, when the preference is given to
the number of effective ports over the priority value, the
procedure first compares the numbers of effective ports in the two
L2 switches, then compares the priority values in the case of
identical numbers of effective ports, and further compares the MAC
addresses in the case of identical priority values. In another
example, when the preference is given to the priority value over
the number of effective ports, the procedure first compares the
priority values in the two L2 switches, then compares the numbers
of effective ports in the case of identical priority values, and
further compares the MAC addresses in the case of identical numbers
of effective ports.
[0049] In the L2 switch 100 of the embodiment, the control module
110 sends and receives control frame signals via the physical lines
connecting with the L2 switch 200. The control frame signal
includes information on the number of effective ports, the priority
value, and the MAC address, in addition to the own working state
and the working state of the opposite device.
[0050] For example, when the preference is given to the number of
effective ports, the control module 110 receives the control frame
signal from the L2 switch 200, extracts the number of effective
ports from the received control frame signal (that is, the number
of effective ports in the L2 switch 200), and compares the own
number of effective ports in the L2 switch 100 with the extracted
number of effective ports. When the extracted number of effective
ports in the L2 switch 200 is greater than the own number of
effective ports in the L2 switch 100, the backup mode is selected.
When the own number of effective ports in the L2 switch 100 is
greater than the extracted number of effective ports in the L2
switch 200, on the other hand, the master mode is selected. In the
case of identical numbers of effective ports, the control module
110 subsequently extracts the priority value from the control frame
signal (that is, the priority value in the L2 switch 200) and
compares the own priority value in the L2 switch 100 with the
extracted priority value. When the extracted priority value in the
L2 switch 200 is higher than the own priority value in the L2
switch 100, the backup mode is selected. When the own priority
value in the L2 switch 100 is higher than the extracted priority
value in the L2 switch 200, on the other hand, the master mode is
selected. In the case of identical priority values, the control
module 110 then extracts the MAC address from the control frame
signal (that is, the MAC address in the L2 switch 200) and compares
the own MAC address in the L2 switch 100 with the extracted MAC
address. When the extracted MAC address in the L2 switch 200 is
smaller than the own MAC address in the L2 switch 100, the backup
mode is selected. When the own MAC address in the L2 switch 100 is
smaller than the extracted MAC address in the L2 switch 200, on the
other hand, the master mode is selected.
[0051] The control module 110 changes the working state as shown in
FIG. 3 in response to selection of either the master mode or the
backup mode.
[0052] FIG. 3 is a state transition diagram showing a transition of
the working state in the L2 switch 100 of the embodiment.
[0053] The L2 switch 100 takes one of four available states for its
working state, that is, `backup`, `backup (unknown adjacency)`,
`backup (master standby)`, and `master`, as shown in FIG. 3. The
working state changes according to the situation. Here the backup
(master standby) state is equivalent to the first intermediate
state of the invention, and the backup (unknown adjacency) state is
equivalent to the second intermediate state of the invention.
[0054] In the system of this embodiment, the transition of the
working state of the pairing L2 switch 200, as well as the working
state of the L2 switch 100, follows the state transition diagram of
FIG. 3.
[0055] The L2 switch 100 of the embodiment changes its working
state from the startup backup state to the master state by a route
discussed below, while sending and receiving the control frame
signals to and from the L2 switch 200.
[0056] FIG. 4 shows a transition of the working state of the L2
switch 100 on a start-up and transmission of control frame signals.
The control frame signal includes the own working state and the
working state of the opposite device as mentioned previously. These
workings states are shown in brackets in FIG. 4. The symbol `S`
represents the own working state, and the symbol `O` represents the
working state of the opposite device. The arrow t denotes lapse of
time.
[0057] On a start-up, the L2 switch 100 is set in the backup state
as shown in FIG. 3. At the start-up, no connection has yet been
established between the L2 switch 100 and the L2 switch 200. The
control module 110 accordingly does not receive the control frame
signal from the L2 switch 200 in a preset time period T and changes
the working state of the L2 switch 100 to the backup (unknown
adjacency) state in response to a control frame signal time-out.
The L2 switch 200 similarly changes its working state to the backup
(unknown adjacency) state in response to the control frame signal
time-out.
[0058] On establishment of the connection between the L2 switches
100 and 200, the control module 110 of the L2 switch 100 sends the
control frame signal to the L2 switch 200 as shown in FIG. 4. The
working state of the L2 switch 100 is currently the backup (unknown
adjacency) state, whereas the working state of the opposite device
or the L2 switch 200 is unknown. The control module 110 thus sends
the control frame signal with an entry of the backup (unknown
adjacency) state for the own working state and with no entry for
the working state of the opposite device.
[0059] The control module of the L2 switch 200 set in the backup
(unknown adjacency) state receives the control frame signal from
the L2 switch 100 and selects either the master mode or the backup
mode, based on the received control frame signal as discussed
above. For example, in response to selection of the backup mode,
the control module changes the working state of the L2 switch 200
to the backup state as shown in FIG. 3.
[0060] The control module of the L2 switch 200 then sends the
control frame signal to the L2 switch 100. The working state of the
L2 switch 200 has been changed to the backup state, so that the
control module of the L2 switch 200 sends the control frame signal
with an entry of the backup state for the own working state and
with an entry of the backup (unknown adjacency) state for the
working state of the opposite device or the L2 switch 100.
[0061] The control module 110 of the L2 switch 100 set in the
backup (unknown adjacency) state receives the control frame signal
from the L2 switch 200 and selects either the master mode or the
backup mode, based on the received control frame signal. In this
illustrated example, since the L2 switch 200 has already selected
the backup mode, the control module 110 of the L2 switch 100
inevitably selects the master mode. The control module 110 then
changes the working state of the L2 switch 100 to the backup
(master standby) state as shown in FIG. 3.
[0062] The control module 110 subsequently sends the control frame
signal to the L2 switch 200. The working state of the L2 switch 100
has been changed to the backup (master standby) state, so that the
control module 110 of the L2 switch 100 sends the control frame
signal with an entry of the backup (master standby) state for the
own working state and with an entry of the backup state for the
working state of the opposite device or the L2 switch 200.
[0063] The control module of the L2 switch 200 set in the backup
state receives the control frame signal from the L2 switch 100 and
selects either the master mode or the backup mode, based on the
received control frame signal. Unless there is any variation in
number of effective ports or another affecting piece of
information, the backup mode is continuously selected. The L2
switch 200 thus keeps the backup state as its working state as
shown in FIG. 3.
[0064] The control module of the L2 switch 200 then sends the
control frame signal to the L2 switch 100. The L2 switch 200 keeps
the backup state as its working state, so that the control module
of the L2 switch 200 sends the control frame signal with an entry
of the backup state for the own working state and with an entry of
the backup (master standby) state for the working state of the
opposite device or the L2 switch 100.
[0065] The control module 110 of the L2 switch 100 set in the
backup (master standby) state receives the control frame signal
from the L2 switch 200 and extracts the working state of the
opposite device or the L2 switch 200 from the received control
frame signal. After confirmation that the extracted working state
of the opposite device is the backup state, the control module 110
changes the working state of the L2 switch 100 to the master state
as shown in FIG. 3.
[0066] The control module 110 subsequently sends the control frame
signal to the L2 switch 200. The working state of the L2 switch 100
has been changed to the master state, so that the control module
110 of the L2 switch 100 sends the control frame signal with an
entry of the master state for the own working state and with an
entry of the backup state for the working state of the opposite
device or the L2 switch 200.
[0067] According to the above series of operations, the L2 switch
100 out of the paired L2 switches 100 and 200 is set in the master
mode, while the L2 switch 200 is set in the backup mode. The
communication module of the L2 switch 200 set in the backup mode is
under control of the communication module and blocks off the
respective ports connecting with the L2 switches 300 through 600
and disconnects the physical lines linked to the L2 switches 300
through 600. The communication module of the L2 switch 200,
however, continues transmission of the control frame signals to and
from the L2 switch 100.
[0068] In the L2 switch 100 set in the master mode, on the other
hand, the communication module 120 is under control of the control
module 110 and opens the respective ports connecting with the L2
switches 300 through 600 and enables data transmission to and from
the L2 switches 300 through 600 via the respective physical lines.
The control module 110 outputs a switchover message, which shows
that the L2 switch 100 is currently set in the master mode, to a
management terminal (not shown) in the network. The network
administrator reads the switchover message on a display unit of the
management terminal and is thus notified of the fact that the L2
switch 100 is currently set in the master mode.
[0069] As described above, in the structure of the embodiment, the
working state of the L2 switch 100 changes from the backup state to
the master state via the backup (master standby) state as shown in
FIG. 3. The L2 switch 100 accordingly changes its working state to
the master state after confirmation that the working state of the
pairing L2 switch 200 is the backup state. This arrangement
effectively prevents both the paired L2 switches 100 and 200 from
being simultaneously set in the master state (double master
situation) and thereby restrains the occurrence of a loop in the
network.
[0070] The following describes a transition of the working state in
the L2 switch 100 of the embodiment set in the backup mode, in the
case of failed transmission of the control frame signal from the L2
switch 200 set in the master mode.
[0071] FIG. 5 shows a transition of the working state of the L2
switch 100 and transmission of control frame signals in the case of
failed reception of the control frame signal.
[0072] In this illustrated example, the L2 switch 100 is set in the
backup mode and the L2 switch 200 is set in the master mode, unlike
the above description. In the normal conditions, the L2 switch 100
and the L2 switch 200 send and receive the control frame signals to
and from each other at regular intervals for mutual confirmation of
the effective presence and the working state.
[0073] When the control packet process or the CPU is busy in the
control module of the L2 switch 200 set in the master mode, the
control module may fail to send the control frame signal to the L2
switch 100 set in the backup mode. The communication module
generally carries out the hardware processing and thus attains
normal transfer of packets even in the busy status of the control
packet process or the CPU.
[0074] In the case of failed transmission of the control frame
signal from the L2 switch 200 set in the master mode, the control
module 110 of the L2 switch 100 set in the backup mode fails to
receive the control frame signal from the L2 switch 200 in the
preset time period T as shown in FIG. 5. The control module 110 of
the L2 switch 100 changes the working state of the L2 switch 100
from the backup state to the backup (unknown adjacency) state in
response to the control frame signal time-out as shown in FIG. 3.
On the change of the working state to the backup (unknown
adjacency) state, the control module 110 outputs an alarm message
to the management terminal (not shown) in the network.
[0075] In this case, the failed transmission of the control frame
signal is ascribed to the busy status of the control packet process
or the CPU in the control module. In response to cancellation of
the busy status, the control module of the L2 switch 200 set in the
master mode immediately resumes transmission of the control frame
signal to the L2 switch 100 set in the backup state.
[0076] The control module 110 of the L2 switch 100 set in the
backup mode thus resumes reception of the control frame signal as
shown in FIG. 5. The control module 110 selects either the master
mode or the backup mode, based on the received control frame
signal. Unless there is any variation in number of effective ports
or another affecting piece of information, the backup mode is
continuously selected. The control module 110 thus changes the
working state of the L2 switch 100 from the backup (unknown
adjacency) state to the backup state as shown in FIG. 3. This
restores the normal operations as shown in FIG. 5.
[0077] In the case of any variation in number of effective ports,
the control module 110 selects the master mode and changes the
working state of the L2 switch 100 from the backup (unknown
adjacency) state to the backup (master standby) state. After
confirmation that the working state of the L2 switch 200 is the
backup state, the L2 switch 100 changes its working state to the
master state, as described previously.
[0078] As described above, when the control module of the L2 switch
200 set in the master state fails to send the control frame signal
due to the busy status of the control packet process or the CPU,
the control module 110 of the L2 switch 100 set in the backup state
naturally fails to receive the control frame signal in the preset
time period T. The control module 110 changes the working state of
the L2 switch 100 to the backup (unknown adjacency) state in
response to the control frame signal time-out. Namely the L2 switch
100 does not immediately change its working state to the master
state. When the control module of the L2 switch 200 resumes
transmission of the control frame signal in response to
cancellation of the busy status, the control module 110 of the L2
switch 100 resumes reception of the control frame signal and
selects either the master mode or the backup mode. The working
state is changed to the backup (master standby) state in response
to selection of the master mode, while being changed to the backup
state in response to selection of the backup mode. In this case,
the arrangement of the embodiment thus effectively prevents the
double master situation.
[0079] FIG. 6 shows a transition of the working state of the L2
switch 100 and transmission of control frame signals in the case of
failed reception of the control frame signal, as in the case of
FIG. 5.
[0080] In this illustrated example, the L2 switch 100 is set in the
backup mode and the L2 switch 200 is set in the master mode.
[0081] In the case of occurrence of any trouble or failure in the
L2 switch 200 set in the master mode, the control module of the L2
switch 200 fails to send the control frame signal to the L2 switch
100 set in the backup mode.
[0082] In the case of failed transmission of the control frame
signal from the L2 switch 200 set in the master mode, the control
module 110 of the L2 switch 100 set in the backup mode fails to
receive the control frame signal from the L2 switch 200 in the
preset time period T as shown in FIG. 6. As in the illustrated
example of FIG. 5, the control module 110 of the L2 switch 100
changes the working state of the L2 switch 100 from the backup
state to the backup (unknown adjacency) state in response to the
control frame signal time-out. On the change of the working state
to the backup (unknown adjacency) state, the control module 110
outputs an alarm message to the management terminal (not shown) in
the network.
[0083] The network administrator reads the alarm message on the
display unit of the management terminal and is notified of the fact
that the L2 switch 100 fails to receive the control frame signal
from the L2 switch 200 due to some reason.
[0084] In this case, the failed transmission of the control frame
signal is ascribed to the occurrence of some trouble or failure in
the L2 switch 200. Until fixation of the trouble or replacement of
the failed part, no control frame signal is transmitted from the L2
switch 200 set in the master mode to the L2 switch 100 set in the
backup mode.
[0085] When the alarm message is not cancelled even after some
time, the network administrator manipulates the management terminal
and outputs a master switchover command to switch over the working
state to the master state to the L2 switch 100 via the network. The
control module 110 of the L2 switch 100 receives the master
switchover command and changes the working state of the L2 switch
100 directly from the backup (unknown adjacency) state to the
master state.
[0086] The L2 switch 100 thus switches over the selection from the
backup mode to the master mode. The communication module 120
accordingly opens the respective ports connecting with the L2
switches 300 through 600 and enables data transmission to and from
the L2 switches 300 through 600 via the physical lines.
[0087] The master switchover command is equivalent to the
transition instruction to the master state in the invention.
[0088] As described above, in the event of failed transmission of
the control frame signal due to the occurrence of any trouble or
failure in the L2 switch 200 set in the master mode, the control
module 110 of the L2 switch 100 set in the backup mode changes the
working state of the L2 switch 100 to the backup (unknown
adjacency) state after elapse of the preset time period T. In the
case of the occurrence of some trouble or failure, it is expected
that failed reception of the control frame signal from the L2
switch 200 continues. The working state is directly changed to the
master state, in response to input of the master switchover command
by the network administrator. The L2 switch 100 thus takes over the
master mode in place of the failed L2 switch 200. This attains a
changeover from the active system to the standby system in the
network and thereby ensures the redundancy of the network.
[0089] In the above example, in the event of failed transmission of
the control frame signal from the L2 switch 200 for the preset time
period T, the control module 110 of the L2 switch 100 changes the
working state of the L2 switch 100 from the backup state to the
backup (unknown adjacency) state. The similar series of operations
is applicable to the L2 switch 100 in the backup (master standby)
state. In the event of failed transmission of the control frame
signal from the L2 switch 200 for the preset time period T, the
control module 110 of the L2 switch 100 changes the working state
of the L2 switch 100 from the backup (master standby) state to the
backup (unknown adjacency) state as shown in FIG. 3. The subsequent
series of operations are identical with those in the case of the
transition from the backup state to the backup (unknown adjacency)
state.
[0090] D. Modifications
[0091] The embodiment discussed above is to be considered in all
aspects as illustrative and not restrictive. There may be many
modifications, changes, and alterations without departing from the
scope or spirit of the main characteristics of the present
invention.
[0092] The technique of the invention is applicable to a virtual
LAN established in the network. In the virtual LAN system, while
sending and receiving the control frame signals to and from the
pairing L2 switch 200, the control module 110 of the L2 switch 100
compares the respective numbers of effective ports or priority
values in each group of a single virtual LAN or multiple virtual
LANs to select either the master mode or the backup mode and
manages the working state in each group as shown in FIG. 3. The
communication module 120 opens and blocks off the respective ports
in each group under control of the control module 110. The L2
switch 100 may be set in the master mode and the L2 switch 200 may
be set in the backup mode in one group, while the L2 switch 100 is
set in the backup mode and the L2 switch 200 is set in the master
mode in another group.
[0093] Such management and control are carried out for each group
of a single virtual LAN or multiple virtual LANs. This effectively
prevents the double-master situation in each group and restrains
the occurrence of a loop in each virtual LAN.
[0094] The above embodiment regards the application of the
invention to the L2 switch as one of the network relay devices. The
technique of the invention is, however, not restricted to the L2
switches at all but is applicable to diversity of other network
relay devices.
[0095] Finally, the present application claims the priority based
on Japanese Patent Application No. 2004-172451 filed on Jun. 10,
2004, which is herein incorporated by reference.
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