1. An information processing apparatus comprising: a plurality of ports that transmit and receive data; a transmission unit that transmits loop detection data including transmission origin port information to detect a loop configuration from each of the plurality of ports; a determination unit that determines whether other port having received the loop detection data is in a closing state, when the loop detection data transmitted from one port among the plurality of ports is received by other port; and a port control unit that executes a process for causing one port having transmitted the loop detection data to enter the closing state, when other port having received the loop detection data is not in the closing state at the time of a determination process by the determination unit, and does not execute the process on one port, when other port is in the closing state.

2. The information processing apparatus according to claim 1, wherein there is a time lag until the determination unit determines whether other port having received the loop 34 detection data is in the closing state, after the loop detection data is received by other port.

3. The information processing apparatus according to claim 1 or 2, wherein when a loop suppression function using a route selection algorithm starts, the port control unit monitors states of the plurality of ports, and in the case where there is a port of which a state has changed from a blocking state in which the data is not transferred by the loop suppression function to a nonblocking state, the port control unit transmits the loop detection data from the port.

4. The information processing apparatus according to claim 1, wherein the transmission unit multicasts the loop detection data from all of the plurality of ports.

5. A network system comprising at least a first information processing apparatus, a second information processing apparatus, and a third information processing apparatus, wherein the first information processing apparatus comprises: a plurality of ports that have a port connected to the second information processing apparatus and a port 35 connected to the third information processing apparatus and transmit and receive data; a transmission unit that transmits loop detection data including transmission origin port information to detect a loop configuration from each of the plurality of ports; a determination unit that determines whether other port having received the loop detection data is in a closing state, when the loop detection data transmitted from one port among the plurality of ports is received by other port; and a port control unit that executes a process for causing one port having transmitted the loop detection data to enter the closing state, when other port having received the loop detection data is not in the closing state at the time of a determination process by the determination unit, and does not execute the process on one port, when other port is in the closing state.

TITLE OF THE INVENTION
INFORMATION PROCESSING APPARATUS AND NETWORK SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information
processing apparatus and a network system and more
particularly, to technology for preventing a loop in a
switch device of a backbone network and a network system
configured using switch devices disposed under control of
the switch device.
2. Description of the Related Art
As a loop suppression function on a network, a
spanning tree such as a spanning tree protocol (STP) and a
rapid spanning tree protocol (RSTP) is known. Generally,
in a switch device disposed on a backbone network, the loop
suppression function starts. The spanning tree is a route
selection algorithm to suppress infinite circulation (loop)
of frames in a network between a plurality of bridges
connected in parallel. The algorithm of the spanning tree
is standardized as IEEE 802.1d.
In the switch device under control of the backbone
network, port extension is carried out frequently and a
device is often disposed for a temporary use. If the STP
is started by the switch device disposed simply, a topology
3
change occurs frequently and affects the backbone network.
For this reason, the loop suppression function such as the
STP may not be started. In such an environment, when a
loop failure occurs under the control of the backbone
network, the loop failure affects the whole network and a
loop detection function is started by each switch device
under the control of the backbone network.
For example, technology for transmitting a loop
detection frame from a port of the switch device of the
backbone network at a fixed cycle, receiving the loop
detection frame by the switch device, and detecting a loop
configuration exists as the loop detection function
according to the related art.
JP-2009-207028-A discloses a switch device including
a loop detection function in which port identification is
set to a port starting the loop detection function. In the
loop detection function, in an upper port of the switch
device connected to a backbone network or an upper switch
device, on the basis of the set port identification, only
reception of a loop detection frame is performed and
transmission is not performed. When the loop detection
frame is received by the upper port of the switch device,
closing control of a lower port of a transmission origin
having transmitted the loop detection frame in the same
switch device is executed.
4
SUMMARY OF THE INVENTION
However, in the switch device enabling the loop
detection function, if a loop occurs when port detection
frames are transmitted from a plurality of ports at the
fixed cycle, the loop detection frames are received by the
plurality of ports and the ports are closed. As such, if
the plurality of ports are closed, communication enabling
ports decrease and a communication range (communication
path number) of the network is greatly reduced.
In addition, in the switch device disclosed in JP-
2009-207028-A, it is difficult for a general user to set
the port identification. When loop damage occurs, a
portion becoming the loop configuration may not be
separated immediately.
Accordingly, the present invention has been made in
view of the above circumstances and it is an object of the
present invention to perform port closing to prevent a loop
while maintaining a communication range of a network
maximally, without requiring complex setting of port
identification.
An information processing apparatus according to an
aspect of the present invention includes a plurality of
ports that transmit and receive data, a transmission unit,
a determination unit, and a port control unit.
5
The transmission unit transmits loop detection data
including transmission origin port information to detect a
loop configuration from each of the plurality of ports.
The determination unit determines whether other port
having received the loop detection data is in a closing
state, when the loop detection data transmitted from one
port among the plurality of ports is received by other port.
The port control unit executes a process for causing
one port to enter the closing state, when other port having
received the loop detection data is not in the closing
state at the time of a determination process by the
determination unit, and does not execute the process on one
port, when other port is in the closing state.
A network system according to another aspect of the
present invention is a network system that includes at
least a first information processing apparatus, a second
information processing apparatus, and a third information
processing apparatus.
The first information processing apparatus includes
a plurality of ports that have a port connected to the
second information processing apparatus and a port
connected to the third information processing apparatus and
transmit and receive data, the transmission unit, the
determination unit, and the port control unit.
6
At least an aspect of the present invention can
prevent a plurality of ports having received loop detection
data from being closed and can maintain a range
(communication path number) in which communication of a
network can be maintained widely.
Other problems, configurations and effects of the
invention will become apparent from the following
description of embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram illustrating a
configuration example of a network system according to a
first embodiment of the present invention;
Fig. 2 is a diagram illustrating a motion of a loop
detection frame when a loop occurs, in the network system
of Fig. 1;
Fig. 3 is a block diagram illustrating an internal
configuration example of a switch device including a loop
detection function;
Fig. 4 is a diagram illustrating an example of a
frame format of the loop detection frame;
Fig. 5 is a flowchart illustrating a loop detection
determination process according to the first embodiment of
the present invention;
7
Fig. 6 is a sequence diagram illustrating an outline
of loop occurrence at the time of erroneous network
connection in the first embodiment of the present
invention;
Fig. 7 is a diagram illustrating a state before a
blocking state of the switch device changes;
Fig. 8 is a diagram illustrating a state after the
blocking state of the switch device changes;
Fig. 9 is a flowchart illustrating a port state
change monitor process according to a second embodiment of
the present invention; and
Fig. 10 is a block diagram illustrating a
configuration example of a network system according to a
third embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will
be described in detail below with reference to the
accompanying drawings, wherein like reference numerals
refer to like parts throughout. The description is given
in the following order.
1. First embodiment (example of loop detection
determination process)
2. Second embodiment (example of port state change monitor
process)
8
3. Third embodiment (example of case where number of ports
of switch device is four)
<1. First embodiment>
This embodiment prevents infinite circulation of
frames (broadcast frames) transmitted from a switch device
to many and unspecified transmission destinations without
port designation, due to erroneous connection of a network
system, and prevents breakdown of the whole network system
due to the infinite circulation of the frames.
Fig. 1 is a block diagram illustrating a
configuration example of a network system according to the
first embodiment of the present invention.
In a network system 1 illustrated in Fig. 1, a
switch device 101 (example of an information processing
apparatus) is connected to a backbone network 100 via a
communication line 201. The switch device 101 is a switch
device including a loop detection function and is a socalled
intelligence-type switching hub. An unshielded
twist pair (UTP) cable of a category 5e of an Ethernet
(registered trademark) can be used in the communication
line of the network system 1, but the cable is not limited
to this example.
A first port of the switch device 101 is connected
to a switch device 102 via a communication line 202. In
9
addition, a second port of the switch device 101 is
connected to a switch device 103 via a communication line
203. That is, the switch devices 102 and 103 are disposed
under control of the switch device 101 disposed on the
backbone network 100. The switch devices 102 and 103 do
not include a loop detection function. Hereinafter, a
network configured using the switch devices 102 and 103
disposed under the control of the switch device 101
connected to the backbone network 100 is called a “lower
network”.
Three communication apparatuses 111 to 113 are
connected to the switch device 102 via communication lines
211 to 213. In addition, three communication apparatuses
114 to 116 are connected to the switch device 103 via
communication lines 214 to 216.
The switch device 101 transmits loop detection
frames 221 and 222 (example of loop detection data), which
are L2 control frames for loop detection, from the first
and second ports at a fixed cycle (for example, an interval
of five seconds).
Fig. 2 is a diagram illustrating a motion of a loop
detection frame when a loop occurs, in the network system
of Fig. 1.
As illustrated in Fig. 2, the switch devices 102 and
103 under the control of the switch device 101 are
10
erroneously connected directly by a communication line 210,
so that a loop 231 in which the loop detection frame 221
transmitted from the first port of the switch device 101 to
the switch device 102 is input to the second port of the
switch device 101 to be a transmission origin via the
switch devices 102 and 103 is formed. That is, a loop
failure in which the loop detection frame 221 transmitted
from the first port of the switch device 101 is received by
the second port of the switch device 101 to be the
transmission origin through a path of the loop 231 occurs.
Likewise, the switch devices 102 and 103 are
erroneously connected directly by the communication line
210, so that a loop 232 in which the loop detection frame
222 transmitted from the second port of the switch device
101 to the switch device 103 is input to the first port of
the switch device 101 to be the transmission origin via the
switch devices 103 and 102 is formed. That is, a loop
failure in which the loop detection frame 222 transmitted
from the second port of the switch device 101 is received
by the first port of the switch device 101 to be the
transmission origin through a path of the loop 232 occurs.
In a switch device according to the related art, a
closing process (port closing) is executed on a port having
received a loop detection frame. For this reason, as
illustrated in Fig. 2, when the switch device connected to
11
the backbone network has the two ports capable of
performing communication with the lower network, the two
ports are closed. Therefore, the backbone network and the
lower network are completely separated from each other. As
such, if a loop occurs, network damage may become serious.
Therefore, the network damage needs to be prevented by
discovering the loop early.
In this embodiment, transmission origin port
information is added to the loop detection frame and when
the loop detection frame is received by any port 301 of the
switch device 101, a closing state of the reception port is
checked in the switch device 101. As a check result, if
the reception port is in a non-closing state, the switch
device 101 changes a state of the transmission origin port
to the closing state, on the basis of the transmission
origin port information acquired from the loop detection
frame.
In Figs. 1 and 2, the example of the configuration
in which the loop is configured in the switch devices 101
to 103 via the communication line 210 erroneously connected
between the switch device 102 and the switch device 103 has
been described. However, the loop configuration is not
limited to the above example. For example, the following
loop configurations are considered.
12
(1) Case where one port and the other port of the switch
device 101 are connected (erroneous cable connection in the
same switch device)
(2) Case where, when the ports are erroneously connected in
the switch device 102 or 103 under the control of the
switch device 101, a frame transmitted from the switch
device 101 to the switch device 102 or 103 is transmitted
to the switch device 101 due to erroneous connection
between the ports in the switch device 102 or 103 and a
loop is configured.
(3) Case where a frame transmitted from the switch device
101 to the switch device 102 or 103 is transmitted from the
switch device 103 or 102 to the switch device 101 via
switch devices (not illustrated in the drawings) under
control of the switch devices 102 and 103 and a loop is
configured.
(4) Case where a frame transmitted from the switch device
101 is received by the switch device 101 to be the
transmission origin via the backbone network 100 from the
switch device 102 or 103 of the lower network.
Fig. 3 is a block diagram illustrating an internal
configuration example of the switch device 101 including
the loop detection function and illustrates a path along
which a loop detection frame to be an example of loop
13
detection data is transmitted to internal components of the
switch device 101.
The switch device 101 includes a plurality of ports
301-1 to 301-3 to exchange data with an external device and
a plurality of physical layers 302-1 to 302-3. The switch
device 101 further includes a frame transfer/port control
unit 303, a loop detection frame reception control unit
304-1, a loop detection frame transmission control unit
304-2, and a loop detection control unit 305. Hereinafter,
when the ports 301-1, 301-2, and 301-3 do not need to
distinguish from each other in particular or are
collectively called, they are described as the port 301.
Likewise, when the physical layers 302-1, 302-2, and 302-3
do not need to distinguish from each other in particular or
are collectively called, they are described as the physical
layer 302.
The physical layer 302 corresponds to a first layer
that defines physical connection and a transmission method
of a network in an OSI reference model established by the
International Organization for Standardization (OSI: Open
Systems Interconnection), for example.
The frame transfer/port control unit 303 (example of
a transmission unit and a port control unit) has a frame
transfer function for performing transfer (input/output
process) of all frames processed by the switch device 101,
14
including the loop detection frames, and a port control
function for executing a closing process and an opening
(non-closing) process of the port 301. When the frame
transfer/port control unit 303 closes the port, the frame
transfer/port control unit 303 does not link up
(communication enabling state) with the port 301 of a
closing target. That is, the frame transfer/port control
unit 303 executes an interception process on the physical
layer 302 connected to the port 301 of the closing target
and links down (communication disabling state) with the
port 301 of the closing target. As a result, even when the
physical layer 302 receives the frame by the port 301, the
received frame is not transferred to the frame
transfer/port control unit 303.
The loop detection frame reception control unit 304-
1 receives only the loop detection frame among all of the
frames processed by the switch device 101 from the frame
transfer/port control unit 303 and transmits the loop
detection frame to the loop detection control unit 305.
The loop detection frame transmission control unit
304-2 receives only the loop detection frame among all of
the frames processed by the switch device 101 from the loop
detection control unit 305 and transmits the loop detection
frame to the frame transfer/port control unit 303.
15
The loop detection control unit 305 (example of a
determination unit) receives the loop detection frame from
the loop detection frame reception control unit 304-1 or
transmits the loop detection frame to the loop detection
frame transmission control unit 304-2.
When the loop detection frame is received by the
port 301-1 (example of one port), the loop detection frame
is transmitted to the physical layer 302-1 via a signal
line 312. The loop detection frame is transmitted from the
physical layer 302-1 to the frame transfer/port control
unit 303 controlling transmission and reception of all of
the frames in the switch device 101 via a signal line 322.
Then, the loop detection frame is transmitted to the loop
detection frame reception control unit 304-1 via a signal
line 331 and is transmitted to the loop detection control
unit 305 via a signal line 341.
When the loop detection frame is transmitted from
the port 301-1, the loop detection frame is transmitted
from the loop detection control unit 305 to the loop
detection frame transmission control unit 304-2 via a
signal line 342 and is transmitted to the frame
transfer/port control unit 303 via a signal line 332. Then,
the loop detection frame is transmitted to the physical
layer 302-1 via a signal line 321 and is transmitted to the
port 301-1 via a signal line 311.
16
Similarly, even when the frame is transmitted and
received by the port 301-2 (example of other port), the
frame is transmitted and received between the port 301-2
and the physical layer 302-2 via signal lines 313 and 314.
In addition, the frame is transmitted and received between
the physical layer 302-2 and the frame transfer/port
control unit 303 via signal lines 323 and 324.
For the port 301-3 connected to the backbone network
100 via the communication line 201, a transmission path of
the frame is the same. The frame is transmitted and
received between the port 301-3 and the physical layer 302-
3 via signal lines 315 and 316. In addition, the frame is
transmitted and received between the physical layer 302-3
and the frame transfer/port control unit 303 via signal
lines 325 and 326.
When the port 301 is closed, a port closing command
350 is issued from the loop detection control unit 305 and
is received in the frame transfer/port control unit 303.
In addition, the frame transfer/port control unit 303 has a
structure in which port closing control is executed on the
physical layer 302 and the corresponding port 301 is closed.
When the loop is detected or the port closing by the
loop detection is performed, information thereof may be
provided to a user or a terminal. For example, the
information for the loop detection or the port closing may
17
be written to a management information base (MIB) to allow
the user to view the information. Alternatively, the
information may be displayed on an LED provided in the
corresponding port or may be displayed on a terminal
connected to the switch device 101 and a notification
mechanism does not matter.
In the following description, when transmission and
reception of the frame between the loop detection control
unit 305 and the port 301 are described, description of the
physical layer 302, the frame transfer/port control unit
303, the loop detection frame reception control unit 304-1,
and the loop detection frame transmission control unit 304-
2 existing between the loop detection control unit 305 and
the port 301 is appropriately omitted.
[Frame format of loop detection frame]
Here, a frame format of the loop detection frame
transmitted and received by the switch device 101 will be
described.
Fig. 4 is a diagram illustrating an example of the
frame format of the loop detection frame.
The loop detection frame uses the L2 control frame
and has a DA 401, an SA 402, a first fixed value 403, a
second fixed value 404, a transmission time 405, a MAC
address 406, a third fixed value 407, a transmission origin
port number 408, a fourth fixed value 409, a padding 410,
18
and a frame check sequence (FCS) 411 as fields. The fields
from the second fixed value 404 to the fourth fixed value
409 are unique information of the loop detection frame.
The DA 401 is a destination MAC address and uses a
reserved unique MAC address. The SA 402 is a transmission
origin MAC address and uses a MAC address of a self device.
Each of the first fixed value 403, the second fixed value
404, the third fixed value 407, and the fourth fixed value
409 is a bit string inserted to set a data length of the
loop detection frame to a fixed data length.
The transmission time 405 is a time when the loop
detection frame is transmitted from the self device. The
MAC address 406 is a MAC address of a port of a
transmission origin having transmitted the loop detection
frame. The transmission origin port number 408 is a port
number of the port of the transmission origin having
transmitted the loop detection frame.
The padding 410 is a field having any data length
(in Fig. 4, 10 bytes), which is inserted for a padding
process to set the data length of the loop detection frame
to the fixed data length (for example, 64 bytes). The FCS
411 is a field added to check whether there is no error in
the received frame. As an example of the FCS, a cyclic
redundancy check (CRC) is used.
19
In this embodiment, the transmission origin port
number 408 in the loop detection frame is used as the
transmission origin port information. When the reception
port is not in the closing state, a process for closing the
port of the transmission origin is executed.
[Loop detection determination process]
Fig. 5 is a flowchart illustrating a loop detection
determination process according to the first embodiment of
the present invention. Here, an example of the case where
the loop detection frame is received by the two ports (for
example, the ports 301-1 and 301-2) connected to the lower
network of the switch device 101 will be described.
As a premise, the loop detection control unit 305 of
the switch device 101 causes the ports 301-1 to 301-3 to
enter a non-closing state (enable) by default and enables
communication by the ports 301-1 to 301-3 (linkup).
The loop detection control unit 305 executes control
such that the loop detection frames are simultaneously
transmitted (multicast transmission) from the ports 301-1
to 301-3 to many and unspecified transmission destinations
by the frame transfer/port control unit 303 at a fixed
cycle. In actuality, for the convenience of a process of
the frame transfer/port control unit 303, the loop
detection frames are sequentially transmitted from the
ports 301-1 to 301-3 with a slight time difference. At
20
this time, information of a transmission origin port number
is included as information (transmission origin port
information) regarding the port transmitting each loop
detection frame in each of the transmitted loop detection
frames (refer to Fig. 4). In addition, information showing
multicast is included in the DA 401 (destination MAC
address) of the frame detection frame (refer to Fig. 4).
In an actual network system, a loop is formed by a
further complex path. The transmission and reception ports
are not fixed and the loop detection frames are transmitted
from all of the ports of the switch device 101, so that
omission of a check is removed. The loop detection frames
are preferably transmitted from a large number of ports.
When the frame is received by the port 301, the loop
detection control unit 305 determines whether the received
frame is the loop detection frame, that is, whether the
loop detection frame is received (step S1). When the loop
detection frame is not received (NO of step S1), the loop
detection control unit 305 continuously monitors the loop
detection frame. When the loop detection frame is not
detected for a constant time, the loop detection
determination process ends.
Meanwhile, in the determination process of step S1,
when the loop detection frame is received (YES of step S1),
the loop detection control unit 305 acquires that the loop
21
detection frame is received by the port 301 and acquires a
port number (reception port number) of the corresponding
port 301 (step S2).
Next, the loop detection control unit 305 acquires
the transmission origin port number 408 from the received
loop detection frame (step S3).
Then, the loop detection control unit 305 acquires
ON/OFF information of port closing of the port 301
corresponding to the reception port number, that is, state
information showing whether the port is closed (step S4).
When the port closing is turned on, the port is in the
closing state and when the port closing is turned off, the
port is not in the closing state.
Next, the loop detection control unit 305 determines
whether the port closing of the port 301 corresponding to
the reception port number is turned off (step S5). The
loop detection control unit 305 executes a determination
process sequentially from the port having received the loop
detection frame. At the time of the determination process,
when the port closing of the port 301 is turned off (YES of
step S5), the loop detection control unit 305 executes a
process for closing the transmission origin port by the
frame transfer/port control unit 303 (step S6). After the
process ends, the loop detection control unit 305 ends the
loop detection determination process.
22
In the determination process of step S5, when the
port closing of the port 301 corresponding to the reception
port number is turned on (NO of step S5), the loop
detection control unit 305 ends the loop detection
determination process with no process executed on the port
301.
[Specific example of loop detection determination process]
A specific example of the loop detection
determination process will be described with reference to
Fig. 6.
Fig. 6 is a sequence diagram illustrating an outline
of loop occurrence at the time of erroneous network
connection in the first embodiment of the present invention.
Here, an example of the case where the loop detection
frames are transmitted from the ports 301-1 and 301-2 of
the switch device 101 will be described.
First, the loop detection control unit 305 of the
switch device 101 transmits (multicasts) the loop detection
frames from the port 301-1 (hereinafter, referred to as the
“first port”) and the port 301-2 (hereinafter, referred to
as the “second port”) to many and unspecified transmission
destinations (steps S11 and S12). At this time,
transmission origin port information is added to each of
the loop detection frames transmitted from the first port
and the second port.
23
In addition, the loop detection control unit 305 of
the switch device 101 receives the loop detection frame
transmitted from the first port by the second port (step
S13). Next, the switch device 101 receives the loop
detection frame transmitted from the second port by the
first port (step S14).
The switch device 101 executes a determination
process on a state of the second port having received the
loop detection frame with a predetermined time lag after
the second port receives the loop detection frame. The
time lag changes according to a process speed of the loop
detection control unit 305. In addition, when the second
port is not in the closing state, the loop detection
control unit 305 of the switch device 101 executes a
process (port closing) for closing the first port to be a
transmission origin of the loop detection frame by the
frame transfer/port control unit 303 (step S15).
Next, the loop detection control unit 305 of the
switch device 101 executes the determination process on a
state of the first port having received the loop detection
frame later than the second port (step S16). Here, there
is the time lag until the loop detection control unit 305
executes the determination process on the state of the
first port after the loop detection control unit 305
detects that the loop detection frame has been received by
24
the first port. For this reason, when the determination
process is executed, the first port is already closed and
the loop detection control unit 305 determines that the
first port is closed. In addition, the loop detection
control unit 305 ends the loop detection determination
process without closing the second port to be the
transmission origin of the loop detection frame received by
the first port.
In the first embodiment configured as described
above, the transmission origin port number is included in
the loop detection frame transmitted from the port of the
switch device 101 connected to the backbone network 100.
In addition, when the loop detection frame is detected by
the switch device 101, the process for causing the
transmission origin port to enter the closing state is
executed in the case where the reception port having
received the loop detection frame is not in the closing
state and the process for causing the transmission origin
port to enter the closing state is not executed in the case
where the reception port is in the closing state. By the
loop detection determination process, a situation where all
of the ports having received the loop detection frames are
closed can be prevented. Therefore, complex setting is not
necessary as in the related art, a communication
maintenance range of a network can be widely maintained at
25
the time of an operation of a loop configuration prevention
function using the loop detection frames, and a loop
configuration can be prevented without reducing a
communication range.
By the loop detection determination process, a loop
(infinite circulation) of a broadcast frame can be
prevented by executing the closing process on the port
quickly, when the loop occurs in the network. Therefore,
the breakdown of the whole network system can be prevented
from occurring due to the loop of the broadcast frame.
<2. Second embodiment>
Next, a second embodiment of the present invention
will be described with reference to Figs. 7 and 9.
In a spanning tree (route selection algorithm) such
as an STP and a rapid STP (RSTP), one normally used path is
set by exchanging control information called a bridge
protocol data unit (BPDU) between bridges, on the basis of
given priority, and the other paths are set as bypass paths
at the time of a failure. In the spanning tree, a blocking
state in which a frame is not transferred to each port and
a non-blocking state (hereinafter, referred to as the
“forwarding state”) in which the frame is transferred are
switched, a path of frames is set, and a loop configuration
is prevented logically. The RSTP is obtained by improving
26
the STP and shortening a time until the path is completely
switched when there is a topology change.
In the blocking state, in a configuration of a
network system, even though a loop is formed, a path is set
by software, so that a loop detection control unit 305 does
not receive a loop detection frame. For this reason, the
blocking state of the port changes to the forwarding state
due to a certain factor, so that the loop may be formed.
Therefore, in the second embodiment, a change in the
blocking state of a port of a switch device is monitored
and the loop detection determination process (refer to Fig.
5) in the first embodiment is executed according to a
result thereof.
Fig. 7 is a diagram illustrating a state before the
blocking state of the switch device changes.
Fig. 8 is a diagram illustrating a state after the
blocking state of the switch device changes.
Fig. 9 is a flowchart illustrating a blocking state
change monitor process according to the second embodiment
of the present invention.
A configuration of a network system 1A illustrated
in Figs. 7 and 8 is the same as the configuration of the
network system 1 of Fig. 2. That is, a port of a switch
device 102 and a port of a switch device 103 are
erroneously connected to each other. In addition, a
27
configuration of a switch device 101A of the network system
1A is the same as the configuration of the switch device
101 of Fig. 3. However, in the switch device 101A of the
network system 1A, the spanning tree (for example, the STP
or the RSTP) to be a type of loop suppression function
starts. A port 301-1 of the switch device 101A is set as a
first port and a port 301-2 thereof is set as a second port.
The second port of the switch device 101A
illustrated in Fig. 7 is set to the blocking state by
setting the STP/RSTP. When the second port of the switch
device 101A is in the blocking state, the blocking state of
the second port is released due to a certain failure and
the state of the second port changes to the non-blocking
state (forwarding state) as illustrated in Fig. 8. The
state of the second port of the switch device 101A changes
to the forwarding state, so that a loop using the switch
devices 101A, 102, and 103 as a path is formed, and a
broadcast frame may circulate infinitely. To prevent such
a situation, the port state change monitor process
illustrated in Fig. 9 is executed in the switch device 101A.
[Port state change monitor process]
First, a loop detection control unit 305 of the
switch device 101A acquires blocking state information (a)
of each port (step S21).
28
With a delay (standby time) of a predetermined time
(for example, one second) after a process of step S21 is
executed (step S22), the loop detection control unit 305
acquires blocking state information (b) of each port again
(step S23).
Then, the loop detection control unit 305 determines
whether the state of the second port changes from the
blocking state to the forwarding state, on the basis of the
blocking state information (a) of each port acquired in
step S21 and the blocking state information (b) of each
port acquired in step S23 (step S24). When the state of
each port does not change from the blocking state to the
forwarding state (NO of step S24), the loop detection
control unit 305 ends the port state change monitor process.
In a determination process of step S24, when the
state of the port changes from the blocking state to the
forwarding state (YES of step S24), the loop detection
control unit 305 executes a process for transmitting a loop
detection frame from the port (second port) of which the
state has changed from the blocking state to the forwarding
state (step S25).
Then, because a loop configuration occurs due to a
communication line 210 to be erroneously connected, the
loop detection frame is received by a different port (first
29
port) of the switch device 101A and the loop detection
determination process of Fig. 5 operates (step S26).
In addition, in the loop detection determination
process, when the port (first port) having received the
loop detection frame is not in the closing state, a closing
process is executed on the second port to be a transmission
origin of the loop detection frame. Therefore, frames
cannot be transmitted and received between the second port
of the switch device 101A and the switch device 103 and a
state of a network system returns to an original state
(refer to Fig. 7) in which the frames do not loop.
According to the second embodiment having the
configuration described above, the loop can be prevented
surely by combining the loop suppression function such as
the spanning tree according to the related art and the loop
detection determination process according to the first
embodiment.
In the second embodiment, when it is determined that
the state of the port changes from the blocking state to
the forwarding state, by the blocking state change monitor
process illustrated in Fig. 9, the loop detection
determination process of Fig. 5 is executed. For this
reason, when the state of the port of the switch device
changes from the blocking state to the forwarding state and
the loop of the loop detection frame occurs, the closing
30
process is executed quickly on the corresponding port and
the loop (infinite circulation) of the broadcast frame is
prevented. Therefore, breakdown of the whole network
system can be prevented from occurring due to the loop of
the broadcast frame.
<3. Third embodiment>
Next, a third embodiment of the present invention
will be described with reference to Fig. 10.
The number of ports of a switch device connected to
a backbone network may be four or more. The third
embodiment illustrates an example of the case where the
number of ports of the switch device connected to the
backbone network is four or more.
Fig. 10 is a block diagram illustrating a
configuration example of a network system according to the
third embodiment of the present invention. In a network
system 1B illustrated in Fig. 10, a switch device 101B
connected to a backbone network 100 includes a port 301-4
in addition to ports 301-1 to 301-3. The port 301-4 of the
switch device 101B is connected to a switch device 104 of a
lower network via a communication line 204. Three
communication apparatuses 117 to 119 are connected to the
switch device 104 via communication lines 217 to 219.
31
The port 301-4 exchanges a loop detection frame with
a frame transfer/port control unit 303 via signal lines 317
and 318, a physical layer 302-4, and signal lines 327 and
328.
The present invention is not limited to the
embodiments described above and various applications and
modifications can be made without departing from the scope
of the present invention.
For example, the configurations of the devices and
the systems are described specifically in the embodiments
to facilitate the description of the present invention and
the embodiments are not limited to embodiments in which all
of the described configurations are included. In addition,
a part of the configurations of the certain embodiment can
be replaced by the configurations of another embodiment.
In addition, the configurations of another embodiment can
be added to the configurations of the certain embodiment.
In addition, for a part of the configurations of the
individual embodiments, other configurations can be added,
deleted, and replaced.
In addition, a part or all of the individual
configurations, functions, processing units, and processing
mechanisms may be designed by integrated circuits and may
be realized by hardware. In addition, the individual
configurations and functions may be realized by software by
32
analyzing programs for realizing the functions by a
processor and executing the programs by the processor.
Information such as the programs for realizing the
individual functions, the tables, and the files may be
stored in a recording device such as a memory, a hard disk,
and a solid state drive (SSD) or a recording medium such as
an IC card, an SD card, and a DVD.
In addition, only control lines or information lines
necessary for explanation are illustrated and the control
lines or information lines do not mean all control lines or
information lines necessary for a product. In actuality,
almost all configurations may be connected to each other.
In addition, in the present specification, the
process steps describing the time-series processes include
processes executed in time series according to described
order and processes (for example, parallel processes or
object processes) executed in parallel or individually,
without being executed in time series.
33
We claim:
1. An information processing apparatus comprising:
a plurality of ports that transmit and receive data;
a transmission unit that transmits loop detection
data including transmission origin port information to
detect a loop configuration from each of the plurality of
ports;
a determination unit that determines whether other
port having received the loop detection data is in a
closing state, when the loop detection data transmitted
from one port among the plurality of ports is received by
other port; and
a port control unit that executes a process for
causing one port having transmitted the loop detection data
to enter the closing state, when other port having received
the loop detection data is not in the closing state at the
time of a determination process by the determination unit,
and does not execute the process on one port, when other
port is in the closing state.
2. The information processing apparatus according to
claim 1, wherein
there is a time lag until the determination unit
determines whether other port having received the loop
34
detection data is in the closing state, after the loop
detection data is received by other port.
3. The information processing apparatus according to
claim 1 or 2, wherein
when a loop suppression function using a route
selection algorithm starts, the port control unit monitors
states of the plurality of ports, and
in the case where there is a port of which a state
has changed from a blocking state in which the data is not
transferred by the loop suppression function to a nonblocking
state, the port control unit transmits the loop
detection data from the port.
4. The information processing apparatus according to
claim 1, wherein
the transmission unit multicasts the loop detection
data from all of the plurality of ports.
5. A network system comprising at least a first
information processing apparatus, a second information
processing apparatus, and a third information processing
apparatus, wherein
the first information processing apparatus
comprises:
a plurality of ports that have a port connected to
the second information processing apparatus and a port
35
connected to the third information processing apparatus and
transmit and receive data;
a transmission unit that transmits loop detection
data including transmission origin port information to
detect a loop configuration from each of the plurality of
ports;
a determination unit that determines whether other
port having received the loop detection data is in a
closing state, when the loop detection data transmitted
from one port among the plurality of ports is received by
other port; and
a port control unit that executes a process for
causing one port having transmitted the loop detection data
to enter the closing state, when other port having received
the loop detection data is not in the closing state at the
time of a determination process by the determination unit,
and does not execute the process on one port, when other
port is in the closing state.