JPH0738597A - Bridge device - Google Patents

Abstract

(57) [Summary] [Purpose] To make it possible to easily identify address duplication where there are multiple terminals with the same address. [Structure] For example, a frame from a terminal C is transferred to a bridge device 1
When received by 0-1 to 10-3, the address b of the terminal C
Search the address learning tables 12-1 to 12-3 with
If the address information including the address b is registered,
The branch line LAN address in the same address information is checked for a match with the address of the branch line LAN interface 11-3 connected to the terminal C via the network n3. If they do not match, the terminal having the address b is checked. Address information about the source terminal C is registered in the duplicate address tables 13-1 to 13-3 as a plurality of terminals, and the address information about the terminal B having the address b is stored in the table 12.
Even if the address information is registered in -1 to 12-3, the address information is not rewritten.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bridge device for connecting networks and relaying frames between them.

[0002]

2. Description of the Related Art Generally, all networks connected by a bridge device of this type must behave as the same network. Therefore, when a bridge device receives a frame from a network, it normally sends the frame to all networks to which it is connected.

However, if this is always continued, too many frames will flow on the network and the network will be congested. It can be said that the role of the bridge device is to organize them. That is, the bridge device learns the network to which the source terminal is connected from the source address of the frame that has passed through the device once, and the frame addressed to the terminal device is directly transmitted to the network.

A conventional frame transmission process of the bridge device having such an address learning function will be described with reference to FIGS. FIG. 5 shows that optical network N serving as a trunk LAN and bus networks n1 to n3 serving as branch LANs are connected to bridge devices 1-1 to 1 respectively.
An example of a network system connected via -3 is shown. Here, the optical ring type network N is not seen as a network from the outside.

The bridge devices 1-1, 1-2, 1-3 are network interfaces (hereinafter referred to as branch line LAN interfaces) 11-1, 11-2, 11-3 connected to the networks n1, n2, n3. , And address learning tables 12-1, 12-2, 12-3. The addresses of the branch line LAN interfaces 11-1, 11-2, 11-3 (internal addresses handled by the bridge devices 1-1, 1-2, 1-3, and hereinafter referred to as branch line LAN addresses) are "00".
20 "," 0120 ", and" 0220 ".

Terminals A, B and C are connected to the networks n1, n2 and n3, respectively. This terminal A,
The addresses of B and C (terminal addresses) are a,
b and c.

For example, the bridge device 1-1 of the system shown in FIG.
In the state where nothing has been transmitted yet, nothing is recorded in the address learning table 12-1. In this state, when a frame is transmitted from the terminal A on the network n1 to the terminal B as indicated by reference numeral 501 in FIG. 5, the bridge device 1-1 receives the frame addressed to the terminal B. (FIG. 7, step 701).

In this case, the bridge device 1-1 retrieves the address of the destination terminal B from the address learning table 12-1 (step 702 in FIG. 7), but since the same address has not been learned yet, the address learning table 12 is obtained. -1 does not exist, the frame is transmitted to all networks (except network n1), that is, networks n2 and n3 (to which terminals B and C are connected) (step 703 in FIG. 7).

Next, the bridge device 1-1 has an address (address of the branch LAN interface 11-1) "002".
The address information indicating that the terminal A is connected to 0 "(a set of the address a of the terminal A and" 0020 ") is shown in FIG.
As shown in FIG. 7, address learning to be registered in the entry (the first-stage entry in the figure) in the address learning table 12-1 is performed (steps 705 and 706 in FIG. 7). Similar learning is also performed by the bridge devices 1-2 and 1-3.

As a result of the learning in the bridge device 1-1, when the bridge device 1-1 receives a frame whose destination address is the address a (addressed to the terminal A), the bridge device 1-1 receives the frame. Can be delivered to A.

Next, assuming that the frame transmission from the terminal B to the terminal A is performed as indicated by reference numeral 502 in FIG. 5, each of the bridge devices 1-1 to 1-3 has the above-mentioned terminal A to the terminal A. In the same manner as in the case of frame transmission to B, terminal B
Learn the connected network of. As a result, the content of the address learning table 12-1 of the bridge device 1-1 becomes as shown in FIG. 6B, for example.

Similarly, when a frame is transmitted from the terminal C as indicated by reference numeral 503 in FIG. 5, each of the bridge devices 1-1 to 1-3 learns the network to which the terminal C is connected. As a result, the content of the address learning table 12-1 of the bridge device 1-1 becomes, for example, as shown in FIG. 6C, which means that the addresses of all the terminals A to C have been learned. This also applies to the other bridge devices 1-2 and 1-3.

When the frame transmission addressed to the terminal learned as described above is relayed, it is transmitted only to the network existing between them (step 704 in FIG. 7), and is not transmitted to other networks, so that the network traffic is lost. Leads to a decrease in For example, when transmitting from terminal A to terminal B, if it is before learning, terminal C
Is also transmitted to the network n3 connected to the destination terminal B (steps 702 and 703 in FIG. 7), but if it is learned, it is transmitted only to the network n2 connected to the destination terminal B (steps 702 and 704 in FIG. 7) and terminal C. Network n
3 is not sent.

Address learning tables 12-1 to 12-12
-3 needs to be updated as the network changes, in addition to the above learning. Therefore, generally, when the address is learned (registered) in step 706 of FIG. 7, the initial value of the survival time is registered (recorded) at the same time, and the survival time is subtracted with the lapse of time. When it becomes "0", the address is deleted (erased) from the tables 12-1 to 12-3. If the corresponding terminal transmits before this survival time becomes “0”, the survival time is updated to the initial value again (step 7 in FIG. 7).
05, 707, 708) and continue the subtraction.

As described above, the address learning tables 12-1 to 12-1 ...
The registration information in 12-3 is deleted from the tables 12-1 to 12-3. There are two reasons for performing this erasing.

First, it is unlikely that a terminal that is not communicating (not transmitting) exists in the network indicated by the addresses recorded in the address learning tables 12-1 to 12-3, and This is because there is a high possibility that they have moved to the other network. That is, when the terminal is moving on the network, communication cannot be made forever if the previous record is used.

Second, address learning tables 12-1 to 12-1
The number of terminals that can be recorded in 2-3 is finite, and if there are many terminals that communicate through the bridge devices 1-1 to 1-3, the processing cannot be completed or the processing speed becomes slow. This is because it is better to delete the address information for the terminals that are not used. In this way, by deleting the address information of the terminals that are not used much from the address learning tables 12-1 to 12-3, the table 12
-1 to 12-3 becomes small, the number of addresses to be managed decreases, and the processing speed of the bridge devices 1-1 to 1-3 is improved.

However, in the network system in which the networks are connected by the conventional bridge device having the address learning function as described above, there is a problem when a plurality of terminals having the same address exist. Regarding this problem, the flowchart of FIG.
It will be described with reference to FIGS. The same parts as those in FIG. 5 are designated by the same reference numerals.

First, as shown in FIG.
The communication is performed only by the terminals A and B connected to the terminals 1 and n2, and the frame transmission from the terminal A indicated by the reference numeral 801 to the terminal B is performed first, and then the communication from the terminal B indicated by the reference numeral 802 to the terminal A.
It is assumed that the transmission is made to. At this time, it is assumed that no terminal is connected to the network n3.

Then, the contents of the address learning table 12-1 of the bridge device 1-1 are initially as shown in FIG. 9 (a).
After that, it becomes as shown in FIG. As long as frame transmission is performed only between the terminals A and B in the state of FIG. 9B,
Communication is performed only by the network n1 and the network n2.

Here, the terminal B is designated by reference numeral 80 in FIG.
4, the network n2 to the network n
3 and transmits from the terminal B (here, reference numeral 80
It has been transmitted to the terminal A as indicated by 3.

Then, in response to changes in the network,
In the address learning table 12-1 of the bridge device 1-1,
As shown in FIG. 9C, the second-stage entry in which the address information about the terminal B is registered (that is, the address b of the terminal B and the bridge device 1 in which the terminal B is connected via the network n2). The bridge device 1 connected to the address b of the terminal B and the network n3 to which the terminal B has moved is registered in the entry registered with the address "0120" of the branch LAN interface 11-2 of -2). Address "0" of branch line LAN interface 11-3 of 3
220 "is overwritten (step 705 in FIG. 7).
707, 709). In this way, when transmission is performed from the terminal B moved from the network n2 to the network n3, the address information registered in the learning table 12-1 for the terminal B is re-registered as new address information. .

As a result, when the frame is transmitted from the terminal A to the terminal B thereafter, the frame from the terminal A (not the network n2) is transmitted to the terminal B of the network n3.
Can be delivered to.

Next, a case where there are a plurality of terminals having the same address will be described. First, as shown in FIG. 10, it is assumed that the terminals B and C have the same address b. Here, as indicated by reference numerals 1001 and 1002 in FIG. 10, as a result of communication being performed only between the terminals A and B, the contents of the address learning table 12-1 are shown in FIG.
After changing as shown in (a) and (b), when the terminal C transmits (transmits to the terminal A as indicated by reference numeral 1003 here), the terminal B sees from the bridge device 1-1 and the terminal B transmits to the network n.
This is the same as moving from 2 to network n3.

In this case, in the address learning table 12-1 of the bridge device 1-1, as shown in FIG.
The set of the address b of the terminal C and the address “0220” of the branch line LAN interface 11-3 of the bridge device 1-3 is overwritten (in the second entry in which the address information of the terminal B is registered) (see FIG. 7 Steps 705, 707, 7
09). The contents of the address learning table 12-1 shown in FIG. 11C are the same as when the terminal B shown in FIG. 9C moves from the network n2 to the network n3.

Therefore, after this, for example, even if the terminal A tries to transmit a frame to the terminal B, the address information (address learning result) of the terminal B disappears from the address learning table 12-1 and instead has the same address b. Since the address information of the terminal C is written, the frame from the terminal A is transmitted to the network n3 (terminal C above).

When terminal B again transmits in this state, the address learning table 12-1 is shown in FIG.
Return to the state of (b). Then, contrary to the case of the state of FIG. 11C, while the communication to the terminal B becomes possible,
Communication with the terminal C becomes impossible.

As described above, when the addresses of different terminals are duplicated, communication to that terminal may or may not be executed depending on the timing, resulting in an unstable state. Also, due to this instability, the cause is difficult to find.

[0029]

As described above, in the network system to which the conventional bridge device is applied, when there are a plurality of terminals having the same address, in some cases, it operates normally normally, In some cases, it takes time, and in some cases, communication becomes unstable, and communication becomes unstable.

On the other hand, the communication protocol often performs mutual transmission / reception due to complicated operations, and often retransmits data when the data does not reach the transmission destination. There is a problem that it is difficult to find an abnormality in the network because communication is often possible even in such a state.

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a bridge device in which a plurality of terminals having the same address exist and address duplication can be easily determined.

[0032]

The bridge device of the present invention comprises a detecting means for detecting a transmission from a terminal having the same address as a terminal whose address information is registered in the address learning table but having a different connection destination network. , A duplicate address table for registering address information about the terminal detected by the detecting means and the network to which the terminal is connected, and the address information is registered in the address learning table by the detecting means. When transmission from a terminal that has the same address as the terminal but a different connection destination network is detected, this connection destination network is replaced by replacing the address information with the address information of the terminal whose connection destination network is different. Register the address information of different terminals in the above duplicate address table. It is characterized in.

[0033]

In the above configuration, for example, in a state where the address information about a certain terminal B and the network to which the terminal B is connected is already registered in the address learning table,
It is assumed that another terminal C having the same address as the terminal B has transmitted.

In this case, conventionally, it is assumed that the terminal has moved from the network indicated by the address information registered in the address learning table to another network indicated by the source address, and has already been registered in the address learning table. Since the address information of was rewritten to new address information, the original address information did not remain in the address learning table. Therefore, there is no problem if the terminal actually moves to another network, but if it is another terminal C having the same address and connected to another network as described above, Since the address information of B is lost and the address of terminal C is learned instead, even if a certain terminal tries to send to terminal B, it is sent to the network to which terminal C is connected. However, the inconvenience described in the section [Problems to be solved by the invention] occurs.

On the other hand, in the above configuration, the address information about the terminal B is not rewritten to the address information about the terminal C having the same address.
The address information about the terminal B is left in the address learning table, and instead, the address information about the terminal C is registered (recorded) in the duplicate address table.

Therefore, when a certain terminal tries to transmit to the terminal B, since the address information about the terminal B is left in the address learning table, it is correctly transmitted to the network to which the terminal B is connected. To be done.
Further, by checking the contents of the duplicate address table, the address of the duplicated terminal and the connection destination network of the terminal can be easily grasped.

On the other hand, if the transmitting terminal is the terminal B moved to another network, communication from the network before the movement by the terminal B (frame transmission) is stopped.
Therefore, the address information about the terminal B before moving, which remains in the address learning table, is erased after a certain period of time, and thereafter, the address information about the terminal B after moving is registered in the address learning table. hand,
Communication according to the address information becomes possible.

[0038]

1 is a block diagram showing an embodiment of a network system to which a bridge device of the present invention is applied. The same parts as those in FIGS. 5, 8 and 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the system of FIG. 1, the conventional bridge device 1-1 used in FIGS. 5, 8 and 10 is used.
Instead of 1-2 and 1-3, a bridge device 10- having a new configuration
1, 10-2, 10-3 are used. The bridge devices 10-1, 10-2 and 10-3 are conventional bridge devices 1-
Similar to 1, 1-2, 1-3, the branch line LAN interfaces 11-1, 1-2, 1-3 and the address learning table whose addresses (branch LAN addresses) are “0020”, “0120”, and “0220”. In addition to having 12-1, 12-2, 12-3,
It newly has duplicate address tables 13-1, 13-2, 13-3.

Duplicate address table 13-i (i = 1 to 1
3) shows that while the address information of the terminals registered in the address learning table 12-i is held in the table 12-i, other terminals having the same address (other terminals connected to other networks) This is used to register the address information of the other terminal instead of overwriting (rewriting the address information) to the address learning table 12-i when the terminal transmits.

Next, the operation of the bridge devices 10-1 to 10-3 in the system of FIG. 1 will be described with reference to FIGS. 2 is a diagram showing an example of the contents of the address learning table 12-1 of the bridge device 10-1, FIG. 3 is a diagram showing an example of the contents of the duplicate address table 13-1 of the bridge device 10-1, and FIG. 3 is a flowchart for explaining a frame transmission procedure of the bridge devices 10-1 to 10-3.

First, in the example of the system shown in FIG. 1, a terminal B connected to the bridge device 11-2 via the network n2 and a terminal C connected to the bridge device 10-3 via the network n3, It is assumed that they have the same address b.

Here, in the system of FIG. 1, no transmission has been performed yet, and therefore the bridge devices 10-1 to 10-1.
It is assumed that nothing is recorded in the address learning tables 12-1 to 12-3 of 0-3.

In this state, when the frame transmission from the terminal A to the terminal B on the network n1 is performed, as indicated by reference numeral 101 in FIG. 1, for example, the bridge device 10
-1 receives the frame addressed to the terminal B (step 401 in FIG. 4).

In this case, the bridge device 10-1 searches the address learning table 12-1 for the address of the destination terminal B (step 402 in FIG. 4), but since the address has not been learned yet, the address learning table 12 is obtained. -1 does not exist, the frame is transmitted to all networks (except network n1), that is, networks n2 and n3 (to which terminals B and C are connected) (step 403 in FIG. 4).

Next, the bridge device 10-1 has an address (address of the branch line LAN interface 11-1) "00".
The address information indicating that the terminal A is connected to 20 "(the set of the address a of the terminal A and" 0020 ") is shown in FIG.
As shown in (a), address learning to be registered in the entry (first entry in the figure) in the address learning table 12-1 is performed (steps 405 and 406 in FIG. 4). Similar learning is also performed by the bridge devices 10-2 and 10-3.

Address learning tables 12-1 to 12
When registering the address information to -3, the initial value of the survival time is registered in addition to the address information. The survival time added to the address information registered in the address learning tables 12-1 to 12-3 is subtracted as time passes. The bridge devices 10-1 to 10-3 erase the address information to which the survival time is added from the tables 12-1 to 12-3 when the survival time becomes "0". If the corresponding terminal transmits before this survival time becomes "0", the bridge devices 10-1 to 10-3
Resets the survival time to the initial value again (step 40 in FIG. 4).
5, 407, 408) and the subtraction is continued.

Next, assuming that the frame transmission from the terminal B to the terminal A is performed as indicated by reference numeral 102 in FIG. 1, the bridge devices 1-1 to 1-3 have the above-mentioned terminal A to the terminal A, respectively. In the same manner as in the case of frame transmission to B, terminal B
Learn the connected network of. The contents of the address learning table 12-1 at this time are shown in FIG.

Next, it is assumed that the frame transmission from the terminal C having the same address b as the terminal B to the terminal A is performed as shown by reference numeral 103 in FIG. At this time, in the address learning table 12-1 of the bridge device 10-1,
As shown in (b), the address information about the destination terminal A is registered, and the same address information is registered in the address learning tables 12-2, 12-3 of the other bridge devices 10-2, 10-3. There is. Therefore, when the bridge device 1-3 receives a frame having the address a as the destination address (addressed to the terminal A) from the terminal C via the network n3, the frame is received via the bridge device 10-1. It can be delivered to terminal A (steps 401 and 40 in FIG. 4).
2, 404).

When a frame is transmitted from the terminal C to the terminal A, each of the bridge devices 1-1 to 1-3 is connected to the terminal A.
Since the address information including the address b of the transmission source terminal C of the addressed frame is registered in the address learning tables 12-1 to 12-3, the branch line LAN address (“0120” in this case) in the registered address information. ) And the same terminal C are connected via the network n3 to the address of the branch LAN interface 11-3 (here, “022
0 ") (steps 405 and 407 in FIG. 4). In this example, a mismatch between both branch line LAN addresses is detected.

There are two reasons why the terminal address b matches and the branch LAN interface does not match. The first factor is that different networks n
This is the case where the addresses of different terminals B and C connected to the terminals 2, 2 and 3 overlap. The second factor is the network n
This is a case where the terminal B is moved from 2 to the network n3 and the terminal B after the movement is the terminal C.

In such a case, the bridge devices 1-1 to 1-3
Is different from the conventional one, assuming that the first factor is used instead of the second factor, and the terminal address b is duplicated in a plurality of terminals, the frame from the source terminal C to the terminal A addressed to Address information including the address b of the terminal C obtained from the address C and the address “0220” of the branch LAN interface 11-3 to which the terminal C is connected via the network n3 is registered in the duplicate address tables 13-1 to 13-3. (Step 409 in FIG. 4). At this time, note that unlike the conventional case, the address information for the terminal B having the same terminal address b on the address learning tables 12-1 to 12-3 is not rewritten by the address information.

The contents of the address learning table 12-1 at this time are shown in FIG. 2C, and the contents of the duplicate address table 13-1 are shown in FIG. As is clear from FIG. 2 (c), the contents of the address learning table 12-1 are the same as those in the state shown in FIG. 2 (b) before the frame transmission from the terminal C, and the address for the terminal B is not changed. Information is retained. This also applies to the other address learning tables 12-2 and 12-3.

Therefore, when a certain terminal tries to transmit to the terminal B, since the address information about the terminal B remains in the address learning tables 12-1 to 12-3, the terminal B is connected. Correctly transmitted to the network n2 that has been set up.

Further, the duplicate address tables 13-1 to 13-13
-3, the address information of the terminals having the duplicated addresses is registered, so that the same tables 13-1 to 13-3 are registered.
-By obtaining this information from -3, the address b of the terminal C that overlaps with other terminals and the branch line LA to which the terminal C is connected
The address "0220" of the N interface 11-3 can be easily grasped. As a result, the maintainability of the network is improved as compared with the conventional case. In order to obtain the information of the duplicate address from the duplicate address tables 13-1 to 13-3, the bridge management device, the network management device, or the monitoring protocol ( In accordance with a method of notifying management (monitoring) means such as SNMP) and outputting the information to the outside by the means, a method of displaying and outputting the information on a directly connected console device, or an instruction operation from a maintenance person, A method of outputting or the like can be applied.

Next, the mismatch of the branch LAN addresses is caused by the second factor, which is different from the present embodiment.
That is, a case where the transmission source terminal C is the terminal B moved from the network n2 to the network n3 will be described. In this case, since the terminal B does not exist on the network n2, communication (frame transmission) from the network n2 by the terminal B no longer occurs. Therefore,
The address information about the terminal B before moving, which remains in the address learning tables 12-1 to 12-3, is erased after the set survival time (fixed time) elapses.

When the frame information is transmitted from the terminal B after the movement, that is, the terminal C after the address information about the terminal B before the movement is deleted, the address information including the address b of the terminal C is stored in the address learning table. 12-1 to 12-3
Address of the terminal C, that is, an address including the address b of the terminal C and the address “0220” of the branch LAN interface 11-3 to which the terminal C is connected (via the network n3). The information is registered in the address learning tables 12-1 to 12-3 (steps 405 and 406 in FIG. 4). As a result, thereafter, the frame transmission to the terminal C is performed only to the network n3 connected to the terminal C according to the address information.

As described above, even if the cause of the mismatch of the branch LAN addresses is the movement of the terminals, even if the processing is performed as if the terminal addresses are duplicated, after the survival time (a fixed time) elapses, When the transmission to the terminal after the movement occurs, the address information about the terminal after the movement is registered in the address learning table, so that the communication according to the address information becomes possible.

In the above embodiment, when the terminal addresses are duplicated, the corresponding address information is unconditionally registered in the duplicate address tables 13-1 to 13-3. It may be possible to check whether the address information has already been registered, and register the duplicate address information only when it is not registered.

Further, the address information (and the survival time) about the source terminal is stored in the address learning tables 12-1 to 12-3.
Duplicate address table 1 when learning addresses to be registered in
3-1 to 13-3, and if the same address information exists, it is assumed that one terminal has moved to the network instead of a plurality of terminals having the same address.
The address information is stored in the duplicate address tables 13-1 to 13-13.
You may erase from -3.

[0061]

As described above in detail, according to the present invention,
Detects frame transmission from a terminal that has the same address as the terminal whose address information is registered in the address learning table but has a different network to connect to, and depending on this detection result, displays the corresponding address information in the address learning table. Since the address information of the terminals with different connection destination networks is registered in the duplicate address table without rewriting, from the information of this duplicate address table,
The address of the overlapping terminal and the network to which the terminal is connected can be easily grasped, and the maintainability of the network is improved.

Moreover, since the address information in the address learning table is not rewritten, even if there are a plurality of terminals having the same address, an unstable state such that communication can be performed or cannot be performed with respect to a certain terminal depending on the timing. Will not be invited.

Further, as a result of the terminal whose address information is registered in the address learning table moving to another network and the frame transmission from that terminal being performed thereafter, the terminals have overlapping addresses. Even if it is processed, the communication (frame transmission) from the network before moving by the terminal does not occur anymore, so the address information of the terminal before moving that remains in the address learning table is erased after a certain period of time. After that, since the address information about the terminal after the movement is registered in the address learning table and the communication is performed according to the address information, there is no inconvenience.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing an embodiment of a network system to which a bridge device of the present invention is applied.

FIG. 2 is a diagram showing an example of contents change of an address learning table 12-1 of a bridge device 10-1 in the system of FIG.

3 is a diagram showing an example of contents of a duplicate address table 13-1 of a bridge device 10-1 in the system of FIG.

FIG. 4 is a bridge device 10-1 to 10-3 in the embodiment.
6 is a flowchart for explaining the frame transmission procedure of FIG.

FIG. 5 is a diagram showing an example of a network system at the time of normal use to which a conventional bridge device is applied.

FIG. 6 is a diagram showing an example of changing the contents of an address learning table 12-1 of the bridge device 1-1 in the system of FIG.

FIG. 7 is a flowchart for explaining a frame transmission procedure of a conventional bridge device.

FIG. 8 is a diagram showing an example of a network system in which a terminal device is moved to which a conventional bridge device is applied.

9 is a diagram showing an example of changes in the contents of the address learning table 12-1 of the bridge device 10-1 in the system of FIG.

FIG. 10 is a diagram showing an example of a network system including a plurality of terminals having the same address to which a conventional bridge device is applied.

11 is a bridge device 10 in the system of FIG.
6 is a diagram showing an example of the contents of the address learning table 12-1 of No.

[Explanation of symbols]

10-1 to 10-3 ... Bridge device, 11-1 to 11-3 ... Branch line LAN interface, 12-1 to 12-3 ... Address learning table, 13-1 to 13-3 ... Duplicate address table, A
~ C ... terminal, N ... network (main line LAN), n1 ~
n3 ... Network (branch LAN).

Claims (1)

[Claims] 1. A bridge device that connects networks and relays a frame between them, and a network in which the source address of a frame once passed through the device itself and the address of the source terminal are connected to each other. Learning means for learning the relationship between, and an address learning table for registering address information about the terminal learned by this learning means and the network to which the terminal is connected,
In a bridge device having an erasing means for erasing the registration information in the address learning table for terminals that do not communicate even after a certain period of time, a terminal and an address in which the address information is registered in the address learning table A detection means for detecting transmission from terminals having the same connection destination but different connection networks; and a duplicate address table for registering the address information of the terminals detected by the detection means and the connection destination network of the terminal. If the detecting unit detects a transmission from a terminal having the same address as the terminal in which the address information is registered in the address learning table and having a different connection destination network, the address information is Instead of rewriting the address information of the terminal whose connection destination network is different, Bridge apparatus characterized by the connection destination network is the address information of different terminals to be registered in the duplicate address table.