JP2005064710A - Switching hub - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching hub cpable of controlling the time limit of a filtering database and suppressing the frequency of flooding. <P>SOLUTION: This hub is provided with a plurality of ports 2, a filtering database 3 to which addresses of terminals are registered in accordance with the ports 2 and an aging timer deleting a registered content of the filtering database 3 when it becomes the time limit. The switching hub 1 performs filtering or flooding by referring to the filtering database 3. When the number of registered data in the filtering database 3 reaches an upper limit which is previously set, the time limit of the aging timer is shortened, and the time limit of the aging timer is prolonged when frequency when flooding is performed reaches the upper limit which is previously set. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching hub that relays frames based on the address of a terminal, and more particularly, to a switching hub that can adjust the time limit of a filtering database and suppress the frequency of flooding.

  The switching hub includes a plurality of ports, a filtering database (hereinafter referred to as FDB) in which terminal addresses are registered corresponding to these ports, and an aging timer that deletes the registered contents of the FDB when a predetermined time limit expires. And, when a frame received at a port is relayed from another port, filtering or flooding is performed with reference to this FDB.

  When a switching hub receives a frame at a port, it reads the transmission source MAC address of the received frame, and if the MAC address is not registered in the FDB, the MAC address is registered in the FDB in association with the reception port of the frame. To do. Thereby, it is learned that a terminal having the registered MAC address is connected to the port. This operation is called address learning. At the same time as this registration, the aging timer is started, and the value of the aging timer, which was 0 at first, becomes larger as time passes thereafter.

  When the time elapses and the value of the aging timer reaches a preset time limit value, the registered content is deleted.

  If the MAC address read from the received frame is already registered in the FDB before the value of the aging timer reaches a preset time limit value, the aging timer is reset and the value is returned to zero. As a result, the time limit is apparently extended, so that the MAC address of the terminal that repeatedly transmits the frame is kept in the FDB for a long time, and the MAC address of the terminal that rarely transmits the frame is the time. The deadline comes and it will be deleted from the FDB. When the time limit is short, only the MAC address of the terminal that sends the frame quite often remains in the FDB. However, when the time limit is long, the MAC address of the terminal that occasionally transmits the frame also remains in the FDB. Become.

  On the other hand, the switching hub performs filtering or flooding on the received frame with reference to the FDB. That is, when the destination MAC address of the received frame is read and the MAC address is registered in the FDB, the port registered corresponding to the MAC address is set as the transfer destination port, and the received frame is transmitted only to the transfer destination port. Forward. Since it is learned that the terminal having the registered MAC address is connected to the transfer destination port as described above, the frame is correctly relayed to the terminal having the destination MAC address. In this way, transferring a received frame only to a port that is known to be connected to a terminal is called filtering.

  If the destination MAC address of the received frame is not registered in the FDB, this MAC address is unlearned (including deletion due to time expiration). In other words, since it is unclear to which port the terminal having this MAC address is connected, the received frame is transferred to all ports except the receiving port. Thus, if a terminal having the destination MAC address is connected to some port, it can be expected that the frame is relayed to the terminal. Transferring received frames to all ports in this way is called flooding.

  Patent Document 1 is a prior art document in this field. In Patent Document 1, the time limit can be adjusted. In other words, by extending the time limit for the registered contents for which the aging timer has been reset, the aging time of the MAC address newly registered in the FDB is made different, and unnecessary relay to the port to which the terminal has been moved is reduced. ing.

JP 2000-196643 A

  By the way, the number of items that can be registered in the FDB is limited. This is because incorporating an excessively large memory as an FDB is an obstacle to downsizing and cost reduction of the switching hub. A CAM (Content Address Memory) is often used to increase the filtering speed, but a large-capacity CAM is very expensive.

  If the number of registrations increases and the FDB becomes full, no more registrations can be made, so that a terminal that has transmitted a new frame cannot be learned. Then, since the frame destined for the terminal is flooded, the frequency of flooding increases. Further, if the time limit set for aging is shortened, the registered contents that have already been registered are easily deleted, and the frequency of flooding increases. On the other hand, if the time limit set for aging is lengthened, the registered contents are less likely to be deleted, so the FDB is likely to become full, and eventually the frequency of flooding increases.

  In flooding, frames are transmitted from all ports except the receiving port, which increases the load on the network. Increasing the frequency of flooding is not desirable because it increases the load on the network.

  In order to reduce the frequency of flooding, the time limit may not be so long that the FDB is full, and the time limit may not be so short that the registered contents are deleted immediately.

  Therefore, an object of the present invention is to provide a switching hub capable of solving the above-described problems, adjusting the time limit of a filtering database, and suppressing the frequency of flooding.

  In order to achieve the above object, the present invention includes a plurality of ports, a filtering database in which terminal addresses are registered corresponding to these ports, and an aging timer for deleting the registered contents of the filtering database when the time limit expires. In the switching hub that performs filtering by referring to this filtering database or performs flooding, the frequency of performing flooding by shortening the time limit of the aging timer when the registered number of the filtering database reaches a preset upper limit When the value reaches the preset upper limit, the time limit of the aging timer is lengthened.

  There may be provided a registered number counting circuit that counts up by 1 when new registration is made in the filtering database and counts down by 1 when there is a deletion.

  A flooding frequency counting circuit that counts up by 1 when flooding is performed and counts down by 1 every predetermined time after performing flooding may be provided.

  The present invention exhibits the following excellent effects.

  (1) The frequency of flooding can be suppressed.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a switching hub 1 according to the present invention includes a plurality of ports 2, a filtering database (hereinafter referred to as FDB) 3 in which terminal addresses are registered corresponding to these ports 2, and the FDB 3 It has an aging timer that deletes registered contents when the time expires, and performs filtering or flooding with reference to this FDB3.

  The switching hub 1 counts up by 1 when there is a new registration in the FDB 3, and counts up by 1 when the flooding is performed. A flooding frequency counting circuit 5 that counts down by 1 every predetermined time after flooding is provided. When the number of registrations in the FDB 3 reaches a preset upper limit, the time limit of the aging timer is shortened, and the frequency of flooding is preset. When the set upper limit is reached, the time limit of the aging timer is extended.

  The time limit adjusting unit 6 adjusts the time limit of the aging timer by comprehensively judging the number of registrations output from the registration number counting circuit 4 and the flooding frequency output from the flooding frequency counting circuit 5.

  The FDB 3 includes a MAC address column, a VID column, a port number column, and an aging timer column, and one registration content includes information stored in each column for one horizontal row in FIG. For example, looking at the registration contents in the top row, a terminal with a MAC address of 00: 40: 66: 95: 35: F8 and a VID of 3 is connected to the port 15 and finally receives a frame from this terminal. It can be seen that 30 hours have passed since then. The time unit for counting by the aging timer may be anything, and is incremented by one by a regular clock. Although the time limit is not illustrated, the value stored in the aging timer column is incremented and gradually increases. When the time limit is reached, the registered content is deleted. When a frame having the MAC address as the transmission source is received from the port, the value stored in the aging timer column is reset to 0 (timer update).

  Although the upper limit of the number of registrations may be set smaller than full, it is assumed here that FDB3 is full. That is, the adjustment for shortening the time limit is not performed before the FDB 3 is full, and the adjustment for shortening the time limit is performed when the FDB 3 is full.

  You may set the upper limit of flooding frequency suitably.

  A maximum adjustable value is determined for the time limit of the aging timer, and the time limit is set to the maximum value when the switching hub 1 is started up. Subsequent adjustments will increase or decrease the time limit, but will not exceed the maximum value.

  The operation of time limit adjustment in the switching hub 1 of FIG. 1 will be described.

  When receiving a frame, the switching hub 1 learns an address, starts or resets an aging timer, and performs filtering or flooding as in the prior art. By receiving frames from various terminals, the number of registrations in the FDB 3 increases, and the number of registrations counted by the registration number counting circuit 4 increases. Of course, the registration contents may be deleted over time, but here, it is assumed that the number of new registrations is larger than the number of deletions. On the other hand, the progress of address learning in this way does not increase the number of floods.

  When the FDB 3 is full of registration, the number of registrations in the registration number counting circuit 4 reaches the upper limit. Therefore, the switching hub 1 shortens the time limit of the aging timer by a predetermined value. Because the time limit is shortened, the number of cases deleted from the FDB 3 becomes larger than before. As a result, empty space is likely to occur in the FDB 3, so that registration by learning a new address becomes possible, and flooding due to the full FDB 3 is suppressed. However, if the pace of new registration exceeds the pace of deletion, the number of registrations in the registration number counting circuit 4 reaches the upper limit. At that time, the switching hub 1 further shortens the time limit of the aging timer.

  If the rate of deletion exceeds the pace of new registration, the number of registrations in FDB3 will gradually decrease. This increases the capacity to accept registration by learning a new address, but increases the frequency of flooding.

  The flooding frequency counting circuit 5 counts up by 1 when flooding is performed, and counts down by 1 every predetermined time after performing flooding. When the frame addressed to the MAC address registered in the FDB3 and the frame addressed to the MAC address not registered in the FDB3 are received at an appropriate ratio, the value counted by the flooding frequency counting circuit 5 Although the value changes moderately, if the number of registrations in the FDB 3 decreases, the probability of filtering received frames correspondingly decreases and the probability of flooding increases. For this reason, the count value of the flooding frequency counting circuit 5 increases.

  When the count value of the flooding frequency count circuit 5 reaches the upper limit, the switching hub 1 increases the time limit of the aging timer by a predetermined value. Due to the longer time limit, the number of cases deleted from the FDB 3 becomes smaller than before. As a result, the probability that the received frame is filtered increases and the probability that it is flooded decreases.

  With the above operation, the time limit of the aging timer is appropriately changed between the maximum value and a value smaller than the maximum value, the FDB 3 is not full, the number of registrations is not too small, and the frequency of flooding is suppressed. The

  Next, another embodiment of the present invention will be described.

  The procedure shown in FIG. 2 shortens the time limit when a new address cannot be registered in the FDB 3.

  In the upper right of FIG. 2, a full FDB 3, a full detection unit 8 that detects and stores an event in which a new address could not be registered, and a flood detection unit 9 that detects and stores a flooded event, A time limit adjusting unit 10 for adjusting the time limit of the aging timer is shown.

  First, in step S1 for obtaining frame information, a destination MAC address (DA), a source address (SA), and a virtual LAN identification number (VID) are obtained from the received frame. In step S2 of learning and timer reset, FDB3 is searched by SA and VID, and when an appropriate entry (registered one) is found, the aging timer is reset, and the process proceeds to step S3. If no entry is found, the SA and VID are registered (address learning) in association with the receiving port, and the process proceeds to step S3.

  In the filtering and flooding step S3, if the DA is a multicast or broadcast address M / B, after flooding is performed, the process proceeds to step S4. If it is not the multicast or broadcast address M / B, the FDB 3 is searched by DA and VID. If no corresponding entry is found, flooding is performed, and then the process proceeds to step S4. If a corresponding entry is found, the frame is discarded if the port in the entry matches the receiving port. If the port does not match, filtering is performed using the port in the entry as a relay destination, and then step S4 is performed. Proceed to In flooding when a virtual LAN is constructed, the received frame is transferred to all ports belonging to the same virtual LAN group other than the receiving port.

  In step S4 of time limit adjustment, it is checked whether or not a new address could not be registered in the address learning process of step S1. Although not shown, it is a matter of course that such an event is stored in step S1. If the address cannot be registered, it is determined that the FDB 3 is already full. In step S4, it is checked whether flooding has been performed on the received frame in step S3. If flooding has been performed, it is determined that the FDB 3 is full and flooding is being performed, and the time limit is shortened. The time limit may be shortened on condition that the FDB 3 is full. Step S4 is executed by the fullness detection unit 8, the flooding detection unit 9, and the time limit adjustment unit 10.

  The procedure shown in FIG. 3 extends the time limit when a large amount of flooding occurs even though the FDB 3 is free.

  In the upper right of FIG. 3, the FDB 3 having a space, the registerable detection unit 11 for detecting and storing that a new address can be registered in the FDB 3, and a large amount of flooding exceeding a threshold value are detected and stored. A mass flooding detection unit 12 and a time limit adjustment unit 10 that adjusts the time limit of the aging timer are shown.

  Steps S1 to S3 are the same as those in FIG.

  In step S5 for adjusting the time limit, it is checked whether a large amount of flooding has occurred even though a new address can be registered in the FDB3. If a large amount of flooding occurs even though a new address can be registered in the FDB 3, the time limit is lengthened. Step S <b> 5 is executed by the registration enable detection unit 11, the large flooding detection unit 12, and the time limit adjustment unit 10.

  In the configurations of FIGS. 2 and 3, as in the configuration of FIG. 1, the time limit of the aging timer is shortened when the number of registrations in the FDB 3 reaches full, and when the frequency of flooding reaches a threshold, Since the time limit is lengthened, the frequency of flooding is suppressed.

It is a block diagram of the switching hub which shows one Embodiment of this invention. It is the flowchart which shows one Embodiment of this invention, and the circuit diagram around a filtering database. It is the flowchart which shows one Embodiment of this invention, and the circuit diagram around a filtering database.

Explanation of symbols

1 Switching hub 2 Port 3 Filtering database (FDB)
4 Registered number counting circuit 5 Flooding frequency counting circuit 6 Time limit adjustment unit

Claims (3)

  It has a plurality of ports, a filtering database in which the address of the terminal is registered corresponding to these ports, and an aging timer that deletes the registered contents of this filtering database when the time expires. Filtering with reference to this filtering database In the switching hub for performing flooding or flooding, the time limit of the aging timer is shortened when the number of registrations in the filtering database reaches a preset upper limit, and when the frequency of flooding reaches a preset upper limit, the aging timer A switching hub characterized by extending the time limit of   2. The switching hub according to claim 1, further comprising a registration number counting circuit that counts up by one when new registration is made in the filtering database and counts down by one when deleted.   3. The switching hub according to claim 1, further comprising a flooding frequency count circuit that counts up by 1 when flooding is performed and counts down by 1 every predetermined time after performing flooding.

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