WO2015070787A1

WO2015070787A1 - Stacking system

Info

Publication number: WO2015070787A1
Application number: PCT/CN2014/091077
Authority: WO
Inventors: Hui LV
Original assignee: Hangzhou H3C Technologies Co., Ltd.
Priority date: 2013-11-14
Filing date: 2014-11-14
Publication date: 2015-05-21
Also published as: CN105794157A; CN104639437A; CN105794157B

Abstract

The present disclosure describes a stacking system. In the stacking system, a member device receives a broadcast packet within a VLAN, determines whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forwards the broadcast packet out through the stack port.

Description

Stacking System

Background

A stacking system is to connect multiple devices together, and after necessary configurations, virtualize these devices into one device. Thus a stacking system may form a virtual device by stacking multiple devices. Intelligent resilient framework (IRF) is one example of a stacking system.

Brief Description of Drawings

By way of non-limiting examples, the present disclosure will be described with reference to the following drawings, in which:

Fig. 1 is a schematic diagram illustrating a method for forwarding a broadcast packet in a stacking system according to an example of the present disclosure；

Fig. 2 is a schematic diagram illustrating a method of calculating whether a stack port allows a VLAN to pass through or not according to an example of the present disclosure；

Fig. 3a and Fig. 3b are schematic diagrams illustrating structures of a ring stacking topology according to an example of the present disclosure；

Fig. 4 is a schematic diagram illustrating a structure of another ring stacking topology according to an example of the present disclosure；

Fig. 5a and Fig. 5b are schematic diagrams illustrating the structure of a ring stacking topology according to an example of the present disclosure；

Fig. 6 is a schematic diagram illustrating a structure of a ring stacking topology according to an example of the present disclosure；

Fig. 7a and Fig. 7b are schematic diagrams illustrating structures of a chain stacking topology according to an example of the present disclosure；

Fig. 8 is a schematic diagram illustrating a structure of a ring stacking topology according to an example of the present disclosure；

Fig. 9 is a schematic diagram illustrating a structure of a chain stacking topology according to an example of the present disclosure；

Fig. 10 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet according to an example of the present disclosure；

Fig. 11 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure；

Fig. 12 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure；

Fig. 13 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure；

Fig. 14 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure； and

Fig. 15 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure.

Detailed Description

For simplicity and illustrative purposes, the present disclosure is described by referring mainly to examples thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be readily apparent however, that the present disclosure may be practiced without limitation to these specific details. In other instances, some methods and structures have not been described in detail so as not to unnecessarily obscure the present disclosure. As used herein, the terms “a” and “an” are intended to denote at least one of a particular element, the term “includes” means includes but not limited to, the term “including” means including but not limited to, and the term “based on” means based at least in part on.

Fig. 1 is a schematic diagram illustrating a method for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. A stack port on a member device may be configured to allow broadcast packets of certain virtual local area networks (VLANs) to pass through. As shown in Fig. 1, the method may include the following process. At block 101, a member device receives a broadcast packet within a VLAN. At block 102, the member device determines whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through. If there is, then the member device forwards the broadcast packet out through the stack port. It can be known that in the present example, when the member device sends the broadcast packet, it forwards the broadcast packet to a member device according to whether the member device joins the VLAN or not, and tries to avoid sending/forwarding the broadcast packet to a member device that has not joined the VLAN. This approach may suppress unnecessary broadcast packets on stack links and reduce pressure on the stack links.

In the stacking system there are a plurality of member devices. Master member device is elected from among the member devices. The master member device manages the entire stacking system. In the stacking system, only one member device can be master member device at a time. In the stacking system, except for the master member device, other member devices are slave member devices. A slave member device is also a member device, and is elected from the member devices. In the stacking system, there may be a plurality of slave member devices. The member devices may be switches or other member devices, which is not limited herein. For each member device, two stack ports may be configured and respectively referred to as stack port 1 and stack port 2. In addition, each member device may be configured with multiple service ports. A stack port of the member device is a port that performs stack link connections between member devices in the stacking system. Member devices perform data forwarding through stack links between them. When a member device receives a packet from a network (generally from a service port) , the member device may forward the packet to other member devices via stack links established via stack ports. For example, in an IRF system, member devices establish communication connections by establishing IRF links (namely, stack links) , and a port on a member device that connects with an IRF link is an IRF port (namely, a stack port) . A service port refers to a port on a member device that connects with devices outside the stacking system. Via a service port, a member device may receive packets from a network, or may send packets to the network.

Fig. 2 is a schematic diagram illustrating a method of calculating whether a stack port allows a VLAN to pass through or not, according to an example of the present disclosure. The phrase ‘allows a VLAN to pass through or not’ means whether or not a packet belonging to a particular VLAN can pass through. For instance, in one example, a packet that is tagged as belonging to a first VLAN may be allowed to pass, while a packet that is tagged as belonging to a second VLAN may not be allowed to pass. As shown in Fig. 2, the method may include the following process.

At block 201, the master member device in the stacking system receives an update packet periodically from a slave member device. The update packet includes a bitmap of VLANs which the respective service ports of the member device allow to pass through.

At block 202, the master member device updates a VLAN based topology maintained by the master member device according to the update packet. The VLAN based topology includes location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through.

At block 203, based on the VLAN based topology, the master member device, for each VLAN, according to member devices that allow the VLAN to pass through, calculates a shortest broadcast path to allow the VLAN to pass through and notifies the stacking system of the shortest broadcast path, so that when a broadcast packet of the VLAN enters the stacking system, the broadcast packet is forwarded along the shortest broadcast path, that is, calculating a shortest broadcast path that allows the broadcast packet of the VLAN to be broadcasted to all member devices that have a service port to allow the VLAN to pass through.

The master member device records VLANs that are allowed or not allowed to pass through each stack port of the master member device respectively, and sends a notification packet to each slave member device to notify the corresponding slave member device of VLANs allowed or not allowed to pass through respective stack ports of the slave member device. When a slave member device receives a notification packet from the master member device, it records VLANs that are allowed or not allowed to pass through respective stack ports of it according to the notification packet.

At block 203, if the stacking system is a ring stack link, calculating a shortest broadcast path to allow the VLAN to pass through may include the following process. The master member device calculates the number of hops between stack ports of respective neighbouring member devices which have service ports to allow the VLAN to pass through. Stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbid the VLAN passing through, while other stack ports on the ring stack link allow the VLAN to pass through. When there are multiple pairs of stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the numbers of hops are the largest, the master member device selects one pair out of them. The selected pair of stack ports and stack ports between the selected pair of stack ports are stack ports that do not allow the VLAN to pass through, while other stack ports allow the VLAN to pass through.

In one example, when the master member device selects one pair of stack ports, if a VLAN is an even VLAN, starting from stack port 1 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； and when a VLAN is an odd VLAN, starting from stack port 2 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through.

At block 203, if the stacking system is a chain stack link, calculating the shortest broadcast path may include: determining two member devices which are respectively nearest to two ends of the chain stack link from the member devices that have service ports to allow the VLAN to pass through, stack ports between the two member devices allowing the VLAN to pass through.

In the following, four VLANs (VLAN1-VLAN4) are used for example to illustrate the present disclosure.

Fig. 3a and Fig. 3b are schematic diagrams illustrating structures of a ring stacking topology according to an example of the present disclosure. In the stacking system, there are member devices A, B, C, D, M, and P. Member device M is configured with stack ports a and b and a service port g； member device A is configured with stack ports c and d and a service port h； member device C is configured with stack ports i and j； member device P is configured with stack ports e and f and a service port o； member device D is configured with stack ports l and k； and member device B is configured with stack ports m and n. Among them, the stack port a of the member device M is connected with the stack port c of the member device A, the stack port d of the member device A is connected with the stack port i of the member device C, the stack port j of the member device C is connected with the stack port e of the member device P, the stack port f of the member device P is connected with the stack port k of the member device D, the stack port l of the member device D is connected with the stack port m of the member device B, and the stack port n of the member device B is connected with the stack port b of the member device M.

Initially, after the respective member devices in the stacking system are started up, each member device in the stacking system exchanges Hello packets with directly connected neighbouring member devices to collect a topology of the entire stacking system. A Hello packet may carry topology information, specifically including stack port connections, member device identities, priority of member devices, bridge MAC addresses of member devices, etc. Assuming that finally the member device M is elected as master member device, a ring topology as shown in Fig. 3 will be maintained on the master member device M.

Then, the master member device M receives update packets periodically sent from other member devices (slave member devices) . A period of the update packets may be configured flexibly, and it may be conformity with a period of stack heartbeat packets which are used to maintain neighbouring relation between member devices.

Assuming that initially after the respective member devices in the stacking system are started up, service ports of the respective member devices only allow VLAN1 to pass through, then the member devices A, B, C, D, and P send update packets to the master member device M respectively. For example, for the member device A, the content of its update packet may be a bitmap as shown in Table 1.

1	0
1	0	0	0

Table 1

As shown by the bitmap in Table 1, the member device A allows VLAN1 to pass through (indicated by “1” ) , and forbids VLAN2, VLAN3, and VLAN4 passing through (indicated by “0” ) . Similarly, bitmaps in update packets sent from the member devices B, C, D, and P to the master member device M respectively are as shown in Table 1.

After the master member device M receives the bitmaps of the respective member devices as shown in Table 1, it forms a VLAN based topology, including location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through.

The location relations between the respective member devices may be obtained according to the topology of the stacking system formed after the respective member devices in the stacking system are started up. In one example, the stack port a of the member device M is connected with the stack port c of the member device A, the stack port d of the member device A is connected with the stack port i of the member device C, the stack port j of the member device C is connected with the stack port e of the member device P, the stack port f of the member device P is connected with the stack port k of the member device D, the stack port l of the member device D is connected with the stack port m of the member device B, and the stack port n of the member device B is connected with the stack port b of the member device M.

The bitmap of the VLANs which the respective member devices allow to pass through is shown as Table 2.

Table 2

For the member devices A, B, C, D, M, and P that allow VLAN1 to pass through, the master member device M calculates a shortest broadcast path to allow VLAN1 to pass through according to Table 2, that is, calculating a shortest broadcast path that allows a broadcast packet of VLAN1 to be broadcasted to all the member devices which have a service port to allow VLAN1 to pass through.

The method for determining the shortest broadcast path for a VLAN may include: calculating the number of hops between stack ports of respective neighbouring member devices which have service ports to allow the VLAN to pass through. Stack ports of the respective neighbouring member devices between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbid the VLAN passing through, while other stack ports on the ring stack link allow the VLAN to pass through i.e., the shortest broadcast path allowing the VLAN to pass through.

Since in the present example, all member devices A, B， C, D, M, and P allow VLAN1 to pass through, the numbers of hops between stack ports of respective neighbouring member devices which have service ports to allow VLAN1 to pass through are all 1, i.e., the numbers of hops being the same. In this case, the master member device may select stack ports between any two neighbouring member devices as stack ports which do not allow VLAN1 to pass through, while other stack ports as stack ports which allow VLAN1 to pass through. As an example, the master member device M sets the stack ports b and n between it and the member device B as stack ports that do not allow VLAN1 to pass through.

After the calculation, the bitmaps on the stack port b of the member device M and on the stack port n of the member device B are as shown in Table 3.

0	0
0	0	0	0

Table 3

The bitmaps on the stack port a of the member device M, on the stack port m of the member device B, and on the stack ports of the other member devices are as shown in Table 4.

1	0
1	0	0	0

Table 4

Then, refer to Fig. 3b. Assume that the service port g of the master member device M joins VLAN4, a bitmap of VLANs which the respective service ports of the master member device M allow to pass through are as shown in Table 5.

1	0
1	0	0	1

Table 5

As shown by the bitmap in Table 5, the member device M allows VLAN1 and VLAN4 to pass through (indicated by “1” ) , and forbidding VLAN2 and VLAN3 passing through (indicated by “0” ) .

The master member device M updates a VLAN based topology maintained by itself according to the bitmap shown in Table 5, and the bitmap of VLANs which the respective member devices allow to pass through is changed from Table 2 to Table 6.

Table 6

Then the master member device M according to Table 6, for member device M that allows VLAN4 to pass through, calculates a shortest broadcast path to allow VLAN4 to pass through.

Since in the VLAN4 based topology, only the member device M allows VLAN4 to pass through, two stack ports between which the number of hops is the largest, a and b, and stack ports between them, stack ports c, d, i, j, e, f, k, l, m, and n, all forbid VLAN4 passing through.

The member device M sends notification packets to other member devices to notify corresponding member devices of VLANs allowed or not allowed to pass through each stack port of the corresponding member devices, so that a stack port of a corresponding member device keeps a bitmap of VLANs allowed or not allowed to pass through it. After a member device receives a broadcast packet within a VLAN, no matter from a service port or from a stack port, the member device first determines whether there is a stack port on the member device to allow the broadcast packet of the VLAN to pass through. If there is, then the broadcast packet of the VLAN is forwarded via a corresponding stack port, or otherwise, the broadcast packet will not be processed. It is to be understood that if a member device receives the broadcast packet from one of its stack ports, then it can determine whether the other stack port allow the broadcast packet to pass through or not.

In this case, bitmaps kept on the stack port b of the member device M and on the stack port n of the member device B are as shown in Table 3.

Bitmaps kept on the stack port a of the member device M, on the stack port m of the member device B, and on the stack ports of the other member devices are as shown in Table 7.

1	0
1	0	0	0

Table 7

If the master member device M receives a broadcast packet of VLAN4 through the service port g, then since the stack ports a and b both forbid VLAN4 passing through, the broadcast packet will not be forwarded to other member devices, which effectively reduces the pressure on the stack link between the stack ports a and b.

Fig. 4 is a schematic diagram illustrating a structure of another ring stacking topology according to an example of the present disclosure. Based on the previous example, in the present example, assume that the service port h of the member device A also joins VLAN4. The member device A sends an update packet to the master member device M. The update packet includes a bitmap of VLANs which the respective service ports of the member device A allow to pass through, as shown in Table 8:

1	0
1	0	0	1

Table 8

As shown by the bitmap in Table 8, the master member device M allows VLAN1 and VLAN4 to pass through (indicated by “1” ) , and forbids VLAN2 and VLAN3 passing through (indicated by “0” ) .

The master member device M updates a topology maintained by itself according to the bitmap shown in Table 8, and the bitmap of VLANs the respective member devices allow to pass through is changed from Table 6 to Table 9.

Table 9

Then, the master member device M, according to Table 9, for the member devices A and M that allow VLAN4 to pass through, calculates a shortest broadcast path to allow VLAN4 to pass through.

Since in the VLAN4 based topology, the member devices A and M allow VLAN4 to pass through, for the number of hops between the member device M and a neighbouring member device that allows VLAN4 to pass through, i.e., the member device A, when the master member device M searches for the member device A from its stack port b side, the number of hops is 5, and when the member device M searches for the member device A from its stack port a side, then the number of hops is 1. Similarly, when the member device A searches for the master member device M from its stack port c side, the number of hops is 1, and when the member device A searches for the master member device M from its stack port d side, the number of hops is 5. So the two stack ports d and b between which the number of hops is 5, and stack ports between them, i, j, e, f, k, l, m, and n, all forbid VLAN4 passing through, while the two stack ports a and c the number of hops between which is 1 allow VLAN4 to pass through.

The master member device M may notify each corresponding member device of VLANs allowed or not allowed to pass through each stack port of the corresponding member device, so that a stack port of the corresponding member device keeps a bitmap of VLANs allowed or not allowed to pass through it.

Bitmaps kept on the stack port b of the member device M and on the stack port n of the member device B are as shown in Table 3.

Bitmaps kept on the stack port a of the member device M and on the stack port c of the member device A are as shown in Table 10.

1	0
1	0	0	1

Table 10

Bitmaps maintained on the stack port m of the member device B, on the stack port d of the member device A, and on the stack ports of the other member devices are as shown in Table 11.

1	0
1	0	0	0

Table 11

If the service port g of the member device M receives a broadcast packet of VLAN4, since the stack ports a and c allow VLAN4 to pass through, the broadcast packet is forwarded from the member device M to the member device A, but will not enter the stack link between the stack ports d and b, which effectively reduces the pressure on the stack link between the stack ports d and b.

Fig. 5a and Fig. 5b are schematic diagrams illustrating the structure of a ring stacking topology according to an example of the present disclosure.

As shown in Fig. 5a, based on the implementation of Fig. 3b, in the present example, assuming that the service port o of the member device P joins VLAN4 too, the member device P sends an update packet to the master member device M, the update packet including a bitmap of VLANs which the respective service ports of the member device P allow to pass through, as shown in Table 12.

1	0
1	0	0	1

Table 12

As shown by the bitmap in Table 12, the member device P allows VLAN1 and VLAN4 to pass through (indicated by “1” ) , and forbidding VLAN2 and VLAN3 passing through (indicated by “0” ) .

The master member device M updates the VLAN based topology maintained on it based on the bitmap shown in Table 12, and the bitmap of VLANs which the respective member devices allow to pass through is changed from Table 6 to Table 13.

Table 13

Then, the master member device M, according to Table 13, for the member devices M and P that allow VLAN4 to pass through, calculates a shortest broadcast path to allow VLAN4 to pass through.

Since in the VLAN4 based topology, the member devices P and M allow VLAN 4 to pass through, for the number of hops between the member device M and its neighbouring member device that allows VLAN4 to pass through, i.e., the member device P, when the member device M searches for the member device P from the stack port b side of the member device M, the number of hops is 3, and when the member device M searches for the member device P from its stack port a side, the number of hops is 3 too. Assuming that the stack port a of the master member device M is stack port 1 and the stack port b of the master member device is stack port 2, then the stack port a of the member device M and the stack port e of the member device P, and the stack ports c, d, i, and j between them all forbid VLAN4 passing through.

The member device M may notify each corresponding member device of VLANs allowed or not allowed to pass through each stack port of the corresponding member device, so that a stack port of a corresponding member device keeps a bitmap of VLANs allowed or not allowed to pass through it.

Bitmaps kept on the stack port b of the member device M and on the stack port n of the member device B are as shown in Table 14.

0	0
0	0	0	1

Table 14

Bitmaps maintained on the stack port a of the member device M, on the stack port e of the member device P, and on the stack ports of the member devices A and C are as shown in Table 15.

1	0
1	0	0	0

Table 15

Bitmaps maintained on the stack port f of the member device P, on the stack port m of the member device B, and on the stack ports of member device D are as shown in Table 16.

1	0
1	0	0	1

Table 16

If the service port g of the member device M receives a broadcast packet of VLAN4, the broadcast packet is forwarded from the member device M, via the member device B, the member device D, to the member device P, but will not enter the stack link between the stack ports a and e, which effectively reduces the pressure on the stack link between the stack ports a and e.

In addition, as shown in Fig. 5b, for the number of hops between the member device M and the member device P, when the member device M searches for the member device P from its stack port b side, the number of hops is 3, and when the member device M searches for member device P from its stack port a side, then the number of hops is 3 too. The shortest broadcast path may be selected by: selecting the stack port b of the member device M, the stack port f of the member device P, and the stack ports k, l, m, and n between the stack port b and the stack port f to forbid VLAN4 passing through. If the service port of the member device M receives a broadcast packet of VLAN4, the broadcast packet is forwarded from the member device M, then through the member devices A and C, to the member device P, while the broadcast packet will not enter the stack link between the stack ports b and f, which effectively reduce the pressure on the stack link between the stack ports b and f.

When there are multiple pairs of stack ports of neighbouring member devices between which the numbers of hops are the largest, the master member device selects one pair out of them. The selected pair of stack ports and stack ports between them are stack ports that do not allow the VLAN to pass through, while other stack ports allow the VLAN to pass through. As an example, starting from stack port 1 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； or starting from stack port 2 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through. As an example, depending on the VLAN, if the VLAN is an even VLAN, starting from the stack port 1 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； and when the VLAN is an odd VLAN, starting from the stack port 2 of the master member device, the master member device selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have a service port to allow the VLAN to pass through, so as to try to balance the flow of the stack links.

Fig. 6 is a schematic diagram illustrating a structure of a ring stacking topology according to an example of the present disclosure.

Based on Fig. 4, i.e., based on the service port g of the member device M joining VLAN4 and the service port h of the member device A joining VLAN4, assuming that the service port o of the member device P also joins VLAN4. The member device P sends an update packet to the master member device M, the update packet including a bitmap of VLANs which the respective service ports of the member device P allow to pass through, as shown in Table 17.

1	0
1	0	0	1

Table 17

As shown in Table 17, the member device P allows VLAN1 and VLAN4 to pass through (indicated by “1” ) and forbids VLAN2 and VLAN3 passing through (indicated by “0” ) .

The master member device M updates the VLAN based topology maintained by itself according to the bitmap shown in Table 17. The bitmap of VLANs which the respective member devices allow to pass through is changed from Table 9 to Table 18.

Table 18

Then the master member device M according to Table 18, for the member devices M, A, and P that allow VLAN4 to pass through, calculates a shortest broadcast path to allow VLAN4 to pass through.

Since in the VLAN4 based topology, the member devices A, P, and M allow VLAN4 to pass through, for the number of hops between the member device M and its neighbouring member devices A and P, when the member device M searches for the member device P from its stack port b side of it, the number of hops is 3, and when the member device M searches for the member device A from its stack port a side, then the number of hops is 1. Similarly, for the number of hops between the member device A and its neighbouring member devices M and P, when the member device A searches for the member device M from its stack port c side, the number of hops is 1, and when the member device A searches for the member device P from its tack port d side, the number of hops is 2； for the number of hops between the member device P and its neighbouring member devices A and M, when the member device P searches for the member device A from its stack port e side, the number of hops is 2, and when the member device P searches for the member device M from its stack port f side, the number of hops is 3. Thus, it can be seen that the number of hops between the stack ports of the member devices M and P is the largest, i.e., 3, and therefore, the two stack ports b and f and the stack ports k, l, m, and n between them forbid VLAN4 passing through.

Bitmaps maintained on the stack port f of the member device P, on the stack port m of the member device B, and on the stack ports of the member device D are as shown in Table 19.

1	0
1	0	0	0

Table 19

Bitmaps maintained on the stack port a of the member device M, on the stack port e of the member device P, and on the stack ports of the member devices A and C are as shown in Table 20.

1	0
1	0	0	1

Table 20

If the service port g of the member device M receives a broadcast packet of VLAN4, the broadcast packet is forwarded from the member device M, via the member device A and the member device C, to the member device P, but will not enter the stack link between the stack ports b and f, which effectively reduces the pressure on the stack link between the stack ports b and f.

Fig. 7a and Fig. 7b are schematic diagrams illustrating the structures of a chain stacking topology according to an example of the present disclosure. The stacking system includes member devices X, Y, Z, and K. Assume that the member device Y is configured with stack ports p and q and a service port v； the member device X is configured with a stack port r, the member device Z is configured with stack ports s and t； and the member device K is configured with a stack port u and a service port w. Among them, the stack port r of the member device X connects with the stack port p of the member device Y, the stack port s of the member device Z connects with the stack port q of the member device Y, and the stack port u of the member device K connects with the stack port t of the member device Z.

Refer to Fig. 7a, after the respective member devices in the stacking system are started up, each member device in the stacking system exchanges Hello packets with directly connected neighbouring member devices to collect a topology of the entire stacking system. A Hello packet may carry topology information, specifically including stack port connections, member device identities, priority of member devices, bridge MAC addresses of member devices, etc. Assuming that finally the member device Y is elected as master member device, a chain topology as shown in Fig. 7a will be maintained on the master member device Y.

Then, the master member device receives update packets periodically sent from slave member devices. A period of the update packet may be configured flexibly, and it may be conformity with a period of stack heartbeat packets which are used to maintain neighbouring relation between member devices.

Assuming that initially after the respective member devices in the stacking system are started up, service ports of the respective member devices only allow VLAN1 to pass through, then the member devices X, Z, and K send update packets to the master member device Y respectively. For example, for the member device X, the content of its update packet may be a bitmap as shown in Table 21.

1	0
1	0	0	0

Table 21

As shown by the bitmap in Table 21, the member device X may allow VLAN1 to pass through (indicated by “1” ) , and forbid VLAN2, VLAN3, and VLAN4 passing through (indicated by “0” ) . Similarly, bitmaps in update packets sent from the member devices Z and K to the master member device Y respectively are as shown in Table 21.

After the master member device Y receives the bitmaps of the respective member devices as shown in Table 21, it forms a VLAN based topology, including location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through.

The location relations between the respective member devices may be obtained according to the topology of the stacking system formed after the respective member devices in the stacking system are started up. Specifically, the stack port r of the member device X is connected with the stack port p of the member device Y, the stack port s of the member device Z is connected with the stack port q of the member device Y, and the stack port u of the member device K is connected with the stack port t of the member device Z.

The bitmap of the VLANs which the respective member devices allow to pass through is shown as Table 22.

Table 22

The master member device Y calculates a shortest broadcast path to allow VLAN1 to pass through, that is, calculating a shortest broadcast path to allow a broadcast packet of VLAN1 to be broadcasted to all the member devices which have a service port to allow VLAN1 to pass through.

The method for determining the shortest broadcast path for a VLAN may include: determining two member devices that are nearest to the two ends of the chain stack link respectively from the member devices that have a service port to allow the VLAN to pass through. Stack ports between the two member devices allow the VLAN to pass through.

Since the service ports of the respective member devices all allow VLAN1 to pass through, the member devices that have a service port to allow VLAN1 to pass through and are nearest to the two ends of the chain stack link respectively are the member devices X and K. Therefore, the stack ports r and u, and the stack ports between them, stack ports p, q, s, and t all allow VLAN1 to pass through.

After the calculation, bitmaps on the stack ports of the respective member devices are as shown in Table 23.

1	0
1	0	0	0

Table 23

Refer to Fig. 7b. Assuming that the service port v of the member device Y joins VLAN4 and the service port w of the member device K joins VLAN4, a bitmap of VLANs which the respective service ports of the master member device Y allow to pass through may be as shown in Table 24.

1	0
1	0	0	1

Table 24

As shown by the bitmap in Table 24, the member device Y allows VLAN1 and VLAN4 to pass through (indicated by “1” ) , and forbid VLAN2 and VLAN3 passing through (indicated by “0” ) .

The member device K sends an update packet to the master member device Y, and the update packet includes a bitmap of VLANs which the respective service ports of the member device K allow to pass through, as shown in Table 24.

The master member device Y updates a VLAN based topology maintained by itself according to the bitmap shown in Table 24, and the bitmap of VLANs which the respective member devices allow to pass through is changed from Table 22 to Table 25.

Table 25

Then the master member device Y according to Table 25, for the member devices Y and K that allow VLAN4 to pass through, calculates a shortest broadcast path to allow VLAN4 to pass through.

First, two member devices that are nearest to the two ends of the chain stack link respectively and have a service port to allow VLAN4 to pass through are determined to be the member devices Y and K, and then the stack link between the member devices Y and K is determined as the shortest broadcast path that allows VLAN4 to pass through. Therefore, the stack port q and the stack port u and the stack ports s and t between them all allow VLAN4 to pass through.

The member device Y may notify each member device of VLANs allowed or not allowed to pass through each stack port of the corresponding member device, so that the corresponding member device may keep a bitmap of VLANs allowed or not allowed to pass through a stack port on the stack port.

Bitmaps kept on the stack port q of the member device Y, on the stack port u of the member device K, and on the stack ports of the member device Z are as shown in Table 26.

1	0
1	0	0	1

Table 26

Bitmaps kept on the stack port p of the member device Y and on the stack port r of the member device X are as shown in Table 27.

1	0
1	0	0	0

Table 27

If the service port v of the member device Y receives a broadcast packet of VLAN4, since the stack ports p and r do not allow VLAN4 to pass through, the member device X will not receive the broadcast packet, which effectively reduces the pressure on the stack link between the stack ports p and r.

In summary, the master member device receives an update packet sent periodically from a slave member device. The update packet includes a bitmap of VLANs which the respective service ports of the slave member device allow to pass through. The master member device updates a VLAN based topology maintained by the master member device according to the update packet. The VLAN based topology may include location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through. Based on the VLAN based topology, the master member device, for each VLAN, according to member devices that allow the VLAN to pass through, calculates a shortest broadcast path to allow the VLAN to pass through, so that when a broadcast packet of the VLAN enters a stack link, the broadcast packet is forwarded along the shortest broadcast path. In this way, unnecessary broadcast packets on the stack links are suppressed and the pressure on the stack links is alleviated.

It is to be noted that, in the stacking system, a service port may be in an “Up” state or in a “Down” state. However, no matter a service port is in the “Up” state or in the “Down” state, as long as there is a VLAN change on the service port, a member device to which the stack port belongs will send an update packet to the master member device.

To avoid unnecessary forwarding of broadcast packets, in an example, it may be defined that only when a service port in the “Up” state has a VLAN change, the member device to which the stack port belongs sends the update packet to the master member device.

The present disclosure also provides another example of determining whether a VLAN is allowed to pass through a stack port or not.

A member device in the stacking system sends an update packet of bitmaps of VLANs which the respective service ports of the member device allow to pass through through stack port 1 and stack port 2 of the member device to other member devices. Meanwhile, the member device receives an update packet of bitmaps of VLANs which the respective service ports of the member device allow to pass through from each of the other member devices. A stack port that receives the update packet allows the VLANs that are allowed to pass through in the update packet to pass through.

In an example, the update packet also includes the number of hops to be sent by the update packet. When the stacking system is a ring stack link, the number of hops is obtained by dividing the number of member devices in the ring stack link by 2 and then rounding a divided quotient. When the stacking system is a chain stack link, the number of hops is the number of the member devices in the chain stack link minus 1.

Fig. 8 is a schematic diagram illustrating a structure of a ring stacking topology according to an example of the present disclosure. As shown in Fig. 8, the stacking system includes member devices A, B, C, D, M, and P.

Assuming that the service port g of the member device M joins VLAN1, then the member device M sends update packets respectively through the stack port a and stack port b. The content of the update packets may be a bitmap as shown in Table 28.

1	0
1	0	0	0

Table 28

Since the update packets also include the number of hops (or time to live (TTL) ) to be sent by the update packets, for a ring stacking topology, the number of hops is the number of member devices in the ring stacking topology divided by 2 and then being rounded. In the present example, TTL to be sent in the update packets is TTL＝6/2＝3, so the member device M sends an update packet to the member devices A, C, and P through the stack port a. The stack ports c, i, and e that receive the update packet allow VLAN1 to pass through. The member device M sends an update packet to the member devices B, D, and P through the stack port b. The stack ports n, l, and f that receive the update packet allow VLAN1 to pass through.

In the following, assuming that the service port h of the member device A also joins VLAN1, then the member device A sends update packets through the stack ports c and d respectively. The content of the update packets may be a bitmap as shown in Table 29.

1	0
1	0	0	0

Table 29

According to TTL＝6/2＝3, the member devices C, P, and D receive the update packets, and thus the stack ports i, e, and k allow VLAN1 to pass through. Meanwhile, the member devices M, B, and D also receive the update packets, and the stack ports a, n, and l allow VLAN1 to pass through. Thus, the stack ports a, c, i, e, f, k, l, and n all allow VLAN1 to pass through. In this way, all the member devices maintain VLANs that are allowed to pass through stack ports of them, so that when a member device receives a broadcast packet within a VLAN, it can determine a stack port of it which allows the VLAN to pass through, so as to forward the broadcast packet.

If the member device M receives a broadcast packet of VLAN1, it will send the broadcast packet through the stack port a to the member device A. Since the stack port b and the stack port d do not allow VLAN1 to pass through, the stack link to the member devices B, D, P, and C is protected, which effectively reduces the pressure on the stack link.

Fig. 9 is a schematic diagram illustrating a structure of a chain stacking topology according to an example of the present disclosure. As shown in Fig. 9, the stacking system includes member devices X, Y, Z, and K.

Assuming that the service port v of the member device Y joins VLAN1, then the member device Y sends broadcast packets through the stack port p and the stack port q of the member device Y respectively. The content of the broadcast packets may be a bitmap as shown in Table 30.

1	0
1	0	0	0

Table 30

Since the update packet also includes the number of hops (TTL) to be sent, for a chain stacking topology, the number of hops is the number of member devices in the chain stacking topology minus 1. In the present example, TTL in the update packet is TTL＝4-1＝3, so the member device Y sends an update packet to the member device X through the stack port p, and the stack port r that receives the update packet allows VLAN1 to pass through. The member device Y sends an update packet to the member devices Z and K, and the stack ports s and u which receive the update packet allow VLAN1 to pass through.

In the following, assuming that the service port of the member device X also joins VLAN1, then the member device X sends an update packet through the stack port r. The content of the update packet may be a bitmap as shown in Table 31.

1	0
1	0	0	0

Table 31

According to TTL＝4-1＝3, the member devices Y, Z, and K receive the update packets, and thus the stack ports p, s, and u allow VLAN1 to pass through. On the whole, the stack ports r, p, s, and u all allow VLAN1 to pass through.

If the service port v of the member device Y receives a broadcast packet of VLAN1, it will send the broadcast packet to the member device X through the stack port p. Since the stack port q does not allow VLAN1 to pass through, the stack link between the member devices Z and K is protected, which effectively reduces the pressure on the stack link.

Fig. 10 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet according to an example of the present disclosure. The apparatus may be implemented in a master member device.

As shown in Fig. 10, the apparatus 1000 includes a receiving unit 1001 and a VLAN determination unit 1002. The receiving unit 1001 is configured to receive a broadcast packet within a VLAN. The VLAN determination unit 1002 is configured to determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.

Fig. 11 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. As shown in Fig. 11, based on the apparatus shown in Fig. 10, the apparatus further includes an updating unit 1003, a path calculation unit 1004, a sending unit 1005, and a recording unit 1006.

The receiving unit 1001 is further configured to receive update packets sent periodically from other member devices in the stacking system. An update packet sent from a member device includes a bitmap of VLANs which service ports of the member device allow to pass through.

The updating unit 1003 is configured to update a VLAN based topology maintained by the apparatus according to the update packet. The VLAN based topology includes location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through.

The path calculation unit 1004 is configured to, for each VLAN, according to member devices that allow the VLAN to pass through, calculate a shortest broadcast path to allow the VLAN to pass through and notify the stacking system of the shortest broadcast path, so that when a broadcast packet of the VLAN enters the stacking system, the broadcast packet is forwarded along the shortest broadcast path.

The sending unit 1005 is configured to send notification packets to slave member devices in the stacking system to notify corresponding slave member devices of VLANs allowed or not allowed to pass through respective stack ports of the slave member devices.

The recording unit 1006 is configured to record VLANs allowed or not allowed to pass through on each stack port of the master member device.

For a ring stack link, the path calculation unit 1004 is configured to calculate the number of hops between stack ports of respective neighbouring member devices which have service ports to allow a VLAN to pass through. Stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbid the VLAN passing through, while other stack ports on the ring stack link allow the VLAN to pass through. When there are multiple pairs of stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the numbers of hops are the largest, the path calculation unit 1004 selects one pair out of them. The selected pair of stack ports and stack ports between the selected pair of stack ports forbid the VLAN passing through, while other stack ports allow the VLAN to pass through.

When the VLAN is an even VLAN, starting from stack port 1 of the apparatus, the path calculation unit 1004 selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； and when the VLAN is an odd VLAN, starting from stack port 2 of the apparatus, the path calculation unit 1004 selects a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through.

For a chain stack link, the path calculation unit 1004 is configured to determine two member devices which are respectively nearest to two ends of the chain stack link from the member devices that have service ports to allow the VLAN to pass through, stack ports between the two member devices allowing the VLAN to pass through.

Fig. 12 is a schematic diagram of an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. Based on the apparatus shown in Fig. 10, the apparatus further includes a sending unit 1203 and a setting unit 1204.

The sending unit 1203 is configured to send an update packet containing a bitmap of VLANs which respective service ports of the member device allow to pass through to other member devices through port 1 and port 2 of the apparatus.

The receiving unit 1001 is further configured to receive update packets that carry bitmaps of VLANs which respective service ports of the other member devices allow to pass through through their stack port 1 and stack port 2.

The setting unit 1204 configured to set a stack port which receives an update packet to allow VLANs which are in the update packet and respective service ports of the other member devices allow to pass through to pass through.

In the forgoing, the update packet further includes the number of hops to be sent by the update packet. When the stacking system is a ring stack link, the number of hops is obtained by dividing the number of member devices in the ring stack link by 2 and then rounding a divided quotient. When the stacking system is a chain stack link, the number of hops is the number of the member devices in the chain stack link minus 1.

Fig. 13 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. the apparatus may be located in a slave member device. As shown in Fig. 13, the apparatus 1300 includes a receiving unit 1301 and a VLAN determination unit 1302. The receiving unit 1301 is configured to receive a broadcast packet within a VLAN. The VLAN determination unit 1302 is configured to determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.

In an example, the receiving unit 1301 is further configured to receive a notification packet sent from a master member device.

The apparatus 1300 further includes a recording unit 1303 configured to record the VLANs allowed or not allowed to pass through the respective stack ports of the member device according to the notification packet.

In an example, the apparatus 1300 further includes a sending unit 1304 configured to send an update packet of a bitmap of VLANs which respective service ports of the member device allow to pass through to the master member device in the stacking system.

Fig. 14 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. As shown in Fig. 14, the apparatus 1400 includes a processor 1401 and a memory 1402. The processor 1401 communicates with the memory 1402 and executes computer program instructions 1403 stored in the memory 1402. The apparatus 1400 may be implemented on a master member device.

The computer program instructions 1403 further includes a receiving instruction 1404 and a VLAN determination instruction 1405.

The receiving instruction 1404 is executed by the processor 1401 to receive a broadcast packet within a VLAN； the VLAN determination instruction 1405 is executed to determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.

In an example, the receiving instruction 1404 is further executed to: receive an update packet periodically from a slave member device, the update packet including a information of VLANs which service ports of the slave member device allow to pass through. The information of VLANs for example is a bitmap of VLANs which service ports of the slave member device allow to pass through.

The instructions 1403 are further executed to update a VLAN based topology maintained by the apparatus according to the update packet, the VLAN based topology including location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through； based on the VLAN based topology, for a VLAN, according to member devices that allow the VLAN to pass through, calculate a shortest broadcast path to allow the VLAN to pass through and notify the stacking system of the shortest broadcast path, so that when a broadcast packet of the VLAN enters the stacking system, the broadcast packet is forwarded along the shortest broadcast path； record VLANs that are allowed or not allowed to pass through each stack port of the apparatus； and send notification packets to other slave member devices to notify corresponding slave member devices of VLANs allowed or not allowed to pass through respective stack ports of the slave member devices.

The computer program instructions 1403 are executed to: calculate the number of hops between stack ports of respective neighbouring member devices which have service ports to allow the VLAN to pass through, stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbidding the VLAN passing through, while other stack ports on the ring stack link allowing the VLAN to pass through； when there are multiple pairs of stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the numbers of hops are the largest, select one pair out of the multiple pairs； the selected pair of stack ports and stack ports between the selected pair of stack ports forbidding the VLAN to pass through, while other stack ports allowing the VLAN to pass through.

The computer program instructions 1403 are further executed to: if the VLAN is an even VLAN, starting from a first stack port of the master member device, select a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； and when the VLAN is an odd VLAN, starting from a second stack port of the master member device, select a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through.

If the stacking system is a chain stack link, the computer program instructions 1403 are executed to determine two member devices which are respectively nearest to two ends of the chain stack link from the member devices that have service ports to allow the VLAN to pass through, stack ports between the two member devices allowing the VLAN to pass through.

In another example, the computer program instructions 1403 are further executed to send an update packet containing a bitmap of VLANs which respective service ports of the apparatus allow to pass through to other member devices through stack port 1 and stack port 2 of the apparatus； receive update packets of bitmaps of VLANs which respective service ports of other member devices allow to pass through from the other member devices through stack port 1 and stack port 2 of the other member devices； and set a stack port which receives an update packet to allow VLANs in the update packet to pass through.

The update packet further includes the number of hops to be sent by the update packet. When the stacking system is a ring stack link, the number of hops is obtained by dividing the number of member devices in the ring stack link by 2 and then rounding a divided quotient, and when the stacking system is a chain stack link, the number of hops is the number of the member devices in the chain stack link minus 1.

Fig. 15 is a schematic diagram illustrating an apparatus for forwarding a broadcast packet in a stacking system according to an example of the present disclosure. As shown in Fig. 15, the apparatus 1500 includes a processor 1501 and a memory 1502. The processor 1501 communicates with the memory 1502 and executes computer program instructions 1503 stored in the memory 1502. The apparatus may be implemented in a slave member device.

The computer program instructions 1503 may include a receiving instruction 1504 and a VLAN determination instruction 1505.

The receiving instruction 1504 is executed to: receive a broadcast packet within a VLAN； and the VLAN determination instruction 1505 is executed to determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.

The receiving instruction 1504 may be further executed to receive a notification packet sent from a master member device.

The instructions 1503 may further include a recording instruction 1506 executed to record VLANs allowed or not allowed to pass through respective stack ports of the apparatus according to the notification packet.

The computer program instructions 1503 may further include a sending instruction 1507 executed to send an update packet of information of VLANs which respective service ports of the apparatus allow to pass through to the master member device in the stacking system. The information of VLANs may be a bitmap of VLANs which respective service ports of the apparatus allow to pass through.

In the above examples, the memories may be a volatile or non-volatile memory, such as dynamic random access memory (DRAM) , electrically erasable programmable read-only memory (EEPROM) , magnetoresistive random access memory (MRAM) , memristor, flash memory, floppy disk, a compact disc read only memory (CD-ROM) , a digital video disc read only memory (DVD-ROM) , or other optical or magnetic media, and the like, on which software may be stored.

The term ‘processor’ is to be interpreted broadly to include a processing unit, ASIC, logic unit, or programmable gate array etc. The processes, methods and functional units may all be performed by the one or more processors； reference in this disclosure or the claims to a ‘processor’ should thus be interpreted to mean ‘one or more processors’ .

The figures are only illustrations of examples, in which the units or procedures shown in the figures are not necessarily essential for implementing the present disclosure. Those skilled in the art will understand that the units in the devices of the examples can be arranged in the devices in the examples as described, or can be alternatively located in one or more devices different from that in the examples. The units in the examples described can be combined into one module or further divided into a plurality of sub-units.

In the forgoing examples of the present disclosure, the bitmaps are only shown to illustrate the present disclosure and should not be construed as limitations to the present disclosure.

Although the flowcharts described show a specific order of execution, the order of execution may differ from that which is depicted. For example, the order of execution of two or more blocks may be changed relative to the order shown. Also, two or more blocks shown in succession may be executed concurrently or with partial concurrence. All such variations are within the scope of the present disclosure.

Throughout the present disclosure, the word "comprise" , or variations such as "comprises" or "comprising" , will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

A method for forwarding a broadcast packet in a stacking system, the method comprising:

a member device receiving a broadcast packet within a VLAN；

the member device determining whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then the member device forwarding the broadcast packet out through the stack port.
The method of claim 1, further comprising:

when the member device is a master member device,

the master member device receiving an update packet periodically from a slave member device, wherein the update packet comprises information of VLANs which are allowed to pass through service ports of the slave member device；

the master member device updating a VLAN based topology maintained by the master member device according to the update packet； and

the master member device, based on the VLAN based topology, for a VLAN, according to member devices that allow the VLAN to pass through, calculating a shortest broadcast path to allow the VLAN to pass through and notifying the stacking system of the shortest broadcast path, so that when a broadcast packet of the VLAN enters the stacking system, the broadcast packet being forwarded along the shortest broadcast path.
The method of claim 2, wherein

the information of the VLANs which are allowed to pass through the service ports of the salve member device comprises a bitmap of VLANs which are allowed to pass through the service ports of the salve member device；

the VLAN based topology comprises location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through； and

the master member device notifying the stacking system of the shortest broadcast path comprises:

the master member device recording VLANs that are allowed or not allowed to pass through each stack port of the master member device respectively, and sending a notification packet to each slave member device to notify the corresponding slave member device of VLANs allowed or not allowed to pass through respective stack ports of the slave member device.
The method of claim 3, wherein if the stacking system is a ring stack link, calculating a shortest broadcast path to allow the VLAN to pass through comprises:

the master member device calculating the number of hops between stack ports of respective neighbouring member devices which have service ports to allow the VLAN to pass through；

stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbidding the VLAN passing through, while other stack ports on the ring stack link allowing the VLAN to pass through；

when there are multiple pairs of stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the numbers of hops are the largest, the master member device selecting one pair out of the multiple pairs； and

the selected pair of stack ports and stack ports between the selected pair of stack ports forbidding the VLAN passing through, while other stack ports allowing the VLAN to pass through.
The method of claim 4, wherein the master member device selecting one pair out of the multiple pairs comprises:

if the VLAN is an even VLAN, starting from a first stack port of the master member device, the master member device selecting a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through； and when the VLAN is an odd VLAN, starting from a second stack port of the master member device, the master member device selecting a nearest pair of stack ports between which the number of hops is the largest on neighbouring member devices which have service ports to allow the VLAN to pass through.
The method of claim 3, wherein if the stacking system is a chain stack link, calculating a shortest broadcast path to allow the VLAN to pass through comprises: determining two member devices which are respectively nearest to two ends of the chain stack link from the member devices that have service ports to allow the VLAN to pass through, stack ports between the two member devices allowing the VLAN to pass through.
The method of claim 2, wherein when the member device is a slave member device, the slave member device receiving a notification packet from a master member device and recording VLANs that are allowed or not allowed to pass through each stack port of the slave member device according to the notification packet.
The method of claim 1, further comprising:

the member device sending an update packet containing a bitmap of VLANs which respective service ports of the member device allow to pass through to other member devices through a first stack port and a second stack port of the member device；

the member device receiving an update packet of bitmaps of VLANs which respective service ports of a member device allow to pass through from each of the other member devices； and a stack port that receives the broadcast packet allowing the VLANs that are allowed to pass through in the update packet to pass through.
The method of claim 8, wherein the update packet further comprises the number of hops to be sent by the update packet, wherein when the stacking system is a ring stack link, the number of hops is obtained by dividing the number of member devices in the ring stack link by 2 and then rounding a divided quotient； and when the stacking system is a chain stack link, the number of hops is the number of the member devices in the chain stack link minus 1.
An apparatus for forwarding a broadcast packet in a stacking system, implemented in a master member device, the apparatus comprising:

a processor, and

a non-transitory storage medium on which is to store machine readable instructions that when executed by the processor cause the processor to:

receive a broadcast packet within a VLAN； and

determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.
The apparatus of claim 10, wherein the machine readable instructions are further to cause the processor to:

receive an update packet periodically from a slave member device, wherein the update packet comprises information of VLANs which are allowed to pass through service ports of the slave member device；

update a VLAN based topology maintained by the apparatus according to the update packet, wherein the VLAN based topology comprises location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through； and

based on the VLAN based topology, for a VLAN, according to member devices that allow the VLAN to pass through, calculate a shortest broadcast path to allow the VLAN to pass through and notify the stacking system of the shortest broadcast path, so that when a broadcast packet of the VLAN enters the stacking system, the broadcast packet is forwarded along the shortest broadcast path.
The apparatus of claim 11, wherein

the information of the VLANs which are allowed to pass through the service ports of the salve member device comprises a bitmap of VLANs which are allowed to pass through the service ports of the salve member device；

the VLAN based topology comprises location relations between respective member devices and a bitmap of VLANs which the respective member devices allow to pass through； and

when notify the stacking system of the shortest broadcast path, the machine readable instructions are further to cause the processor to:

record VLANs that are allowed or not allowed to pass through each stack port of the apparatus； and

send a notification packet to each slave member device to notify the corresponding slave member device of VLANs allowed or not allowed to pass through respective stack ports of the slave member devices.
The apparatus of claim 12, wherein

if the stacking system is a ring stack link, the machine readable instructions are further to cause the processor to: calculate the number of hops between stack ports of respective neighbouring member devices which have service ports to allow the VLAN to pass through, wherein stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the number of hops is the largest and stack ports between the stack ports of the neighbouring member devices forbid the VLAN passing through, while other stack ports on the ring stack link allow the VLAN to pass through； and when there are multiple pairs of stack ports of neighbouring member devices which have service ports to allow the VLAN to pass through and between which the numbers of hops are the largest, the master member device select one pair out of the multiple pairs； wherein the selected pair of stack ports and stack ports between the selected pair of stack ports forbid the VLAN passing through, while other stack ports allow the VLAN to pass through； and/or

if the stacking system is a chain stack link, the machine readable instructions are further to cause the processor to: determine two member devices which are respectively nearest to two ends of the chain stack link from the member devices that have service ports to allow the VLAN to pass through, stack ports between the two member devices allowing the VLAN to pass through.
The apparatus of claim 10, wherein the machine readable instructions are further to cause the processor to:

send an update packet containing a bitmap of VLANs which respective service ports of the member device allow to pass through to other member devices through a first stack port and a second stack port of the apparatus；

receive an update packet of bitmaps of VLANs which respective service ports of a member device allow to pass through from each of the other member devices； and

set a stack port which receives an update packet to allow VLANs in the update packet to pass through.
An apparatus for forwarding a broadcast packet in a stacking system, implemented in a slave member device, the apparatus comprising:

a processor, and

a non-transitory storage medium on which is to store machine readable instructions that when executed by the processor cause the processor to:

send an update packet periodically, wherein the update packet comprises a bitmap of VLANs which service ports of the member device allow to pass through；

receive a notification packet sent from a master member device and receive a broadcast packet within a VLAN；

record VLANs that are allowed or not allowed to pass through each stack port of the member device according to the notification packet； and

determine whether there is a stack port other than a port that receives the broadcast packet on the member device to allow the broadcast packet to pass through, and if there is, then forward the broadcast packet out through the stack port.