CN1153409C

CN1153409C - Apparatus and method for multicast forwarding in a virtual local area network environment

Info

Publication number: CN1153409C
Application number: CNB011328711A
Authority: CN
Inventors: 刘广治; 李枋壅
Original assignee: Acute Tech Corp
Current assignee: Acute Tech Corp
Priority date: 2001-09-12
Filing date: 2001-09-12
Publication date: 2004-06-09
Anticipated expiration: 2021-09-12
Also published as: CN1404258A

Abstract

An apparatus for performing IP multicast forwarding in a Virtual Local Area Network (VLAN) environment is adapted to forward multicast information to multicast addresses between network ports of network devices. The multicast address within the network device may include a plurality of VLANs, each VLAN having a multicast destination subset of one or more destination ports designated from among the network ports of the network device. The device comprises a generating device, an inquirer, a transmitter and a plurality of translators. The generating device generates a multicast destination port set. The lookup engine is used to map the multicast address to an index value. A switch is coupled to the querier and distributes the index value and the multicast information to the multicast destination port group of the network device based on the bit string. The network device has a translator on each network port, and each translator of the network ports belonging to the multicast destination port group independently performs translation of VLAN identification codes (VIDs) in parallel.

Description

The device and method of multipoint transmission in virtual LAN environment

Technical field

The present invention relates to the devices and methods therefor of distributing information in computer network, particularly the devices and methods therefor of distributing ip multileaving effectively (IPMulticast) information in Virtual Local Area Network (Virtual Local Area Network) environment.

Background technology

Virtual Local Area Network (Virtual Local Area Network, hereinafter to be referred as VLAN) be the network of switch type, can be being organized as the basis, rather than according to entity or geographical position, according to function, do in logic differentiation according to working team or according to the difference of using.For instance, the employed work station of a certain particular job group is all linked same VLAN, and no matter the fact that the physical connection of its network or they may mix with other team.Resetting of network configuration can needn't pull up with mobile device or cable practically by the execution of software.United States Patent (USP) the 5th, 394, a kind of arrangement that can combine any network port (Port) on the interchanger (Switch) with any specific isolation network group was once proposed for No. 402, according to this piece patent, in conjunction with the network port and a specific VLAN destination, any amount of physical network port can this VLAN arrangement and any amount of group of interior combination of interchanger by virtually.In addition, each VLAN has unique Virtual Local Area Network identification code (VLAN Identifier, hereinafter to be referred as VID), when from the data frame (Frame) of a certain VLAN when crossing backbone network, VID and reach the target of VLAN exchange in the mode of tag (Tagging) under will being loaded with.No matter from based on the network port (Port-based), based on address (Address-based) or based on the viewpoint of the vlan topology of agreement (Protocol-based), VID makes VLAN interchanger or router (Router) can optionally pass on information to the network port that has identical VID.VID is motor and (the Institute of Electrical and Electronic Engineers of Electronic Engineering Association, hereinafter referred IEEE) 802.1Q standard (or 802.1v, at based on agreement) employed VLAN identification code, 12 (bit) are arranged, can discern 4096 VLAN altogether.

For increasing the flexibility ratio of network, Internet Protocol (IP Protocol) can be implemented within the LAN.When the IP multileaving in Internet Protocol (IP Multicast hereinafter all is called for short IP Multicast with " multileaving " two words) combines with VLAN in LAN, the more flexible but application of the complexity that becomes below the generation.For example, can provide transmission information to one predetermined work station group, this group comprises the work station of different VLAN destination, multileaving (Multicast) information of such information known to being.For example, a work station group wants to receive certain category information that is produced from a source work station, and these work stations can cross the upward registration of the network equipment (for example router or multi-protocol layer interchanger) that the VLAN scope is transmitted information in one or more control.Be used for allowing the Internet Group Management Protocol (Internet Group Management Protocol, hereinafter referred IGMP) of various operations of work station member adding group can reach registration and subscribe to the purpose of multileaving information via definition.The above-mentioned network equipment also can utilize security mechanism to prevent the work station member with particular vlan destination the multileaving information of subscribing to be delivered to the work station of having no right to use.

When receiving multileaving information, traditional network equipment can be checked multicast address and VLAN group tandem that multicast address is relevant therewith of this multileaving information, VLAN group tandem operates with the data structure of link tandem usually, it comprises the node project (Node) of a tandem, the multileaving purpose subclass that each node project has VID separately and is associated with its VID, usually multileaving purpose subclass is to represent with a kind of bitmap (Bitmap) form that is called outlet port (Port-On-Exit, hereinafter referred POE).Each significance bit among the POE is being represented a destination interface, if predetermined several VLAN and the network port delivered to of multileaving information, traditional network equipment will be to examine the mode of all node projects of VLAN group tandem closely one by one, the destination interface of inquiring about each VID in this tandem and being associated with its VID, after in case destination interface has determined, the traditional network equipment just the multileaving message transport to the destination interface that is associated with VID, and label the VLAN place in this multileaving bag with the VID under in this node project, so repetitiousness from first to last disposes up to VLAN group tandem.Therefore, the program that legacy network devices is carried out above-mentioned inquiry-pass on is to examine the tandem node that multicast address is associated one by one closely, and its design principle is to be the inquiry basis that viewpoint is set out with VLAN out of the ordinary.Yet, known to execution mode following shortcoming is but arranged:

(1) serve as that the way on inquiry basis is a kind of concentrating and the processing of list type (Serialized) with VLAN out of the ordinary, such way is not utilized the resource of system fully, even the output queue on the network port of the network equipment (Output Queue) still can be for utilizing.

(2) exist time of delay in above-mentioned VID inquiry with between passing on, the VLAN that is associated with multicast address the more then will accumulate time of delay the more, make multileaving information to pass on linear velocity (Wire-speed) at a high speed.

Summary of the invention

In view of this, need provide a kind of can be between the network port of the network equipment efficient distribution multileaving information and can not reduce the mechanism of network equipment efficient.

The purpose of this invention is to provide a kind of device and can in vlan environment, distribute multileaving information effectively.

An other purpose of the present invention provides a kind of based on VLAN, and multileaving information is transferred to method on the network equipment destination interface effectively.

For reaching above-mentioned purpose, the invention provides a kind of in vlan environment the device of multipoint transmission, be applicable to the multileaving information that distribution combines with a multicast address between a plurality of network ports of a network equipment, have a plurality of VLAN to be designated to this multicast address in this network equipment, this device comprises that one produces the generation device of multileaving destination interface group and is arranged at a plurality of transfer interpreters on each network port of the network equipment respectively.This multileaving destination interface group is by joining collection and produce being designated to each multileaving purpose subclass in whole VLAN of this multicast address in the network equipment.This multipoint transmission device comprises that also a requestor and is coupled to the transmitter of this requestor.Requestor is used for multicast address is mapped to an index value, and with multicast address and represent the position word string of multileaving destination interface group to be assigned to this index value; Transmitter then is used for the multileaving destination interface group of giving the network equipment according to this word string distribution index value and multileaving information.Belong to each transfer interpreter on the network port in the multileaving destination interface group, with independent and carry out the work that is translated into VID from identification code label tandem abreast separately.

The present invention also provide a kind of in virtual LAN environment the method for multipoint transmission, be applicable to the multileaving information that distribution combines with a multicast address between a plurality of network ports of a network equipment, there are a plurality of Virtual Local Area Networks to be designated to this multicast address in this network equipment, each Virtual Local Area Network has a multileaving purpose subclass, this multileaving purpose subclass is made of at least one destination interface, this destination interface is specified among the described network port of this network equipment, its method comprises the following steps: that A. provides a multileaving destination interface group, one index value, at least one identification code is chosen pointer, and a plurality of identification code label tandems, each these identification code label tandem is separately corresponding to each described network port of this network equipment; B. inquire about this multileaving destination interface group according to this index value that is assigned to this multicast address; C. the multileaving information of passing on is given this multileaving destination interface group of this network equipment; And D. is independent and find out whole Virtual Local Area Network identification codes that each described network port is relevant to this multicast address abreast, and the described Virtual Local Area Network identification code of each of each described network port is chosen pointer and translated generation successively corresponding to each described identification code label tandem of each described network port by described index value, described identification code; Wherein, this multileaving destination interface group is above-mentioned whole destination interfaces that this network equipment is designated to this multicast address; This index value is designated to this multicast address; This identification code is chosen pointer and is associated with this index value.

With regard to operating, requestor only need be carried out once to find the multileaving destination interface group that is associated with multicast address, and report to transmitter, afterwards, respond the report of this requestor, the destination interface that transmitter only is associated multileaving distribution of information to multileaving therewith, and these destination interfaces can be handled their VID separately abreast and translate and the output queue task.Thus, the method that the present invention proposes will be utilized required output queue resource as much as possible, also can reach in inquiry and the purpose of short delaing time of passing between the multileaving information.

Description of drawings

For above-mentioned purpose of the present invention, feature and advantage can be become apparent, a preferred embodiment cited below particularly, and conjunction with figs. are described in detail below:

Figure 1A is the schematic diagram of 3-D access model of the present invention;

Figure 1B is the multileaving table key diagram that extracts from 3-D access model;

Fig. 1 C extracts from the VID table key diagram of 3-D access model based on the network port;

Fig. 2 be the present invention the schematic diagram that designs a model implemented according to this;

Fig. 3 is the square key diagram of the embodiment of the invention;

Fig. 4 is the key diagram of organizing of address lookup table;

Fig. 5 A is that the identification code that comes from the multileaving table is chosen the table key diagram;

Fig. 5 B is that coming from the network port is the identification code label tandem key diagram that basic VID shows;

Fig. 6 comprises in the requestor that one carries out the calcspar of network linking polymerization (Link Aggregation) processing unit.

The reference numeral explanation:

10～3-D access model; 11～design a model;

12～identification code is chosen pointer; 13～query steps;

15～pass on-translation step; 20～multileaving table;

The bitmap of 22～multileaving table entry;

30～based on the VID of network port table;

32～identification code label tandem; 40～requestor;

42～address lookup table; The project of 44～address lookup table;

45～processing unit; 46～search key;

47～index value; 48～position word string;

50～transmitter; 60～network port;

62～transfer interpreter; 70～identification code is chosen table;

72～identification code is chosen bitmap; 80～identification code label tandem;

90～CPU; 100～generation device.

Embodiment

Describe hereinbefore and cross a plurality of VLAN scopes and pass on the problem of multileaving information, can simplify is 3-D inquiry problem, Figure 1A is the schematic diagram of the 3-D access model according to the present invention, three axles of 3-D access model 10 are respectively multileaving identification code (Multicast-id, hereinafter to be referred as Mid), network port identification code (Port-id, hereinafter to be referred as Pid) and Virtual Local Area Network identification code (VLAN-id, hereinafter to be referred as VID), also have one to be called identification code and to choose the auxiliary pointer of pointer 12 in order to choose VID.Each Mid is the unique index value that is assigned to each multicast address, in addition, and the Pid of all designated correspondence of each network port of the network equipment, and can draw identification code from Mid and Pid and choose pointer 12 (describing in detail after a while).Identification code is chosen pointer 12 and is picked out the VID that is associated with multicast address from identification code label tandem, and each is to (Mid Pid) keeps an identification code label tandem.With reference to Figure 1B, multileaving table 20 has a plurality of projects, each project is the bitmap (bitmap) 22 that is associated with separately Mid, and for each network port of the network equipment, each significance bit of bitmap 22 (numerical value is 1) maps to an identification code and chooses pointer 12.Shown in Fig. 1 C, based on the VID table 30 of the network port a plurality of identification code label tandems are arranged, each identification code label tandem 32 is associated with a Pid separately.

Fig. 2 is that the present invention who is based upon on 3-D access model 10 bases designs a model 11,11 spirit of having utilized " single instruction stream; multiplex data stream (Single InstructionStream; Multiple Data Stream-SIMD) " in the distributing process field design a model, design a model and 11 comprise query steps 13 and pass on-translation step 15 that wherein each network port has the identification code label tandem 32 of oneself.Mid among Fig. 2 and POE connection collection (hereinafter to be referred as UPOE) are to preestablish (describing in detail after a while), and generation device 100 has the means that produce the UPOE function.UPOE has represented the multileaving destination interface group that is assigned to multicast address, that is to say angle from system, each significance bit among the UPOE is the physical network port that is assigned to multicast address, and generation device 100 is made the connection collection by all destination interfaces in whole VLAN that will participate in multileaving and produced UPOE.One of them crucial running of the present invention is exactly to configure separately UPOE for each multileaving group (address), as the single instruction stream in the SIMD design concept.Another crucial running then is independent and translate out the VID that is associated with this multicast address abreast on all destination interfaces, this can be regarded as the multiplex data stream in the SIMD design concept.These two crucial runnings will be done more detailed description after a while.

13 of query steps need to carry out once to find UPOE and the Mid that is associated with multicast address, and report to and pass on-translation step 15, then, respond the report of this query steps 13, pass on-destination interface that translation step 15 only is associated multileaving distribution of information to multileaving therewith, and these destination interfaces can be handled their VID separately abreast and translate and the output queue task.So, even there are several VLAN to participate in this multipoint transmission, query steps only need be carried out once, and is then, independent and pass on abreast and the VID translation step on each destination interface.Aforementioned 3-D access model 10 is conceptual models that a VID translates, and has the network equipment of 8 network ports and example that each network port can hold 4 VID at the most just to illustrative purposes, and is non-in order to limit the present invention.

Fig. 3 explains the calcspar in the network equipment (not shown) of the present invention, this network equipment has a preferred embodiment, it comprises requestor 40, be coupled to this requestor 40 transmitter 50 and and transmitter 50 do a plurality of network ports 60 of communication, each network port 60 comprises a transfer interpreter 62.With reference to figure 4, requestor 40 preferably includes the address lookup table 42 (Address LookupTable is hereinafter to be referred as ALT) with a plurality of projects 44, and each project 44 comprises that one searches key 46, an index value 47 and a word string 48.The content of searching key 46 is multicast address, and its to seek matching method can be to gather assorted (hash-based) or with Content Addressable Memory (content addressablememory, CAM) be the basis, the enforcement practice on ALT 42 is decided, yet those skilled in the art must be clear that: other can be the present invention in order to the technology of searching ALT 42 and consider the scope implemented.Index value 47 representatives are assigned to the Mid of this multicast address, and the UPOE that is associated with this multicast address then deposits word string 48 on the throne.Position word string 48 is as the usefulness of a port shade, a network port of each corresponding network equipment of this port shade, and according to the port shade with the multileaving destination interface group of multileaving message transport to the network equipment.For example, if the value that position word string 48 stores is ' 11010110 ', representing according to this multicast address, the physical network port of these 5 network equipments of Pid=1, Pid=2, Pid=4, Pid=6 and Pid=7 is destination interfaces of this multicast address.

Shown in Fig. 5 A, 5B, one identification code is chosen the notion of table 70 and an identification code label tandem 80 3-D access model from viewpoint specific implementation Figure 1A that distributing is handled, mean that the identification code that each network port has oneself chooses information and identification code label tandem, and each network port can be independently and carry out VID abreast and translate.Each network port of the network equipment all has the identification code that is associated with it to choose table 70 and identification code label tandem 80, for instance, as No. 2 network ports (Pid=2) among Fig. 5 A, the 5B, each network port in the preferred embodiment has the identification code of oneself to choose table 70 and identification code label tandem 80.Choosing table 70 according to the index value 47 (Mid) that is assigned to multicast address from identification code picks out corresponding identification code and chooses bitmap 72, it is the shades of choosing as identification code label tandem 80 that identification code is chosen bitmap 72, this identification code of each network port of choosing each significance bit symbol network equipment of shade is chosen pointer, and this identification code is chosen pointer pick out the corresponding VID that is associated with multicast address from identification code label tandem 80.For example, the identification code of No. 2 network ports is chosen bitmap 72 and is ' 0011 ', expression position 1 and position 0 are for selecting two significance bits of VID from identification code label tandem 80, and the result that VID chooses makes No. 2 network ports continuously VID=1 and VID=5 be tagged on the multileaving information of sending outside.

Refer again to Fig. 3,4,5A, 5B, receiving Internet Group Management Protocol (Internet GroupManagement Protocol, be called for short IGMP) during service request, CPU 90 does the content of requestor 40 and whole transfer interpreters 62 at once and reconfigures, in other words, CPU 90 leaves a new multicast address in the requestor 40 ALT 42 with as searching key 46, when setting up new multileaving group, CPU 90 also specifies a Mid to give multicast address and leaves the index value 47 of ALT 42 in, and CPU 90 also can combine all destination interfaces and destination interface done to join and deposit word string 48 on the throne after collecting with multicast address.Answer the IGMP service request, CPU 90 optionally upgrades the identification code of 62 li of all transfer interpreters and chooses table 70 and identification code label tandem 80.

For instance, suppose that the multileaving information that combines with a multicast address A can be transferred to following 3 VLAN:

VID=1, its POE are POE ₁=' 11010100 '

VID=3, its POE are POE ₂=' 01010010 '

VID=5, its POE are POE ₃=' 01000100 '

Wherein POE represents the multileaving purpose subclass in the VLAN, and this multileaving purpose subclass is made of at least one destination interface, and destination interface is then specified among the network port of the network equipment.For example, POE ₃The network equipment of one 8 network ports of=' 01000100 ' expression, its Pid=2 and Pid=6 are the destination interface that is associated with VLAN 5 (VID=5) (port numbering are by 0 least significant bit that starts from POE).The UPOE that is associated with multicast address (being exactly multileaving destination interface group) can make the connection collection by all destination interfaces in whole VLAN that will participate in multileaving and produce.Therefore, generation device 100 can logic OR (Logical OR) computing obtain UPOE in this example:

UPOE＝POE ₁?or?POE ₂?or?POE ₃

＝‘11010100’or‘01010010’or‘01000100’

＝‘11010110’

Yet what need to understand is: other skills that can obtain UPOE are all considered the scope implemented in the present invention.Mid=2 is assigned to multicast address A and leaves the index value 47 of ALT 42 in, and UPOE also leaves in the position word string 48 of ALT 42.With regard to multicast address A, CPU 90 can pre-set all relevant informations (identification code of searching key 46, index value 47, position word string 48 and each network port is chosen bitmap 72 and identification code label tandem 80).

When receiving the multileaving information that combines with multicast address A, 40 of requestors can carry out once with multicast address A mapping to Mid=2 and the position word string 48 that comprises its UPOE, as previously mentioned, from the angle of all POE connection collection of associated VLAN, UPOE represents multileaving destination interface group.Then, transmitter 50 is distributed to the destination interface of the network equipment to multileaving information and Mid=2 according to UPOE, and wherein the Pid of destination interface is in the multileaving destination interface group: Pid=1, Pid=2, Pid=4, Pid=6 and Pid=7.Afterwards, these belong to each transfer interpreter on the network port in the multileaving destination interface group, will be independent separately and carry out VID abreast and translate work.For example, transfer interpreter 62 on No. 2 network ports can be chosen table 70 from identification code according to Mid=2 and obtain identification code and choose bitmap 72, self-demarking code is chosen in the bitmap 72 and to be taken out first identification code and choose pointer then, then, transfer interpreter 62 is chosen pointer according to first identification code and is obtained first VID=1 from identification code label tandem 80, come, No. 2 the network port can add the VID=1 label and carry out the output queue task sending multileaving information outside again.Then again, transfer interpreter 62 self-demarking codes on No. 2 network ports are chosen and are taken out second identification code in the bitmap 72 and choose pointer, then, transfer interpreter 62 is chosen pointer according to second identification code and is obtained second VID=5 from identification code label tandem 80, come, No. 2 the network port can add the VID=5 label and carry out the output queue task equally sending multileaving information outside again.Each network port of the network equipment handle above-mentioned program abreast until each network port will identification code separately choose all positions of bitmap 72 inspect finish till.The example of the network equipment of 8 network ports is not that those skilled in the art can apply the present invention on the network equipment with arbitrary number network port in order to qualification the present invention just to illustrative purposes.

In another embodiment of the present invention, with reference to figure 6, requestor 40 comprises that also one carries out the processing unit 45 of network linking polymerization (Link Aggregation) function of observing the IEEE802.3ad standard, this processing unit 45 can be gathered the logic connection that a plurality of physical network ports form higher bandwidth, and can make network have more elasticity.

Comprehensive the above, the invention provides a kind of can be when crossing a plurality of VLAN distribution multileaving information, the devices and methods therefor that can pass on more efficiently not only can make full use of the resource of output queue on the network port, also do not inquire about and pass between ask the problem of accumulation when postponing.

Though the present invention discloses as above with a specific embodiment; so it is only in order to be easy to illustrate technology contents of the present invention; and be not with narrow sense of the present invention be defined in this embodiment; any those skilled in the art; without departing from the spirit and scope of the present invention; when can doing a little change and retouching, so protection scope of the present invention should be defined by the appended claims.

Claims

1. A device for multicast forwarding in a virtual local area network environment, which is suitable for distributing multicast information combined with a multicast address between multiple network ports of a network device. There are multiple Virtual local area networks are assigned to the multicast address, each virtual local area network has a multicast destination subset, the multicast destination subset is composed of at least one destination port, the destination port is from the network device specified among the network ports, the device includes:

a generating means for generating a multicast destination port-set by uniting each sub-set of multicast destinations in all said virtual local area networks assigned to the multicast address in the network device; and

A plurality of translators are respectively set on each network port of the network device, wherein each translator belonging to the network port in the multicast destination port group executes a virtual local area network identification code independently and in parallel translation of

Wherein, the multicast destination port group is all destination ports assigned to the multicast address by the network device;

The multicast forwarding device also includes:

a queryer for mapping the multicast address to an index value to which the multicast address and a bit string representing the multicast destination port group are assigned; and

A forwarder, coupled to the querier, is used for distributing the index value and multicast information to the group of multicast destination ports of the network device according to the bit string.

2. The multicast forwarding device as claimed in claim 1, wherein each of the translators translates the index value and an ID selection indicator into the VLAN ID.

3. The multicast forwarding device as claimed in claim 1, wherein the query device includes a bit address lookup table with a plurality of entries, each of which includes the multicast bit address, the index value, and The bit string.

4. The multicast transfer device as claimed in claim 1, wherein the bit string is used as a port mask, and each bit of the port mask corresponds to one of the network ports of the network device, and according to the port mask Forwarding multicast information to the multicast destination port group of the network device.

5. The multicast forwarding device of claim 1, wherein each of said translators comprises:

an ID tag serial, each of the network ports of the network device has a corresponding ID tag serial; and

An identification code selection table has a plurality of identification code selection bitmaps, each of the identification code selection bitmaps corresponds to the index value, wherein each of the identification code selection bitmaps is used as a selection mask for the corresponding network port Each valid bit of the select mask represents the ID select pointer for each of said network ports of the network device, and the ID select pointer selects from the sequence of ID tags associated with a multicast address The corresponding virtual local area network identification code of the connection.

6. The multicast forwarding device as claimed in claim 5, wherein each of said network ports of said network device can extract each said identification code selection bitmap from said identification code selection bitmap corresponding to said index value index.

7. A method for multicast forwarding in a virtual local area network environment, which is suitable for distributing multicast information combined with a multicast address between multiple network ports of a network device. There are multiple Virtual local area networks are assigned to the multicast address, each virtual local area network has a multicast destination subset, the multicast destination subset is composed of at least one destination port, the destination port is from the network device specified among the network ports, the method comprises the following steps:

A. Provide a multicast destination port group, an index value, at least one identification code selection indicator, and a plurality of identification code label serials, each of the identification code label serials respectively corresponding to each of the network equipment the above network port;

B. querying the multicast destination port group according to the index value assigned to the multicast address;

C. forwarding multicast information to the multicast destination port group of the network device; and

D. independently and in parallel find out all the virtual local area network identification codes of each of the network ports related to the multicast bit address, each of the virtual local area network identification codes of each of the network ports is determined by the index value , the identification code selection index and each of the identification code labels corresponding to each of the network ports are serially translated and generated;

Wherein, the multicast destination port group is all the above-mentioned destination ports assigned to the multicast bit address by the network device;

wherein the index value is assigned to the multicast address;

Wherein, the identification code selection pointer is associated with the index value.

8. The multicast forwarding method as claimed in claim 7, wherein step A comprises:

A1. Unionizing each sub-set of multicast destinations in all of the virtual local area networks assigned to the multicast bit address in the network device to generate the multicast destination port group;

A2. Store the multicast destination port group, the index value and the multicast address in one of a plurality of items in an address lookup table, wherein the multicast destination port group is stored in one of the items bit string; and

A3. Store the identification code selection pointer in one of the plurality of identification code selection bitmaps in an identification code selection table.

9. The multicast forwarding method as claimed in claim 8, wherein steps A1-A3 are performed in response to an IGMP service request.

10. The multicast forwarding method as claimed in claim 8, wherein step D comprises:

D1. Corresponding to the index value, select one of the identification code selection bitmaps from the identification code selection table;

D2. Take out the identification code selection pointers related to each of the network ports from the identification code selection bitmap;

D3. According to the identification code selection index obtained in step D2 and each of the identification code labels corresponding to each of the network ports in series, independently and in parallel to take out the virtual virtual address associated with the multicast address of each of the network ports LAN ID; and

D4. Steps D2 and D3 are repeated until all bits in the bitmap are selected for the identification code.

11. The multicast forwarding method as claimed in claim 8, further comprising the steps of:

E. Appending a tag to outgoing multicast messages for each of said network ports of the network device independently and in parallel.