CN1458771A - Multicasting messag transmission method base on two layer exchange device - Google Patents

Abstract

The invention discloses a method for forwarding multicast messages based on a layer-2 switching device. In the method, the layer-2 switching device first receives an Internet Group Management Protocol (IGMP) message from an access port, and judges whether there is a virtual local area network in the message (VLAN) header, if not, add the virtual LAN identifier (VLANID) of the access port to the message to form a virtual LAN header, and then generate the VLANID and multicast media access control (MAC) address of the access port to receive The mapping relationship table of the physical port of the IGMP message, and the mapping relationship table of the virtual local area network identification and the multicast media access control address of the generated uplink port to the physical port receiving the IGMP message, and finally perform according to the above mapping relationship table Forwarding of multicast packets; adopting the above scheme can solve the problem that the multicast data packets without VLAN headers received by the uplink port of the layer 2 switching device cannot be effectively forwarded, and can avoid the waste of network resources.

Description

A method for forwarding multicast packets based on Layer 2 switching equipment

technical field

The invention relates to a message forwarding method in a communication network, in particular to a multicast message forwarding method based on a two-layer switching device.

Background technique

Currently, in a broadband network, a user terminal usually accesses the network through a Layer 2 switching device, and the most common Layer 2 switching device is an Ethernet Layer 2 switch (LANSWITCH) supporting the 802.1Q protocol. The following uses LANSWITCH as an example to illustrate the forwarding of multicast packets. All packets sent by LANSWITCH user terminals connected to the network must be added with a special tag for user terminal identification. In practice, this tag is usually a virtual local area network (VLAN: Virtual Local Area Network) tag. This VLAN The label can uniquely identify the specific physical interface where the user terminal accesses LANSWITCH, that is, the Ethernet format message sent by the user from the access port will be added with a VLAN header to identify the port location of the user's access after passing through the switch. The forwarding method of LANSWITCH for all received messages is as follows: Search the Layer 2 forwarding table according to the destination MAC address in the message and the VLAN ID in the VLAN header, that is, the mapping table from the MAC address and VLAN ID to the physical port. If a match is found, Then the message is forwarded from the corresponding physical port; if no match is found, the message is forwarded to all physical ports corresponding to the VLANID in the VLAN header, which is equivalent to broadcast sending. Since the Layer 2 forwarding table is generated based on the source MAC address and VLAN ID in the packet and the physical port that received the packet, and since the multicast MAC address cannot be used as the unicast MAC address to identify the terminal device, the multicast The packet uses a multicast MAC address that does not appear as the source MAC address at all as the destination MAC address of the packet. If no special processing is performed, LANSWITCH cannot generate a Layer 2 forwarding table for the multicast MAC address. , LANSWITCH can only broadcast multicast packets to all ports, which greatly wastes system bandwidth resources and seriously affects the performance of LANSWITCH. In order to improve LANSWITCH's processing of multicast messages, LANSWITCH intercepts the user's Internet Group Management Protocol (IGMP) message, and uses the VLAN ID (VLANID) and multicast MAC address of the port that received the IGMP message to generate information about the multicast message. For the Layer 2 forwarding table of the MAC address, once LANSWITCH generates the Layer 2 forwarding table for the multicast MAC address, for the multicast data message received later, it can search the Layer 2 forwarding table for forwarding in the same way as ordinary messages , so as to prevent LANSWITCH from broadcasting and forwarding multicast packets.

It can be seen from the processing of the message by LANSWITCH above that when LANSWITCH receives a message without a VLAN header, it will automatically extend a VLAN header to the message, and the VLAN header is based on receiving the message. The VLANID of the port is constructed. When LANSWITCH generates a Layer 2 forwarding table about the multicast MAC address, its VLAN ID uses the VLAN ID of the access port on the user side that received the IGMP message. For data packets (actually, the sources of multicast programs are all on the network side, and the multicast data packets are all sent from the uplink port of LANSWITCH), LANSWITCH will add a VLAN header composed of the VLANID of the uplink port to the packet, However, the VLAN IDs of the user-side port and the uplink-side port are different, so the generated Layer 2 forwarding table about the multicast MAC address has no As a result, LANSWITCH will still treat multicast packets as broadcast packets, and forward them according to the physical port corresponding to the VLANID, which will still waste a lot of network resources.

Contents of the invention

The purpose of the present invention is to provide a layer-2 switching device-based multicast message forwarding method that avoids waste of network resources.

In order to achieve the above object, the multicast message forwarding method based on the two-layer switching equipment provided by the present invention includes:

(1) Layer 2 switching device receives Internet Group Management Protocol (IGMP) message from the access port;

(2) judge whether there is a virtual local area network (VLAN) head in the message, if there is, go to step (3), otherwise add the virtual local area network identification (VLANID) of the access port to the message to form a virtual local area network head;

(3) generate the virtual local area network identification (VLANID) of the access port and the mapping relationship table of the multicast media access control (MAC) address to the physical port receiving the IGMP message, and generate the virtual local area network identification and group of the uplink port A mapping relationship table from the broadcast media access control address to the physical port receiving the IGMP message;

(4) Forwarding the multicast message according to the above mapping relationship table.

The present invention has used the VLANID of the uplink port of LANSWITCH when generating the multicast two-layer forwarding table, has increased the VLANID of the uplink port of LANSWITCH and the mapping relationship table of the multicast MAC address to the physical port that receives this IGMP message, because Create two forwarding tables when generating the multicast Layer 2 forwarding table: the VLANID in one forwarding table uses the VLANID of the user-side port that received the IGMP join message, and the VLANID in the other forwarding table uses the VLANID of the uplink port of LANSWITCH, Therefore, the problem that the multicast data message without the VLAN header received by the LANSWITCH uplink port cannot be effectively forwarded is solved, so the method of the present invention can avoid the waste of network resources by forwarding the IGMP multicast message.

Description of drawings

Fig. 1 is the flow chart of the embodiment of the method of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Generally, there are two types of multicast packets processed by Layer 2 switching devices: IGMP packets and multicast data packets. These are two different types of messages, although they both use the multicast MAC address as the destination MAC address: the IGMP message is a signaling control message for the user terminal to notify the network device that a certain multicast service is needed. When a certain multicast service is provided, the corresponding IGMP message will be sent out, and the destination MAC address of the IGMP message and the destination MAC address of the corresponding multicast data message use exactly the same multicast MAC address; while the multicast data message The text is the real data packet carrying the content of the multicast service. Therefore, the generation of the Layer 2 forwarding table of the multicast message by the Layer 2 switching device requires the participation of the IGMP message, and then the Layer 2 forwarding table is used to forward the multicast data message.

In order to enable the two-layer switching equipment to realize the non-broadcast forwarding of multicast messages with VLAN headers and without VLAN headers, the present invention sets up a second-layer forwarding table when generating the multicast two-layer forwarding table, so that through two The Layer 2 forwarding table can implement non-broadcast forwarding of multicast packets with and without VLAN headers. The present invention will be described below by taking an Ethernet Layer 2 switch (LANSWITCH) as an example.

Fig. 1 is the flow chart of the embodiment of the method of the present invention. According to Fig. 1, realize the present invention has 5 steps altogether. First, LANSWITCH receives the Internet Group Management Protocol (IGMP) message from the access port in step 1, then judges in step 2 whether there is a virtual local area network (VLAN) header in the message, if so, turn to step 4, otherwise in step 2 3 Add the virtual local area network identifier (VLANID) of the access port to the message to form a virtual local area network header, for example, the IGMP message sent by a user terminal that does not support the 802.1Q protocol will not have a VLAN header, so the IGMP message The VLAN header is automatically added by LANSWITCH, and is composed of the virtual local area network identification (VLANID) of the access port; then turn to step 4; in step 4, generate the virtual local area network identification (VLANID) and multicast of the access port The mapping relationship table from the media access control (MAC) address (that is, the destination MAC address of the IGMP message) to the physical port that receives the IGMP message. This table is generated by the function of traditional LANSWITCH. This is done for compatibility with traditional , because if the upper layer equipment connected on LANSWITCH supports the 802.1Q protocol, it can send out a multicast data packet with the VLANID of the access port; simultaneously generate the virtual local area network identification and the multicast media access control address of the uplink port (ie The destination MAC address of IGMP message) to the mapping relationship table of the physical port that receives this IGMP message; Finally in step 5, carry out the forwarding of multicast data message according to above-mentioned mapping relationship table.

When the LANSWITCH uplink port receives a multicast data packet without a VLAN header, LANSWITCH will automatically add a VLAN header composed of the VLANID of the uplink port to the packet, and then LANSWITCH will use the multicast MAC address in the packet, that is, the group The destination MAC address of the broadcast data message and the VLANID of the uplink port are searched for the Layer 2 forwarding table, because step 3 has generated the mapping relationship table of the VLANID of the uplink port and the corresponding multicast MAC address to the physical port receiving the IGMP message , LANSWITCH directly forwards the multicast data message to this physical port, which ensures that the user who sends the IGMP message can receive the multicast data message and obtain the multicast service.

Claims (2)

1. A method for forwarding multicast packets based on a Layer 2 switching device, comprising: (1) Layer 2 switching device receives Internet Group Management Protocol (IGMP) message from the access port; (2) judge whether there is a virtual local area network (VLAN) head in the message, if there is, go to step (3), otherwise add the virtual local area network identification (VLANID) of the access port to the message to form a virtual local area network head; (3) generate the virtual local area network identification (VLANID) of the access port and the mapping relationship table of the multicast media access control (MAC) address to the physical port receiving the IGMP message, and generate the virtual local area network identification and group of the uplink port A mapping relationship table from the broadcast media access control address to the physical port receiving the IGMP message; (4) Forwarding the multicast message according to the above mapping relationship table. 2. The multicast packet forwarding method according to claim 1, characterized in that: the layer-2 switching device is a layer-2 Ethernet switch.

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