WO2011144048A2 - Multicast realization method and network device - Google Patents

Abstract

The present invention discloses a multicast realization method and a network device. The method includes: a first network device receives an Internet Group Management Protocol (IGMP) message from a terminal, wherein the IGMP message includes a multicast group information requested by the terminal; a multicast backup information is obtained, and the multicast backup information includes the information of the port through which the IGMP message is received, the information of the terminal and the multicast group information; the multicast backup information is sent to a second network device so as to enable the second network device to forward a multicast stream to the terminal according to the multicast backup information when the first network device fails. By adopting the technical solution provided by embodiments of the present invention, the problems of the interruption of Internet Protocol Television (IPTV) service caused by the failure of a master router or a master link and bad user experience in the art are solved.

Description

 Description

 Method and network device for implementing multicast

 The present invention relates to the field of network communications, and in particular, to a multicast implementation method and a network device. Background technique

 When deploying IPTV (Internet Protocol Television) services, because IPTV has high reliability requirements, it is usually necessary to adopt a redundant method. At least two routers are deployed on the edge of the IP backbone network, and a DR (Designated Router) is selected. The router is elected to back up the router. The DR is responsible for replicating the multicast stream to the downstream terminal. When the DR is faulty, the BDR is upgraded to the primary role and is responsible for replicating the multicast stream downstream. However, the IPTV service will be interrupted for a long time and the user experience is poor. Summary of the invention

 The embodiments of the present invention provide a multicast implementation method and a network device to solve the problem that the IPTV service is interrupted due to a network device or link failure, and the user experience is poor.

 To solve the above technical problem, an embodiment of the present invention provides a multicast implementation method, including:

 The first network device receives the multicast group management protocol IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal;

Obtaining multicast backup information, where the multicast backup information includes receiving the IGMP message. Port information, information of the terminal, and the multicast group information;

 Sending the multicast backup information to the second network device, so that the second network device forwards the multicast stream to the terminal according to the multicast backup information when the first network device is faulty. The embodiment of the present invention provides a multicast network device, including: a first receiver, configured to receive a multicast group management protocol IGMP message from a terminal, where the IGMP message includes the multicast requested by the terminal Group information

 An acquiring module, configured to obtain multicast backup information, where the multicast backup information includes port information for receiving the IGMP message, information about the terminal, and the multicast group information; The second network device sends the multicast backup information, so that the second network device forwards the multicast stream to the terminal according to the multicast backup information when the network device is faulty. The embodiment of the present invention provides a second network device implemented by multicast, including: a second receiver, configured to receive multicast backup information from a first network device, where the multicast backup information includes the first network The device receives the port information of the multicast group management protocol IGMP message from the terminal, the information of the terminal, and the multicast group information;

 An update module, configured to update local IGMP group information according to the multicast group backup information;

 And a second transmitter, configured to forward the multicast stream to the terminal according to the local IGMP group information when the first network device is faulty.

By using the technical solution provided by the embodiment of the present invention, the multicast group information of the terminal is backed up on the second network device. When the first network device is faulty, the multicast network is forwarded by the second network device, and the IPTV service is not interrupted. The user experience. DRAWINGS

 1 is a schematic diagram of a network for deploying an IPTV service by using a dual-system hot backup technology; FIG. 2 is a flowchart of a multicast implementation method according to an embodiment of the present invention; FIG. 3 is a multicast implementation according to an embodiment of the present invention. Network device block diagram; FIG. 4 is a block diagram of a second network device implemented by a multicast according to an embodiment of the present invention. detailed description

 The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

 The embodiment of the invention provides a multicast implementation method and a network device. The method includes: receiving, by the first network device, a multicast group management protocol IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal; acquiring multicast backup information, the multicast backup information And including the port information of the IGMP message, the information about the terminal, and the multicast group information; and sending the multicast backup information to the second network device, so that the second network device is in the first When the network device is faulty, the multicast stream is forwarded to the terminal according to the multicast backup information. The technical solution provided by the embodiment of the present invention can solve the problem that the IPTV service is interrupted due to the failure of the primary router or the primary link, and the user experience is poor.

The deployment of IPTV services requires the use of IP multicast technology. The IP multicast technology is used by the multicast source to send IP packets. The destination IP address of the packet is the multicast group address. Only the terminal device that joins the multicast group can receive the IP multicast packet. To implement IP multicast packet forwarding on the network, that is, multicast stream transmission, an interoperable IP multicast protocol must be run on the device. IP multicast protocol includes multicast group management protocol IGMP (Internet Group)

Management Protocol ) is a mechanism for establishing and maintaining multicast membership between a terminal and a router. In the IGMP protocol, when the terminal wants to join the specified multicast group, it sends an IGMP Report message carrying the multicast group address. When the terminal wants to leave the specified multicast group, it sends the IGMP carrying the multicast group address. Leave message. The router periodically checks whether a member of a known multicast group is active through the IGMP protocol, and collects and maintains the membership of the connected network group.

 In order to provide IPTV service reliability, dual-system hot backup technology can be adopted. The dual-system refers to the two primary and secondary network devices. The two network devices use the active and standby election protocols, such as the Virtual Router Redundancy Protocol (VRRP) to determine the primary and backup relationships. The aggregation switch is dual-homed to this. On two network devices. The link, port, or VLAN of each pair of primary and secondary relationships is called a protection group and can pass the protection group ID (identification). The protection group relationship table is stored on the primary and backup network devices, including the port number of the primary network device, the protection group ID, and the port number of the standby network device. Figure 1 is a network diagram for deploying IPTV services using dual-system hot backup technology. The first network device is in a standby state, and the second network device is in a standby state. The switch 1 is dual-homed to the first network device and the second network device, and the port 1 of the first network device and the port 4 of the second network device are a pair. Active and standby ports. Example 1

 FIG. 2 is a flowchart of a multicast implementation method according to an embodiment of the present invention, where the method includes:

The first network device receives the IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal. The multicast group information includes a multicast group address, a multicast source address may further include _£ The first network device updates the local IGMP group information according to the IGMP message, where the IGMP group information includes multicast group information and an egress port list.

 The first network device updates the outbound port list of the local IGMP group information according to the port that receives the IGMP message.

 For example, as shown in FIG. 1 , the first network device receives the IGMP Report message of the terminal 1 through the port 1 and requests to join the multicast group 1; when there is no multicast group 1 in the local IGMP group information of the first network device, Add multicast group 1 address and port 1; when there is already multicast group 1, add port 1 to the outbound port list of multicast group 1. If the terminal 1 sends an IGMP Leave message to the multicast group 1, the port 1 is deleted from the outbound port list in multicast group 1 in the IGMP group information.

 The first network device may establish a multicast path with the multicast source according to the local IGMP group information, and receive the multicast stream from the multicast source. For example, according to the local IGMP group information, PIM (Protocol Independent Multicast) is applied. The PIM protocol is applied to multicast routers to establish and maintain multicast routes. A multicast source establishes a secondary multicast source. A data transmission path to multiple receiving ends) establishes a multicast path with a multicast source.

 The first network device may generate a multicast forwarding table according to the local IGMP group information, and forward the multicast stream to the terminal, where the multicast forwarding table includes an ingress port, a multicast group information, and an egress port list.

 102: Obtain multicast backup information, where the multicast backup information includes port information of receiving the IGMP message, information about the terminal, and the multicast group information.

 The first network device may obtain information about the terminal according to the link layer encapsulation information of the IGMP. The information of the terminal includes an IP address of the terminal, a MAC address of the terminal, a VLAN tag (for example, a public network VLAN tag, a private network VLAN tag), and the like.

103: Send the multicast backup information to a second network device, so that the second network When the first network device fails, the network device forwards the multicast stream to the terminal according to the multicast backup information.

 The first network device and the second network device may be a service gateway or a router, such as a BRAS (Broadband Remote Access Server).

 The first network device and the second network device are in a master-slave relationship.

 The first network device and the second network device can determine the relationship between the master and the backup through the active and standby election protocols, for example, VRRP, and maintain the relationship between the master and the backup.

 The first network device and the second network device store a protection group relationship table, including a correspondence between a primary network device port number, a protection group ID, and a backup network device port number.

 The port information may be a port number or a protection group ID. For example, the protection group ID can be obtained by querying the protection group relationship table according to the port number of the IGMP message.

 Before receiving the IGMP message from the terminal, the first network device may establish a PPOOE (Point-to-Point Protocol over Ethernet) session with the terminal, and in the The PPPOE session information is backed up on the network device, so that the second network device maintains a PPPOE session with the terminal when the first network device fails.

 The IGMP message can be encapsulated by PPPOE.

 The first network device may send the multicast backup information to the second network device by using a control plane, such as a signaling channel. Or,

 The first network device may also establish a reliable transmission channel, such as a TCP connection, with the second network device, and send the multicast backup information to the second network device through the reliable transmission channel.

The second network device may query the protection group relationship table according to the port information, and obtain an outbound port that the second network device forwards the multicast stream to the terminal. For example, as shown in FIG. 1, the first network device receives the IGMP message from the terminal 1 through the port 1, and the port information sent by the first network device to the second network device is the port number 1, and the second network device Query the entry in the protection group relationship table with the primary port number being 1, and obtain the corresponding backup port number 4. That is, when the first network device fails, the second network device sends the multicast data to the terminal. Port 4.

 The second network device may update the local IGMP group information according to the multicast group information and the egress port.

 The network device may also generate an IGMP copy message, where the IGMP copy message includes at least the IGMP message and the data link layer header from the terminal. For example, the format of the IGMP replication packet is as follows:

 0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- +■ - + - +■ -+-

1 Vers ion | Type 1 Length 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- +

1 Packet Length 1 reserved 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+

1 Packet 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+

1 Attributes ...

 +' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+ where:

 Version: Protocol version number, this field is 1 byte. For example, you can fill in 0x01, which means version 1;

Type: Type of the message. This field is 1 byte. For example, you can define the values as follows:

1 : IGMP packet type;

 Length: Defines the length of the entire multicast group request message. The field is 2 bytes and its value is >=4 bytes.

 Packet Length: defines the length of the Packet part, which is 2 bytes; Reserved: Reserved field, this field is 2 bytes;

Packet: The packet body, which may include a data link layer header and an IGMP packet, and has a variable length; Attributes: An attribute field, which is a variable length field, can contain multiple attributes, each of which is in TLV (Type Length Value) format. E.g:

+ + +

 I AttrType | AttrLen | Att rValue

 + + +

 AttrType: Describes the type of the attribute, which is 1 byte. For example, you can define the following attribute types:

 1: Indicates the VRF (VPN Routing and Forwarding Table) name attribute, which is used to identify which Layer 3 VPN the terminal belongs to.

Private Network, virtual private network) domain.

 The first network device sends the foregoing packet to the second network device.

 The second network device can simulate the manner in which the terminal sends IGMP messages, and constructs a packet format that can be processed by the IGMP protocol stack according to the foregoing packet.

 The second network device may update the local IGMP group information according to the foregoing packet. The second network device may establish a multicast path with the multicast source according to the local IGMP group information, and receive the multicast stream from the multicast source.

 The second network device may send a port list to the forwarding plane according to the local IGMP group information, and generate a multicast forwarding table. When the second network device is in the standby state, the second network device does not perform multicast data. Encapsulating, not forwarding the multicast stream to the egress port; when the first network device fails, the second network device switches to the primary state, the second network device encapsulates the multicast data, and forwards the data to the egress port Multicast stream. Or, when the second network device is in the standby state, the second network device does not send the port list to the forwarding plane, and because there is no out port, the multicast stream is not forwarded to the terminal; when the first network device When the second network device is switched to the primary state, the second network device sends a port list according to the local IGMP group information, generates a multicast forwarding table, and encapsulates the multicast data, and forwards the multicast stream to the terminal. .

The technical solution provided by the embodiment of the present invention is backed up on the second network device. The IGMP group information of the terminal, when the first network device fails, the second network device continues to forward the multicast stream to the terminal, and the IPTV service is not interrupted, thereby ensuring the user experience. Example 2

 FIG. 3 is a block diagram of a network device implemented by a multicast according to an embodiment of the present invention. The network device includes a first receiver 201, an obtaining module 202, and a first transmitter 203. among them:

 The first receiver 201 is configured to receive an IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal;

 The obtaining module 202 is configured to obtain multicast backup information, where the multicast backup information includes port information of the IGMP message, information about the terminal, and the multicast group information.

 The first transmitter 203 is configured to send the multicast backup information to the second network device, so that the second network device sends the multicast backup information to the terminal according to the multicast backup information when the network device is faulty. Forward the multicast stream.

 Can

 The multicast group information includes a multicast group address, and may also include a multicast source address. The network device is further configured to update the local IGMP group information according to the IGMP message, where the IGMP group information includes the multicast group information and the outbound port list.

 The network device updates the outbound port list of the local IGMP group information according to the port that receives the IGMP message.

 The network device may establish a multicast path with the multicast source according to the local IGMP group information, and receive the multicast stream from the multicast source.

The obtaining module 202 may obtain information about the terminal according to the link layer encapsulation information of the IGMP. The information of the terminal includes an IP address of the terminal, and the terminal MAC address, VLAN tag (such as public network VLAN tag, private network VLAN tag).

 The network device and the second network device may be routers, such as BRAS.

 The network device and the second network device are in a master-slave relationship.

 The network device may further include:

 The master/slave relationship module 204 is configured to run an active/standby election protocol, such as VRRP, to maintain a master-slave relationship with the second network device.

 The network device and the second network device store a protection group relationship table, including a correspondence between a primary network device port number, a protection group ID, and a backup network device port number.

 The port information may be a port number or a protection group ID. For example, the protection group ID can be obtained by querying the protection group relationship table according to the port number of the IGMP message.

 The network device may establish a PPPOE session with the terminal before receiving the IGMP message from the terminal. The network device may back up the PPPOE session information on the second network device, so that the second network device maintains a PPPOE session with the terminal when the network device fails.

 The IGMP message can be encapsulated by PPPOE.

 The transmitter 203 may send the port information, the information of the terminal, and the multicast group information to a second network device by using a control plane, such as a signaling channel.

 The network device may also establish a reliable transmission channel, such as a TCP connection, with the second network device, and the transmitter 203 sends the port information and the device to the second network device by using the reliable transmission channel. The information about the terminal and the multicast group information.

The second network device queries the protection group relationship table according to the port information, and obtains an egress port that the second network device forwards the multicast stream to the terminal. The second network device may update the local IGMP group information according to the multicast group information and the egress port.

 The network device may also generate an IGMP copy message, where the IGMP copy message includes at least the IGMP message and the data link layer header from the terminal.

 For example, the format of the IGMP copy is as follows:

 0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+- +-+ -+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+ - + - -+-+-+-+ -+- +■ - + - + - + - +

1 Vers ion | Type 1 Length 1

+- +-+ -+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+ - + - -+-+-+-+ -+- - + - + - + - ' +

1 Packet Length 1 reserved 1

+- +-+ -+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+ - + - -+-+-+-+ -+- - + - + - + - ' +

1 Packet 1

+- +-+ -+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+ - + - -+-+-+-+ -+- - + - + - + - ' +

1 Attributes ...

 +- + -+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+ - + - -+-+-+-+-+- - + - + - + - ' +

Version: Protocol version number, this field is 1 byte. For example, you can fill in 0x01, which means version 1;

 Type: Type of the message. This field is 1 byte. For example, the values can be defined as follows: 1 : IGMP message type;

 Length: Defines the length of the entire multicast group request message. The field is 2 bytes and its value is >=4 bytes.

 Packet Length: defines the length of the Packet part, which is 2 bytes; Reserved: Reserved field, this field is 2 bytes;

 Packet: The packet body, which may include a data link layer header and an IGMP packet, and has a variable length;

 Attributes: An attribute field, which is a variable length field, can contain multiple attributes, each of which is in TLV (Type Length Value) format. E.g:

 + + +

 I AttrType | AttrLen | Att rValue

+ + + AttrType: Describes the type of the attribute, which is 1 byte. For example, you can define the following attribute types:

 1: Indicates the VRF (VPN Routing and Forwarding Table) name attribute, which is used to identify the domain of the Layer 3 VPN (Virtual Private Network) to which the terminal belongs.

 The network device sends the foregoing packet to the second network device.

 The second network device can simulate the manner in which the terminal sends IGMP messages, and constructs a packet format that can be processed by the IGMP protocol stack according to the foregoing packet.

 The second network device may update the local IGMP group information according to the foregoing packet. When the network device fails and the second network device is switched to the primary state, the second network device forwards the multicast stream to the terminal according to the multicast forwarding table generated by the local IGMP group information. Example 3

 Referring to FIG. 4, it is a block diagram of a second network device implemented by a multicast according to an embodiment of the present invention. The second network device includes a second receiver 301, an update module 302, and a second transmitter 303. among them:

 The second receiver 301 is configured to receive multicast backup information from the first network device, where the multicast backup information includes the port information that the first network device receives the multicast group management protocol IGMP message from the terminal. The information about the terminal and the multicast group information; the update module 302 is configured to update the local IGMP group information according to the multicast group backup information;

 The second transmitter 303 is configured to forward the multicast stream to the terminal according to the local IGMP group information when the first network device is faulty.

The first network device obtains multicast backup information, where the multicast backup information includes port information that the first network device receives an IGMP message from the terminal, where the terminal Information and the multicast group information.

 The port information may be a port number or a protection group ID.

 The multicast group information includes a multicast group address, and may also include a multicast source address.

 The information of the terminal includes an IP address of the terminal, a MAC address of the terminal, a VLAN tag (for example, a public network VLAN tag, a private network VLAN tag), and the like.

 The first network device and the second network device may be routers, such as BRAS.

 The first network device and the second network device are in a master-slave relationship.

 The second network device may also run an active/standby election protocol, such as VRRP, to maintain a master-slave relationship with the first network device.

 The second network device stores a protection group relationship table, including a correspondence between a primary network device port number, a protection group ID, and a backup network device port number.

 Before the multicast backup information from the first network device, the second receiver 301 receives PPPOE session information from the terminal of the first network device; when the first network device fails, the The second network device is further configured to maintain a PPPOE session with the terminal according to the PPPOE session information.

 The second network device may update the local IGMP group information according to the multicast backup information. specifically,

 The second network device queries the protection group relationship table according to the port information, and obtains an outbound port that the second network device forwards the multicast stream to the terminal;

 The second network device updates the local IGMP group information according to the multicast group information and the egress port.

The second network device may receive an IGMP copy message from the first network device, where the IGMP copy message includes at least the IGMP message and the data link layer header from the terminal. For example, the format of the IGMP copy message is as follows:

 0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- +■ - + - +■ -+-

1 Vers ion | Type 1 Length 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- +

1 Packet Length 1 reserved 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+

1 Packet 1

+' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+

1 Attributes ...

 +' -+-+-+-+-+-+-+-+ -+-+-+-+- +-+-+-+- - + - -+■ -+- -+-+-+ -+-+- - + - -+- '+ where:

 Version: Protocol version number, this field is 1 byte. For example, you can fill in 0x01, which means version 1;

Type: Type of the message. This field is 1 byte. For example, the values can be defined as follows: 1 : IGMP message type;

 Length: Defines the length of the entire multicast group request message. The field is 2 bytes and its value is >=4 bytes.

 Packet Length: defines the length of the Packet part, which is 2 bytes; Reserved: Reserved field, this field is 2 bytes;

 Packet: The packet body, which may include a data link layer header and an IGMP packet, and has a variable length;

 Attributes: An attribute field, which is a variable length field, can contain multiple attributes, each of which is in TLV (Type Length Value) format. E.g:

 + + +

 I AttrType | AttrLen | Att rValue

 + + +

 AttrType: Describes the type of the attribute, which is 1 byte. For example, you can define the following attribute types:

1: Indicates the VRF (VPN Routing and Forwarding Table) name attribute, which is used to identify the domain of the Layer 3 VPN (Virtual Private Network) to which the terminal belongs. The second network device may simulate a manner in which the terminal sends an IGMP message, and construct a packet format that can be processed by the IGMP protocol stack according to the IGMP copy message.

 The second network device may update the local IGMP group information according to the IGMP copy message.

 The second network device may establish a multicast path with the multicast source according to the local IGMP group information, and receive the multicast stream from the multicast source.

 The second network device may send a port list to the forwarding plane according to the local IGMP group information, and generate a multicast forwarding table. When the second network device is in the standby state, the second network device does not perform multicast data. Encapsulating, not forwarding the multicast stream to the egress port; when the first network device fails, the second network device switches to the primary state, the second network device encapsulates the multicast data, and forwards the data to the egress port Multicast stream. Or, when the second network device is in the standby state, the second network device does not send the port list to the forwarding plane, and because there is no out port, the multicast stream is not forwarded to the terminal; when the first network device When the second network device is switched to the primary state, the second network device sends a port list according to the local IGMP group information, generates a multicast forwarding table, and encapsulates the multicast data, and forwards the multicast stream to the terminal. . The technical solution provided by the embodiment of the present invention is also applicable to the control of the primary and backup links by using MC-LAG (Multi-Chassis Link Aggregation Group) or Smartlink (Flexible Link, or Backup Link) technology. Network scenario.

 According to the technical solution provided by the embodiment of the present invention, when the IGMP group information of the terminal is backed up on the second network device, when the first network device fails, the second network device maintains the IGMP group information of the terminal, and the second The network device can continue to forward the multicast stream to the terminal, and the IPTV service is not interrupted, thereby ensuring the user experience. In the prior art, when the primary router fails, the IPTV service is interrupted, and the user experience is poor.

Those skilled in the art can understand that all of the above embodiments are implemented or Part of the steps may be completed by a program to instruct related hardware, and the program may be stored in a computer readable storage medium, which may be a ROM/RAM, a magnetic disk or an optical disk or the like.

 The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of changes or within the technical scope disclosed by the present invention. Alternatives are intended to be covered by the scope of the present invention.

Claims

Claim  A multicast implementation method, comprising:  The first network device receives the multicast group management protocol IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal;  Obtaining the multicast backup information, where the multicast backup information includes the port information of the IGMP message, the information about the terminal, and the multicast group information.  Sending the multicast backup information to the second network device, so that the second network device forwards the multicast stream to the terminal according to the multicast backup information when the first network device is faulty.  2. The method according to claim 1, further comprising: transmitting the multicast backup information to the second network device by using a control plane; or  Transmitting the multicast backup information to the second network device by using a reliable transmission channel established between the second network device.  The method according to claim 1 or 2, wherein the first network device and the second network device are in a master-slave relationship.  A network device implemented by multicast, which is characterized in that:  a first receiver, configured to receive a multicast group management protocol IGMP message from the terminal, where the IGMP message includes the multicast group information requested by the terminal;  An acquiring module, configured to obtain multicast backup information, where the multicast backup information includes port information for receiving the IGMP message, information about the terminal, and the multicast group information; The second network device sends the multicast backup information, so that the second network device forwards the multicast stream to the terminal according to the multicast backup information when the network device is faulty. 5. The network device according to claim 4, wherein the transmitter Specifically used,  Transmitting the multicast backup information to the second network device by using a control plane; or  Transmitting the multicast backup information to the second network device by using a reliable transmission channel established between the second network device.  The network device according to claim 4, wherein the network device further comprises:  An active/standby relationship module is configured to run an active/standby election protocol to maintain a primary and backup relationship with the second network device.  A second network device implemented by the multicast, comprising: a second receiver, configured to receive multicast backup information from the first network device, where the multicast backup information includes the first network The device receives the port information of the multicast group management protocol IGMP message from the terminal, the information of the terminal, and the multicast group information;  An update module, configured to update local IGMP group information according to the multicast group backup information;  And a second transmitter, configured to forward the multicast stream to the terminal according to the local IGMP group information when the first network device is faulty.  The second network device according to claim 7, wherein the second network device is further configured to:  Before updating the local IGMP group information according to the multicast group backup information, querying the protection group relationship table according to the port information, and obtaining an outgoing port for forwarding the multicast stream to the terminal. The second network device according to claim 7 or 8, wherein the second network device is further configured to send a port list to the forwarding plane to generate a multicast forwarding table. When the second network device is in the standby state, the second transmitter does not forward the multicast stream to the egress port;  When the first network device fails and the second network device is switched to the primary state, the second transmitter forwards the multicast stream to the terminal according to the multicast forwarding table.  The second network device according to claim 7 or 8, wherein the second network device is further configured to:  When the second network device is in the standby state, the port list is not sent to the forwarding plane;  When the first network device fails, the second network device switches to a primary state, and sends a port list to the forwarding plane to generate a multicast forwarding table; the second transmitter sends the multicast forwarding table to the terminal according to the multicast forwarding table. Forward the multicast stream.