Cisco's proprietary Cisco Group Management Protocol (CGMP) takes the multicast information, such as which hosts are members of which groups, and allows the routers/layer 3 switches to directly write the information to the layer 2 forwarding tables of the switches so that the switches can dynamically switch the IP multicasts at switch speed. If non-Cisco routers are using multicast, say with Distance Vector Multicast Routing Protocol (DVMRP), then although Cisco does not fully support DVMRP, the router will 'proxy' for these other routers and feed this information into the switches configured for CGMP。
思科公司独有的思科分组管理协议（CGMP）包含了多目广播信息，意思是说任何一个主机可以是任何一个组的成员，并且为了便于交换机能够在正常的交换速度下交换IP多目广播数据，允许路由器或三层交换机直接向二层交换机的地址转发表写入相应的信息。如果没有思科的路由器在使用多目广播，也就是说使用了距离矢量多目广播路由协议（DVMRP）这样的情况下虽然思科并不完全支持DVMRP，路由器会代理其他路由器并且为便于使用CGMP而将这个DVMRP信息放到交换机的配置中去。

In CGMP, the multicast router is considered to be the server since it has done all the work and the layer 2 switch is the CGMP client that uses the router's information to construct its forwarding tables (CAM) i.e. the router produces the CGMP packet and the switch reads it.
在CGMP协议中，多目广播路由器在所有服务完全启动后被认为是一个服务器并且二层交换机是使用路由器的信息来建立地址转发表的客户端。由路由器来处理CGMP数据包而交换机只能读懂这些数据包。
A CGMP router starts by sending a Join packet with the Group Destination MAC Address set to all zeros (meaning all multicast groups) and the source address as its own MAC address. This packet is sent every 60 seconds so that connected switches know that a CGMP router is online。
一个支持CGMP的路由器在发现网络上发送了一个带有分组目的MAC地址全为0（指所有的多目广播分组）的数据包后就会启动，源地址是它自己的地址。这个数据包每秒会发送一次以便于连接在网络上的交换机知道有一个CGMP路由器是在线可用的。
When a multicast router sees a client's IGMP packet it creates a CGMP packet. It maps the client's MAC address to the multicast MAC address within the CGMP packet. The CGMP packet contains a type field (Join or Leave a multicast group), the MAC address of the IGMP client and the multicast address of the group. The router is considered a CGMP server and the switch is the CGMP client. CGMP multicast packets are sent to the switches using the well-known multicast address 0x0100.0cdd.dddd. The switches take the CGMP mapping information and the forwarding table is programmed because the switch knows which client MAC address needs to see data from the multicast MAC address and adds the port to its list of forwarding ports for that particular mulicast group. Similarly, when a client wishes to leave a multicast group, a CGMP Leave message is created by the router and this results in the switch removing the client port from the forwarding table, thereby minimising the traffic throughput.
当一个多目广播路由发现一个客户端的IGMP协议数据包建立了一个CGMP数据包。它将客户端的MAC地址定位到多目广播MAC地址到数据包里。CGMP数据包含一个字段类型（加入或离开一个多目文播分组），它们分别是IGMP客户端的MAC地址和分组的多目广播地址。路由器被作为一个CGMP服务器而交换机是CGMP的客户端。将多目广播数据包发送到交换机时，使用的是众所周知的多目广播地址：0x0100.0cdd.ddd。交换机能够使用CGMP的地址映射信息和地址转发表是必须具备的功能，这是因为交换机要想知道哪个客户端MAC地址需要从多目广播MAC地址中找到自己所需的数据，并且为部分多目广播分组功能的实现在自己的转发端口添加相应的端口。同样地当一个客户端希望离开多目广播组，将由路由器建立一个拆除信息，而这将导致在交换机从地址转发表中移除客户端的端口，从而减少交换机的通信量。Cisco's proprietary Cisco Group Management Protocol (CGMP) takes the multicast information, such as which hosts are members of which groups, and allows the routers/layer 3 switches to directly write the information to the layer 2 forwarding tables of the switches so that the switches can dynamically switch the IP multicasts at switch speed. If non-Cisco routers are using multicast, say with Distance Vector Multicast Routing Protocol (DVMRP), then although Cisco does not fully support DVMRP, the router will 'proxy' for these other routers and feed this information into the switches configured for CGMP。
思科公司独有的思科分组管理协议（CGMP）包含了多目广播信息，意思是说任何一个主机可以是任何一个组的成员，并且为了便于交换机能够在正常的交换速度下交换IP多目广播数据，允许路由器或三层交换机直接向二层交换机的地址转发表写入相应的信息。如果没有思科的路由器在使用多目广播，也就是说使用了距离矢量多目广播路由协议（DVMRP）这样的情况下虽然思科并不完全支持DVMRP，路由器会代理其他路由器并且为便于使用CGMP而将这个DVMRP信息放到交换机的配置中去。

In CGMP, the multicast router is considered to be the server since it has done all the work and the layer 2 switch is the CGMP client that uses the router's information to construct its forwarding tables (CAM) i.e. the router produces the CGMP packet and the switch reads it.
在CGMP协议中，多目广播路由器在所有服务完全启动后被认为是一个服务器，而二层交换机是使用路由器的信息来建立地址转发表的客户端。由路由器来处理CGMP数据包而交换机只能读懂这些数据包。
A CGMP router starts by sending a Join packet with the Group Destination MAC Address set to all zeros (meaning all multicast groups) and the source address as its own MAC address. This packet is sent every 60 seconds so that connected switches know that a CGMP router is online。
一个支持CGMP的路由器在发现网络上发送了一个带有分组目的MAC地址全为0（指所有的多目广播分组）的数据包后就会启动，源地址是它自己的地址。这个数据包每秒会发送一次以便于连接在网络上的交换机知道有一个CGMP路由器是在线可用的。
When a multicast router sees a client's IGMP packet it creates a CGMP packet. It maps the client's MAC address to the multicast MAC address within the CGMP packet. The CGMP packet contains a type field (Join or Leave a multicast group), the MAC address of the IGMP client and the multicast address of the group. The router is considered a CGMP server and the switch is the CGMP client. CGMP multicast packets are sent to the switches using the well-known multicast address 0x0100.0cdd.dddd. The switches take the CGMP mapping information and the forwarding table is programmed because the switch knows which client MAC address needs to see data from the multicast MAC address and adds the port to its list of forwarding ports for that particular mulicast group. Similarly, when a client wishes to leave a multicast group, a CGMP Leave message is created by the router and this results in the switch removing the client port from the forwarding table, thereby minimising the traffic throughput.
当一个多目广播路由发现一个客户端的IGMP协议数据包建立了一个CGMP数据包。它将客户端的MAC地址定位到多目广播MAC地址到数据包里。CGMP数据包含一个字段类型（加入或离开一个多目文播分组），它们分别是IGMP客户端的MAC地址和分组的多目广播地址路由器被作为一个CGMP服务器而交换机是CGMP的客户端。将多目广播数据包发送到交换机时，使用的是众所周知的多目广播地址：0x0100.0cdd.ddd。交换机能够使用CGMP的地址映射信息和地址转发表是必须具备的功能，这是因为交换机要想知道哪个客户端MAC地址需要从多目广播MAC地址中找到自己所需的数据，并且为部分多目广播分组功能的实现在自己的转发端口添加相应的端口。同样地当一个客户端希望离开多目广播组，将由路由器建立一个拆除信息，而这将导致在交换机从地址转发表中移除客户端的端口，从而减少交换机的数据流量。

本人E文看不太懂，所以PFPF！