About IGMP snooping and IGMP proxies

At present, in the IP network, the operator's network to provide more services for the purpose, no longer in the form of xDSL to provide users, but directly provide a unified width interface, in some broadband community this form is particularly common.

At present, in the broadband community to apply the most in addition to Internet services, more is to provide IPTV applications. In the promotion of IPTV, for the involved access layer switching equipment, the device is generally required to support VLAN technology and multicast technology. For the access layer switch, there are two types of support for multicast: IGMP snooping and IGMP Proxy.

IGMP snooping is relatively simple, and it is a multicast table entry for a multicast by listening for IGMP messages between the client and the router side. The mapping of multicast addresses, physical ports, and VLANs is included. By using IGMP snooping, you can create a multicast table on a two-layer switching device that does not support IGMP, thus saving bandwidth and controlling the forwarding direction of the group broadcast text.

Here is a focus on IGMP Proxy, because for the original switching device, does not support snooping almost no, but the support for Proxy is not.

IGMP Proxy is based on intercepting the IGMP message between the user and the router to establish the multicast table, the proxy device's uplink port executes the host role, and the Xia Lian Port executes the router's role.

1. The Xia Lian Port performs the role of the router in full compliance with the mechanisms specified in IGMP V2, including the polling mechanism, sending generic query information periodically, sending specific queries when leaving the package, etc.

2. The role of the main port execution host, in response to queries from the router, when the new user group or a group of the last user exits, the active sending member report package or leave the package.

IGMP Proxy in two ports to achieve a different function, the workload is relatively large, the advantage is that when there is no router in the network, IGMP Proxy device can serve as the role of the query, and if you want to extend the multicast routing function, Proxy is more convenient than snooping.

It is not difficult to see that IGMP snooping only listens for IGMP packets to create a multicast table, and IGMP packets are generated by routers and clients on the upper end. In other words, if there is no router, the establishment of the multicast table can not be realized, but the transmission of the data can only be realized by means of broadcast. The proxy is more involved, it is directly with the client and the router at the top of the dialogue, and is no longer a fully transparent role. Because it does more local processing, it reduces the reliance on the router at the top, but also increases the local system burden. However, on the other hand, using IGMP proxy can reduce the load on the upper router. As mentioned above, the proxy will participate in the establishment of the multicast group, when there is a user request to submit, proxy first will check the local multicast group, if the local already has this multicast group exists, then it will be added to the multicast group members, and do not need to send to the upper router to join the request Conversely, if the corresponding multicast group is not found locally, then proxy will send the request to the router on the upper end and establish the multicast group locally. When the multicast member exits, proxy also checks to see if there are other multicast members in the multicast group, and if so, it simply deletes the member who applied for the withdrawal in the multicast group, otherwise it notifies the router at the upper end and logs off the multicast group.

Therefore, the above two application options have pros and cons, based on the application should depend on the overall environment.

It should be added that the multicast functions implemented in the LAN environment are similar in Dslam and XDSL environments, where the DSLAM device acts as a switch that supports IGMP snooping or proxy in the LAN, and the principle is the same.

Go from: http://blog.163.com/song_jk/blog/static/235693562007022112149449/