IP hosts and routers use the IGMP management protocol to group network devices. Internet Group Management Protocol governs multicast (group) data transmission in networks. It resides at the network level and connects the client computer to the local router in order to transfer data between them. The multicast traffic is then routed to the rest of the clients via the PIM protocol. It links the local router to the remote one. Thanks to the use of IGMP, the network resources of a number of applications (online games, video streaming) can be used more efficiently.
You can use the IGMP snooping function to make a decision about broadcasting traffic to certain interfaces. What it is? This is the process of tracking IGMP requests from consumers (hosts) to providers (multicast routers).
The concept and purpose of IGMP snooping
Snooping means "eavesdropping" in English. When it is turned on, an intermediate network device (router or communicator) begins to analyze the transfer of all data packets between client computers,connected to it, and routers that supply multicast traffic. When a connection request is detected, the port to which the consumer (client) is connected is switched on, in the opposite situation (Leave request), the corresponding port is removed from the group list.
In most communicators, IGMP snooping is available, but requires prior activation.
Why monitor network traffic?
Multicast traffic can also be transmitted to computers that are not interested in it. This is called broadcast relay. To prevent it, in order to reduce the load on the network, IGMP snooping is used. At the same time, this kind of filtering requires additional memory costs and increases the load on the communicator. However, she is justified.
If the communicator starts broadcasting multicast traffic on all its ports, then:
- this process is useless;
- problems may arise in the operation of the final recipient (network device), forced to process a large stream of unnecessary data.
To avoid such situations, there is the IGMP snooping function, which significantly improves the performance of the entire network. It takes into account the needs at the network (third) level and thus optimizes the channel (second) level of data transmission.
Enabling the wiretapping function
In order to monitor multicast traffic, you must first enable IGMP snooping and configure it yourself. Let's see how to do it on communicatorsD-Link when implementing a multicast data transfer scheme. Commands to activate network listening:
In order to exclude a port from the network group when the communicator receives a Leave request from the client, use the IGMP Snooping Fast Leave feature. It allows you to stop the transmission of unnecessary data streams over the network in order to make it work more efficiently. To activate this function use the following command:
Used when it is necessary to enable multicast filtering of the switch with a connected node participating in data transmission.
Types of IGMP sniffing
IGMP snooping can be either passive or active. How does this manifest itself?
- Passive does not filter traffic, it just monitors it.
- Active - listening and filtering data packets to reduce the load on the group router.
The second type of implementation of this function is the most preferable, as it allows minimizing the amount of transmitted information by filtering requests to connect to and disconnect from the router.
The functionality of the IGMP snooping communicator helps reduce network load by monitoring the exchange of data between providers (local routers) and consumers (client computers) of multicast traffic.
