Multicast traffic addresses many IP addresses rather than a specific IP address. Earlier, the unicast mode failed to handle excessive network load and bandwidth. Thus, IGMP Snooping came into play, and network switches use this protocol to determine multicast groups. A multicast group is a colony of computers or network-enabled devices that receive the same network traffic.
With IGMP Snooping allowed, network switches can forward data packets to the device that should receive the message or traffic. IGMP stands for the Internet Group Management Protocol, and it’s situated in the Network layer. All the devices connected to the same network share an IP address to use IGMP Snooping.
In other words, IGMP Snooping manipulates concerned multicast groups via snooping. Additionally, the protocol analyses how multicast packets can be exchanged between the downstream hosts and the upstream layer 3 multicast device. You can enable IGMP Snooping on your router if required.
Let’s find out how IGMP Snooping works, how it can benefit, and more in this guide.
IGMP Snooping: How it Works
IGMP Snooping can save you from false flooding caused by overloading web traffic for multicast traffic. The protocol optimises the overhead performance, and your router or switch can decide the deserving device to receive the next multicast traffic. It also helps in improving the network speed.
The IGMP Snooping protocol takes place with 3 distinct message types – Query, Report, and Leave. However, a device with enabled IGMP Snooping Layer 2 might react differently according to the message type.
First, the multicast switch or router sends a message to every host residing in the multicast group. If there’s no multicast router with IGMP protocol, this function will evoke every host’s group membership information. The querier sends IGMP messages periodically to each host and router on the established local subnet. This step checks whether the host or router exists in the network.
The snooping switch receives the IGMP general query and then forwards the query to all the ports in the VLAN. Although, the receiving port doesn’t get the query.
Report or Join
Next, the host will send a message to the querier. This indicates that the host is already a member of the multicast group or it wants to be a member of that group. The snooping switch forwards the report sent by the host via all the router ports.
Here’s how a host can report or join according to its circumstances:
- If the snooping switch can’t find a match, it forwards the receiving port, like an outgoing interface. Additionally, it initiates a group membership expiry timer and tracks the time for the multicast router to determine that there are no more members left in the group.
- If there’s a match yet the entry doesn’t have the receiving port, then the receiving port gets added to the outgoing interface list. The group membership expiry timer gets started, as well.
- The snooping switch reboots the group membership expiry timer for a port if it locates a match for the matching forwarding entry and the receiving port.
A host sends the Leave Group message when it can’t be a multicast group member. Remember that a receiver host of IGMPv1 never sends a leave message while leaving a multicast group. Instead, an IGMPv2 or IGMPv3 host can send such an IGMP to leave a message. The switch forwards the ‘leave’ message to all router ports after receiving one.
After that, the querier sends a group-associated IGMP query to the multicast group. This message aims to identify whether all the active members have already been attached to the receiving port. Once they receive the group-specific query, the switch forwards it via all member and VLAN network router ports.
If the port fails to receive an IGMP report message after the group membership timer gets invalid, the snooping switch eliminates the port from the multicast group’s forwarding entry.
Applications of IGMP Snooping
The prime purpose of IGMP Snooping is to restrict bandwidth waste and leakage of network information. Network switches with active multicast snooping can efficiently transmit packets to the deserving receiver in a multicast group. IGMP Snooping can tackle high traffic, and the chances of network congestion become minimal.
In addition, you can avoid network information leakage with IGMP Snooping. Cybercriminals are more likely to break down a multicast network through safe leaks. This might resemble a DoS or DDoS attack. Enabling the IGMP Snooping command can save you from hostile and unexpected attacks on your multicast network.
Hosts who have registered for the multicast request will only receive multicast packets. However, IGMP Snooping appears to be the best deal for multicast traffic dealing with a lot of traffic. If you’re using a router for basic browsing, or gaming purposes, then IGMP Snooping doesn’t add any value.
You can’t resolve Wi-Fi performance and speed issues with IGMP Snooping. If you think whether IGMP Snooping doesn’t suit a domestic need, then it’s not true. You can use the protocol for streaming or screen mirroring purposes. For instance, you can enable IGMP Snooping if you use Chromecast or Apple TV more often.
Reportedly, Apple TV fails abruptly while using the AirPlay feature for screen mirroring. Try enabling IGMP Snooping if you encounter issues with Apple TV or similar applications. However, we recommend you keep the feature disabled if you have no special requirements.
Advantages of IGMP Snooping
IGMP Snooping can potentially benefit a multicast group from flooding traffic and unnecessary network congestion. Network switches can listen to the IGMP conversations happening between routers and hosts. Thus, the switch can keep track of the roadmap of the necessary links that require IP multicast streams.
Let’s have a look at the perks of IGMP Snooping:
Safeguards Network from Traffic Floods
If a switch doesn’t know whether a particular device belongs to the multicast group, it forwards all the multicast traffic it has received. This will result in confusion, and every device will get more traffic than required.
Therefore, they must apply computing powers to eliminate those unwanted packets. Consequently, this leads to a slowdown of the entire network, and normal networking functions might come to a halt.
With IGMP Snooping, the switch ensures that the deserving host receives the multicast packet. If the multicast network lacks an IGMP Snooping, network information leakage might lure attackers. A denial-of-service attack might exploit the entire multicast network. IGMP Snooping can reduce such chances of vulnerability and enhances networking performance.
Offers Faster Network
Since IGMP Snooping helps the multicast network to manage its traffic, the network grows faster. The more traffic any network acquires, the less bandwidth it can have. Therefore, your multicast network can prevent bandwidth wastage as the IGMP Snooping protocol saves unnecessary traffic transmission by the switches. The more bandwidth you can avail, the faster your network becomes.
How can You Enable IGMP Snooping and Multicast on Your Router?
By default, IGMP Snooping remains disabled for most routers. In the VLAN network, flood multicast traffic is the default value for any router. To enable IGMP Snooping in a VLAN network, you have to access the VLAN network and execute a few commands.
You must use the command first, followed by the switch (config) # prompt: vlan 2. Enter the network in the space of ‘vlan 2’ in your case, and this command will configure the VLAN setup.
Next, you must execute the enable or disable command to activate or deactivate the IGMP Snooping protocol. Enter the following command: ip igmp snooping enable. If you have to disable IGMP Snooping, you must use the command: ip igmp snooping disable.
You can enable IGMP Snooping through your router’s web-based admin portal. However, the method for enabling IGMP Snooping varies from one router model to another. Yet, here we have shown the steps for a Netgear Nighthawk switch:
- Connect a computer to the network to which the switch is connected. You can connect the computer over a Wi-Fi mean or Ethernet cable.
- Next, open an internet browser and provide the switch’s IP address to open the login page.
- You must enter the switch’s gateway password to open up the home page.
- Next, you need to locate the Advanced Settings option and click it.
- Under the Preset Modes page, choose the Multicast option.
- You can enable or disable the IGMP Snooping from there. If it’s already enabled, you can notice a blue slider; otherwise, the slider will appear white.
In addition, you can enable or disable the blocking system for unknown multicast traffic. To do so, go to the section that says, ‘Block unknown multicast address’. Make sure that you click the Apply button to save your preferences.
If you own any other router, you can go through its user guide to know more about IGMP Snooping and its activation. Or, you can simply contact the switch’s technical support to learn how to activate IGMP Snooping.