hi there, i have a question about igmp snooping and if this option has issues with another options or is only advantages when is activated, i use in my house much devices that simultaneusly use streaming apps such as netflix youtube, chromecast twitch etc, this option helps to improve the traffic of the packages of the network? thanks a lot for the help
Hmm that is a good question.
I think igmp is used alot when something needs to be routed via igmp its older than vlan.
But igmp can also be used for television streams from your isp.
Igmp works with multicast alot, there are some sources on the internet which say that no multicast improves the latency or speed on a network like here:
Optimizing Multicast Rate for Home Use - Router Guide they state this:
click to expand
Imagine two scenarios: Your router is located in your living room and a) You have a single laptop in your bedroom. and b) You have multiple tablets and mobile devices streaming music, plus AppleTV or Chromecast streaming Netflix in your living room. In this case, the scenario b will benefit from higher multicast settings. However, too high of a multicast rate can hinder the performance of your laptop inside the bedroom, as the multicast will take away the available bandwidth
I think that is a fair point, so to your question I think it really depends on your use case 
Edit
In my setup my modem which is a openwrt ax6s serves igmp through a igmp supported switch to communicate with my isps tv box this goes via isolated interface via vlan, so basicly I limit igmp only between there and not on my main lan, in where my Flint is located as a second router.
Basicly in lay man terms, how I understand it, is that igmp is constantly broadcasting multicast packets to all devices to communicate with 224.0.0.x range to discover devices like a tv box, or chromecast, however depending how much multicast is around in the network, this can slow down your network aswell because not every device needs to be discovered, so I think if you use alot of devices like on a 24 port switch it will broadcast it to all ports… You will get a very bussy router when maybe only a few devices needed this.
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Wouldn’t all the devices have to watch the same content from Netflix, YouTube, etc. at the same time?
Kinda, its a yes and a no.
For example if you game alot and really care about latency in online games, multicast can really cause issues related to latency.
If someone further watches a video stream of multicast there is a chance the traffic gets broadcasted to all the network over the 224.0.0.x subnet.
In that scenario the router cpu needs to do alot more work which further degrades traffic/latency performance from other devices.
well for a few devices or small network this wouldn’t be such big issue unless you really care about the latency, but multicast could form a issue on larger networks and then you might want to Isolate multicast more, its purely the broadcasting what might could slow down your network also on wifi.
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no, for example people seeing different content in 5 devices, in this case does not apply the igmp? is enough with a good policy of qos? thanks for the help
I think u can be fine with both.
Note that QoS is also heavily depended on cpu, but if your network is not so full with devices requiring igmp/multicast you should be fine anyway with both.
If you had like 20 devices then you might could consider isolating igmp to specific devices.
Like my example I figured I only needed it for my tv box so I made a br-iptv in luci>network>interfaces>devices (tab) with multicast checked along with igmpproxy for this (edit: I removed one port from br-lan from this)
This way snooping behaviour doesn’t go over the full br-lan device and my online games have a bit latency improvement (barely noticeable because my network is not so big), and with QoS you can indeed make it better extra 
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Leaving aside gaming and iptv (which I do not have), I do not understand how igmp would be of benefit to 5 different devices watching 5 different on-demand programs at the same time, with no 2 or more devices watching the same program:
- Device 1 watching “Stranger Things” on Netflix
- Device 2 watching “House of the Dragon” on HBO
- Device 3 watching “The Rings of Power” on Amazon Prime Video
- Device 4 watching Justin Bieber music videos on YouTube
- Device 5 watching Gordon Ramsay cooking on YouTube
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Its questionable also if those devices use igmp aswell, by the scenario of the given example.
Maybe you can better see igmp more of a solution in which it makes it easier for devices to find each other, besides some use streaming through igmp.
But I believe the examples like netflix don’t use igmp, I rather would see this more comming from a isp tv box.
The only possible other multicast come from chromecasts but I dont think its using igmp as protocol but I’m not 100% sure on this.
So I think it won’t benefit you, you could better use qos for this
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I believe on-demand streaming services like Netflix, HBO, Amazon Prime Video, YouTube are all unicast.
With a limited Internet download speed, QoS should be able to “divide” the available capacity among devices. Streaming services usually dynamically adapt the video resolution, frame rate and/or bitrate accordingly, so the programs are watchable albeit may not be in 4K UHD or 1080p FHD. Also, YouTube allows you to manually set the video resolution, but not on Netflix and others.
I am still on cable TV and have not yet switched over to my provider’s IPTV. They use Comcast Xfinity technology with a hidden wifi on a separate VLAN on the modem/router to settop boxes, so I do not know if it is possible to use igmp with it.
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i start to believe that too, the igmp is cool on iptv apps and maybe on chromecast devices, for streaming apps such as netflix hbo, etc qos is a well option if you have low bandwith for share, thanks for the help!
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Can be useful in home automation that has a central network and when running a plex server.
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