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therealbraderz
Aspiring Contributor
2,865 Views
Message 1 of 24

Constant IGMP traffic

Hi,

I noticed that all day today the activity light on my draytek modem was constantly blinking.  After performing some resets and the problem didn't go away I lookep deeper into this.

All of the activity lights on my switches were also constant and I look at wireshark to see what the traffic was and it seems to be IGMP traffic.  Now I know that the youview box uses IGMP but if i disconnect this then the traffic doesn't stop.  If I turn off the IGMP proxy on my draytek router then the traffic no longer forwards to the whole lan but the modem continues to receive this traffic.

I am attaching a screenshot of wireshark, can anybody help with this?Wireshark.jpg

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therealbraderz
Aspiring Contributor
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Message 2 of 24

Re: Constant IGMP traffic

I found the only solution is to disconnect the youview box and then reboot the router and modem and leave the youview disconnected.  I guess a lot of people would not notice this if they were using just a home hub as it has no activity indicator.

Of course I could move the youview connection to it's own managed port to prevent the multicast going to other ports on the unmanaged switch, but that would still leave the modem light annoyingly blinking away.

The youview box never used to behave in this way and I don't know if it is an intentional change by BT or some kind of bug.

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Jonkarra
Expert
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Message 3 of 24

Re: Constant IGMP traffic

IGMP is used to multicast network traffic to multiple locations and as such is used by BT TV. Everyone on BT receives this. I've not got youview or BT TV and I can see the drops for multicast traffic in my router logs.
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therealbraderz
Aspiring Contributor
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Message 4 of 24

Re: Constant IGMP traffic

Oh I know I have always had them but just not in such large volumes and frequency.

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Distinguished Sage
Distinguished Sage
2,771 Views
Message 5 of 24

Re: Constant IGMP traffic

Turning on the IGMP proxy is the only way to stop the traffic on the LAN ports that do not request multicast.

 

You are not going to be able to stop it on the activity light, while you subscribe to the extra channels. The same thing happens if people have an Openreach modem and a home hub 5. The activity light on the Openreach modem flashes all the time.

 

If you have the YouView box directly connected to the Draytek modem/router, then the multicast traffic will only be directed to that port if you have IGMP proxy on.

 

Without IGMP proxy turned on, the only way to stop multicast on your LAN, would be to use managed switches which implement IGMP snooping.

 

johnbsid
Aspiring Contributor
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Message 6 of 24

Re: Constant IGMP traffic

So glad I noticed this thread, had BTTV for 2 yrs, last 2-3 months noticed the LAN 1 light flashing constantly on the Openreach modem, turned everything off to no avail and was about to blame the Echo Dot which I had recently bought.

 

This answers the query, strange that its only recently started though.

 

 

 

 

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Distinguished Sage
Distinguished Sage
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Message 7 of 24

Re: Constant IGMP traffic

 


@johnbsid wrote:

So glad I noticed this thread, had BTTV for 2 yrs, last 2-3 months noticed the LAN 1 light flashing constantly on the Openreach modem, turned everything off to no avail and was about to blame the Echo Dot which I had recently bought.

 

This answers the query, strange that its only recently started though.

 


It would only show if you subscribe to any of the BT YouView extra channels, or BT Sport, which are delivered using Multicast.

The very early BT Vision services were delivered by unicast, which would not show a lot of activity unless you were streaming a programme.

 

Multicast can cause issues if you have an "dumb" Ethernet switch.

 

See Problems sharing the signal to the YouView box with other devices.

 

smf22
Recognised Expert
2,736 Views
Message 8 of 24

Re: Constant IGMP traffic

@therealbraderz

 

To be pedantic, the traffic you're seeing in the Wireshark capture is not IGMP. IGMP uses multicast groups 224.0.0.1 and 224.0.0.2 with IGMP version 2 or 224.0.0.22 with IGMP version 3.

 

The way multicast works is that a device e.g., the YouView, sends an IGMP 'join' to signal to an upstream router that it wishes to receive a multicast stream on a specific group. In the case of the capture you showed earlier the YouView box has requested to receive the TV stream that is being sent on the multicast group 234.81.130.251. The traffic you captured was the actual multicast UDP stream with the audio and video that would be displayed on your TV.

 

What should also happen is that when a device no longer wants to receive a stream e.g., you change to a different channel or turn the box off, it should send an IGMP 'leave' to signal the router it no longer wants to receive the stream. The router should send an IGMP 'leave' to the upstream BT router, and the stream should no longer be delivered to your home.

 

If you're still receiving the stream after you've selected a different channel or turned the YouView box off, then it could be that the YouView or the Draytek is not sending the IGMP leave. Even if the IGMP leave is not sent, the traffic should stop after a short period (around 3-minutes) of turning the YouView off as the router should not be still sending the IGMP joins to the upstream BT router if there are no clients on your LAN that wish to receive a stream.

 

If you're watching an IP TV channel, then as Keith points out, the way to stop that traffic being sent on all LAN ports is to use a switch that supports IGMP snooping.

therealbraderz
Aspiring Contributor
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Message 9 of 24

Re: Constant IGMP traffic

Okay so I moved the youview box so that it is connected directly to the draytek router rather than to the unmanaged switch. This takes care of the traffic being forwarded across all ports on that switch as the router has snooping.

It's still weird that the amount of traffic has increased only recently. I have had BT TV for a long while. Although the amount of bandwidth used by this when not watching a multicast channel is still miniscule.
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therealbraderz
Aspiring Contributor
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Message 10 of 24

Re: Constant IGMP traffic

Just to clarify the traffic captured cannot be the actual video stream as it is only using around 40kbps of bandwidth. When I am watching a channel it uses around 5mbps. It seems to be information about the channels but not the actual video stream.

The data of each packet seems to run in a cycle advertising what is currently being shown on each channel.
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