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Forum Discussion
Multicast not forwarded to mrouter port
I have several GS728TPPv1, v2, and GS110TPv2, v3 switches that are part of a network that has a Cisco 9300 Layer 3 switch at its core. The 9300 is also the IGMP Snooping Querier for all vlans. ...
Hi John,
Thanks for getting back to me. I reviewed that article and was able to do some more testing today.
The Netgear (728TPv2) does seem to identify the mrouter port. If the encoder and receiver are both on the Netgear, traffic is forwarded to the Cisco (on the mrouter port). The switch also passes mDNS traffic between two ports, and to/from elsewhere on the network - so I don't think "Block unknown multicast" is in play. The v2 switch doesn't even seem to have that option - but the v1 did. On a TP110 I have, "block unknown multicast" would block the mDNS as well.
Anyway - without a receiver connected to the Netgear, the multicast goes nowhere. It does not go towards the Cisco / mrouter port. We are using 239.200.1.20 for our multicast address. I noticed that mDNS was still being transmitted. If i change the encoder to output to a 224.0.0.x address - it gets transmitted (flooded actually) which I believe is correct for that address range.
I guess the main question I have is whether the Netgear is supposed to be sending all multicast traffic towards the mrouter port - or does it only send IGMP join requests/reports and queries? It doesn't seem to be sending all unless something on the switch is also receiving that stream. On an earlier firmware version for this switch, the command "ip igmp snooping unknown-multicast action router-port" would send those packets to the mrouter port without flooding other ports on the switch. I couldn't find an option in the GUI for that - and the command isn't even present in newer versions.
Thanks,
Glyn
Not convinced the switches are supposed to deal with unassigned relative addresses even if this is within the Organization-Local Scope range.
Thi is why the UPnP one are going out - and yours don't.
Of course it's always about the IGMP joined only.
Thanks schumaku
It sure seems like that. Everything I've read though seems to say that unknown multicast should be sent to the mrouter port (per multicast design). That's the way the Cisco's are behaving.
I've put in a ticket with the encoder manufacturer to see if they can explain why they have the option to Join IGMP Group - their literature basically says "for enhanced switch compatibility" 😀
I have the exact same problem on two different Netgear switches both with the latest firmware. I noticed this several years ago on the GS108T switch. I just received a GS308T and it is doing the exact same thing as you report. It auto detects the mrouter port correctly as it is seeing incoming queries from an external switch. However the Netgear is not forwarding any streams from my streaming device toward the mrouter UNLESS another receiver on the Netgear is asking for the same stream.
I did contact Netgear technical support a few years ago any they could not help me. I don't even think they fully understood the problem. This is a very technical issue that requires in depth knowledge of IGMP.
I really just wanted a low cost and small switch to carry around to help troubleshoot IGMP issues. Anyone know of one that actually works according to the standard?
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