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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.
I'm struggling to find the appropriate configuration settings for multicast on the Netgears. I have a video encoder sending UDP multicast connected to a Netgear. With a receiver on another Netgear, I'm unable to see the multicast. The activity lights on the Netgear show the port attached to the encoder receiving lots of traffic, but the trunk port connected to the Cisco is blinking slowly.
The Netgear does not seem to be sending multicast towards the mrouter port, and my understanding is that it should be. If I connect the encoder to a Cisco switch that is in turn connected to the core, traffic is forwarded to the mrouter port, and the receiver attached to the Netgear switch sees the stream.
If there is something attached to the encoder switch that is also receiving that stream (ie another receiver, or an encoder configured to "Join its own Group"), then the stream will propogate out the trunk port to the core, and appear at the other receiver.
The other confusing thing is the "Block Unknown Multicast" option. If I uncheck that, the stream is flooded and seen on the receiver. But of course, it's flooded to all ports on the switch - which we don't want.
I have tried it with Snooping Querier enabled and disabled on the Netgear. Given that you can also choose whether the switch will take place in querier election - it's not clear to me if this option needs to be enabled for the switch to even start looking for a querier elsewhere on the network.
I can get to a point where the Netgear switches recognize that the Cisco Switch is the IGMP Querier for the vlan (it shows the Cisco's IP address) - but still, the multicast traffic is not sent to the mrouter port.
Any pointers greatly appreciated.
Thanks,
Glyn
5 Replies
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.
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