Multicast between Switches

[HubertMaier]

Hi All,

we have the following hardware setup:

4x SG350X-48 (Access)

1x SG350XG-24F (Core)

All of the 48 port switches have a 40Gig LAG with 4x 10Gig SFPs to Core switch. So the Core switch have 4x 40Gig LAGs with 4x 10Gig SFPs per LAG to the Access switches.

On one access switche are up to 40 special video multicast boxes connected. The box can transmit one multicast video stream with 1Gig or receive one 1Gig video multicast stream. The box can switch between transmitting and receiving with some clicks. The setup can be that we have 159 transmitting boxes and 1 receiving box and the receiving box can select which of the 159 available streams should be received OR we have 1 transmitter and 159 receiver OR something between.

The IGMP querier is running on the core switch. The access switches learned from the querier that the LAG to the core is a mrouter port. The LAGs on the core to the access switches aren't mrouter ports.

All the multicast things working perfect within 1 switch. If a receiver on switch 1 receiving a stream from a transmitter on switch 1, I'm also able to get the stream with a receiver on another switch, because in this case the switch starting streaming the multicast stream over the mport also to the core. My problem is when I want to receive a stream from a different switch and on source switch currently no receiver joined the multicast group. It looks like that the access switch forward the join request over the mport to the core, but the core not forward this request to the other access switch, because the LAGs on the core switch are't configured as mrouter ports.

If I configure the LAGs on the core also as mrouter ports, the core forward all multicast stream to all mrouter ports. So if I have 40 transmitters on switch 1 and 40 on switch 2, the core try to transmit 80Gig over the 40Gig LAG to switch 3 &4.

Any ideas how to configure this correctly?

Andreas

[Aleksandra Dargiel]

Hi StreCres,

I was doing the same setup some time ago and it was a challenging task for me as well because:

1. mrouter port will stream all multicast down to this link, even if you do not have host joining those groups - as you have noticed on your LAG

Multicast routers needs to receive multicast traffic in order to bridge multicast traffic on other ports on the LAN (in case a switch is connected to the Mrouter port), and route them to other LANs (in case a router is connected to the Mrouter port).   Those switches conforms to the RFC.

2. theoretically you could use IGMP querier however please note that the IGMP snooping querier on those switches is simplified.  It can act as a querier, but the doesn't function the same as a full router IGMP querier. 

If we have multiple queriers, then the connected ports will automatically become mrouter ports and therefore send multicasts out that port.   This is expected behavior.

I hope this answer your question.

Aleksandra