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EmilPopov86633
Beginner

IGMP snooping issue with multiple SG250

Hi,

I have the following arrangement:

PC1 <-->Port2 SG250(IP.245) Port6<-->Port4 SG250(IP.246) Port2<--> PC2

The switches are pretty much set to default except I have upgraded their firmware to latest, set static IPs and enabled IGMP snooping. IGMP Querier is only enabled on IP.245

PC1 is sending multicasts to 238.238.238.1 and receiving 239.239.239.1

PC2 is sending multicasts to 239.239.239.1 and receiving 238.238.238.1

My problem is that PC2 receives the multicasts from PC1, but PC1 does NOT receive the multicasts from PC2

 

It appears that IP.245 being the querier, it knows to pass 239.239.239.1 to PC1, but it does not pass the IGMP report from PC1 on to IP.246 therefor IP.246 is not aware that anybody is interested in receiving 239.239.239.1

On IP.246, since there is no querier, the queries from IP.245 get passed on to PC2 and the reports get forwarded back to IP.245 and that causes IP.245 to be aware of PC2 wanting to receive 238.238.238.1

 

I need help figuring out how to make this work. I'm not terribly familiar with IGMP Snooping and IGMP Queriers, but there should be a way for the network to figure this out and also adapt to changes like for example adding a 3-rd switch and a 3-rd PC.

 

One more detail.... IP.246 ( where there is no querier ) recognizes that port4 hast a Multicast Router connected to it and in the Multicast Router Port page, sets PE4 to "Dynamic" This is great because I believe this causes the IGMP reports to be forwarded to this port.

On IP.245 though, none of the ports on the Multicast Router Port page get set to "Dynamic" and I believe this is why the IGMP reports from PC1 never get forwarded to IP.246

 

Any ideas how to make this configuration work?

 

1 REPLY 1
EmilPopov86633
Beginner

A small update....

I stopped the IGMP querier on both switched and ran a querier on PC2. Immediately, IP.246 designated its port2 as Multicast Router Port and IP.245 designated its port6 as Multicast Router Port

The IGMP reports from PC1 were now reaching PC2 however, the IGMP reports from PC2 were not reaching back to PC1

Therefor, P1's packets to 238.238.238.1 were never allowed to reach PC2.

 

This all looks very weird. It appears that once a port is designated as a Multicast Router Port, IGMP reports get forwarded to that port, but IGMP reports coming into this port never get forwarded to other ports. This is all very confusing. I'm trying to make multicasts work on a normal local network. I'm not trying to route multicasts between networks, yet it appears that my end devices ( PC1 and PC2 ) should act like routers to make the SG250s happy.... Could anyone explain this? Also what makes the switch designate a port as Multicast Router Port?

 

I did one more experiment, I stopped my IGMP querier on PC2, and enabled the IGMP querier on both sg250 switches. I also allowed them to participate in election so they could figure out who is going to do it on their own. If I understand things correctly, the lowest IP wins and IP.245 became the only source of IGMP general queries. I then manually set all ports on both switches to be Multicast Router Ports. This caused all IGMP reports to be sent everywhere and both PC1 and PC2 began receiving their respective multicasts. All looked fine except now, every 30sec I was seeing 2 IGMP general queries. Both coming from IP.245 and spaced less than 1ms apart. It makes no sense that IP.245 all of a sudden began sending 2 queries.... It's more like something caused the packet to be duplicated but that is concerning because it makes me think I will begin getting 3 or more duplicates if I add another sg250 and another PC. 

 

I understand this is hard to explain..... Any insight into this is greatly appreciated.

Thanks in advance.