Multicast mrouter port issue

[mtu1480]

Hi all,

we are running into a strange problem with multicast in our network. The core of the network consists off two stacked ws-c3850 switches with a couple of Cisco edge switches connected to it. The network is used for carrying multicast audio streams. The core switch is configured as IGMP querier. This all works fine, but problems arise when we are trying to connect an edge switch from a different brand (Artel). This edge switch also has to be able to become a querier in case the connection to the core switch is lost. It has a higher IP address so it should not become querier in normal situations. But as soon as you connect the Artel switch, the port on the Cisco becomes a mrouter port, which results in all multicast traffic being flooded to the Artel. This causes overruns on the link to the Artel switch. The core switch is still the querier though.
While searching for a solution I came across documentation for other Cisco devices which support the command 'ip igmp snooping vlan forbidden mrouter’ or something similar. This would prevent the switch to elect the specified port as a mrouter port. But I can't find anything similar for the c3850. Is there a way to prevent a port from becoming a mrouter port?
Thanks

[MHM Cisco World]

Prevent port to be mroute' you can not config ip pim under that port.

[Flavio Miranda]

Hi

  It seems the 3850 does not have the command you need.  On this case, I believe you can take a look on the Artel side. In one guide from Artel I saw this config below.  I believe you can play with the two command I highlighted and see if the situation changes

# show run int vlan 1
Building configuration...
interface vlan 1
ip address 10.0.0.103 255.255.255.0
ip igmp snooping
ip igmp snooping querier election
ip igmp snooping querier address 192.0.0.1
ip igmp snooping compatibility auto
ip igmp snooping priority 0
ip igmp snooping robustness-variable 2
ip igmp snooping query-max-response-time 100
ip igmp snooping query-interval 125
ip igmp snooping last-member-query-interval 10
ip igmp snooping unsolicited-report-interval 1
!
end

[mtu1480]

Hi,

thanks for your response. We've already played around with those settings. Currently we have the querier election disabled on the Artel ('no ip igmp snooping querier election'). The strange thing is, that with the election disabled and the Artel stating its Querier Status as IDLE, the Artel is still sending out General Membership Queries. These MQ's sent by the Artel seem to trigger the Cisco that it's connected to a multicast router on that port and causing the issues.
The Artel also has a IGMP proxy function ('ip igmp host-proxy'). This functions more or less as a querier. When disabling this proxy function, the Artel stops sending out the General MQ's and the problem is gone. But this defeats the purpose of it all. With only IGMP snooping enabled on the Artel, it cannot operate standalone from the core switch.

We have our supplier looking into this right now.

One strange anomaly on the Cisco side is, that when the Artel is unplugged and at a later moment another switch or host is plugged into the same port on the Cisco, it also get's flooded with multicast. Although the Cisco does not have that port listed as a mrouter port anymore. Only a reboot seems to fix that..

[MHM Cisco World]

You dont clear' 

The multicast is work in two layers 

L2 via igmp snooping 

L3 via pim  <<- here you can use show mroute not in l2.

So as I understand are Core and other vendor use multicast routing (l3) confirm this.

[mtu1480]

Hi,

the network consists of a single VLAN. Only layer 2, we don't use multicast routing.

[MHM Cisco World]

so why you always mention mroute ? can I see what command you use to see mroute 

[mtu1480]

I was referring to the output of the command 'show ip igmp snooping mrouter'. This command shows which ports are dynamically learned (or statically configured) as multicast router interfaces. This does not only apply to PIM routing, but also ports on which IGMP queries are received.

[MHM Cisco World]

Mrouter learn dynamically if it receive 

Igmp enquiry or pim hello message.

Different between two mrouter ports is type' 

In show igmp snooping mrouter 

You can see router or interface?

Anyway if you want to get red from issue of multicast you can disable igmp snooping and add multicast mac to vlan' this make SW forwarding the traffic to all port without snooping which port need and which one not need 

[mtu1480]

The 'show igmp snooping mrouter' shows the interface of the Cisco where the Artel switch is connected.
We can't disable IGMP snooping, this would flood all the ports and give much bigger problems. Thanks for the help.

[MHM Cisco World]

Can I see show igmp snooping mrouter ?
still waiting 
there are many solution for multicast between two SW's , check below link 
I suggest one which is disable snooping.
https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/68131-cat-multicast-prob.html

[mtu1480]

Thanks for the link. As i said earlier, disabling IGMP snooping is just not an option. In an environment with 300+ multicast streams at 4 Mbit each this would instantly overload all the ports on the switch.

Our supplier is looking into it. Hopefully they have a solution.
Have a nice weekend.

[Flavio Miranda]

It can be a bug. If you have the possibility I´d also put cisco to see it.  It seems the behavior does not seems right.

[mtu1480]

Yes, we'll do that. Thanks for the help.