Multicast communication on L2 vlan

[Nitish_Gupta]

I have two servers S1 and S2 connected to extreme BD switches Sw1 and Sw2 resp. We want to exchange the heartbeat from S1 to S2 via S1 - SW1 - SW2 - S2 over the multicast range. Both the servers are in same vlan. For accomplishing this if i disable the igmp on that vlan will it start forwarding the multicast traffic.

If any other node connected to that vlan do we need to take that node out of that vlan if they do not want to receive that traffic.

[Henrique]

If you assign an IP address to that vlan, you should be able to send unicast traffic also.

[Nitish_Gupta]

So, the vlan that should be given the IP address, should be from the multicast range of the group i want to communicate through. And on that vlan i want to send some unicast traffic as well.

In case i assign Ip address to the vlan from the multicast range, so i will not be able to send the unicast traffic over that.

Thanks!!

[Henrique]

Hi Nitish,

With IGMP enabled, when a switch sends an IGMP join packet to the mcast group, the switch will add the group + subscribers interfaces and included them in a IGMP table due to IGMP snooping configuration.

After that, the communication between the application should work.

Let's say that the application went into a "hold state" for 5 minutes without sending any mcast packets to that group and the mcast entry was removed from the switch. Then the application started sending the mcast packets again (not a IGMP join) and that won't be forwarded since the switch removed the entry.

If you have an IP configured in that mcast vlan (just an IP without routing the vlan), then the switch will periodic query to check if the group should be active in the switch table. That "IGMP querier" acts like a "mcast group keepalive" between the switch and the application device.

Note: Only one device in that vlan would need an IP address for the above scenario.

[Henrique]

For more information, please check the article below:

https://gtacknowledge.extremenetworks.com/articles/How_To/How-to-configure-switch-as-IGMP-querier

[Nitish_Gupta]

Hi Henrique,

Currently below is o/p for show igmp vlan

Interface on VLAN R1 is enabled and up.
inet 0.0.0.0/0
Locally registered multicast addresses:

Learned multicast addresses(Last Querier=0.0.0.0):

s = static igmp member

Flags:
IP Fwding NO IPmc Fwding NO IGMP YES
IGMP Ver V2 Snooping YES Proxy Query YES
XmitRtrAlrt YES RcvRtrAlrtReq NO

This vlan is an L2 vlan, when you say i have to add Ip address to vlan does it mean i have to make it L3 and as switch have to join that mcast group?