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Multicast communication on L2 vlan


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.

14 replies

Userlevel 6
Disable igmp Snooping is what your looking for.

Are you sure they wont communicate without disabling this. Most work with IGMP, and IGMP snooping enabled.
Not sure, i have not disable or enabled it yet.

As per one of the documentation from Extreme it states that -

"IGMP Snooping - IGMP snooping is a Layer 2 function of the switch; it does not require multicast routing to be enabled. In IGMP snooping, the Layer 2 switch keeps track of IGMP reports and only forwards multicast traffic to that part of the local network that requires it. IGMP snooping optimizes the use of network bandwidth and prevents multicast traffic from being flooded to parts of the local network that do not need it. The switch does not reduce any IP multicast traffic in the local multicast domain (224.0.0.x). IGMP snooping is enabled by default on all VLANs and VMANs in the switch. If IGMP snooping is disabled on a VLAN or VMAN, all IGMP and IP multicast traffic floods within the VLAN or VMAN. IGMP snooping expects at least one device on every VLAN to periodically generate IGMP query messages. To enable or disable IGMP snooping, use the following command:

enable igmp snooping {forward-mcrouter-only | {vlan} name | with-proxy vr vrname}

disable igmp snooping {forward-mcrouter-only | {vlan} name | with-proxy vrvrname}"

So i am looking for the option if i can do it with this. Or i do not require to do anything from my end.
Userlevel 6
Disabling IGMP snooping makes all multicast traffic act like broadcast within that VLAN.

Do the two servers communicate without doing anything to the switches?
As of now we have to share the design. So if we keep the default feature so that set up will work?
Userlevel 6
Hi Nitish, I believe that using default value the setup would work. However it depends on the application requirements. I would recommend you to keep both IGMP and IGMP Snooping enabled and test.

Also, to have the switch acting as a IGMP querier, you have to add an ipaddress to the vlan. This will be needed just in case the application "sleeps" for long time. If that happens, the switch will check if the subscriber is still alive by sending an IGMP packet, avoiding traffic issue.
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?
Userlevel 6
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.
Userlevel 6
Henrique wrote:

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.

For more information, please check the article below:

https://gtacknowledge.extremenetworks.com/articles/How_To/How-to-configure-switch-as-IGMP-querier
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!!
Userlevel 6
If you assign an IP address to that vlan, you should be able to send unicast traffic also.
Even if thats from the multicast range..I am not sure which ip should i assign to the new vlan, multicast or unicast one?
Userlevel 6
That IP should be in the same subnet that your S1 and S2 servers. Not the mcast group.
So, i have to do below -

1. Enable IGMP and IGMP Snooping on the vlan level, which is enabled by default.

2. Make that vlan L3, assign an unicast range Ip address.

3. Add the Multicast ip address to make the switches join the multicast group.

This configuration is to be done on both the Switches Sw1 and 2.

Thanks
Userlevel 6
Hello Nitish,

1. Enable IGMP and IGMP Snooping on the vlan level, which is enabled by default.2. Assign an IP to the vlan with the same subnet that S1 and S2 servers. (To have an IGMP querier)

3. When you start the mcast application, the server will join a mcast group that will be created in the switch. (That's is automatic through IGMP protocol)

For IGMP querier election you just need IP address configured to 1 switch. However you can have this configuration applied on both switches.

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