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Community Member

Nexus 5596UP multicast to 228.8.8.9

Hi,

We seem to have a multicast issue on Nexus switches. We have a server that can send a multicast packet to 224.0.0.150 that is received and replied to by a client. But if the same server sends the multicast packet to the address 228.8.8.9 or 228.8.8.10, these don’t get delivered across the Nexus switch. This has been proved by running tcpdumps on the server and client. Both devices are connected to the same Nexus 5596UP switch running version 5.0(3)N1(1c) and the interfaces (10G GEM) are configured as simple switchport access vlan 216.

Do you have any ideas how to troubleshoot and fix this?

Thanks,

Graham

1 ACCEPTED SOLUTION

Accepted Solutions

Nexus 5596UP multicast to 228.8.8.9

Hi Graham,

If you don't have PIM enabled, and hence no IGMP querier, then you will need to configure an IGMP snooping querier for the VLAN. As per Configuring IGMP Snooping in the Cisco Nexus 5000 Series NX-OS Software Configuration Guide:

IGMP Snooping Querier

When there is no multicast router in the VLAN to originate the queries, you must configure an IGMP snooping querier to send membership queries.

As you're probably aware, when a host joins a multicast group via IGMP it will periodically report that it is still interested in receiving traffic destined to the multicast group, something it does by way of an IGMP Report message. The trigger for a host to send an IGMP report is an IGMP Query, which is usually originated by the PIM router.

When you don't have a PIM router enabled, there are no IGMP queries and so no IGMP Reports from the hosts, with the result that the switch considers there are no longer any hosts interested in the multicast stream.


What you will need to add is something along the lines of the following:

!

vlan 216

  ip igmp snooping querier

!

The IP address in the above is any free IP address in VLAN 216. This will causse the switch to generate the IGMP queries for the VLAN and hopefully you're problem will be solved.

Regards

8 REPLIES

Nexus 5596UP multicast to 228.8.8.9

Hi Graham,

There's a difference between the working and non-working multicast groups that you're using here. The 224.0.0.150 is a link-local address, and by design, all link local addresses are flooded on all active ports of a VLAN irrespective of whether there's actually a registered receiver for the group on the port. By contrast, the 228.8.8.9 and 228.8.8.10 are not link local which means the switch will only send multicast traffic out a port when there's a registered receiver on the port.

Can you paste the output of the show ip igmp snooping groups command here so we can ensure the switch is seeing the IGMP registration from the client? It may be that the port to which the client is connected is not having the traffic sent on it due to IGMP snooping.

Regards

Community Member

Nexus 5596UP multicast to 228.8.8.9

Hi Steve,

Thanks for getting back to me and the detailed explanation. All the switches use default multicast configuration. Below is the output from show ip igmp snooping groups:

Type: S - Static, D - Dynamic, R - Router port

Vlan Group Address     Ver Type Port list

1     */*               -   R     Po10

102   */*               -   R     Po10

200   */*               -   R     Po10 Po13

200   228.200.200.201   v2

201   */*               -   R     Po10

202   */*               -   R     Po10 Po13

202   228.200.200.201   v2

202   232.0.1.10         v2

204   */*               -   R     Po10 Po13

204   228.200.200.201   v2

204   239.255.255.250   v2

204   239.255.255.253   v2

206   */*               -   R     Po10 Po13

206   224.0.1.60         v2

206   224.0.75.75       v2

206   228.200.200.201   v2

206   230.0.0.4         v2

206   239.255.255.250   v2

216   */*               -   R     Po10

666   */*                -   R     Po10

Po10 is the vPC Peer Link.

Thanks again.

Nexus 5596UP multicast to 228.8.8.9

If the client is in VLAN 216 and joining 228.8.8.9 then it's odd that we don't see any entry for it here. Can you confirm the server was sending and the client was registered and joined to the group at the time the output was captured?

Can you also provide a little more detail as to the topology you have? You say the client and server are connected to the same switch, but is this a layer-2 only device? If that's the case how is the router that's running PIM connected to this switch? It appears to be Po10 which you say is the vPC peer-link.

As far the client and server, are these connected to vPC ports on a pair of Nexus or simply connected to this one switch, and what OS type and application are you using to test?

Regards

Community Member

Nexus 5596UP multicast to 228.8.8.9

I suspect the guys configuring the servers weren't working when I got the output, hence no entry. We don't have PIM configured in our network - the switches are out-of -the box when it comes to multicast. The topology is very simple two N5ks connected together with a 20G vPC, and then vPC uplinks to the L3 switches.The servers interfaces are physically connected to the same L2 switch and they are trying to set up a JBoss cluster. They are testing with a java jgroup tool.

Thanks

Nexus 5596UP multicast to 228.8.8.9

Hi Graham,

If you don't have PIM enabled, and hence no IGMP querier, then you will need to configure an IGMP snooping querier for the VLAN. As per Configuring IGMP Snooping in the Cisco Nexus 5000 Series NX-OS Software Configuration Guide:

IGMP Snooping Querier

When there is no multicast router in the VLAN to originate the queries, you must configure an IGMP snooping querier to send membership queries.

As you're probably aware, when a host joins a multicast group via IGMP it will periodically report that it is still interested in receiving traffic destined to the multicast group, something it does by way of an IGMP Report message. The trigger for a host to send an IGMP report is an IGMP Query, which is usually originated by the PIM router.

When you don't have a PIM router enabled, there are no IGMP queries and so no IGMP Reports from the hosts, with the result that the switch considers there are no longer any hosts interested in the multicast stream.


What you will need to add is something along the lines of the following:

!

vlan 216

  ip igmp snooping querier

!

The IP address in the above is any free IP address in VLAN 216. This will causse the switch to generate the IGMP queries for the VLAN and hopefully you're problem will be solved.

Regards

Community Member

Nexus 5596UP multicast to 228.8.8.9

Thanks Steve,

That's excellent, I will configure that and report back.

Regards,

Graham

Community Member

Nexus 5596UP multicast to 228.8.8.9

Implemented and all now working

Thanks again Steve.

Community Member

Great answer however I seem

Great answer however I seem to have a problem with that command within the vlan configuration. I do have the Layer 3 modules installed but they are not being used because we needed IOS features on SVI's NX-OS couldn't do.

Is there a feature I need to enable or is it because of the Layer 3 modules in my 5596's that I would be forced to do Layer 3 multicast.

We have the default IGMP config:

 

Switch# sho run all | i igmp
ip igmp event-history mtrace size small
ip igmp event-history igmp-internal size small
ip igmp event-history vrf size small
ip igmp event-history group-events size medium
ip igmp event-history group-debugs size medium
ip igmp event-history policy size small
ip igmp event-history cli size small
ip igmp event-history ha size small
ip igmp snooping
ip igmp snooping report-suppression
ip igmp snooping link-local-groups-suppression
ip igmp snooping optimise-multicast-flood
ip igmp snooping mrouter vpc-peer-link
ip igmp snooping event-history vlan size medium
ip igmp snooping event-history vlan-events size small
ip igmp snooping event-history igmp-snoop-internal size small
ip igmp snooping event-history mfdm size small
ip igmp snooping event-history mfdm-sum size small
ip igmp snooping event-history vpc size small
ip igmp snooping event-history rib size large

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