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vSwitch not forwarding Multicast in VLAN

I have an IBM x3100 running ESXi 5.5

The problem I'm having is, that a vSwitch doesn't appear to forward multicast packets in a VLAN to an individual port group configured to that VLAN.

I have vSwitch1 connected to vmnic1, which is connected to a trunk port on an upstream switch. In this trunk traverse VLAN IDs 50, 60 and 1000.

I have a port group with VLAN ID 60 assigned to it and that port group is connected to one Ubuntu VM. That VM can get an address from a DHCP server in VLAN 60 and communicates fine with unicast traffic in VLAN 60. However, it doesn't receive Multicast packets that reach the vSwitch on VLAN 60.

If instead of the VLAN 60 port group I connect a port group with VLAN ID All (4095) to the same virtual machine, and a VLAN 60 interface on that machine using vconfig, I can see the multicast packets on that interface and everything works fine. However, this defeats the purpose of VLANs in that the VM is only supposed to have access to VLAN 60.

Using tcpdump I can see the multicast packets at ens33.60 when connected to VLAN ID 4095, but not with ens33 when connected to VLAN ID 60 port group.

The VM is listening for multicast packets on the address. Netstat -l shows:

udp        0      0         *:*

If I have an identically configured physical machine connected to a VLAN 60 configured port on a physical switch, once again multicast works fine.

It just seems that the vSwitch doesn't do its IGMP snooping (or VMWare equivalent) properly and drops multicast packets instead of forwarding them to the VM when it's connected to the VLAN 60 port group.

Have any of you run into the same kind of issue? Any ideas on how to diagnose this further?

2 Replies

Hi, do you solve this issue yet?



Refer more on Understanding IP Multicast in ESXi,

Understanding IP Multicast in ESXi/ESX (2044735) | VMware KB  

Multicast Filtering  

Please consider marking this answer "correct" or "helpful" if you think your query have been answered correctly. Thanks, Srini
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