XenServer and Multicast with IGMP support

Today I tried to add a virtual Terminal Server within a XenServer to a NLB cluster. The current NLB cluster contained only physical servers. When adding the virtual server to the NLB cluster with the NLB manager, the server lost all IP communication. It isn’t possible to connect to or from the server. Together with the system administrator, we searched multiple forums and we found the solution to the problem.

It looks like XenServer doesn’t support multicast by default, because of the bridge design of the network interfaces. We found an interesting article on the internet to enable multicast on the virtual interface.

In the end we took the following steps to enable multicast support on the virtual interface of the XenServer.

1. Install the XenServer tools on the virtual server;
2. Execute the ifconfig command, like shown below, to enable multicast on the virtual interface;

# Retrieve the DOMID of the virtual server
xe vm-list name-label=<VMNAME> params=dom-id

# Enable multicast on the virtual interface of the virtual server
ifconfig vif<DOMID>.0 multicast

We restarted the virtual server and the DOMID changed, but multicast with IGMP support was still working and the server was still part of the NLB cluster. The system administrator will do some more testing and he will try to add another virtual server to the NLB cluster.