How to Resolve Connectivity Issues with Virtual IP in Windows NLB Multicast Mode

Zyxel_Lucious

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How to Resolve Connectivity Issues with Virtual IP in Windows NLB Multicast Mode

If you're experiencing connectivity issues with a virtual IP in a Windows NLB multicast mode setup, the following steps can help you resolve the problem:

1. Configure a 'Static Multicast Forwarding By MAC' entry for the NLB multicast MAC address on the relevant switch ports:
   Steps: Go to Web GUI > SWITCHING > Multicast > Static Multicast Forwarding By MAC and add the multicast MAC address for the RDP load balancer.
2. Set the 'Unknown Multicast Frame' action to 'Flooding':
   Steps: Navigate to Web GUI > SWITCHING > Multicast > IPv4 Multicast > IGMP Snooping > Unknown Multicast Frame and configure the action as "Flooding."

Remember to apply these settings to all affected switches in your network.

Why is this Necessary?

• Windows NLB multicast mode uses a multicast MAC address for the virtual IP, which may not be dynamically learned in the MAC address table by default on switches.
• By adding a static multicast forwarding entry and enabling "Flooding" for unknown multicast frames, you ensure that traffic is forwarded appropriately to the virtual IP.
• Misconfigured settings, such as "Drop" behavior for unknown multicast frames, could block traffic and cause connectivity issues.

This solution has been successfully confirmed in troubleshooting scenarios and is effective for a network topology using Zyxel switches like XGS2220. Following these steps ensures reliable access to your Windows NLB resources. Thank you for choosing Zyxel!

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