Setting up NLB Multicast Mode
- Multicast mode does not have the problem that unicast operation does since the servers can communicate with each other via the original addresses of their NLB network cards.
- Each server’s NLB network card operating in multicast mode has two MAC addresses (the original one and the virtual one for the cluster) causes some problems on its own. Most routers reject the ARP replies sent by hosts in the cluster, since the router sees the response to the ARP request that contains a unicast IP address with a multicast MAC address. The router considers this to be invalid and rejects the update to the ARP table. In this case you’ll need to manually Configure Static ARP Resolution at Switch or router for each port connecting to ESX’s NICS. See also 1006525 (Network Load Balancing (NLB) Multicast mode over routed subnet – Cisco Switch Static ARP Config)
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