This article was previously published under Q197862
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A cluster address can be reached from other computers on the same subnet asthe cluster, but computers on remote subnets cannot ping the clusteraddress.
The cluster hosts may be unreachable from an outside network.
Your router needs to accept ARP replies that have a media access control address in the payload of the ARP structure that is different from the media access control address the frame arrived from. If you are using multicast support, you may find that your router has difficulty resolving the primary IP address into a multicast network address using the ARP protocol.
If you are using unicast support, the cluster NIC could not change its network address. This problem only occurs when using a unicast network address (instead of a multicast address).
To resolve these issues, use the corresponding resolutions below:
Verify that you can PING the dedicated IP addresses for the cluster hosts from a system outside the router. If this test fails and you are using multiple NICs, the cluster is unreachable because of a problem unrelated to Windows NT Load Balancing Service (WLBS). If you are using a single NIC for both the dedicated and cluster IP addresses, go to the next step.
Verify that you can PING the cluster from a client on the cluster's subnet and that you can ping the cluster hosts' dedicated IP addresses from a system outside the router. If these tests work properly, the router is probably at fault. You should be able to add a static ARP entry for the cluster address to the router to circumvent the problem. You can also turn off WLBS's multicast support and use a unicast network address without a switch.
Either switch to a different cluster adapter card, or use WLBS's multicast support.