PRB: Address Conflict When You Change an Application Center NLB Cluster to Multicast Mode (282023)

SYMPTOMS

After you change Network Load Balancing (NLB) from unicast mode to multicast mode on the cluster controller of an Application Center 2000 cluster, all cluster members receive the following error message:

The system has detected an IP address conflict with another system on the network. The local interface has been disabled. More details are available in the system event log. Consult your network administrator to resolve the conflict.

The following event is logged in the System Event Log:

Event ID : 4198
Source : TCP/IP
Description: The system detected an address conflict for IP address
129.0.0.1 with the system having hardware address
02:A0:8C:DE:00:FD the local interface is being disabled.

NOTE: Actual addresses are different from the example.

The cluster does not recover automatically from this state, and the multicast attribute is not replicated to other cluster members.

CAUSE

When you use unicast NLB, a virtual media access control (MAC) address is generated automatically based on the cluster IP address. When you run in multicast mode, a multicast MAC address is used. The address conflict occurs because the multicast MAC address and the unicast MAC address do not match.

RESOLUTION

To run a cluster in multicast mode, configure the controller for multicast before you add any new members. This enables multicast support for all new members when they are added to the cluster. On an operational cluster, you must manually enable multicast on each member in the NLB configuration settings, which causes a temporary availability problem for the cluster.

REFERENCES

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

264645 IP Address Conflict Switching Between Unicast and Multicast NLB