In some systems, usually in large networks it is disadvantageous to modify IP address – Media Access Control (MAC) pairs, because certain routers do not refresh their ARP cache, causing problems in the network traffic. In this case the failover functionality is realized by taking over the Media Access Control (MAC) address.
In such systems, all nodes use the same fix IP and hardware MAC address in the network and the nodes are differentiated by the state of the servicing interface. The master (active) node has the interface in up state while the slave nodes' interfaces are kept down. If the service fails over to the other node, the interfaces get into up state. Client requests are serviced by the node having the interface in up state.
Transferring MAC address is beneficial if the resources need to be relocated very quickly.
| Warning |
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Multiple interfaces with the same IP or MAC address connecting to a network as a result of a failed takeover can destabilize the network. Consequently, it is important to monitor the takeover process and to completely remove (for example, power off) the failed server from the network. It is the user's responsibility to devise an appropriate method for this, possibly through a notify script, such as power off via ILO/IPMI, or using a network-connected smart PDU. Furthermore, intentional switchovers must also be monitored as they will deactivate the slave as well. See Section 12.5, Keepalived for High Availability for details. |
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