Server interchange is the process within a duplex server pair of a standby server becoming an active server. An arbiter process analyzes the state-of-health of both the active and standby servers and initiates a server interchange if the state of health of the active server is less than the state of health of the standby server. During this process, the standby server sends a request for the alias address. The ARP module resolves the IP address and sends an ARP reply packet with its Ethernet MAC address. The active server is seen by all the devices in the same subnet.

Each server has a unique IP address for the Processor Ethernet interface. A separate shared alias IP address is assigned to this interface on the active server and is used for connections to the Processor Ethernet interface on the active server. As part of the operations for a server interchange, the alias address is removed from the Processor Ethernet network interface on the server going standby, and it is added to the Processor Ethernet network on the server going active. After the interchange, a gratuitous ARP message is sent out from the Processor Ethernet interface on the server going active to update the MAC address in the ARP data cache stored in the IP endpoints on the local LAN that need to be connected to the PE interface.

The IP connection for the Processor-Ethernet-connected endpoints is not available during the server interchange. This is similar to a network outage. After the interchange, the Processor-Ethernet-connected endpoints use a short network IP address of the active server.