Managing HP Serviceguard for Linux, Seventh Edition, July 2007

Understanding Serviceguard Software Components
How the Network Manager Works
Chapter 3 77
Remote Switching
A remote switch (that is, a package switch) involves moving packages
and their associated IP addresses to a new system. The new system must
already have the same subnetwork configured and working properly,
otherwise the packages will not be started. With remote switching, TCP
connections are lost. TCP applications must reconnect to regain
connectivity; this is not handled automatically. Note that if the package
is dependent on multiple subnetworks, all subnetworks must be
available on the target node before the package will be started.
The remote switching of relocatable IP addresses was shown previously
in Figure 3-6 and Figure 3-7.
ARP Messages after Switching
When a floating IP address is moved to a new interface, either locally or
remotely, an ARP message is broadcast to indicate the new mapping
between IP address and link layer address. An ARP message is sent for
each IP address that has been moved. All systems receiving the
broadcast should update the associated ARP cache entry to reflect the
change. Currently, the ARP messages are sent at the time the IP address
is added to the new system. An ARP message is sent in the form of an
ARP request. The sender and receiver protocol address fields of the ARP
request message are both set to the same floating IP address. This
ensures that nodes receiving the message will not send replies.