Routers and switches
cache IP-to-MAC address tables. Depending on the size of your internal network, or if
you??™re going over the Internet, there may be an unexpected and indefinable delay.
Redirect DNS
The most complicated technique for redirecting clients to the new primary server is to
actually change the DNS name for the principal server so that it resolves to the IP address
of the standby server. Again, as with the name/IP-address change, unexpected and indefinable
delays can occur as the IP address gets propagated to all DNS servers. If the clients
and server are on a small internal network with its own DNS server, there will be no discernable
delay. If the network involved is a large wide area network (or, in the worst case,
the Internet), it could take some time for all of the DNS servers to be updated.
nNote I??™m deliberately being a bit vague about the steps required for changing the DNS name for a number
of reasons. First, different DNS servers are out there, and the process can vary from server to server.
Second, unless you know exactly what you??™re doing, you could be doing more harm than good.
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