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Since the notion of a virtual server gets used in a variety
of ways, here it means to have an IP that represents the virtual server,
for which there is no real device to which this IP belongs to, and
several other IPs, for each of which there is a real device. When
a host connects to the virtual IP the NAT device exchanges the destination
address, which is the virtual IP, against an IP of one of the real
devices. Depending on the algorithm that is used to select the (real)
server IP, virtual servers can serve various purposes.
Example:
- Nat rule: create a virtual server using IP 138.201.14.100
- use the two hosts with the IPs 138.201.14.111 and 148.201.14.112,
respectively, as (real) servers for the virtual server
- now connections from outside to the virtual server are remapped by
the NAT-router to use one of the two hosts
- which of the two hosts available is actually used for a new connection
(that is not yet in the virtual server table) depends on the algorithm
used, whereby any algorithm one can think of can be plugged in
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Michael Hasenstein
8/22/1997