User`s guide

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TCP/IP Network Basics
IP Address Configuration Methods
Duplicate IP
Addresses on non-
DHCP Networks
Generally, duplicate IP addresses only occur on a manually configured IP
address network that does not use DHCP and Auto-IP/ZEROCONF. For
example, a user may try to determine an IP address for a host by PINGing
IP addresses on the network until an IP address is selected that does not
respond.
Based on this non-response, the user may assume the IP address is unused
and assign it to their device. However, at a later date, a host that legitimately
has that IP address will attempt to use it. As a result, both hosts will
experience network problems that can be very difficult to track down.
A duplicate IP address can also happen when a user makes an error during
manual entry of an IP address and accidentally configures an IP address
already in use elsewhere.
Duplicate IP
Addresses on
DHCP Networks
Duplicate IP addresses on DHCP systems are unlikely but they are possible.
The DHCP specification (RFC 2131) specifies how a duplicate IP address
check should be done within the DHCP Discover/Offer/Request/
Acknowledgement protocol sequence. Ideally, the network interface should
be disabled when a duplicate IP address is detected. Windows informs the
user of the duplicate IP address, but does NOT disable the network
interface.
If two or more devices on the network have the same IP address, the first
device that starts using the duplicate IP address will not detect a problem
because it is the only device using that IP address. However, when a second
device starts and attempts to use the duplicate IP address, a duplicate IP
address error is reported.
To recover from a duplicate IP address condition, eliminate the duplicate
IP address condition and then restart the affected devices. For example, an
instrument can be restarted (to clear up the error) by disconnecting the
Ethernet port long enough to be detected by the Ethernet connection
monitoring or by cycling power to the instrument.