Operation diagnosis
Basic - L3P
Release
4.0
11/07
9.9
Detecting IP address conflicts
23
9.9 Detecting IP address con-
flicts
9.9.1 Description of IP address conflicts
By definition, each IP address may only be assigned once within a subnet-
work. Should two or more devices erroneously share the same IP address
within one subnetwork, this will inevitably lead to malfunctions, including
communication disruptions with devices that have this IP address.In his In-
ternet draft, Stuart Cheshire describes a mechanism that industrial Ethernet
devices can use to detect and eliminate address conflicts (Address Conflict
Detection, ACD).
Mode Meaning
enable Enables active and passive detection.
disable Disables the function
activeDetectionOnly Enables active detection only. After connecting to a network or after an
IP address has been configured, the Switch immediately checks whether
its IP address already exists within the network.
If the IP address already exists, the switch will return to the previous con-
figuration, if possible, and make another attempt after 15 seconds. At any
rate, the Switch will not connect to the network with a duplicate IP ad-
dress.
passiveOnly Enables passive detection only. The switch listens passively to the net-
work to determine whether its IP address already exists. If it detects a du-
plicate IP address, it will initially defend its address by employing the ACD
mechanism and sending out gratuitous ARPs. If the remote connection
does not disconnect from the network, the management interface of the
local Switch will then disconnect from the network. Every 15 seconds, it
will poll the network to determine if there is still an address conflict. If there
isn't, it will connect back to the network.
Table 18: Possible address conflict operation modes
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