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If a Red Hat or other Linux host has a conflict with an IP address, is there a way to have it display a warning message on the console or in a log, like Windows and MacOS do?

i.e. my computer has an IP address configured (or received from a DHCP server) but finds another device on the network using the assigned address. Will it log the conflict?

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4 Answers 4

up vote 14 down vote accepted

IP Conflict detection is standardised in RFC 5227. One Linux tool that implements it is IPwatchd, which has a GNOME notification component (ipwatchd-gnotify).

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+1 - i've never heard about that standard; thanks! –  pQd Apr 28 '10 at 14:51
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You can use the arping command to detect conflicts over a specific IP address:

arping -I eth0 192.0.2.1

You may find multiple MAC addresses replying for that specific IP address.

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I don't know the exact mechanisism of how it does it, but I've seen warnings in CentOS when bringing up a network device along the lines of "Failed to bring up eth0, a device on the network already has this IP".

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you can use arpwatch to find out about ip conflicts on ethernet segment you are connected to. it will alert about unseen ip-mac combinations or whenever such association change.

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It also warns when it sees one box using multiple IPs. False positives ftl :(. –  sourcejedi May 28 '13 at 16:24
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