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   How to detect IP address conflicts in Linux
  </title><meta charset=utf-8><meta content=width=device-width,initial-scale=1 name=viewport><script async src=https://www.googletagmanager.com/gtag/js?id=UA-31255384-2></script><script>window.dataLayer = window.dataLayer || [];
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var PAGE_IDENTIFIER=461;</script><link href=assets/xmodulo.css rel=stylesheet><body><div class=wrapper><div id=header><a href=https://www.xmodulo.com/> <img src=img/logo.jpg> </a></div><div id=container><h1>How to detect IP address conflicts in Linux</h1><p><em> Last updated on September 5, 2020 by Dan Nanni </em></p><script async src=https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js></script><ins class=adsbygoogle data-ad-client=ca-pub-7245163904660683 data-ad-format=auto data-ad-slot=6357311593 data-full-width-responsive=true style=display:block> </ins><script>(adsbygoogle = window.adsbygoogle || []).push({});</script><p>IP addresses (IPv4) are a scarce resource that is shared by different users and devices. Having an IP address conflict means that there are more than one network device or computer that claims the same IP address. IP address conflict may occur when a DHCP server has assigned an IP address to one computer, and the same IP address happens to be statically assigned to another network device by someone.</p><script async src=https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js></script><ins style="display:block; text-align:center;"class=adsbygoogle data-ad-client=ca-pub-7245163904660683 data-ad-format=fluid data-ad-layout=in-article data-ad-slot=5674857721> </ins><script>(adsbygoogle = window.adsbygoogle || []).push({});</script><p>IP address conflict can also happen when there are more than one DHCP server (typically built in a router) hooked up to the local network, autonomously giving out IP addresses from the same subnet. If you are having flaky network connectivity, and suspect it is due to IP address conflicts, you can use a tool called <code>
      arp-scan
     </code> to <b> detect IP address conflicts in Linux </b> .<h2>Detect IP Address Conflicts with <code>
      arp-scan
     </code></h2><p><code>
      arp-scan
     </code> sends out ARP request packets on local network, and collect (IP address, Ethernet MAC address) pairs from received ARP responses. If there is more than one Ethernet MAC address claiming the same IP address, it means there is an IP conflict.<p>To install <code>
      arp-scan
     </code> on Ubuntu or Debian:<pre id=xterm>$ sudo apt-get install arp-scan</pre><p>To install <code>
      arp-scan
     </code> on CentOS, Fedora or RHEL:<pre id=xterm>$ sudo yum install arp-scan</pre><p>To detect IP address conflicts with <code>
      arp-scan
     </code> , run the following. The <code>
      -I
     </code> option specifies the network interface through which ARP request packets are sent out, and the <code>
      -l
     </code> option lets <code>
      arp-scan
     </code> send ARP probes to every host on the local network that is reachable via the network interface.<pre id=xterm>$ sudo arp-scan -I eth0 -l
</pre><pre id=output>192.168.1.10   00:1b:a9:63:a2:4c       BROTHER INDUSTRIES, LTD.
192.168.1.30   00:1e:8f:58:ec:49       CANON INC.
192.168.1.33   00:25:4b:1b:10:20       Apple, Inc
192.168.1.37   10:9a:dd:55:d7:95       Apple Inc
192.168.1.38   20:c9:d0:27:8d:56       (Unknown)
<strong>192.168.1.39   d4:85:64:4d:35:be       Hewlett Packard
192.168.1.39   00:0b:46:e4:8e:6d       Cisco (DUP: 2)</strong>
192.168.1.40   90:2b:34:18:59:c0       (Unknown)
</pre><p>According to the example output shown above, IP address <code>
      192.168.1.39
     </code> is in conflict, where two different MAC addresses are claiming the same IP address.</p><script async src=https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js></script><ins style="display:block; text-align:center;"class=adsbygoogle data-ad-client=ca-pub-7245163904660683 data-ad-format=fluid data-ad-layout=in-article data-ad-slot=1246960885> </ins><script>(adsbygoogle = window.adsbygoogle || []).push({});</script></div><div id=foobar><h2>Support Xmodulo</h2><p>This website is made possible by minimal ads and your gracious donation via <a href=https://www.paypal.com/donate?hosted_button_id=EX94W7Y4D4MMW rel=nofollow target=_blank> PayPal (Credit Card) </a> or <a href=https://www.coinbase.com/join/dnanni rel=nofollow target=_blank> Bitcoin </a> ( <code>
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