How to: Detect Duplicate IP Address With arpi…

Q.I run quite large network with different subnets. I'd like to know how can I find out duplicate IP address under Linux / UNIX?
A. You can use arppingcommand. The arping utility performs an action similar to ping command,but at the Ethernet layer. You can send
[url=javascript:;]ARP[/url]
REQUEST to a neighbor host/ computers.
Task: Send ARP requestLet us find out  reachability of an IP on the local Ethernet with arping i.e send ARP request 192.168.1.1:
$
[url=javascript:;]sudo[/url]
arping -I eth0 -c 3 192.168.1.1
Output:
ARPING 192.168.1.1 from 192.168.1.106 ra0
Unicast reply from 192.168.1.1 [00:18:39:6A:C6:8B]  2.232ms
Unicast reply from 192.168.1.1 [00:18:39:6A:C6:8B]  1.952ms
Sent 3 probes (1 broadcast(s))
Received 3 response(s)Where,

• -I eth0: Specify network interface i.e. name of network device where to send ARP REQUEST packets. This option is required.
  
• -c 3: Stop after sending 3 ARP REQUEST packets

Task: Find duplicate IPThe -D option specifies duplicate address detection mode (DAD). It returnsexit status 0, if DAD succeededi.e. no replies are received.
$ sudo arping -D -I eth0 -c 2 192.168.1.1
If 192.168.1.1 duplicated you should see zero exit status:
$ echo $?
Always use following syntax for duplicate address detection with arping:
$ sudo arping -D -I  -c 2
$ echo $?

本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u/4206/showart_557887.html

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