How to get a list of all IP addresses (and ideally device names) on a LAN?
Solution 1:
If there's a unix box on the network, you could try arp-scan:
ARP scanner | Linux man page
$ arp-scan --interface=eth0 192.168.0.0/24
Interface: eth0, datalink type: EN10MB (Ethernet)
Starting arp-scan 1.4 with 256 hosts (http://www.nta-monitor.com/tools/arp-scan/)
192.168.0.1 00:c0:9f:09:b8:db QUANTA COMPUTER, INC.
192.168.0.3 00:02:b3:bb:66:98 Intel Corporation
192.168.0.5 00:02:a5:90:c3:e6 Compaq Computer Corporation
192.168.0.6 00:c0:9f:0b:91:d1 QUANTA COMPUTER, INC.
192.168.0.12 00:02:b3:46:0d:4c Intel Corporation
192.168.0.13 00:02:a5:de:c2:17 Compaq Computer Corporation
192.168.0.87 00:0b:db:b2:fa:60 Dell ESG PCBA Test
192.168.0.90 00:02:b3:06:d7:9b Intel Corporation
192.168.0.105 00:13:72:09:ad:76 Dell Inc.
192.168.0.153 00:10:db:26:4d:52 Juniper Networks, Inc.
192.168.0.191 00:01:e6:57:8b:68 Hewlett-Packard Company
192.168.0.251 00:04:27:6a:5d:a1 Cisco Systems, Inc.
192.168.0.196 00:30:c1:5e:58:7d HEWLETT-PACKARD
13 packets received by filter, 0 packets dropped by kernel
Ending arp-scan: 256 hosts scanned in 3.386 seconds (75.61 hosts/sec). 13
responded
Solution 2:
Using nmap to do a sweep of the subnet is one quick and simple way to do this that I've used before, the various options will allow you to do a more detailed inspection also.
Solution 3:
Quick and dirty (on Linux):
$ ping -b 192.168.1.255
$ arp -a
Solution 4:
As mentioned nmap (http://nmap.org/) is probably a good, quick and free option. Just be careful with it, there are some very aggressive options that could crash machines.
This command will do a simple ping sweep of the selected subnet and should be completely safe.
nmap -rP 192.168.1.1/24
Obviously, replace with your own network information.
You mentioned that a duplicate IP address was identified. Both machines should have generated a warning screen, which should allow you to identify the machines. If DHCP is used, then another request should have been generated and the problem may have self resolved.
Solution 5:
A list of IP addresses on the LAN will be of limited help, as the issue is there are two machines trying to use the same IP address.
I would suggest that you attempt to find the MAC addresses of the two machines that are clashing.
What device logged the IP address conflict? Was it a server, router, etc.? Some platforms (Solaris and BSD) will log the MAC address of the offending host along with the error message. If the IP address in question is within one of your DHCP pools, it's also worth checking your DHCP server's logs for the MAC address it's attempting to assign that IP address to.
Failing that, I would recommend logging on to the default router of the subnet that this problem is occurring on, and monitoring the ARP table. There should be one IP address that flips between multiple MAC addresses; again, those two MAC addresses represent the devices you are interested in.
Once you have the MAC addresses of the two devices, you should be able to tie them to specific switch ports. This question provides more information on how to do that. You can also use an OUI lookup tool to help identify the manufacturer of each device.