3

How can I find out the IPs of all the currently active machines on my LAN? How can I write a general program which will work on any subnet?

I'm doing this currently:

  1. Trying if isReachable() reaches all the machins on my subnet.
  2. If they do, store their IP addresses.

Is there anyway to do this other that manually enter subnet mask(increment the IP addresse) and hence reach all the machines(and thus get their IPs)?

Nishant
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P R
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  • possible duplicate of [how to get list of IP connected in LAN using Java](http://stackoverflow.com/questions/3345857/how-to-get-list-of-ip-connected-in-lan-using-java) – jmj Aug 08 '11 at 06:17

2 Answers2

2

You should send out a ICMP echo message to all hosts in the subnet. For example, if you subnet is 192.168.1.0/24 send a ICMP ping to 192.168.1.255 and all hosts would respond.

[06:43:11 :~]$ ping 192.168.0.255
PING 192.168.0.255 (192.168.0.255): 56 data bytes
64 bytes from 192.168.0.12: icmp_seq=0 ttl=64 time=0.159 ms
64 bytes from 192.168.0.1: icmp_seq=0 ttl=64 time=5.581 ms
64 bytes from 192.168.0.12: icmp_seq=1 ttl=64 time=0.135 ms
64 bytes from 192.168.0.1: icmp_seq=1 ttl=64 time=5.540 ms
^C
--- 192.168.0.255 ping statistics ---
2 packets transmitted, 2 packets received, +2 duplicates, 0.0% packet loss
round-trip min/avg/max/stddev = 0.135/2.854/5.581/2.707 ms
[06:43:21 :~]$
jman
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0

You can use DNS, DynamicDNS, WINS, LDAP or Active Directory for each computer to store its IP address is a central repository. You can query this repository to find all the IP address for your local network.

However, if you don't have such a repository, you need to scan your networks IP address like any hacker would.

Peter Lawrey
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