How To Find An Available Ip Address

I visit many customers that do not have an on-site IT person or dept. Ideally, when I'm installing a network device (eg printer), the customer will allocate a spare IP address to use, but nearly of the time information technology's left for me to find one.

If I take admin access to their server, I check their DHCP settings and setup a reservation, or utilize an unused IP from an excluded range. This is all fine, just what do you lot do when you don't have access to their server?

I was just wondering what others would do in a similar situation. Practise you use an IP scanner to observe unused IPs, or do y'all guess an IP and ping etc? The problem with this approach is that a client device might be turned off when yous're trying to find a spare IP, then yous can become conflicts or other network issues.

Please let me know your platonic and worst case scenarios, and any horror stories you'd like to share.

I do an IP browse (endeavour http://www.angryip.org/west/Abode), but so I likewise look for a reverse DNS entry on the server. If I don't have access to the server, doing "nslookup 192.168.1.1" will at least show if in that location is still an entry in there.

If the device is off and they don't take contrary DNS, and you accept no server access, I can't think of anything else you could do.

15 Replies

I exercise an IP scan (try http://www.angryip.org/w/Dwelling), but so I also look for a reverse DNS entry on the server. If I don't take access to the server, doing "nslookup 192.168.1.1" will at least show if there is still an entry in there.

If the device is off and they don't have reverse DNS, and you take no server access, I can't recollect of anything else you could do.

Depends on my client. If they have a server, I would look to DHCP, Wins and DNS to see if there are any entries or at least the range that other network devices might be running in. If it's a smaller office with no server, I would check the DHCP section on the router and there might be a record of what leases may exist active. Worst case - I use a quick IP scanner, cross my fingers and update the local documentation for the address I accept assigned.

I use aroused IP scanner (http://www.angryip.org/w/Download) see what's on the network already, then have one from any looks good. I try to observe a block that's open and choose ane in at that place. If you don't accept access to the DHCP server, I'grand not aware of a way to know what IP addresses are allocated.

John.J Nov 16, 2010 at 07:26 UTC

+i on Angry IP. But remember that some AVs may pick it up every bit a security threat. So you may need to turn off the local AV to download and run it.

Bob Beatty Nov 16, 2010 at 08:22 UTC

I agree with doing an nslookup to see if there is something fastened to that ip that may be close off - but then you may be seeing old data as well if DNS hasn't been taken intendance of..

Briser_fae_the_broch Nov 16, 2010 at ten:24 UTC

If I just want to check the odd IP accost is not in DNS I just use the command ping -a xx.xx.xx.twenty. but like you say it does depend on a clean DNS.

Son of Jor-El November 16, 2010 at eleven:21 UTC

Angry IP (although Symantec Endpoint Protection see it as a virus) Just an FYI

+ane Angry IP. But tend to start at the top and go down. Meaning that if Angry didn't find anything in the 200-255 range, then I'd utilise 254.

I volition also agree with angry IP +one

I as well accept used the Angry IP scanner in the by and have had it deleted on the spot. Apparently the beta version does not go detected: http://world wide web.angryip.org/due west/Download

I didn't think of using the expert ol' "ping -a" command; I'll add that to my repertoire.

Thanks guys.

MrsShrek wrote:

+1 Angry IP. But tend to start at the top and go downwardly. Meaning that if Angry didn't find annihilation in the 200-255 range, then I'd use 254.

Ditto...I'yard a fan of .250, although I'm not sure why!

Merely use this cmd:

FOR /L %i IN (1,1,254) DO ping -n 1 192.168.0.%i | FIND /i "Reply">>c:\ipaddresses.txt

Replace "192.168.0." with the network address of company.

This cmd will tell y'all which IPs are agile right now.

Okay, hither's what I practice. In my environment there are a number of servers that will not respond to ping. That is considering they are web servers and we open up them only on the required ports. 99 percent of the time y'all are going to observe that those not responding to ping are going to be web servers or remote admission controllers. In your Angry IP Scanner set information technology to scan additional ports fourscore, 8080, 443 and add other ports as you notice them useful or relevant. Look under Options>Select Ports... and enter them comma-separated "80,8080,443". Your scan will take longer to determine if there are open ports than it would but doing a pingscan. And then, when you see blanks bank check DNS and DHCP if available. AngryIPScanner is your friend!

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