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I have bought one of those Soekris boxes and installed openBSD (flashrd) on it, but now I can't remember if I gave it a 10.0.0.0/255.0.0.0 or a 192.168.0.0/255.255.0.0 IP address.

Is there a way to tell using Linux?

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Why not use the console? –  Martin Schröder Oct 18 '13 at 8:50

4 Answers 4

up vote 1 down vote accepted

Yes, easy :) Add both a 10. and 192. address with the right subnet masks to the linux box and use a broadcast ping or even if pings are blocked, nmap to scan to see what hosts are up on those subnets. You should be able to find it in short order that way.

Another way is to plugin to the device directly to your linux box with a cross over cable (or just isolate them as the only two devices on your switch. Turn your linux interface into promiscuous mode so that it looks at all the traffic instead of ignoring things not directed at it, then start a tcpdump. When you turn on the firewall device you will see a few things scroll across, maybe some arp requests or whatnot. This should tell you what ip the device is loading up with.

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+1, also use nmap -sP option to look only for up hosts, on local ethernet connections it will send ARP, not ICMP packets if run as root. –  Hubert Kario Oct 3 '10 at 1:43
    
In which file should I add the 10. and 192. addresses? –  Sandra Oct 9 '10 at 23:32

Other than connecting your Soekris Board via a serial cable to your Computer and use Minicom (or any other terminal software)? Not that I'm aware of.

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If its a toss-up between the two ranges, another approach may be to put it onto a network with another system (possible via crossover cable) and scan (via ping if ICMP has not been disabled) those ranges with the other system (switching that system between the two network plans/ranges as needed).

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The easiest way to figure out the IP address of something is to plug it into a computer running tcpdump / wireshark.

Turn on the sniffer, plug your box into the main interface of that box, and look for arps and other traffic generated by the mystery box. Typically can figure it out from that pretty easily.

You can also ask your switch if you've got a managed switch. Connect to it and ask it for the arp / FDB / CAM table for the port the mystery device is plugged into.

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