Questions about 192.168

From: Jim (
Date: 07/08/03

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    Date: Mon, 7 Jul 2003 20:27:17 -0400


    I've been following some of the conversations about 192.168 networks,
    and tried some experimentation, and came up with a few questions:

    1. I've tried the technique mentioned to ping the broadcast address,
    and then check arp -a (on Windows 2000 machines). This didn't seem to
    work. For example, I pinged This should add all
    192.168.100.x IPs into my arp cache, right? But my cable modem didn't
    show up in my arp cache after doing this. However, when I pinged my
    cable modem directly (, it did show up in my arp cache. I
    tried this on a computer on the Internet (which I telneted to), with
    similar results. (Is it because Microsoft recognizes as
    a valid IP?). When I do a traceroute to my cable modem (,
    it is a direct hop.

    2. However, with the computer on the Internet I mentioned (which I am
    telneting to), there were the following IPs:,,,, and - which I found through
    doing an nmap scan. (pinging produced no results in the
    arp table) Three are apparently Cisco routers ( and are both ping-able). When doing nmap, it shows as remote, the others as local. However, when I do a
    traceroute on these supposedly local ones, it shows a number of hops out
    over the Internet, implying that they are not connected locally. Does
    this make sense?

    3. I recently checked my firewall (Network ICE), and noticed an attack
    from this IP: I tried to ping the attacking IP, but no
    response. The attack details were these:
    TCP OS Fingerprint, and then FTP Port Probe. Does this make any sense?
    How can someone use a supposedly local IP (192.168) to attack me?
    (Cable modem with 2 computers hooked up).

    So can someone clarify these things? IE, why does it look like the only
    way to really detect 192.168 devices on your network is to scan for them
    - in other words, the pinging of the broadcast address doesn't work (or
    am I pinging the wrong broadcast address?). Why do 192.168 devices,
    which are supposed to be local, have a number of (internet) hops between
    them when you ping them? And can anyone explain how someone could
    attack me via my cable modem, with a source address of
    (which I was unable to ping or otherwise detect)? In general, why don't
    these 192.168 addresses show up in the routing table, netstat, etc.?



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