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Re: 192.168.x.x oddities
From: Ranjeet Shetye <ranjeet.shetye2 () zultys com>
Date: Thu, 17 Jun 2004 13:33:47 -0700

* Nathaniel Hall (halln () otc edu) wrote:
A common misconception is that the 10.0.0.0, 172.16.0.0 and 192.168.0.0
network are non-routable.  This is NOT true.  Most routers are setup to not
route the addresses, but they can be routed.

To be very precise, RFC 1918 addresses are not *publicly* routable. They
are privately routable e.g. routing such packets between Engineering and
Testing within a company, where all addresses are RFC 1918 addresses.


Your problem could be this or it could be that a system is mis-configured
and is just trying to figure out where it can go.

~~~~~~~~~~~~~~~~~~~~~~~~~~
Nathaniel Hall
Intrusion Detection and Firewall Technician
Ozarks Technical Community College -- Office of Computer Networking
417-799-0552

-----Original Message-----
From: Jimmy Brokaw [mailto:hedgie () hedgie com] 
Sent: Monday, June 14, 2004 4:49 PM
To: security-basics () securityfocus com
Subject: 192.168.x.x oddities

This seems like a stupid question from a non-guru like me, but I've asked
a couple of the "gurus" I know and gotten nothing but strange looks.

I run a small network at home, using a wireless router to connect to a
cable modem.  My internal IPs all fall in the 192.168.0.x range, which is
the only address-space the router is configured to support.  I've got
authentication and logging, so before anyone says "I bet it's a neighbor
using your connection," I've verified nobody else is logging in.

My understanding is that the entire 192.168.x.x range is for internal
networks only (RFC 1918), and unrouteable on the Internet.  When I run the
following command, however, I can see several computers:

[computer]$ nmap 192.168.*.* -sP

I get what looks like four computers (in addition to mine), plus some x.0
and x.255 addresses responding to the pings.  I picked one at random, and
it appears to belong to my ISP.  Doing a traceroute, I found the packet
reached its destination at a public (routeable) address, indicating to me
the machine has two addresses on the same interface.  RFC 1918 states:

   One might be tempted to have both public and private addresses on the
   same physical medium. While this is possible, there are pitfalls to
   such a design (note that the pitfalls have nothing to do with the use
   of private addresses, but are due to the presence of multiple IP
   subnets on a common Data Link subnetwork).  We advise caution when
   proceeding in this area.

Am I therefore correct in my assumption that the ISP is routing my pings
onto their internal network?  Is this a normal response?  It seems like
there ought to be security concerns here, but I can't nail them down,
except the assumption that traffic destined for 192.168.x.x addresses may
not be filtered as well (or at all), since it may be assumed it originated
from within the internal network.




-- 
   \\\\\                       hedgie () hedgie com
  \\\\\\\__o   Bringing hedgehogs to the common folk since 1994.
__\\\\\\\'/________________________________________________________

Visit http://www.hedgie.com for information on my latest book,
"Waiting for War," published by Aventine Press!

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-- 
Ranjeet Shetye
Senior Software Engineer
Zultys Technologies
Ranjeet dot Shetye at Zultys dot com
http://www.zultys.com/
 
The views, opinions, and judgements expressed in this message are solely those of
the author. The message contents have not been reviewed or approved by Zultys.


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any course! All of our class sizes are guaranteed to be 10 students or less 
to facilitate one-on-one interaction with one of our expert instructors. 
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of an Ethical Hacker to better assess the security of your organization. 
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