Security Basics: RE: How to find a changing IP on ethernet network

["Bhavani Suresh" <bhavani.suresh () adnoc-dist co ae>]

Following up this..i want to know at the network level any software can
bind the MAC Addresses to the ports (and to take current MAC Addresses
in the network automatically)so that no new ip address can be allocated
without the consent of the network admin. This will also ensure security
so that non one just plugs in a pc or laptop..

Any idea..

-----Original Message-----
From: Gideon T. Rasmussen, CISSP, CISM, CFSO, SCSA
[mailto:lists () infostruct net]
Sent: Saturday, February 21, 2004 20:12
To: security-basics () securityfocus com
Subject: Re: How to find a changing IP on ethernet network



  Ivan,

This is an interesting situation. Here are a few possible ways to
address it:

1. Send an e-mail to the user community explaining the problem and
asking them to leave their IP address configurations alone.

2. In case you don't know, as the new system boots it announces its IP
address to the network. If another system already has that IP address,
it will reply and the new system will shut down the interface running
the duplicate IP.

a. From the new system, run the arp command (arp -a).

C:\> arp -a

Interface: 192.168.2.100 --- 0x20002
  Internet Address      Physical Address      Type
  192.168.2.1           00-06-25-c0-93-65     dynamic

This will list the IP address and associated MAC (hardware) address
(e.g. 00-06-25-c0-93-65).

b. Now all you need to do is find out which system has that MAC address:

C:\> ipconfig /all (output abbreviated)

        Physical Address. . . . . . . . . : 00-06-25-c0-93-65

3. You could also use tcpdump or windump (http://windump.polito.it) to
sniff the network traffic for that specific IP and view the resulting
dump file with Ethereal (http://www.ethereal.com). This is a bit
advanced for the average user.

If you have any additional questions, please do not hesitate to contact
me.

Kind regards,

Gideon

Gideon T. Rasmussen
CISSP, CISM, CFSO, SCSA
Boca Raton, FL
gideon () infostruct net

National Security Awareness Day - September 10, 2004 - Are you aware?

Subject: How to find a changing IP on ethernet network
From: Ivan Andres Hernandez Puga <ivan.hernandez () globalsis com ar>
Date: Fri, 20 Feb 2004 11:54:29 -0300
To: security-basics () securityfocus com

Hello. I have a client with a simple Ethernet network with HUB's
connecting and there is one person that is changing it's IP and creating

conflicts. What would you do to track down that person? i mean, to find
who does that?

Thanks!

Ivan Hernandez




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