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RE: How to find a changing IP on ethernet network
From: "David Gillett" <gillettdavid () fhda edu>
Date: Fri, 27 Feb 2004 17:17:51 -0800

  If you're using Cisco Catalyst switches, this feature is
called "port security".  Enable it, tell it how many MAC
addresses to allow per port, and whether, when this number 
is exceeded, to issue an SMTP trap to your Network Management 
package, or shut down the switch port.
  Of course, if you're using some other equipment, you need
to find out what features, if any, that equipment offers.

David Gillett


-----Original Message-----
From: Bhavani Suresh [mailto:bhavani.suresh () adnoc-dist co ae]
Sent: Wednesday, February 25, 2004 2:36 AM
To: Gideon T. Rasmussen, CISSP, CISM, CFSO, SCSA;
security-basics () securityfocus com
Subject: RE: How to find a changing IP on ethernet network



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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