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RE: Caching a sniffer
From: "Andrew Shore" <andrew.shore () holistecs com>
Date: Thu, 25 Mar 2004 16:54:22 -0000

Agreed, switches can be made to give up secrets, however, as I have sub
sequentially pointed out if ARP/CAM table poisoning is used switches
will report moving mac address problems to their management tools and
hence you will be able to determine where the sniffer is plugged.

A simple syslog monitoring tool will give you this information.

Any medium to large organisation should be using manageable network
devices (rather than the cheap un-manged small type) and all of these
(to my knowledge) support at least syslog free out of the box. A simple
Linux server will then collect any data, and every company has an old PC
they can acquire for this purpose. 

Just trying to help :)

Andrew Shore
Senior Security Specialist
DDI. 01302 308 165
andrew.shore () holistecs com
Company Number 04943010
VAT Number 828 8635 82
Holistic Technologies Ltd
Unit 7 Shaw Wood Business Park
Shaw Wood Way
South Yorkshire
T. 0870 240 1442
F. 0870 240 1443

-----Original Message-----
From: Shawn Jackson [mailto:sjackson () horizonusa com] 
Sent: 25 March 2004 16:37
To: Andrew Shore; Patrick Toomey
Cc: security-basics () securityfocus com; ksaenz () spinaweb com au;
gillettdavid () fhda edu
Subject: RE: Caching a sniffer

A switch is not a hub/router. In fact it is a micro segmented bridge.

It's nice I get so much attention, you all sure know how to make a man
wanted :-). Now let the rebuttal begin.

As my response to Fernando, which hopefully will get posted to the list
then this message, states that switches have numerous functionality and 
systems that operate at higher layers of the OSI model then just 2. As
most network connected devices they need to have functionality on other
besides the one where their core functionality resides. Case in point,
merely forward traffic destined to address on other interfaces, limiting
in each segment, this is the core functionality of a switch. I will
retract my 
earlier statement in place of this one which better suites the core
of the switch, in this case you guys win.

With that stated, switches can make decisions on traffic based on IP 
information which resides at the Network layer (layer 3) of the OSI
model, as 
opposed to MAC address information which resides at the Data-Link layer 
(layer 2) of the OSI model. Most switches provide IGMP functionality for
to announce they multicast group membership, which is all layer 3 data.
switches allow you to set ACL's or security based on IP information, not
MAC or layer 2 information. Some switch can also make routing or 
'gateway of last resort' decisions.

A switch operates at layer 2 of the OSI model i.e. MAC address layer. 

Layer 2 of the OSI model is the Data Link layer. LLC and MAC are logical
of that layer and not layers themselves.

Therefore if someone has plugged a scanner into a network point they
will not be 
able to sniff any useful information from the network unless that
person has admin 
access to the switch. You can check this by ensuring that none of the
ports on the 
switches are in span mode

Through ARP poising, brought up by David, and MacOf which I mentioned
allow people 
to sniff traffic on a switched network. You don't need to be using SPAN
to sniff 
traffic, that just the way us admins do it.

Shawn Jackson
Systems Administrator
Horizon USA
1190 Trademark Dr #107
Reno NV 89521

Email: sjackson () horizonusa com
Phone: (775) 858-2338
       (800) 325-1199 x338

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