Security Basics mailing list archives
RE: Caching a sniffer
From: "Shawn Jackson" <sjackson () horizonusa com>
Date: Wed, 24 Mar 2004 11:23:20 -0800
In essence if you flood the MAC table of a switch the switch will
turn
into a hub, thus "disabling the switch component of the ports".
Of course, that's not necessarily true. The behavior of a switch when
the MAC
address table is exceeded is not defined by any standard, nor is it
often specified
by the manufacturer.
Of course your correct. But I've tested numerous switches, Cisco being the most tested. Bay Networks, SMC, HP/Compaq network gear have all responded in a somewhat similar fashion.
1. Dump the entire MAC table. Switch acts as if power on reset just
occurred. Seams logical, but I've never seen it implemented. It would halt traffic while learning resumes, in addition if other checks needed to run (Spanning Tree/CDP) it would take much longer.
2. Stop learning. All previously learned MAC addresses remain, and so
only traffic
for unrecognized MAC addresses gets sent to all ports.
That would damage the network. If a new client fires up, they would not get added to the switches tables and not receive any traffic.
3. Partial Purge of table. Some portion of the table gets purged and
the switch
continues, treating those purged MAC addresses as if this was the first
time they
were seen. Depending upon how the purged addresses are selected -
oldest first,
youngest first, random, lowest MAC addresses, highest MAC addresses or
something
else - will cause the switch to act differently for different users.
Seams a better solution out of the bunch, could be a pain to implement.
4. Shutdown port - assume hostile intent and stop forwarding traffic.
Called Port-Security on Cisco switches, don't know about the others.
Do I know of which switches do what? Nope. But we should ALL have
learned the
lessons of depending upon undocumented behaviors and unspecified
conditions with Y2K. Agreed, but all we need to do is ask the manufacturer of the equipment to see how it deals with the problems/attacks we are describing. It's not, "the way it works" it's how they dealt with the problem. Cisco's do it by design, and so do most manufactures.
SPAN/Port Mirroring/Roving Analysis Port(3Com) is intentional and
controlled by the
administrator. Also, how the port handles traffic in excess of it's
capacity
(say you are monitoring 3 100BaseT ports out a single 100BaseT port),
is completely
Mfg dependent and undocumented.
Traffic gets queued, just like any other switch-port. FiFo, Weighted, etc. That's not undocumented, it's just not advertised on most switches. On the better ones you can select your queuing strategy. Shawn Jackson Systems Administrator Horizon USA 1190 Trademark Dr #107 Reno NV 89521 www.horizonusa.com Email: sjackson () horizonusa com Phone: (775) 858-2338 (800) 325-1199 x338 --------------------------------------------------------------------------- Ethical Hacking at the InfoSec Institute. Mention this ad and get $545 off 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. Attend a course taught by an expert instructor with years of in-the-field pen testing experience in our state of the art hacking lab. Master the skills of an Ethical Hacker to better assess the security of your organization. Visit us at: http://www.infosecinstitute.com/courses/ethical_hacking_training.html ----------------------------------------------------------------------------
Current thread:
- RE: Caching a sniffer, (continued)
- RE: Caching a sniffer Shawn Jackson (Mar 24)
- RE: Caching a sniffer Burton M. Strauss III (Mar 25)
- RE: Caching a sniffer Fernando Gont (Mar 25)
- RE: Caching a sniffer Shawn Jackson (Mar 24)
- RE: Caching a sniffer David Gillett (Mar 24)
- RE: Caching a sniffer Fernando Gont (Mar 25)
- RE: Caching a sniffer David Gillett (Mar 25)
- RE: Caching a sniffer David Gillett (Mar 24)
- RE: Caching a sniffer Fernando Gont (Mar 25)
- RE: Caching a sniffer Shawn Jackson (Mar 24)
- RE: Caching a sniffer Shawn Jackson (Mar 25)
- RE: Caching a sniffer David Gillett (Mar 25)
- RE: Caching a sniffer Shawn Jackson (Mar 25)
- RE: Caching a sniffer David Gillett (Mar 25)
- RE: Caching a sniffer Shawn Jackson (Mar 25)
- RE: Caching a sniffer Andrew Shore (Mar 25)
- RE: Caching a sniffer Paul Blackstone (Mar 25)
- RE: Caching a sniffer Byron Copeland (Mar 26)
- Re: Caching a sniffer Aaron (Mar 29)
- RE: Caching a sniffer Paul Blackstone (Mar 25)
- RE: Caching a sniffer David Gillett (Mar 25)