thanks to all who replyed and helped out. i suspected as much, but it's always good to get a second opinion. dave
On Thu, 26 Jun 2003, Meidinger Christopher wrote: > Hi Dave, > > google can probably give you a more complete answer, but the gist of it is > this: > > An (old school) non-switched network worked on the star principle. Every > packet is delivered everywhere in a subnet and each machine grabs the > packets that are for it. Thus, promiscuous mode is what tells a network > interface to not just grab the packets that are intended for that maching, > but to grab everything. You can test this on a hub, just put 4 machines on a > hub, make them talk a bit, and sniff with one of them. You will see that > they all can see the communications intended for each other machine on that > segment. > > A modern switched network directs the packets so that each switch only > delivers the packets to each machine that are intended for that specific > machine. That means that if i sniff on an interface connected to a switch, i > only see packets intended for my machine, and any broadcasts on my segment. > (Routers should [almost] never forward broadcasts.) Test this by sniffing on > any switch, and you will only get your own traffic and broadcasts. > Broadcasts look like packets addressed to either ff.ff.ff.ff.ff.ff or > SUB.NET.255.255 (depending where you are you may see multicasts to 224.x.x.x > addresses as well but that is out of the scope of this answer.) > > NOW, you ask yourself how can i sniff on a switched network if all i get is > stuff for me? > > The answer is, you have to lie to the other machines telling them that you > are either their gateway, or that you are the machines that they want to > talk to. The technical details are out of the scope of this paper, but you > essentially get messages destined for other IP addresses delivered to your > MAC address and then send them yourself to the the real MAC address that > belongs to dst host after keeping a copy of the packet for yourself. This > takes a certain amount of skill (though not that much with automated tools, > see below) to do, but it is not beyond a novice. > > So that is why it is harder. Now for the portion of the question you forgot > to ask: can i try this at home? Will anything bad happen if i do? > > Sure, get a copy of dsniff (www.monkey.org/TILDEdugsong/dsniff.html -- > replace the TILDE with a tilde symbol, my keyboard is busted and i can't > type it ATM) or a copy of ettercap (i think its on sourceforge, do a google > search -- try www.google.com/linux) read the manuals and start them up > sniffing. > > Yes, you should do this in a test network. This kind of activity is fairly > easy for an Intrusion Detection System to pick up, assuming it has a sensor > on the local segment. So you can get in trouble with your network admins. > There is no explanation for the network traffic this will create except > hacking / security testing. Also, if you make a mistake, you can easily put > your entire network segment out of commission (imaginge you claim to be the > gateway, and then forward the traffic to /dev/null instead of to the real > gateway) with a small mistake, which will most likely get you kicked of the > network. > > DISCLAIMER: This is an (exaustive) answer to the question asked, not a guide > on how to sniff on switched networks. Before you do anything read all the > man pages and howtos you can and be sure that you know what you are doing. > If your network admin comes into your office with a shotgun in his hands and > death in his eyes, you alone are responsible. > > If i was wrong on any technical point please email me and the list with > corrections. > > badenIT GmbH > System Support Workstation > > Chris Meidinger > Tullastrasse 70 > 79108 Freiburg > > > -----Ursprüngliche Nachricht----- > Von: David Wallraff [mailto:[EMAIL PROTECTED] > Gesendet: Wednesday, June 25, 2003 5:33 PM > An: Meidinger Christopher > Cc: 'Hilal Hussein'; [EMAIL PROTECTED] Com (E-Mail) > Betreff: Re: AW: security-basics Digest 18 Jun 2003 22:09:15 -0000 Issue > 618 > > > why is it harder to sniff over a switced network? i understand it's > becasue of the switch (natch), but what makes it more difficult? > dave > > > > On Wed, 25 Jun 2003, Meidinger Christopher wrote: > > > Hello Hilal, > > > > Yes, there are many tools that will do that. dsniff, ettercap, ethereal > and > > MANY others will read your password as it goes by on the wire. It is > > slightly more difficult on a switched network, but it can still be done. > > > > You should not use telnet at all, use ssh (www.openssh.org) instead. The > > windows client PuTTY is the most common choice to connect over ssh from > > windows. As far as starting an ssh server on the firewall, you should be > > able to do that in the same way that you started the telnet server. > > > > If you need more exact help, post to the list what type of firewall you > are > > using, and i am certain someone will help you get started. > > > > (Disclaimer: based on your question, you should [IMHO] definately read up > a > > bit on security before configuring a firewall) > > > > badenIT GmbH > > System Support > > > > Chris Meidinger > > Tullastrasse 70 > > 79108 Freiburg > > > > > > -----Ursprüngliche Nachricht----- > > Von: Hilal Hussein [mailto:[EMAIL PROTECTED] > > Gesendet: Tuesday, June 24, 2003 10:08 AM > > An: [EMAIL PROTECTED]; [EMAIL PROTECTED] > > Betreff: Re: security-basics Digest 18 Jun 2003 22:09:15 -0000 Issue 618 > > > > > > > > > > Hello All, > > > > i am not sure if i am asking the right question within the same > subject,but > > i am configuring the firewall throught the telnet connecting / from winxp > > workstation. > > > > Is there any possibility for any internal user to use any tools that will > > haijack my telnet password - password for the firewall too!, and what are > > the measurements for securing the telnet session. > > > > with regards, > > Hilal Hussein > > > > _________________________________________________________________ > > STOP MORE SPAM with the new MSN 8 and get 2 months FREE* > > http://join.msn.com/?page=features/junkmail > > > > > > > --------------------------------------------------------------------------- > > Evaluating SSL VPNs' Consider NEOTERIS, chosen as leader by top analysts! > > The Gartner Group just put Neoteris in the top of its Magic Quadrant, > > while InStat has confirmed Neoteris as the leader in marketshare. > > > > Find out why, and see how you can get plug-n-play secure remote access in > > about an hour, with no client, server changes, or ongoing maintenance. > > > > Visit us at: http://www.neoteris.com/promos/sf-6-9.htm > > > ---------------------------------------------------------------------------- > > > > > --------------------------------------------------------------------------- > > Evaluating SSL VPNs' Consider NEOTERIS, chosen as leader by top analysts! > > The Gartner Group just put Neoteris in the top of its Magic Quadrant, > > while InStat has confirmed Neoteris as the leader in marketshare. > > > > Find out why, and see how you can get plug-n-play secure remote access in > > about an hour, with no client, server changes, or ongoing maintenance. > > > > Visit us at: http://www.neoteris.com/promos/sf-6-9.htm > > > ---------------------------------------------------------------------------- > > > > > --------------------------------------------------------------------------- Evaluating SSL VPNs' Consider NEOTERIS, chosen as leader by top analysts! 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