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Old 10-19-2003, 09:14 PM   #1
SSBN
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Brute force DHCP


Brute force DHCP

I was talking to a guy who deploys systems for hotels high speed internet. He told me they deploy a Linux gatways. When you plug in your laptop in, weather you have your computer with a static ip from another isp or if you have ppoe or any other high speed connection the server forces it’s ip mask and gateway giving you the internet. You just plug it in and you are online. When you unplug all you old high speed settings are restored. He was not a tec so he couldn’t tell me how or what the software was. Have any of you herd of software that will do this.

This is all i can find on it.
http://www.linuxdig.com/rfc/individual/3203.php

how could i set up my dhcp to do this.
 
Old 10-20-2003, 12:51 AM   #2
mcleodnine
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If I had a a static IP setup and an DHCP server was able to orverride that setting I'd be rightly miffed. I could understand if the machine was setup as a simple DHCP client that this scenario would work (as it would for most users), but you do need an active DHCP client to start the negotiation for a DHCP lease and a static I P setup should not do that.
 
Old 10-20-2003, 07:18 AM   #3
SSBN
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When you go to many hotels that have high speed internet that is how it works. If you are the hotel manager it would stop all the calls to the front desk would get about connecting to the internet. Wouldn’t you hate to get rid of all you static ip information if you had that kind of internet and wanted to use a hotel high speed connection. You just plug in get the net unplug go home and no changes need to get back on your home line. I don’t think you would be that miffed would you.
 
Old 10-20-2003, 08:43 AM   #4
mcleodnine
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Yeah I would be if I didn't start/stop the DHCP client myself.

As for the server options, they're a standard part of the DHCP server configuration as in 'option routers 204.254.239.1;' and 'option domain-name "test.isc.org";'.

You can see more by looking at the man pages for dhcpd.conf
 
Old 10-20-2003, 11:53 AM   #5
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mcleodnine:
Hmm you have me a bit confused. Are you telling me my current Linux DHCP can do this and the setting just has to be enabled.

Hmm now that I think about it I wouldn’t want me to force ip information to my computer either. But then most people don’t know what dhcp is so they won’t mind. They will just be glat not to have dile up and have to call tec support. hehehe

Last edited by SSBN; 10-20-2003 at 11:57 AM.
 
Old 10-20-2003, 12:05 PM   #6
mcleodnine
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Yep. You can setup a local DHCP server to do all that fun stuff. 'man dhcpd' and 'man dhcpd.conf' is required reading for this task.
 
Old 10-20-2003, 08:44 PM   #7
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Exclamation

Put yourself in the place of the wireless lan administrator.
You cannot trust everyone to have an authentic unique IP.
Anyone forging an IP could generate untraceable attacks.

DNS routing requires you to use an IP allotted to the hotel.
Your home ISP's DNS can not see you nor route to you.
You must accept the identity of the hotel IP leased to you.

Your machine only responds to wireless if so configured.
 
Old 10-20-2003, 08:57 PM   #8
mcleodnine
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Right. But it was the Brute Force comment that stuck in my craw
 
Old 10-21-2003, 01:29 AM   #9
locutus233
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I think that what the guy told you was a load of Bull.

I do technical support for 3 fairly big WIFI ISP's and we use IP3, nomadix, and Cisco hardware. Along with a special version of OPENBSD customized by this WIFI ISP.

I can tell you that none of these machine support a forced DHCP assignment. It violates the RFC on DHCP and IP. What I could see happening though is some really neat dynamic routing and arpping controls.

Somethings I can tell you some people get on without a problem. Some people don't and have to call us. You will find most hotel frontdesks are staffed by pretty faces and not computer people. I've had calls from people who can figure out the hotel's ISP is down to people who can't even plug in cables or figure out if they have a cat 5 jack in there laptops.

I can tell you that if a technology that forced ip address on clients machines existed that would be wonderfull as it would stop all the problems we have welcha and blaster killing our networks with ICMP traffic.

Upon reading that link for a suggested RFC you've provided I can say that a clients computer must at the very minimum be set to DHCP for that to work. But its practicle purpose is to ensure the clients computer takes the lease assigned by the hotel's dhcp server. In most cases this already happens but in some stuborn clients (non patched version of Windows 9X) this is not always the case as we have one hotel that uses a dlink router that guest always get the wrong ip address and try to browse the web with.
 
Old 10-21-2003, 10:09 AM   #10
stickman
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Quote:
Originally posted by mcleodnine
Right. But it was the Brute Force comment that stuck in my craw
It is possible for a DHCP server to assign gateway, DNS servers, hostnames in addition to the IP address. Whether or not they client machines accept and use them is a totally different story. Most Windows systems using DHCP will use whatever info is passed to them unless configured otherwise. Most other operating systems have "override DHCP" options.
 
Old 10-21-2003, 10:34 AM   #11
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I will find out for sour how it all works. Our company’s are partnering up to work on a large project. He may misunderstand how it works. But I will find out what they are running that will do this and post it.
 
  


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