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Re: Certificate-based DHCP authentication

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Subject Author Date
Re: Certificate-based DHCP authentication Miha Pihler [MVP] 11-24-2005
Posted by Miha Pihler [MVP] on November 24, 2005, 4:03 pm
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Hi Steve,

Sorry I meant to mention it but I forgot. Yes in most cases I use ISA server
and IPSec. It is also a very good way to force people to be part of domain.

I had one case some time ago where employees didn't want to be part of
domain. They said it was too restrictive and they didn't like the idea of
administrator going through their PCs.
What we did with their IT is set up ISA server and made a policy that only
computers that are members of domain can surf the web. Now it was up to the
users if they want to be part of domain. Now that they are part of domain
they get patched, they get antivirus and they can surf the internet...

--
Mike
Microsoft MVP - Windows Security

> "When I do this for a customer, I usually also disable
> access to Internet from clients that are not members of domain... If user
> still brings computer to the network and the computer will get IP address
> assigned, but it can't talk to anyone."
>
> Hey Mike how are you doing that - to block access for a non domain
> computer to the internet. Via ISA server and ipsec or ?? Thanks ---
> Steve
>
>> Hi,
>>
>> Currently there is no easy way of doing this. You get DHCP IP by
>> broadcasting the need for IP. DHCP was not designed with goal of
>> assigning IP addresses to only specific computer (or devices) but to any
>> device that requests it.
>>
>> There are few solutions out there -- but more or less all of them (can)
>> cost quite a bit.
>> - first one to mention is 802.1x where you authenticate computer on
>> switch port. For this to work you need switch that supports
>> authentication and enough ports to connect every PC to one of these
>> ports. Next, you need to setup RADIUS server and certificates etc... In
>> the end you need clients that know how to work with 802.1x (e.g. Windows
>> 2000 SP4 or later).
>> - another option would be to build IPSec policy. In this case you use
>> your existing infrastructure (if you have Active Directory set up). What
>> the policy defines is that only computers joined to domain can talk among
>> themselves. Any computer not member of domain (or that does not have
>> appropriate certificate) will not be able to talk to other computers that
>> members of domain. When I do this for a customer, I usually also disable
>> access to Internet from clients that are not members of domain... If user
>> still brings computer to the network and the computer will get IP address
>> assigned, but it can't talk to anyone.
>>
>> Last option that I also highly recommend is to write a corporate policy
>> where you prohibit connection of any device that is not a property of
>> your company to company network. Of course you must define what
>> consequences are and your management must sign such policy.
>>
>> --
>> Mike
>> Microsoft MVP - Windows Security
>>
>> <Stryder Honeymonkey> wrote in message
>>> Hi All,
>>>
>>> I'm trying to prevent users in my office from bringing PCs and laptops
>>> from home, plugging them into the office network, and ending up on the
>>> same IP subnet as our other office PCs.
>>>
>>> I'm thinking maybe I can use machine certificates to somehow
>>> authenticate valid PCs to the DHCP server before an IP address is
>>> handed out?
>>>
>>> Is my thinking right on this, or is there a better way to accomplish
>>> what I want?
>>>
>>> Your help is appreciated!
>>> 'monkey
>>
>>
>
>



Posted by Steven L Umbach on November 24, 2005, 8:55 pm
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Cool. Thanks for the info! --- Steve


> Hi Steve,
>
> Sorry I meant to mention it but I forgot. Yes in most cases I use ISA
> server and IPSec. It is also a very good way to force people to be part of
> domain.
>
> I had one case some time ago where employees didn't want to be part of
> domain. They said it was too restrictive and they didn't like the idea of
> administrator going through their PCs.
> What we did with their IT is set up ISA server and made a policy that only
> computers that are members of domain can surf the web. Now it was up to
> the users if they want to be part of domain. Now that they are part of
> domain they get patched, they get antivirus and they can surf the
> internet...
>
> --
> Mike
> Microsoft MVP - Windows Security
>
>> "When I do this for a customer, I usually also disable
>> access to Internet from clients that are not members of domain... If user
>> still brings computer to the network and the computer will get IP address
>> assigned, but it can't talk to anyone."
>>
>> Hey Mike how are you doing that - to block access for a non domain
>> computer to the internet. Via ISA server and ipsec or ?? Thanks ---
>> Steve
>>
>>> Hi,
>>>
>>> Currently there is no easy way of doing this. You get DHCP IP by
>>> broadcasting the need for IP. DHCP was not designed with goal of
>>> assigning IP addresses to only specific computer (or devices) but to any
>>> device that requests it.
>>>
>>> There are few solutions out there -- but more or less all of them (can)
>>> cost quite a bit.
>>> - first one to mention is 802.1x where you authenticate computer on
>>> switch port. For this to work you need switch that supports
>>> authentication and enough ports to connect every PC to one of these
>>> ports. Next, you need to setup RADIUS server and certificates etc... In
>>> the end you need clients that know how to work with 802.1x (e.g. Windows
>>> 2000 SP4 or later).
>>> - another option would be to build IPSec policy. In this case you use
>>> your existing infrastructure (if you have Active Directory set up). What
>>> the policy defines is that only computers joined to domain can talk
>>> among themselves. Any computer not member of domain (or that does not
>>> have appropriate certificate) will not be able to talk to other
>>> computers that members of domain. When I do this for a customer, I
>>> usually also disable access to Internet from clients that are not
>>> members of domain... If user still brings computer to the network and
>>> the computer will get IP address assigned, but it can't talk to anyone.
>>>
>>> Last option that I also highly recommend is to write a corporate policy
>>> where you prohibit connection of any device that is not a property of
>>> your company to company network. Of course you must define what
>>> consequences are and your management must sign such policy.
>>>
>>> --
>>> Mike
>>> Microsoft MVP - Windows Security
>>>
>>> <Stryder Honeymonkey> wrote in message
>>>> Hi All,
>>>>
>>>> I'm trying to prevent users in my office from bringing PCs and laptops
>>>> from home, plugging them into the office network, and ending up on the
>>>> same IP subnet as our other office PCs.
>>>>
>>>> I'm thinking maybe I can use machine certificates to somehow
>>>> authenticate valid PCs to the DHCP server before an IP address is
>>>> handed out?
>>>>
>>>> Is my thinking right on this, or is there a better way to accomplish
>>>> what I want?
>>>>
>>>> Your help is appreciated!
>>>> 'monkey
>>>
>>>
>>
>>
>
>



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