How does or does multi-homing protect a server from threats?

I’ve never physically been to this client’s site yet but I was just handed a project to check out this network/server and make sure it's sufficiently secured from the Internet. It’s an SBS 2003 SP1 box. It appears to be multi-homed, where NIC 1 is touching the Internet with a public IP and NIC 2 is serving the LAN with a 192.168 network.

My question for now is how does multi-homing protect a server? I would think we’d want a firewall between the Internet and the server…. call me kooky. Thanks!
WineGeekAsked:
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Olaf De CeusterCommented:
SBS Standard uses NAT and basic firewall functions to limit access to the outside world.
This is set up in the Internet Connection Wizard in Server Management. TO DO LIst> Point 2.
http://www.sbs-rocks.com/sbs2k3/sbs2k3-n2.htm
Make sure to untick the Business website (www.root) to stop access on port 80.
If you are running SBS Premium you have a full blown software firewall with ISA2004.
Certainely doesn't hurt to have a good hardware firewall over and above.
Hope this helps,
Olaf
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WineGeekAuthor Commented:
That excellent stuff olafdc. Maybe I need to re-word my question though: I just want to know how setting up 2 NIC's (multi homing) with different networks assigned to each in a SBS box helps secure the server from Internet threats? Let me know if I'm not making sense please.... :)
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Olaf De CeusterCommented:
Sorry,

It allows you to use the internal firewall functions.
Using one NIC only will exclude some of those functions because it is assumed you have an external firewall.
Isa will only work properly with two NIC's
Olaf
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WineGeekAuthor Commented:
So when you say "internal firewall functions" you're referring to ISA? ISA isn't installed on this SBS box as far as I know, which is all part of what I"m trying to clarify for myself. Your input is helping - thanks.
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Stephen CroftTechnical ArchitectCommented:
Not ISA, but more like an extended windows firewall.

If you wanted to secure it this way, maybe ISA would be worth doing. personally though id put a router between the internet card and the internet. for the cost and the extra reasurrance its worth it.
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Olaf De CeusterCommented:
A i said before: Even SBS standard comes with NAT and basic firewall functions.
If you run the internet connections wizard on a system with one NIC some of these functions are disabled, if you have two NIC's you'll be able to configure all basic firewall functions on the system.
ans if you want a real firewall you need ISA (I'll get shot for this: or the easier alternative: install a hardware firewall)
Please note that the basic firewall functions in SBS2003 are quite OK.
Hope that helps,
Olaf
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