This is something our organization has just begun doing. We are a state
university that has student users on the inside of the network and we have
some of the same fears.

After we began designing it we realized it was actually easier than it
sounds. We have a cisco firewall services module that we us for our head
end. We simply just created another context on this unit but the key was
that it can be done in 'transparent mode' which actually bridges the
interfaces instead of routing them. So, for a given network, you can move
a machine behind a firewall and not even have to renumber it. If it
doesn't work, patch it back to the other side and go find out what was
wrong. It's as simple as having 1 vlan that's not protected and 1 vlan
that's protected.

If you can clearly define your services into roles and create clean
object-groups out of them, it's easy enough to drop a server into a role
then move it to the other vlan.

Jason Mishka - "I'm like a Subway in a land of McDonalds..."

On Mon, 7 May 2007, Dan Lynch wrote:

> Greetings list,
> I'm looking for opinions on internal enterprise network firewalling. Our
> environment is almost exclusively Microsoft Active Directory-based.
> There are general purpose file servers, AD domain controllers, SMS
> servers, Exchange servers, and MS-SQL-based datase app servers. In all
> about 80+ servers for over 2500 users on about 2000 client machines, all
> running Windows XP.
> How prevalent is it to segregate internal use servers away from internal
> clients behind firewalls? What benefits might we gain from the practice?
> What threats are we protected from?
> The firewall/security group argues that servers and clients should exist
> in separate security zones, and that consolidating servers behind
> firewalls allows us to
> - Control which clients connect to which servers on what ports
> - Centralized administration of that network access
> - Centralized logging of network access
> - a single point for intrusion detection and prevention measures
> These benefits protect us from risk associated with internal attackers
> and infected mobile devices or vendor workstations.
> On the other hand, the server team counters that
> - troubleshooting problems becomes more difficult
> - firewall restrictions on which workstations can perform administration
> makes general maintenance inconvenient, esp. in an emergency
> - the threats we're countering are exceedingly rare
> - a broken (or hacked) firewall config breaks all access to servers if
> consolidated behind firewalls
> Any and all thoughts are appreciated.
> Dan Lynch, CISSP
> Information Technology Analyst
> County of Placer
> Auburn, CA
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