“DMZ In a Box”

What is a DMZ?

• As a military term

• As a computing term

DMZ Knowledge

• Stands for Demilitarized Zone, harks back to the Vietnam DMZ / 17th Parallel

• It’s considered “a network sitting between two networks”– Not part of the internal network nor directly part of the

internet

• Used to house public services (mail, web, vpn, ftp, etc.)

• Machines in the DMZ should be considered less secure then those on the LAN

DMZ Diagram (wikipedia.com sourced)

Firewalls• What is a firewall?

– A program or hardware device that filters information coming through one network to another (typically from the internet to private network).

• How do you manage it?– Admins can allow traffic over specific ports/port ranges for both TCP

and UDP traffic. These rules/policies could apply for individual machines or entire groups of machines.

• How do they control traffic?– Three typical ways: Packet filtering, Proxy service, and Stateful

Inspection– Packet Filtering: packets are analyzed against filters/rules– Proxy service: requests to internet are subverted to proxy who fetches

information and returns it to the requesting client– Stateful Inspection: Examines certain parts of packet and ranks it

against known database of trusted information. Information is inspected going out to the internet and then as the response travels back to the network, if it’s deemed trusted by the database it’s allowed to pass.

Firewall Topologies

• Bastion Host– One host filters all

traffic between the internal network and the Internet

• Good for *simple* networks with no public services hosted.

• Issues? Benefits?

Internal Network

Internet

Firewall Topologies

Three-homed firewall– A server with three NICs acts

as a packet filter between the corporate intranet and the internet.

– Advantages?– Disadvantages?

Ex.nic 1 == Internal Traffic

nic 2 == DMZ networknic 3 == Internet

Traffic

aka triple-homed firewall, screened subnet firewall

Internal Network DMZ

Internet

Firewall Appliance

Firewall Topologies

Back-to-Back Firewall• Two firewalls are

used to contain the DMZ from both the Internet and Internal network

• More secure– Why?

• Downsides to this?

Internal Network

DMZ

Internet

DMZ Topologies

• Beyond the back-to-back firewall– Use of more NIC’s to create zones– Use of more firewalls to create multiple DMZ’s– VLANs to create zones within DMZ

Going Virtual

• To create a DMZ in a Box we need to use virtual machines.

• Let’s do a crash course in VMware Networking

Of note…

• VMware users two assigned Vendor ID ranges:– 00:0c:29:*:*:*– 00:50:56:*:*:*

• MAC addresses for Virtual Machines are calculated based on the physical machine’s UUID and some file locations.

• Can use a static MAC, coded into config file.• Internal network traffic between virtual NICs

occurs with NO collisions and at faster than gigabit speeds.

DMZ at Work

• What we do…• Two Dell servers with VMware software

installed:– Virtualized 14 physical servers into VM’s

• Two Cisco PIX (Private Internet Exchange) firewalls in the back-to-back configuration

• Various VLAN implementations also in play• 8U of rack space versus 35U consumption of

former non-virtual DMZ. Less power, less cooling required, less maintenance, less service contracts.

The Main Attraction

Technology Behind the Example• VMware Workstation 5.5

– “DMZ” created virtually within Workstation

– Consists of:• One Router• One Windows XP host within the DMZ• One Linux host within the DMZ• DMZ Network = 192.168.2.x• GW = 192.168.1.1• Firewalls IP = DHCP assigned

(hopefully)

• Freesco Linux Router– http://freesco.org/– Open source linux alternative to Cisco

appliance– Runs off a floppy!– Simple!

• My DMZ is somewhat cheesy. I know.– Simply a Bastion topology DMZ– Some quirks Internal Network

Internet

Whiteboard Exercise

• What would this look like with physical hardware…?– In lieu of a Visio diagram lets visit the

Whiteboard

Demo Time