• As a military term
• As a computing term

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

(wikipedia.com sourced)

• 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.

• 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
Appliance
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 network nic 3 == Internet Traffic aka triple-homed firewall, screened subnet firewall
Internal Network DMZ
Internet

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?
DMZ
Internal Network
Internet

• 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

• To create a DMZ in a Box we need to use virtual machines.
• Let’s do a crash course in VMware
Networking 

• 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.

• What we do…
• Two Dell servers with VMware software installed:
– Virtualized 14 physical servers into VM’s
• Two Cisco PIX ( P rivate I nternet E x change) 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.

•
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

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