1. DMZ (De-Militarized Zone)
Network Security
DMZ (De-Militarized Zone)

2. J. Wang. Computer Network Security Theory and Practice. Springer 2008
General Framework
J. Wang. Computer Network Security Theory and Practice. Springer 2008

3. What is a DMZ?
A DMZ is a computer network that sits between a trusted internal network, such as a corporate private LAN, and an untrusted external network, such as the public Internet
Also known as a
Data Management Zone or
Demarcation Zone
Perimeter Network
Connecting our private network to the un-trusted network (aka the internet), we should control the flow of the traffic in a secured manner by a firewall device. With firewall, all the traffic are forced to pass through a single concentrated checkpoint where all traffic will be controlled, authenticated, filtered, and logged according to the policies set. With this way, we can significantly reduce, but not eliminate the amount of unauthorized traffic reaching our internal network.

4. Typical components of DMZ network
Web servers that need to be made available to the general public, such as company's primary Web presence advertising its products or services.
Public DNS servers that resolve the names in your domain for users outside your organization to the appropriate IP addresses.
Public FTP servers on which you provide files to the public
Downloads of your product manuals or
Software drivers
Anonymous SMTP relays that forward from the Internet to internal mail server(s)
Servers running h complex e-commerce Internet and extranet applications
Proxy Servers
Internet users can access the public resources but they cannot get into our private / internal corporate networks.

5. Split Configurations
Mail services can be split between servers on the DMZ and the internal network.
Internal mail server handles from one computer to another on the internal network.
Mail that comes in or is sent to computers outside the internal network over the Internet is handled by an SMTP gateway located in the DMZ.
For e-commerce systems
Front-end server, directly accessible by Internet users is in the DMZ,
Back-end servers that store sensitive information are on the internal network.

6. DMZ with two firewalls
DMZ that uses two firewalls, called a back to back DMZ.
An advantage of this configuration is that you can put a fast packet filtering firewall/router at the front end (the Internet edge) to increase performance of your public servers,
Place a slower application layer filtering (ALF) firewall at the back end (next to the corporate LAN) to provide more protection to the internal network without negatively impacting performance for your public servers

7. Tri-homed DMZ
When a single firewall is used to create a DMZ, it's called a trihomed DMZ.
The firewall computer or appliance has interfaces to three separate networks:
The internal interface to the trusted network (the internal LAN)
The external interface to the untrusted network (the public Internet)
The interface to the semi-trusted network (the DMZ)

8. Creating a DMZ Infrastructure
Two important characteristics of the DMZ are:
A different network ID from the internal network
A DMZ can use either public or private IP addresses, depending on its architecture
subnet the IP address block that is assigned by your ISP
If using private IP addresses for the DMZ, a Network Address Translation (NAT) device will be required
It is separated from both the Internet and the internal network by a firewall

9. Security of DMZ
The level of security within the DMZ also depends on the nature of the servers that are placed there. We can divide DMZs into two security categories:
DMZs designed for unauthenticated or anonymous access
DMZs designed for authenticated access
The level of security within the DMZ also depends on the nature of the servers that are placed there. We can divide DMZs into two security categories:
DMZs designed for unauthenticated or anonymous access
DMZs designed for authenticated access
If you have a Web server that you want everybody on the Internet to be able to access, (such as a Web presence advertising your company), you'll have to allow anonymous access. You can't easily provide authentication credentials to every stranger who happens upon your site. However, if your Internet-facing servers on the DMZ are used by partners, customers, or employees working off-site, you can require authentication to access them. This makes it more difficult for a hacker to gain access.

10. Host Security on the DMZ
Be sure to set strong passwords and use RADIUS or other certificate based authentication for accessing the management console remotely.
To allow you to manage the router through a Web page, it runs an HTTP server. It is a good security practice to disable the HTTP server, as it can serve as a point of attack.
username richard privilege 15 secret bigXdogYlover 
Router(config)# username natalie privilege 15 secret BIGxDOGyLOVER 
Router(config)# ip http server 
Router(config)# ip http authentication local 
Set up your VTY access for SSH (optional, but recommended): 
Router(config)# username name secret password 
Router(config)# line vty 0 4
Router(config-line)# transport input ssh
Router(config-line)# transport output ssh 
Router(config-line) login local
Different privilege levels to users
Router(config)#privilege exec all level 5 show ip

11. Example Network

12. Specify Traffic exiting corporate network
The corporate network zone houses private servers and internal clients. No other network should be able to access it.
Configure an extended access list to specify which traffic can exit out the network
GAD(config)#access-list 101 permit ip any
GAD(config)#access-list 101 deny ip any any
GAD(config)#interface fa1
GAD(config-if)#ip access-group 101 in
Can Host A ping the Web Server?
Can Host A ping Host B?
Can Host B ping the Web Server?
Can Host B ping Host A?
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13. Limit Traffic allowed into corporate network
traffic can be allowed into the corporate network must be limited.
Traffic entering the corporate network will be coming from either the Internet or the DMZ.
Allow all traffic that originated from the corporate network can be allowed back into that network. Enter the following:
GAD(config)#access-list 102 permit tcp any any established
Permit ICMP into the network. This will allow the internal hosts to receive ICMP messages
GAD(config)#access-list 102 permit icmp any any echo-reply
GAD(config)#access-list 102 permit icmp any any unreachable
No other traffic is desired into the corporate network
GAD(config)#access-list 102 deny ip any any
Finally, apply the access-list to the corporate network Fast Ethernet port.
GAD(config)#interface ethernet1
GAD(config-if)#ip access-group 102 out
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14. Limit Traffic to Corporate Network
Traffic that can be allowed into the corporate network must be limited.
Traffic entering the corporate network will be coming from either the Internet or the DMZ.
Allow all traffic that originated from the corporate network can be allowed back into that network. Enter the following:
GAD(config)#access-list 102 permit tcp any any established
Permit ICMP into the network. This will allow the internal hosts to receive ICMP messages
GAD(config)#access-list 102 permit icmp any any echo-reply
GAD(config)#access-list 102 permit icmp any any unreachable
No other traffic is desired into the corporate network
GAD(config)#access-list 102 deny ip any any
Finally, apply the access-list to the corporate network Fast Ethernet port.
GAD(config)#interface ethernet1
GAD(config-if)#ip access-group 102 out
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Can Host A ping the Web Server?
Can Host A ping Host B?
Can Host B ping the Web Server?
Can Host B ping Host A

15. Protect the DMZ Network
The DMZ network will house only one external server that will provide World Wide Web services
Configure an extended access list to protect the DMZ network
GAD(config)#access-list 111 permit ip any
GAD(config)#access-list 111 deny ip any any
GAD(config)#interface ethernetfa0
GAD(config-if)#ip access-group 111 in
Specify which traffic can enter the DMZ network. Traffic entering the DMZ network will be coming from either the Internet or the corporate network requesting World Wide Web services.
Configure an outbound extended access-list specifying that World Wide Web requests be allowed into the network.
GAD(config)#access-list 112 permit tcp any host eq www
What command would be entered to allow
DNS, and FTP requests into the DMZ?
For management purposes, it would be useful to let corporate users ping the Web Server but not for Internet users.
GAD(config)#access-list 112 permit icmp host
GAD(config)#access-list 112 deny ip any any
GAD(config)#interface fa ethernet 0
GAD(config-if)#ip access-group 112 out
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16. Deter Spoofing
Spoofing - A common method to attempt to forge a valid internal source IP addresses.
To deter spoofing, it is decided to configure an access list so that Internet hosts cannot easily spoof an internal network addresses.
Three common source IP addresses that hackers attempt to forge are valid internal addresses (e.g., ), loopback addresses (i.e.,127.x.x.x), and multicast addresses (i.e., 224.x.x.x – 239.x.x.x).
GAD(config)#access-list 121 deny ip any
GAD(config)#access-list 121 deny ip any
GAD(config)#access-list 121 deny ip any
GAD(config)#access-list 121 permit ip any any
GAD(config)#interface serial 0
GAD(config-if)#ip access-group 121 in
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