If you’re planning to take the SY0-501 version of the Security+ exam, you should have a basic understanding of secure network architecture concepts. These include implementation of different zones and topologies.
For example, can you answer this question?
Q. Your organization hosts a web server and wants to increase its security. You need to separate all web-facing traffic from internal network traffic. Which of the following provides the BEST solution?
A. DMZ
B. VLAN
C. Firewall
D. WAF
More, do you know why the correct answer is correct and the incorrect answers are incorrect? The answer and explanation are available at the end of this post.
Most networks have Internet connectivity, but it’s rare to connect a network directly to the Internet. Instead, it’s common to divide the network into different zones, using different topologies.
DMZ
The demilitarized zone (DMZ) is a buffered zone between a private network and the Internet. Attackers seek out servers on the Internet, so any server placed directly on the Internet has the highest amount of risk. However, the DMZ provides a layer of protection for these Internet-facing servers, while also allowing clients to connect to them.
As an example, the figure shows a common network configuration with a DMZ. The DMZ is the area between the two firewalls (FW1 and FW2) and hosts several Internet-facing servers. Many DMZs have two firewalls, creating a buffer zone between the Internet and the internal network, as shown in the figure, though other DMZ configurations are possible.
Network with DMZ
In this configuration, one firewall separates the DMZ from the Internet. The second firewall separates the DMZ from the internal network. Each firewall includes detailed rules designed to filter traffic and protect both the internal network and the public servers. One way of saying this is that the DMZ provides access to the services hosted in the DMZ, while segmenting access to the internal network.
For example, FW1 can have rules to allow traffic to the servers in the DMZ, but block unsolicited traffic to FW2. The mail server would send and receive email to other email servers on the Internet through port 25 of FW1, and also send and receive email to internal clients through port 25 on FW2. The web server hosts web pages to any Internet users through ports 80 and 443 on FW1, but FW2 blocks incoming traffic using these ports. The Certificate Authority (CA) server validates certificates for Internet clients by answering through FW1.
Notice in the figure that the intranet includes a database server. The web server may use this to create web pages for an e-commerce site. It could hold product data, customer data, and much more. FW2 allows traffic between the web server (and only the web server) and the database server on port 1433. FW2 would block all other Internet traffic to the database server.
It’s also possible for the web server and the database server to be part of an extranet. For example, imagine that the web server hosts a site that business partners can use to place orders. The web server would first authenticate them before granting them full access. After users log on, the web site connects to the back-end database server, allowing them to browse the inventory and place orders. Because this site is only for authorized business partners, it is an extranet.
The DMZ can host any Internet-facing server, not just those shown in the figure. Other examples include FTP servers used for uploading and downloading files and virtual private network (VPN) servers used for providing remote access.
Understanding NAT and PAT
Network Address Translation (NAT) is a protocol that translates public IP addresses to private IP addresses and private addresses back to public. You’ll often see NAT enabled on an Internet-facing firewall. A commonly used form of NAT is network address and port translation, commonly called Port Address Translation (PAT).
If you run a network at your home (such as a wireless network), the router that connects to the Internet is very likely running NAT. Some of the benefits of NAT include:
• Public IP addresses don’t need to be purchased for all clients. A home or company network can include multiple computers that can access the Internet through one router running NAT. Larger companies requiring more bandwidth may use more than one public IP address.
• NAT hides internal computers from the Internet. Computers with private IP addresses are isolated and hidden from the Internet. NAT provides a layer of protection to these private computers because they aren’t as easy to attack and exploit from the Internet.
One of the drawbacks to NAT is that it is not compatible with IPsec. You can use IPsec to create VPN tunnels and use it with L2TP to encrypt VPN traffic. Although there are ways of getting around NAT’s incompatibility with IPsec, if your design includes IPsec going through NAT, you’ll need to look at it closely.
NAT can be either static NAT or dynamic NAT:
• Static NAT. Static NAT uses a single public IP address in a one-to-one mapping. It maps a private IP address with a single public IP address.
• Dynamic NAT. Dynamic NAT uses multiple public IP addresses in a one-to-many mapping. Dynamic NAT decides which public IP address to use based on load. For example, if several users are connected to the Internet on one public IP address, NAT maps the next request to a less-used public IP address.
Q. Your organization hosts a web server and wants to increase its security. You need to separate all web-facing traffic from internal network traffic. Which of the following provides the BEST solution?
A. DMZ
B. VLAN
C. Firewall
D. WAF
Answer is A. A demilitarized zone (DMZ) is a buffered zone between a private network and the Internet, and it will separate the web server’s web-facing traffic from the internal network.
You can use a virtual local area network (VLAN) to group computers together based on job function or some other administrative need, but it is created on switches in the internal network.
A firewall does provide protection for the web server, but doesn’t necessarily separate the web-facing traffic from the internal network.
A web application firewall (WAF) protects a web server from incoming attacks, but it does not necessarily separate Internet and internal network traffic.
See Chapter 3 of the CompTIA Security+: Get Certified Get Ahead: SY0-501 Study Guide for more information on implementing a secure network.