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In my previous article, I covered how to configure NAT overload, or PAT, on a Fortigate firewall. This time around I will cover how to configure static NAT.

Static NAT is used to map one IP address to another. This is typically used to perform translations from public address space to private address space. Many organizations do not put servers directly on the internet. Instead the servers may sit on a private LAN, or even in a DMZ. Static NAT mappings are used in these cases to allow servers that are sitting behind a firewall to extend services to the Internet.

Static NAT Configuration

Fortigate firewalls call the static NAT function “Virtual IP Mapping”. These virtual IP mappings can be used for static or dynamic NAT; however I will only be covering static NAT with a one to one mapping relationship.
A new virtual IP mapping is created on the “Virtual IP” tab under Firewall -> Virtual IP. On the “Virtual IP” tab, click on the “Create New” button. This will bring you to the “Add New Virtual IP Mapping” page as shown below:

Fill in the following information:

• Name – This is a name that will uniquely identify this mapping. It may be easy to use the name of the server that mapping is for just to keep things simple.
• External Interface – This will almost always be set to “external” unless you have a different configuration.
• External IP Address/Range – Here you can enter either the first and last IP addresses in a range, or just a single IP address (Leaving the second text box empty). Remember to use the public IP address here.
• Internal IP Address/Range – Same as the external IP, except this time you will use the private IP address of the server.
• Port Forwarding – Only use this if people will be sending requests from the outside on one port, while your server will be listening on another. For example if people will be requesting web pages on port 80, but your server’s web server runs on port 8080.

Once you have configured the virtual IP mapping it is time to create the corresponding policy. This will be done by going to Firewall -> Policy and then the “Policy” tab. Click on the “Create New” button to create a new policy.

This time we are going to create a policy for traffic entering our network, so the source interface will be “external” and the destination interface will be “internal” (or DMZ depending on your configuration).

The next crucial step is to set the “Destination Address. If you expand the drop down menu, you will see a section titled “Virtual IP”, under which you should see the name of the “Virtual IP Mapping” that was just created. It’s also good practice to only accept traffic for the services that the server will be running. There is no use in accepting incoming HTTP for a server that only runs SMTP services, plus it’s a good security practice.

Finally, in this case you do not need to select “NAT”. The virtual IP mapping will take care of all of the NAT work.

Now you should be armed to configure all of the basic NAT services on a Fortigate.

At work we recently migrated to a different Internet Service Provider. This migration brought many changes, but a big one for me as the network administrator was the fact that we would be handling our own address space and network address translation (NAT). Although Fortigate support was great at confirming the NAT configuration process for me, I found that the documentation of NAT Overload/PAT configuration was lacking. My hope is that someone out there will find this document useful in their work environment.

I will be using the Fortigate web interface for all configuration steps. The unit I am using is a Fortigate 800 running software 4.0.2,build0099. Other versions or Fortigate models may use a different process to configure NAT.

Before starting, ensure that your Fortigate is in NAT mode. This can be accomplished by going to the “Operation” tab under System -> Config. Keep in mind that you will lose many, if not all, of your policies and settings by making this change. Be sure to backup your configuration file first so you have something to fall back on if things go south.

NAT Overload/PAT Configuration

NAT overload, also called Port Address Translation (PAT), is a process used to allow many computers to access the Internet using one or more IP addresses. This is used when you have a large number of computers on your LAN, but your public IP address space does not allow for a one to one mapping of public IP addresses for each computer. Without going into detail, PAT uses one public IP address with a TCP port number appended to the IP address. The port number is what is used to identify which session maps to which computer.

First a public IP address must be assigned to the external interface on your firewall. This can be accomplished by going to System -> Network -> Interface tab. On the Interface tab, click the edit icon for the external interface. You will see the screen below:

Under “Addressing mode”, click “Manual” and enter the IP address and subnet mask. The IP address and subnet mask should be separated by a forward slash like this: “176.16.1.2/255.255.255.0”. Click “Ok” to save your changes.

Next, we need to make sure the firewall knows how to get where it needs to go. This is done through routes under the Router -> Static -> Static Routes tab. Here, you’re probably going to need at least two routes. The first route you will need is a default route, which is represented using “0.0.0.0/0.0.0.0”. Here the gateway address should be set to the next hop of your Internet bound routing equipment.
Now your firewall needs to know how to get back to your LAN subnets. It’s up to you how you configure this, but for simplicity sake we will use a blanket route. Say all of the IP addresses on your LAN subnets start with “10.70.xxx.xxx”, you can simply create a route for all of the subnets that start with “10.70” using the following IP address and subnet mask combination: “10.70.0.0/255.255.0.0”. You may choose to be more specific with your routes.

Below is an example route configuration. This is used on a production Fortigate, so I have blocked out some information to protect the innocent.

Now that the routing has been setup we can create a policy to allow outbound traffic and enable NAT. This is accomplished by going to the “Policy” tab under Firewall -> Policy. Once there, click the “Create New” tab. Here you will be presented with a list of options, but we will focus on a select few.

The “Source Interface” and “Destination Interface” options are self explanatory. We are going to set the source to “Internal” and the destination to “External” since we want to configure internal to external translation (the translation table will automatically handle the reverse mapping). The next crucial step is to ensure that the “NAT” checkbox is selected to enable NAT for this policy. You can create an “allow all” policy for now just to test if NAT is working. Various “what’s my IP” web sites should be able to confirm that the public IP address of the external interface on the firewall is being used for NAT.

One note about the NAT checkbox; it needs to be checked for any internal to external policy that you wish to allow traffic. At work I have a policy that blocks outbound RDP access; however there is one vendor’s server to which we need to permit outbound RDP access. If you create the outbound policy and place it in the appropriate spot on the policy list, but forget to check the NAT option the policy will not work. If things don’t seem to be working as they should, or is seems that the policy is being ignored, always check the Nat checkbox!

That covers NAT overload/PAT configuration on the Fortigate 800. In a follow-up article I will cover static NAT configuration, which is a less involved process.

IP Telephony is something that every network administrator is going to run into at some point in time. Its many features really do help reduce costs across the board. Having a unified network that carries voice and other data services reduces cabling, equipment, and maintenance costs just to name a few. Even with the popularity of IP telephony there are many organizations out there they have yet to take the plunge. This further increases chances that you will find yourself working as part of a telephony project at some point.

If your company has a network with all Cisco devices and a Cisco IP telephony system has been chosen, everything seems straightforward. Cisco is going to make sure their products work well together; otherwise they’re going to have a tough time marketing their telephony system to current Cisco customers. Concerns arise when you have a mixed vendor environment. Will it work? How do the switches need to be configured?

If you have an HP Procurve based network, Procurve has you covered with their interoperability guides. These guides detail how to get phones from various vendors to work with Procurve networking equipment. The guides are very detailed covering configuration of the phones, the switching equipment, and even Call Manager (In the case of Cisco). Each section of the guide includes screen shots of any web interfaces as well as command prompt output you may encounter along the way.

If you are planning to run an IP telephony system on top of HP Procurve gear, these guides will be your source of knowledge more than a few times!

Thanks to “procurvehelp” on Twitter for posting a link to these documents!

In some cases you can use a RADIUS server to perform port authentication based on the MAC address of the connecting device. In other cases the port usage may remain static, but you still may want to lock down the ports without going through the process of configuring a RADIUS server. The ‘port-security’ command can be used to lock down ports without the need for a RADIUS server or even knowing the MAC address of the computers that will connect to the port.

Where would this be useful? At work I use this to secure ports in our computer labs. In the labs the desktops stay in one place. In this situation, seeing multiple MAC addresses through any port (except for the uplink port) would indicate that either someone setup a rouge switch/hub or a game of musical computers is being played. This particular command allows me to set the maximum amount of MAC addresses allowed though a port to one.

The command that makes all of this happen is ‘port-security’. Here is an example of a command that I use in our computer labs at work:

port-security 1-20 address-limit 1 learn-mode static action send-disable

Breaking the command down into sections makes it easier to understand:

‘port-security 1-20’ – Apply the command and all of the following options to ports 1 thru 20. A single port or group of ports can be specified in addition to a range.

‘address-limit 1’ – Set the amount of MAC addresses that can gain access through the switch port(s). Most HP switches support an address limit of up to about 38.

‘learn-mode static’ – This configures how the switch will learn or know the MAC addresses that are allowed to gain access through the port(s).

‘action send-disable’ – This sets the action to be taken once the threshold defined by ‘address-limit’ is crossed. ‘send-disable’ sends an error message and disables the port.

My preferred option for ‘learn-mode’ is static. In this case I do not predefine any MAC addresses, which leaves many people wondering how the switch knows which MAC addresses to allow though which ports. When the above command is first issued, the switch doesn’t know that information. With the ‘learn-mode static’ option the switch will take the first source MAC address is sees on a port and assign that MAC address as an authorized MAC address for that particular port. This process is repeated for each port in this case. The picture below illustrates this process so that it is easier to understand.

Our basic training has told us that when you first take a switch out of the box it is a blank slate. For the sake of explanation we are going to assume this for our scenario. We are also going to assume that the previously discussed ‘port-security’ command has been applied to interfaces one thru twenty. You connect Computer A to interface one of the switch. Soon after that Computer A sends a packet which enters the switch through interface one. The switch reviews the packet and one of the steps it takes is to add the source MAC address (AAAAAA-AAAAAA) to its MAC address table. This accomplishes multiple things at once. First it now tells the switch which interface Computer A is attached to, which allows more efficient forwarding of packets destined for Computer A. This MAC address table is also used by the ‘port-security’ command to determine if another computer should be allowed to gain access to the network through that port.

If some black hat comes by and connects their laptop to interface one, the switch will now see a new source MAC address attached to the packets. In this case the ‘address-limit’ was set to one, and the switch already has one MAC address associated with port one in its MAC address table. This means that the switch will take the ‘send-disable’ action, disabling the interface.

There you have it! This is a quick and easy way to add another layer of security to your network! I caution to use this command wisely as using it in the wrong situation could make you one unpopular network administrator!

As always consult the manual for your HP Procurve switch for the exact command syntax.

I use many different tools to monitor, diagnose, and test my network on a daily basis. One tool that is often overlooked is a cell phone. Cell phones have enjoyed an explosive growth in popularity over the years. PDAs in particular have bridged a major gap, going from a device for business people to a device for the every day consumer. With the popularity of PDAs comes the likelihood that most, if not all, of these phones have a data plan associated to them.

When making changes to any network it is often important to test all services from inside and outside the network. With tightening budgets, you can consider yourself lucky if your employer springs for an Internet connection strictly for testing. That’s ok, since you can use that fancy phone that’s attached to your hip for testing.

At work we recently changed Internet service providers. Along with this change came changes to our address space, DNS zones, firewall policies and more. It was important for me to test connectivity to our external facing services after the migration, particularly since I was taking this opportunity to apply hardened policies to our firewall. Once the migration was complete, I was able to use my cell phone to see check the status of our DNS zone propagation as well as to test how well my firewall policies were working (sometimes they work too well).

Tethering your cell phone to your computer can be a tricky subject. Many carriers charge an extra monthly fee for tethering for one reason or another. There are ways to tether your cell phone to your computer without the need for an additional tethering plan. I caution you in following any of these processes. There is the likelihood that if you abuse the “free” tethering your cell phone provider can find out and you may be stuck with a fat bill.

Moderation is the key here. In my opinion you should only use the free tethering process minimally, such a when you need to do testing. These processes should not be used if you plan to tether regularly, or use your phone as you would a data card.

Below are some links to tutorials on how to setup various cell phones for tethering. Remember; use them wisely and at your own risk.

• Using a Blackberry as a modem
• Windows Mobile phone as a modem
• Tetherbot (Proxy) for Android Phones
• Palm Pre Bluetooth Tethering