5

Chapter 2: Planning Your Network

What is a VPN?

ADSL2 Gateway with 4-Port Switch

Since you use the Gateway to share your DSL Internet connection, contact your ISP to find out if they have

assigned a static IP address to your account. If so, you will need that static IP address when configuring the

Gateway. You can get that information from your ISP.

Dynamic IP Addresses

A dynamic IP address is automatically assigned to a device on the network, such as computers and print servers.

These IP addresses are called “dynamic” because they are only temporarily assigned to the computer or device.

After a certain time period, they expire and may change. If a computer logs onto the network (or the Internet) and

its dynamic IP address has expired, the DHCP server will automatically assign it a new dynamic IP address.

DHCP (Dynamic Host Configuration Protocol) Servers

Computers and other network devices using dynamic IP addressing are assigned a new IP address by a DHCP

server. The computer or network device obtaining an IP address is called the DHCP client. DHCP frees you from

having to assign IP addresses manually every time a new user is added to your network.

A DHCP server can either be a designated computer on the network or another network device, such as the

Gateway. By default, the Gateway’s DHCP Server function is enabled.

If you already have a DHCP server running on your network, you must disable one of the two DHCP servers. If you

run more than one DHCP server on your network, you will experience network errors, such as conflicting IP

addresses. To disable DHCP on the Gateway, see the DHCP section in “Chapter 5: Configuring the Gateway.”

What is a VPN?

A VPN, or Virtual Private Network, is a connection between two endpoints - a VPN Gateway, for instance - in

different networks that allows private data to be sent securely over a shared or public network, such as the

Internet. This establishes a private network that can send data securely between these two locations or

networks.

This is done by creating a “tunnel”. A VPN tunnel connects the two computers or networks and allows data to be

transmitted over the Internet as if it were still within those networks. Not a literal tunnel, it is a connection

secured by encrypting the data sent between the two networks.

VPN was created as a cost-effective alternative to using a private, dedicated, leased line for a private network.

Using industry standard encryption and authentication techniques - IPSec, short for IP Security - the VPN creates

a secure connection that, in effect, operates as if you were directly connected to your local network. Virtual

Private Networking can be used to create secure networks linking a central office with branch offices,

6

Chapter 2: Planning Your Network

Why do I need a VPN?

ADSL2 Gateway with 4-Port Switch

telecommuters, and/or professionals on the road (travelers can connect to a VPN Gateway using any computer

with VPN client software that supports IPSec, such as SSH Sentinel.)

There are two basic ways to create a VPN connection:

•

VPN Gateway to VPN Gateway

•

Computer (using VPN client software that supports IPSec) to VPN Gateway

The VPN Gateway creates a “tunnel” or channel between two endpoints, so that data transmissions between

them are secure. A computer with VPN client software that supports IPSec can be one of the two endpoints. Any

computer with the built-in IPSec Security Manager (Microsoft 2000 and XP) allows the VPN Gateway to create a

VPN tunnel using IPSec (refer to “Appendix C: Configuring IPSec between a Windows 2000 or XP computer and

the VPN Gateway”). Other versions of Microsoft operating systems require additional, third-party VPN client

software applications that support IPSec to be installed.

Computer (using VPN client software that supports IPSec) to VPN Gateway

The following is an example of a computer-to-VPN Gateway VPN. (See Figure 2-2.) In her hotel room, a traveling

businesswoman dials up her ISP. Her notebook computer has VPN client software that is configured with her

office's VPN settings. She accesses the VPN client software that supports IPSec and connects to the VPN Gate-

way at the central office. As VPNs utilize the Internet, distance is not a factor. Using the VPN, the businesswoman

now has a secure connection to the central office's network, as if she were physically connected.

VPN Gateway to VPN Gateway

An example of a VPN Gateway-to-VPN Gateway VPN would be as follows. (See Figure 2-3.) At home, a

telecommuter uses his VPN Gateway for his always-on Internet connection. His Gateway is configured with his

office's VPN settings. When he connects to his office's Gateway, the two Gateways create a VPN tunnel,

encrypting and decrypting data. As VPNs utilize the Internet, distance is not a factor. Using the VPN, the

telecommuter now has a secure connection to the central office's network, as if he were physically connected.

For additional information and instructions about creating your own VPN, please visit Linksys’s international

website at www.linksys.com/international or refer to “Appendix C: Configuring IPSec between a Windows 2000 or

XP computer and the VPN Gateway.”

Why do I need a VPN?

Computer networking provides a flexibility not available when using a paper-based system. With this flexibility,

however, comes an increased risk in security. This is why firewalls were first introduced. Firewalls help to

IMPORTANT:

You must have at least one VPN

Gateway on one end of the VPN tunnel. At the

other end of the VPN tunnel, you must have a

second VPN Gateway or a computer with VPN

client software that supports IPSec.

Figure 2-2: Computer-to-VPN Gateway

7

Chapter 2: Planning Your Network

Why do I need a VPN?

ADSL2 Gateway with 4-Port Switch

protect data inside of a local network. But what do you do once information is sent outside of your local network,

when emails are sent to their destination, or when you have to connect to your company's network when you are

out on the road? How is your data protected?

That is when a VPN can help. VPNs secure data moving outside of your network as if it were still within that

network.

When data is sent out across the Internet from your computer, it is always open to attacks. You may already have

a firewall, which will help protect data moving around or held within your network from being corrupted or

intercepted by entities outside of your network, but once data moves outside of your network - when you send

data to someone via email or communicate with an individual over the Internet - the firewall will no longer protect

that data.

At this point, your data becomes open to hackers using a variety of methods to steal not only the data you are

transmitting but also your network login and security data. Some of the most common methods are as follows:

1) MAC Address Spoofing

Packets transmitted over a network, either your local network or the Internet, are preceded by a packet header.

These packet headers contain both the source and destination information for that packet to transmit efficiently.

A hacker can use this information to spoof (or fake) a MAC address allowed on the network. With this spoofed

MAC address, the hacker can also intercept information meant for another user.

2) Data Sniffing

Data “sniffing” is a method used by hackers to obtain network data as it travels through unsecured networks,

such as the Internet. Tools for just this kind of activity, such as protocol analyzers and network diagnostic tools,

are often built into operating systems and allow the data to be viewed in clear text.

3) Man in the Middle Attacks

Once the hacker has either sniffed or spoofed enough information, he can now perform a “man in the middle”

attack. This attack is performed, when data is being transmitted from one network to another, by rerouting the

data to a new destination. Even though the data is not received by its intended recipient, it appears that way to

the person sending the data.

These are only a few of the methods hackers use and they are always developing more. Without the security of

your VPN, your data is constantly open to such attacks as it travels over the Internet. Data travelling over the

Internet will often pass through many different servers around the world before reaching its final destination.

That's a long way to go for unsecured data and this is when a VPN serves its purpose.

Figure 2-3: VPN Gateway-to-VPN Gateway

8

Chapter 3: Getting to Know the ADSL2 Gateway with 4-Port Switch

The Back Panel

ADSL2 Gateway with 4-Port Switch

Chapter 3: Getting to Know the ADSL2 Gateway with 4-

Port Switch

The Back Panel

The Gateway’s ports, where a network cable is connected, are located on the back panel. The Gateway’s buttons

are also located on the back panel.

LINE

The

LINE

port connects to the ADSL line.

Ethernet (1-4)

The

Ethernet

ports connect to your computer and other network devices.

Reset Button

There are two ways to Reset the Gateway's factory defaults. Either press the

Reset Button

, for

approximately ten seconds, or restore the defaults from the Factory Defaults screen of the

Administration tab in the Gateway’s Web-Based Utility.

Power

The

Power

port is where you will connect the power adapter.

On/Off Switch

This switch is used to turn the Gateway on or off.

With these, and many other, Linksys products, your networking options are limitless. Go to the Linksys

international website at www.linksys.com/international for more information about products that work with the

Gateway.

Important:

Resetting the Gateway to factory

defaults will erase all of your settings

and replace them with the factory defaults. Do

not reset the Gateway if you want to retain

these settings.

Figure 3-1: Back Panel

9

Chapter 3: Getting to Know the ADSL2 Gateway with 4-Port Switch

The Front Panel

ADSL2 Gateway with 4-Port Switch

The Front Panel

The Gateway's LEDs, where information about network activity is displayed, are located on the front panel.

Power

Green. The

Power

LED lights up when the Gateway is powered on.

Ethernet (1-4)

Green. The

LAN

LED serves two purposes. If the LED is continuously lit, the Gateway is

successfully connected to a device through the LAN port. If the LED is blinking, it is an

indication of any network activity.

DSL

Green. The

DSL

LED lights up whenever there is a successful DSL connection. The LED blinks

while establishing the ADSL connection.

Internet

Green. The

Internet

LED lights up green when an Internet connection to the Internet Service

Provider (ISP) session is established. The

Internet

LED lights up red when the connection to

the ISP fails.

Figure 3-2: Front Panel