Netgear Router WGT624 User Manual

							Reference Manual for the 108 Mbps Wireless Firewall Router WGT624
Network, Routing, Firewall, and Basics B-9
M-10153-01
If a device sends data to another station on the network and the destination MAC address is not yet 
recorded, ARP is used. An ARP request is broadcast onto the network. All stations on the network 
receive and read the request. The destination IP address for the chosen station is included as part of 
the message so that only the station with this IP address responds to the ARP request. All other 
stations discard the request. 
Related Documents
The station with the correct IP address responds with its own MAC address directly to the sending 
device. The receiving station provides the transmitting station with the required destination MAC 
address. The IP address data and MAC address data for each station are held in an ARP table. The 
next time data is sent, the address can be obtained from the address information in the table.
For more information about address assignment, refer to the IETF documents RFC 1597, Address 
Allocation for Private Internets, and RFC 1466, Guidelines for Management of IP Address Space.
For more information about IP address translation, refer to RFC 1631, The IP Network Address 
Translator (NAT).
Domain Name Server
Many of the resources on the Internet can be addressed by simple descriptive names such as 
www.NETGEAR.com. This addressing is very helpful at the application level, but the descriptive 
name must be translated to an IP address in order for a user to actually contact the resource. Just as 
a telephone directory maps names to phone numbers, or as an ARP table maps IP addresses to 
MAC addresses, a domain name system (DNS) server maps descriptive names of network 
resources to IP addresses.
When a PC accesses a resource by its descriptive name, it first contacts a DNS server to obtain the 
IP address of the resource. The PC sends the desired message using the IP address. Many large 
organizations, such as ISPs, maintain their own DNS servers and allow their customers to use the 
servers to look up addresses. 
						

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IP Configuration by DHCP
When an IP-based local area network is installed, each PC must be configured with an IP address. 
If the PCs need to access the Internet, they should also be configured with a gateway address and 
one or more DNS server addresses. As an alternative to manual configuration, there is a method by 
which each PC on the network can automatically obtain this configuration information. A device 
on the network may act as a Dynamic Host Configuration Protocol (DHCP) server. The DHCP 
server stores a list or pool of IP addresses, along with other information (such as gateway and DNS 
addresses) that it may assign to the other devices on the network. The WGT624 wireless router has 
the capacity to act as a DHCP server.
The WGT624 wireless router also functions as a DHCP client when connecting to the ISP. The 
firewall can automatically obtain an IP address, subnet mask, DNS server addresses, and a 
gateway address if the ISP provides this information by DHCP.
Internet Security and Firewalls
When your LAN connects to the Internet through a router, an opportunity is created for outsiders 
to access or disrupt your network. A NAT router provides some protection because by the very 
nature of the process, the network behind the router is shielded from access by outsiders on the 
Internet. However, there are methods by which a determined hacker can possibly obtain 
information about your network or at the least can disrupt your Internet access. A greater degree of 
protection is provided by a firewall router.
What is a Firewall?
A firewall is a device that protects one network from another, while allowing communication 
between the two. A firewall incorporates the functions of the NAT router, while adding features for 
dealing with a hacker intrusion or attack. Several known types of intrusion or attack can be 
recognized when they occur. When an incident is detected, the firewall can log details of the 
attempt, and can optionally send email to an administrator notifying them of the incident. Using 
information from the log, the administrator can take action with the ISP of the hacker. In some 
types of intrusions, the firewall can fend off the hacker by discarding all further packets from the 
hacker’s IP address for a period of time. 
						

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Stateful Packet Inspection
Unlike simple Internet sharing routers, a firewall uses a process called stateful packet inspection to 
ensure secure firewall filtering to protect your network from attacks and intrusions. Since 
user-level applications such as FTP and web browsers can create complex patterns of network 
traffic, it is necessary for the firewall to analyze groups of network connection states. Using 
Stateful Packet Inspection, an incoming packet is intercepted at the network layer and then 
analyzed for state-related information associated with all network connections. A central cache 
within the firewall keeps track of the state information associated with all network connections. 
All traffic passing through the firewall is analyzed against the state of these connections in order to 
determine whether or not it will be allowed to pass through or rejected.
Denial of Service Attack
A hacker may be able to prevent your network from operating or communicating by launching a 
Denial of Service (DoS) attack. The method used for such an attack can be as simple as merely 
flooding your site with more requests than it can handle. A more sophisticated attack may attempt 
to exploit some weakness in the operating system used by your router or gateway. Some operating 
systems can be disrupted by simply sending a packet with incorrect length information.
Ethernet Cabling
Most Ethernet networks now use unshielded twisted pair (UTP) cabling. UTP cable has eight 
wires arranged in four twisted pairs, and terminated with an RJ45 connector. Normal straight- 
through UTP Ethernet cable follows the EIA568B standard as described in Ta b l e  B - 1.
Table B-1. UTP Ethernet cable wiring, straight-through
Pin Wire color Signal
1 Orange/White Transmit (Tx) +
2 Orange Transmit (Tx) -
3 Green/White Receive (Rx) +
4Blue
5 Blue/White
6 Green Receive (Rx) -
7 Brown/White
8Brown 
						

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Category 5 Cable Quality
Category 5 distributed cable that meets ANSI/EIA/TIA-568-A building wiring standards can be a 
maximum of 328 feet (ft.) or 100 meters (m) in length, divided as follows:
20 ft. (6 m) between the hub and the patch panel (if used)
295 ft. (90 m) from the wiring closet to the wall outlet
10 ft. (3 m) from the wall outlet to the desktop device
The patch panel and other connecting hardware must meet the requirements for 100 Mbps 
operation (Category 5). Only 0.5 inch (1.5 cm) of untwist in the wire pair is allowed at any 
termination point.
A twisted pair Ethernet network operating at 10 Mbits/second (10BASE-T) will often tolerate low 
quality cables, but at 100 Mbits/second (10BASE-Tx) the cable must be rated as Category 5, or 
Cat 5, by the Electronic Industry Association (EIA). This rating will be printed on the cable jacket. 
A Category 5 cable will meet specified requirements regarding loss and crosstalk. In addition, 
there are restrictions on maximum cable length for both 10 and 100 Mbits/second networks.
Inside Twisted Pair Cables
For two devices to communicate, the transmitter of each device must be connected to the receiver 
of the other device. The crossover function is usually implemented internally as part of the 
circuitry in the device. Computers and workstation adapter cards are usually media-dependent 
interface ports, called MDI or uplink ports. Most repeaters and switch ports are configured as 
media-dependent interfaces with built-in crossover ports, called MDI-X or normal ports.  Auto 
Uplink technology automatically senses which connection, MDI or MDI-X, is needed and makes 
the right connection.
Figure B-1 illustrates straight-through twisted pair cable. 
						

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M-10153-01 Figure B-1:  Straight-Through Twisted-Pair Cable
Figure B-2 illustrates crossover twisted pair cable.
Figure B-2:  Crossover Twisted-Pair Cable
Figure B-3:  Category 5 UTP Cable with Male RJ-45 Plug at Each End 
						

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Note: Flat “silver satin” telephone cable may have the same RJ-45 plug. However, using telephone 
cable results in excessive collisions, causing the attached port to be partitioned or disconnected 
from the network.
Uplink Switches, Crossover Cables, and MDI/MDIX Switching
In the wiring table above, the concept of transmit and receive are from the perspective of the PC, 
which is wired as Media Dependant Interface (MDI). In this wiring, the PC transmits on pins 1 and 
2. At the hub, the perspective is reversed, and the hub receives on pins 1 and 2. This wiring is 
referred to as Media Dependant Interface - Crossover (MDI-X). 
When connecting a PC to a PC, or a hub port to another hub port, the transmit pair must be 
exchanged with the receive pair. This exchange is done by one of two mechanisms. Most hubs 
provide an Uplink switch which will exchange the pairs on one port, allowing that port to be 
connected to another hub using a normal Ethernet cable. The second method is to use a crossover 
cable, which is a special cable in which the transmit and receive pairs are exchanged at one of the 
two cable connectors. Crossover cables are often unmarked as such, and must be identified by 
comparing the two connectors. Since the cable connectors are clear plastic, it is easy to place them 
side by side and view the order of the wire colors on each. On a straight-through cable, the color 
order will be the same on both connectors. On a crossover cable, the orange and blue pairs will be 
exchanged from one connector to the other.
The WGT624 wireless router incorporates Auto Uplink
TM technology (also called MDI/MDIX). 
Each LOCAL Ethernet port will automatically sense whether the Ethernet cable plugged into the 
port should have a normal connection (e.g. connecting to a PC) or an uplink connection (e.g. 
connecting to a router, switch, or hub). That port will then configure itself to the correct 
configuration. This feature also eliminates the need to worry about crossover cables, as Auto 
Uplink
TM will accommodate either type of cable to make the right connection. 
						

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Appendix C
Preparing Your Network
This appendix describes how to prepare your network to connect to the Internet through the 108 
Mbps Wireless Firewall Router WGT624 and how to verify the readiness of broadband Internet 
service from an Internet service provider (ISP).
Preparing Your Computers for TCP/IP Networking
Computers access the Internet using a protocol called TCP/IP (Transmission Control Protocol/
Internet Protocol). Each computer on your network must have TCP/IP installed and selected as its 
networking protocol. If a Network Interface Card (NIC) is already installed in your PC, then TCP/
IP is probably already installed as well.
Most operating systems include the software components you need for networking with TCP/IP:
•Windows
® 95 or later includes the software components for establishing a TCP/IP network. 
• Windows 3.1 does not include a TCP/IP component. You need to purchase a third-party TCP/
IP application package such as NetManage Chameleon.
• Macintosh Operating System 7 or later includes the software components for establishing a 
TCP/IP network.
• All versions of UNIX or Linux include TCP/IP components. Follow the instructions provided 
with your operating system or networking software to install TCP/IP on your computer.
Note: If an ISP technician configured your computer during the installation of a 
broadband modem, or if you configured it using instructions provided by your ISP, you 
may need to copy the current configuration information for use in the configuration of 
your firewall. Write down this information before reconfiguring your computers. Refer 
to “Obtaining ISP Configuration Information for Windows Computers” on page C-19 or 
“Obtaining ISP Configuration Information for Macintosh Computers” on page C-20 for 
further information. 
						

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In your IP network, each PC and the firewall must be assigned a unique IP addresses. Each PC 
must also have certain other IP configuration information such as a subnet mask (netmask), a 
domain name server (DNS) address, and a default gateway address. In most cases, you should 
install TCP/IP so that the PC obtains its specific network configuration information automatically 
from a DHCP server during bootup. For a detailed explanation of the meaning and purpose of 
these configuration items, refer to “Appendix B, “Network, Routing, Firewall, and Basics.” 
The WGT624 wireless router is shipped preconfigured as a DHCP server. The firewall assigns the 
following TCP/IP configuration information automatically when the PCs are rebooted:
• PC or workstation IP addresses—192.168.0.2 through 192.168.0.254
• Subnet mask—255.255.255.0
• Gateway address (the firewall)—192.168.0.1
These addresses are part of the IETF-designated private address range for use in private networks.
Configuring Windows 95, 98, and Me for TCP/IP Networking
As part of the PC preparation process, you need to manually install and configure TCP/IP on each 
networked PC. Before starting, locate your Windows CD; you may need to insert it during the 
TCP/IP installation process.
Install or Verify Windows Networking Components
To install or verify the necessary components for IP networking:
1.On the Windows taskbar, click the Start button, point to Settings, and then click Control Panel.
2.Double-click the Network icon.
The Network window opens, which displays a list of installed components: 
						

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You must have an Ethernet adapter, the TCP/IP protocol, and Client for Microsoft Networks.
If you need to install a new adapter, follow these steps:
a.Click the Add button.
b.Select Adapter, and then click Add.
c.Select the manufacturer and model of your Ethernet adapter, and then click OK.
If you need TCP/IP:
a.Click the Add button.
b.Select Protocol, and then click Add.
c.Select Microsoft.
d.Select TCP/IP, and then click OK.
Note: It is not necessary to remove any other network components shown in the 
Network window in order to install the adapter, TCP/IP, or Client for Microsoft 
Networks.  
						

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If you need Client for Microsoft Networks:
a.Click the Add button.
b.Select Client, and then click Add.
c.Select Microsoft.
d.Select Client for Microsoft Networks, and then click OK.
3.Restart your PC for the changes to take effect.
Enabling DHCP to Automatically Configure TCP/IP Settings
After the TCP/IP protocol components are installed, each PC must be assigned specific 
information about itself and resources that are available on its network. The simplest way to 
configure this information is to allow the PC to obtain the information from a DHCP server in the 
network. 
You will find there are many similarities in the procedures for different Windows systems 
when using DHCP to configure TCP/IP.
The following steps will walk you through the configuration process for each of these 
versions of Windows.
Locate your Network Neighborhood icon.
• If the Network Neighborhood icon is on the Windows desktop, position your mouse 
pointer over it and right-click your mouse button.
• If the icon is not on the desktop,
• Click Sta rt on the task bar located at the bottom left of the window.
• Choose Settings, and then Control Panel. 
• Locate the Network Neighborhood icon and click on it. This will open the Network 
panel as shown below.