Reference Manual for the Double 108 Mbps Wireless Firewall Router WGU624

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Network, Routing, Firewall, and Basics

M-10153-01

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.

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 WGU624 wireless router has

the capacity to act as a DHCP server.

The WGU624 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.

Reference Manual for the Double 108 Mbps Wireless Firewall Router WGU624

Network, Routing, Firewall, and Basics

B-11

M-10153-01

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.

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 the table below.

Reference Manual for the Double 108 Mbps Wireless Firewall Router WGU624

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Network, Routing, Firewall, and Basics

M-10153-01

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.

Table B-3.

UTP Ethernet cable wiring, straight-through

Pin

Wire color

Signal

1

Orange/White

Transmit (Tx) +

2

Orange

Transmit (Tx) -

3

Green/White

Receive (Rx) +

4

Blue

5

Blue/White

6

Green

Receive (Rx) -

7

Brown/White

8

Brown

Reference Manual for the Double 108 Mbps Wireless Firewall Router WGU624

Network, Routing, Firewall, and Basics

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M-10153-01

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.

The figure below illustrates straight-through twisted pair cable.

Figure B-4:

Straight-Through Twisted-Pair Cable

The figure below illustrates crossover twisted pair cable.

Figure B-5:

Crossover Twisted-Pair Cable

Reference Manual for the Double 108 Mbps Wireless Firewall Router WGU624

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Network, Routing, Firewall, and Basics

M-10153-01

Figure B-6:

Category 5 UTP Cable with Male RJ-45 Plug at Each End

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.