NETGEAR ME103v4 Router Manual PDF (Setup & Configuration Guide)

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Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

Network, Routing, Firewall, and Cabling Basics

C-9

August 2003

The ME103 Access Point 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.

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.

Routing Protocols

Two protocols routers use extensively are:

•

Routing Information Protocol (RIP)

•

Address Resolution Protocol (ARP)

These two protocols are introduced below.

RIP

One of the protocols used by a router to build and maintain a picture of the network is RIP. Using

RIP, routers periodically update one another and check for changes to add to the routing table.

The ME103 Access Point supports both the older RIP-1 and the newer RIP-2 protocols. Among

other improvements, RIP-2 supports subnet and multicast protocols. RIP is not required for most

home applications.

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Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

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Network, Routing, Firewall, and Cabling Basics

August 2003

MAC Addresses and ARP

An IP address alone cannot be used to deliver data from one LAN device to another. To send data

between LAN devices, you must convert the IP address of the destination device to its media

access control address (MAC address). Each device on an Ethernet network has a unique MAC

address, which is a 48-bit number assigned to each device by the manufacturer. The technique that

associates the IP address with a MAC address is known as address resolution. Internet Protocol

uses the ARP to resolve MAC addresses.

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.

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

.

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.

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Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

Network, Routing, Firewall, and Cabling Basics

C-11

August 2003

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.

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Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

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Network, Routing, Firewall, and Cabling Basics

August 2003

Ethernet Cabling

Although Ethernet networks originally used thick or thin coaxial cable, most installations currently

use unshielded twisted pair (UTP) cabling. The UTP cable contains eight conductors, arranged in

four twisted pairs, and terminated with an RJ45 type connector. A normal straight-through UTP

Ethernet cable follows the EIA568B standard wiring and pinout as described in

Table 6-1

.

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.

Table 6-1.

UTP Ethernet cable wiring, straight-through

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

Page 95 / 118

Reference Manual for the ME103 802.11b ProSafe Wireless Access Point

Network, Routing, Firewall, and Cabling Basics

C-13

August 2003

The ME103 Access Point incorporates Auto Uplink

TM

technology (also called MDI/MDIX). The

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.

Cable Quality

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 or Cat V, 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.

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