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the DHCP server you are going to use so the Relay Agent can help

to forward the DHCP request to the DHCP server.

DNS Server

Configuration

DNS stands for Domain Name System. Every Internet host must

have a unique IP address, also they may have a human-friendly,

easy to remember name such as www.yahoo.com. The DNS server

converts the user-friendly name into its equivalent IP address

.

Primary IP Address -

You must specify a DNS server IP address

here because your ISP should provide you with usually more than

one DNS Server. If your ISP does not provide it, the router will

automatically apply default DNS Server IP address: 194.109.6.66

to this field.

Secondary IP Address -

You can specify secondary DNS server IP

address here because your ISP often provides you more than one

DNS Server. If your ISP does not provide it, the router will

automatically apply default secondary DNS Server IP address:

194.98.0.1 to this field.

The default DNS Server IP address can be found via Online Status:

If both the Primary IP and Secondary IP Address fields are left

empty, the router will assign its own IP address to local users as a

DNS proxy server and maintain a DNS cache.

If the IP address of a domain name is already in the DNS cache, the

router will resolve the domain name immediately. Otherwise, the

router forwards the DNS query packet to the external DNS server

by establishing a WAN (e.g. DSL/Cable) connection.

There are two common scenarios of LAN settings that stated in Chapter 4. For the

configuration examples, please refer to that chapter to get more information for your

necessity.

3.2.3 Static Route

Go to

LAN

to open setting page and choose

Static Route

.

Index

The number (1 to 10) under Index allows you to open next page to

setup static route.

Destination Address

Displays the destination address of the static route.

Status

Displays the status of the static route.

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Viewing Routing Table

Displays the routing table for your reference.

Add Static Routes to Private and Public Networks

Here is an example of setting Static Route in Main Router so that user A and B locating in

different subnet can talk to each other via the router. Assuming the Internet access has been

configured and the router works properly:

z

use the Main Router to surf the Internet.

z

create a private subnet 192.168.10.0 using an internal Router A (192.168.1.2)

z

create a public subnet 211.100.88.0 via an internal Router B (192.168.1.3).

z

have set Main Router 192.168.1.1 as the default gateway for the Router A 192.168.1.2.

Before setting Static Route, user A cannot talk to user B for Router A can only forward

recognized packets to its default gateway Main Router.

1.

Go to

LAN

page and click

General Setup

, select 1st Subnet as the

RIP Protocol

Control.

Then click the

OK

button.

Note: There are two reasons that we have to apply RIP Protocol Control on

1st Subnet. The first is that the LAN interface can exchange RIP packets

with the neighboring routers via the 1st subnet (192.168.1.0/24). The second

is that those hosts on the internal private subnets (ex. 192.168.10.0/24) can

access the Internet via the router, and continuously exchange of IP routing

information with different subnets.

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2.

Click the

LAN - Static Route

and click on the

Index Number 1.

Please add a static

route as shown below, which regulates all packets destined to 192.168.10.0 will be

forwarded to 192.168.1.2. Click

OK

.

3.

Return to

Static Route

Setup

page. Click on another

Index Number

to add another

static route as show below, which regulates all packets destined to 211.100.88.0 will be

forwarded to 192.168.1.3.

4.

Go to

Diagnostics

and choose

Routing Table

to verify current routing table.

Delete Static Route

1.

Go to

LAN

page and click

Static Route

to open the web page. Select the index number

of the one that you want to delete.

2.

Select

Empty/Clear

from the drop-down menu, and then click the

OK

button to delete

the route.

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38

Disable Static Route

1.

Click the

Index Number

that you want to disable from the

Static Route

Configuration

page.

2.

Select

Inactive/Disable

from the drop-down menu, and then click the

OK

button to

disable the route.

3.3 NAT

Usually, the router serves as an NAT (Network Address Translation) router. NAT is a

mechanism that one or more private IP addresses can be mapped into a single public one.

Public IP address is usually assigned by your ISP, for which you may get charged. Private IP

addresses are recognized only among internal hosts.

When the outgoing packets destined to some public server on the Internet reach the NAT

router, the router will change its source address into the public IP address of the router, select

the available public port, and then forward it. At the same time, the router shall list an entry

in a table to memorize this address/port-mapping relationship. When the public server

response, the incoming traffic, of course, is destined to the router’s public IP address and the

router will do the inversion based on its table. Therefore, the internal host can communicate

with external host smoothly.

The benefit of the NAT includes:

z

Save cost on applying public IP address and apply efficient usage of IP address.

NAT allows the internal IP addresses of local hosts to be translated into one public IP

address, thus you can have only one IP address on behalf of the entire internal hosts.

z

Enhance security of the internal network by obscuring the IP address.

There are

many attacks aiming victims based on the IP address. Since the attacker cannot be

aware of any private IP addresses, the NAT function can protect the internal network.

On NAT page, you will see the private IP address defined in RFC-1918. Usually

we use the 192.168.1.0/24 subnet for the router. As stated before, the NAT facility

can map one or more IP addresses and/or service ports into different specified

services. In other words, the NAT function can be achieved by using port mapping

methods.

Below shows the menu items for NAT.

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3.3.1 Port Redirection

Port Redirection

is

usually set up for server related service inside the local network (LAN),

such as web servers, FTP servers, E-mail servers etc. Most of the case, you need a public IP

address for each server and this public IP address/domain name are recognized by all users.

Since the server is actually located inside the LAN, the network well protected by NAT of

the router, and identified by its private IP address/port, the goal of Port Redirection function

is to forward all access request with public IP address from external users to the mapping

private IP address/port of the server.

The port redirection can only apply to incoming traffic.

To use this function, please go to

NAT

page and choose

Port

Redirection

web page. The

Port Redirection Table

provides 10 port-mapping entries for the internal hosts.

Service Name

Enter the description of the specific network service.