Vigor2710 Series User’s Guide

44

the 2nd subnet with neighboring routers.

DHCP Server

Configuration

DHCP stands for Dynamic Host Configuration Protocol. The

router by factory default acts a DHCP server for your network so

it automatically dispatch related IP settings to any local user

configured as a DHCP client. It is highly recommended that you

leave the router enabled as a DHCP server if you do not have a

DHCP server for your network.

If you want to use another DHCP server in the network other

than the Vigor Router’s, you can let Relay Agent help you to

redirect the DHCP request to the specified location.

Enable Server -

Let the router assign IP address to every host in

the LAN.

Disable Server –

Let you manually assign IP address to every

host in the LAN.

Relay Agent – (1

st

subnet/2

nd

subnet)

Specify which subnet that

DHCP server is located the relay agent should redirect the DHCP

request to.

Start IP Address -

Enter a value of the IP address pool for the

DHCP server to start with when issuing IP addresses. If the 1st IP

address of your router is 192.168.1.1, the starting IP address must

be 192.168.1.2 or greater, but smaller than 192.168.1.254.

IP Pool Counts -

Enter the maximum number of PCs that you

want the DHCP server to assign IP addresses to. The default is 50

and the maximum is 253.

Gateway IP Address -

Enter a value of the gateway IP address

for the DHCP server. The value is usually as same as the 1st IP

address of the router, which means the router is the default

gateway.

DHCP Server IP Address for Relay Agent -

Set the IP address

of 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

.

Force DNS manual setting -

Force Vigor router to use DNS

servers in this page instead of DNS servers given by the Internet

Access server (PPPoE, PPTP, L2TP or DHCP server).

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:

Vigor2710 Series User’s Guide

45

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 5. For the

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

necessity.

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.

Vigor2710 Series User’s Guide

46

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 20 port-mapping entries for the internal hosts.

Press any number under Index to access into next page for configuring port redirection.

Vigor2710 Series User’s Guide

47

Enable

Check this box to enable such port redirection setting.

Mode

Two options (Single and Range) are provided here for you to

choose. To set a range for the specific service, select

Range

. In

Range mode, if the public port (start port and end port) and the

starting IP of private IP had been entered, the system will

calculate and display the ending IP of private IP automatically.

Service Name

Enter the description of the specific network service.

Protocol

Select the transport layer protocol (TCP or UDP).

WAN IP

Select the WAN IP used for port redirection. There are eight

WAN IP alias that can be selected and used for port redirection.

The default setting is

All

which means all the incoming data from

any port will be redirected to specified range of IP address and

port.

Public Port

Specify which port can be redirected to the specified

Private IP

and Port

of the internal host. If you choose

Range

as the port

redirection mode, you will see two boxes on this field. Simply

type the required number on the first box. The second one will be

assigned automatically later.

Private IP

Specify the private IP address of the internal host providing the

service. If you choose

Range

as the port redirection mode, you

will see two boxes on this field. Type a complete IP address in

the first box (as the starting point) and the fourth digits in the

second box (as the end point).

Private Port

Specify the private port number of the service offered by the

internal host.

Note that the router has its own built-in services (servers) such as Telnet, HTTP and FTP etc.

Since the common port numbers of these services (servers) are all the same, you may need to

reset the router in order to avoid confliction.

Vigor2710 Series User’s Guide

48

3.3.2 DMZ Host

As mentioned above,

Port Redirection

can redirect incoming TCP/UDP or other traffic on

particular ports to the specific private IP address/port of host in the LAN. However, other IP

protocols, for example Protocols 50 (ESP) and 51 (AH), do not travel on a fixed port. Vigor

router provides a facility

DMZ Host

that maps ALL unsolicited data on any protocol to a

single host in the LAN. Regular web surfing and other such Internet activities from other

clients will continue to work without inappropriate interruption.

DMZ Host

allows a defined

internal user to be totally exposed to the Internet, which usually helps some special

applications such as Netmeeting or Internet Games etc.

The inherent security properties of NAT are somewhat bypassed if you set up DMZ host.

We suggest you to add additional filter rules or a secondary firewall.

Click

DMZ Host

to open the following page:

If you previously have set up

WAN Alias

for

PPPoE/PPPoA

or

MPoA

mode

,

you will find

them in

Aux. WAN IP

for your selection.