Telewell TW-EA510v3 Router Manual PDF (Setup & Configuration Guide)

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4.3.6 Virtual Server

In TCP/IP and UDP networks a port is a 16-bit number used to identify which application

program (usually a server) incoming connections should be delivered to. Some ports have

numbers that are pre-assigned to them by the IANA (the Internet Assigned Numbers

Authority), and these are referred to as “well-known ports”. Servers follow the well-known

port assignments so clients can locate them.

If you wish to run a server on your network that can be accessed from the WAN (i.e. from

other machines on the Internet that are outside your local network), or any application that

can accept incoming connections (e.g. Peer-to-peer/P2P software such as instant

messaging applications and P2P file-sharing applications) and are using NAT (Network

Address Translation), then you need to configure your router to forward these incoming

connection attempts using specific ports to the PC on your network running the application.

You also need to use port forwarding if you wish to host an online game server.

The reason is that when using NAT, your publicly accessible IP address is used by and

points to your router, which needs to deliver all traffic to the private IP addresses used by

your PCs. Please see the

WAN

configuration section of this manual for information on NAT.

The Internet Assigned Numbers Authority (IANA) is the central coordinator for the

assignment of unique parameter values for Internet protocols. Port numbers range from 0 to

65535, but only port numbers 0 to 1023 are reserved for privileged services and are

designated as “well-known ports”. The registered ports are numbered from 1024 through

49151. The remaining ports, referred to as dynamic ports, or private ports, are numbered

from 49152 through 65535.

Examples of well-known and registered port numbers are shown below, for further

information, please see IANA’s website at:

http://www.iana.org/assignments/port-numbers

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75

Well-known and Registered Ports

Port Number

Protocol

Description

20

TCP

FTP Data

21

TCP

FTP Control

22

TCP & UDP

SSH Remote Login Protocol

23

TCP

Telnet

25

TCP

SMTP (Simple Mail Transfer Protocol)

53

TCP & UDP

DNS (Domain Name Server)

69

UDP

TFTP (Trivial File Transfer Protocol)

80

TCP

World Wide Web HTTP

110

TCP

POP3 (Post Office Protocol Version 3)

119

TCP

NEWS (Network News Transfer Protocol)

123

UDP

NTP (Network Time Protocol)

161

TCP

SNMP

443

TCP & UDP

HTTPS

1503

TCP

T.120

1720

TCP

H.323

4000

TCP

ICQ

7070

UDP

RealAudio

Item:

Item number

Type:

Select

TCP

if you wish to search for connection-based application services on the

remote server using the port number.

Port Start & Port End:

Enter the public port number & range you wish to configure.

IP Address:

Enter the IP address of a specific internal server to which requests from the

specified port is forwarded.

Add:

Click to add a new virtual server rule. Click again and the next figure appears.

Edit:

Check the Rule No. you wish to edit and then click “Edit”.

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Delete:

Check the Rule No. you wish to delete, then click “Delete”.

Item:

Item number

Service select:

Select the service you wish to configure

Protocol:

Automatic when you choose Service select

Start Port & End Port:

Enter the public port number & range you wish to configure.

IP Address:

Enter the IP address of a specific internal server to which requests from the

specified port is forwarded.

Since NAT acts as a “natural” Internet firewall, your router protects your network from access

by outside users, as all incoming connection attempts point to your router unless you

specifically create Virtual Server entries to forward those ports to a PC on your network.

When your router needs to allow outside users to access internal servers, e.g. a web server,

FTP server, Email server or game server, the router can act as a “virtual server”. You can set

up a local server with a specific port number for the service to use, e.g. web/HTTP (port 80),

FTP (port 21), Telnet (port 23), SMTP (port 25), or POP3 (port 110). When an incoming

access request to the router for a specified port is received, it is forwarded to the

corresponding internal server.

For example, if you set the port number 80 (Web/HTTP) to be mapped to the IP Address

192.168.0.2, then all incoming HTTP requests from outside users are forwarded to the local

server (PC) with the IP address of 192.168.0.2. If the port is not listed as a predefined

application, you need to add it manually.

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In addition to specifying the port number used, you also need to specify the protocol used.

The protocol is determined by the particular application. Most applications use TCP or UDP,

however you can specify other protocols using the drop-down

Protocol

menu. Setting the

protocol to “all” causes all incoming connection attempts using all protocols on all port

numbers to be forwarded to the specified IP address.

DMZ:

The DMZ Host is a local computer exposed to the Internet. When setting a particular

internal IP address as the DMZ Host, all incoming packets are checked by the Firewall and

NAT algorithms, then passed to the DMZ host when a packet received does not use a port

number in use by any other Virtual Server entries.

If you disable the NAT option in the WAN-ISP section, the Virtual Server

function becomes invalid.

Attention

If the DHCP server option is enabled, you have to be very careful in assigning

the IP addresses of the virtual servers in order to avoid conflicts. The easiest

way of configuring Virtual Servers is to manually assign a static IP address to

each virtual server PC, with an address that does not fall into the range of IP

addresses that are issued by the DHCP server. You can configure the virtual

server IP address manually, but it must still be in the same subnet as the

router.

Attention

Using port forwarding does have security implications, since outside users

are able to connect to PCs on your network. For this reason you are

advised to use specific Virtual Server entries just for the ports your

application requires instead of simply using DMZ or creating a Virtual

Server entry for “All” protocols, as doing so results in all connection

attempts to your public IP address accessing the specified PC.

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4.3.7 Advanced

Configuration options within the

Advanced

section are for users who wish to take

advantage of the more advanced features of the router. Users who do not understand the

features should not attempt to reconfigure their router, unless advised to do so by support

staff.

There are four items within the

Advanced

section:

Static Route, Dynamic DNS

,

VLan

Control

and

Device Management.

4.3.7.1 Static Route

Click on

Routing Table

and then choose

Create Route

to add a routing table.

Destination:

The destination subnet IP address.

Netmask:

Subnet mask of the destination IP addresses based on above destination.

Gateway:

The gateway IP address to which packets are forwarded.

Interface:

Select the interface through which packets are forwarded.

Cost:

Represents the cost of transmission for routing purposes. The number need not be

precise, but it must be between 0 and 65535.

4.3.7.2 Dynamic DNS

The Dynamic DNS function lets you alias a dynamic IP address to a static hostname, so if

your ISP does not assign you a static IP address you can still use a domain name. This is

especially useful for hosting servers via your ADSL connection, so that anyone wishing to

connect to you may use your domain name, rather than having to use your dynamic IP

address, which changes from time to time. This dynamic IP address is the WAN IP address

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