Specify Internet Port Settings

86

AC1750 WiFi Cable Modem Router

3.

Enter the modem router user name and password.

The user name is

admin

. The default password is

password

. The user name and

password are case-sensitive.

The BASIC Home screen displays.

4.

Select

ADVANCED > Advanced Setup > Port Forwarding/Port Triggering

.

5.

Select the

Port Forwarding

radio button as the service type.

6.

In the table, select the radio button next to the service name.

7.

Click the

Delete Service

button.

Application Example: Make a Local Web Server Public

If you host a web server on your local network, you can use port forwarding to allow web

requests from anyone on the Internet to reach your web server.



To make a local web server public:

1.

Assign your web server either a fixed IP address or a dynamic IP address using DHCP

address reservation.

In this example, your modem router always gives your web server an IP address of

192.168.0.33.

2.

In the Port Forwarding/Port Triggering screen, configure the modem router to forward the

HTTP service to the local address of your web server at

192.168.0.33

.

HTTP (port 80) is the standard protocol for web servers.

3.

(Optional) Register a host name with a Dynamic DNS service, and specify that name in the

Dynamic DNS screen of the modem router.

For more information, see

Dynamic DNS

on page

62.

Dynamic DNS makes it much easier to access a server from the Internet because you

can type the name in the Internet browser. Otherwise, you must know the IP address that

the Internet provider assigned, which typically changes.

How the Modem Router Implements the Port Forwarding

Rule

The following sequence shows the effects of a port forwarding rule:

1.

When you type the URL www.example.com in your browser, the browser sends a web

page request message with the following destination information:

•

Destination address

. The IP address of www.example.com, which is the address of

your modem router.

•

Destination port number

. 80, which is the standard port number for a web server

process.

Specify Internet Port Settings

87

AC1750 WiFi Cable Modem Router

2.

Your modem router receives the message and finds your port forwarding rule for incoming

port 80 traffic.

3.

The modem router changes the destination in the message to IP address 192.168.0.123

and sends the message to that computer.

4.

Your web server at IP address 192.168.0.123 receives the request and sends a reply

message to your modem router.

5.

Your modem router performs Network Address Translation (NAT) on the source IP address,

and sends the reply through the Internet to the computer or wireless device that sent the

web page request.

Set Up Port Triggering

Port triggering is a dynamic extension of port forwarding that is useful in these cases:

•

An application uses port forwarding to more than one local computer (but not

simultaneously).

•

An application opens incoming ports that are different from the outgoing port.

With port triggering, the modem router monitors traffic to the Internet from an outbound

“trigger” port that you specify. For outbound traffic from that port, the modem router saves the

IP address of the computer that sent the traffic. The modem router temporarily opens the

incoming port or ports that you specify in your rule, and forwards that incoming traffic to that

destination.

Port forwarding creates a static mapping of a port number or range of ports to a single local

computer. Port triggering can dynamically open ports to any computer when needed and

close the ports when they are no longer needed.

Note:

If you enabled port triggering because you use applications such as

multiplayer gaming, peer-to-peer connections, real-time

communications such as instant messaging, or remote assistance (a

feature in Windows XP), enable Universal Plug and Play (UPnP). See

Improve Network Connections with Universal Plug and Play

on

page

63.

Add a Port Triggering Service



To add a port triggering service:

1.

Launch a web browser from a computer or wireless device that is connected to the

network.

2.

Type

http://routerlogin.net

or

.

A login screen displays.

3.

Enter the modem router user name and password.

Specify Internet Port Settings

88

AC1750 WiFi Cable Modem Router

The user name is

admin

. The default password is

password

. The user name and

password are case-sensitive.

The BASIC Home screen displays.

4.

Select

ADVANCED > Advanced Setup > Port Forwarding/Port Triggering.

5.

Select the

Port Triggering

radio button.

6.

Click the

Add Service

button.

7.

In the

Service Name

field, type a descriptive service name.

8.

From the

Service User

list, select a user option:

•

Any

(the default) allows any computer on the Internet to use this service.

•

Single address

restricts the service to a particular computer. You must enter the IP

address of the computer to which you want to grant access.

9.

From the

Service Type

list, select a service.

If you are not sure, select

TCP/UDP

.

10.

In the

Triggering Port

field, enter the number of the outbound traffic port that will open the

inbound ports.

Specify Internet Port Settings

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AC1750 WiFi Cable Modem Router

11.

In the

Connection Type

,

Starting Port

, and

Ending Port

fields, enter the inbound

connection port information.

12.

Click the

Apply button

.

The service is added. You must enable port triggering before the modem router uses port

triggering. For information about port triggering, see

Specify When to Use Port Triggering

on page

89.

Specify When to Use Port Triggering



To specify when to use port triggering:

1.

Launch a web browser from a computer or wireless device that is connected to the

network.

2.

Type

http://routerlogin.net

or

.

A login screen displays.

3.

Enter the modem router user name and password.

The user name is

admin

. The default password is

password

. The user name and

password are case-sensitive.

The BASIC Home screen displays.

4.

Select

ADVANCED > Advanced Setup > Port Forwarding/Port Triggering

.

5.

Select the

Port Triggering

radio button.

6.

Specify when you want to use port triggering:

•

Never

. The modem router does not use port triggering even if you added port

triggering settings.

•

Per Schedule

. Port triggering is used based on the schedule you set.

•

Always

. Always use port triggering.

7.

In the

Port Triggering Timeout

field, enter a value up to 9999 minutes.

Specify Internet Port Settings

90

AC1750 WiFi Cable Modem Router

This value controls how long the inbound ports stay open when the modem router detects

no activity. This value is required because the modem router cannot detect when the

application terminates.

Application Example: Port Triggering for Internet Relay Chat

Some application servers, such as FTP and IRC servers, send replies to multiple port

numbers. Using port triggering, you can tell the modem router to open more incoming ports

when a particular outgoing port starts a session.

An example is Internet Relay Chat (IRC). Your computer connects to an IRC server at

destination port 6667. The IRC server not only responds to your originating source port, but

also sends an “identify” message to your computer on port 113. Using port triggering, you can

tell the modem router, “When you initiate a session with destination port 6667, you must also

allow incoming traffic on port 113 to reach the originating computer.” The following sequence

shows the effects of this port triggering rule:

1.

You open an IRC client program to start a chat session on your computer.

2.

Your IRC client composes a request message to an IRC server using a destination port

number of 6667, the standard port number for an IRC server process. Your computer then

sends this request message to your modem router.

3.

Your modem router creates an entry in its internal session table describing this

communication session between your computer and the IRC server. Your modem router

stores the original information, performs Network Address Translation (NAT) on the source

address and port, and sends this request message through the Internet to the IRC server.

4.

Noting your port triggering rule and observing the destination port number of 6667, your

modem router creates another session entry to send any incoming port 113 traffic to your

computer.

5.

The IRC server sends a return message to your modem router using the NAT-assigned

source port (for example, port 33333) as the destination port and sends an “identify”

message to your modem router with destination port 113.

6.

When your modem router receives the incoming message to destination port 33333, it

checks its session table to see if a session is active for port number 33333. Finding an active

session, the modem router restores the original address information replaced by NAT and

sends this reply message to your computer.

7.

When your modem router receives the incoming message to destination port 113, it checks

its session table and finds an active session for port 113 associated with your computer. The

modem router replaces the message’s destination IP address with your computer’s IP

address and forwards the message to your computer.

8.

When you finish your chat session, your modem router eventually senses a period of

inactivity in the communications and removes the session information from its session table,

and incoming traffic is no longer accepted on port numbers 33333 or 113.