Security Settings

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N150 WiFi Router (N150R)

Schedule Services

If you enabled service blocking in the Block Services screen or port forwarding in the Ports

screen, you can set up a schedule for when blocking occurs or when access is not restricted.



To schedule services:

1.

Select

Security > Schedule

.

2.

To block Internet services based on a schedule, select

Every Day

or select one or more

days.

3.

If you want to limit access completely for the selected days, select

All Day

. Otherwise, to

limit access during certain times for the selected days, enter times in the Start Blocking and

End Blocking fields.

Note:

Enter the values in 24-hour time format. For example, 10:30 a.m. would

be 10 hours and 30 minutes, and 10:30 p.m. would be 22 hours and 30

minutes. If you set the start time after the end time, the schedule is effective

through midnight the next day.

4.

Click

Apply

to save your settings.

Security Settings

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N150 WiFi Router (N150R)

Set Up Email Alerts

To receive logs and alerts by email, provide your email information in the E-mail screen and

specify which alerts you want to receive and how often.

Select

Security >

Email Alert

to display the following screen:

Figure 6. E-Mail screen

•

Turn E-mail Notification On

. Select this check box if you want to receive email logs and

alerts from the router.

•

Send to This E-mail Address

. Enter the email address where you want logs and alerts

sent. This email address is also used as the From address. If you leave this field blank,

log and alert messages are not sent by email.

•

Your Outgoing Mail Server

. Enter the name or IP address of your ISP’s outgoing

(SMTP) mail server (such as mail.myISP.com). You might be able to find this information

in the configuration settings of your email program. Enter the email address to which logs

and alerts are sent. This email address is also used as the From address. If you leave

this field blank, log and alert messages are not sent by email.

•

My mail server requires authentication

. If you use an outgoing mail server provided by

your current ISP, you do not need to select this field. If you use an email account that is

not provided by your ISP, select this field, and enter the required user name and

password information.

•

Send Alerts Immediately

.

Select the corresponding check box if you would like

immediate notification of a significant security event, such as a known attack, port scan,

or attempted access to a blocked site.

•

Send logs according to this schedule

.

Specifies how often to send the logs: Hourly,

Daily, Weekly, or When Full.

-

Days

. This setting specifies which day of the week to send the log. This is relevant

when the log is sent weekly.

Security Settings

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N150 WiFi Router (N150R)

-

Time

. This setting specifies the time of day to send the log. This is relevant when the

log is sent daily or weekly.

Note:

If the Weekly, Daily, or Hourly option is selected and the log fills up

before the specified period, the log is automatically emailed to the

specified email address. After the log is sent, it is cleared from the

router’s memory. If the router cannot email the log file, the log buffer

might fill up. In this case, the router overwrites the log and discards

its contents.

Port Forwarding and Triggering

By default, the router blocks inbound traffic from the Internet to your computers except

replies to your outbound traffic. You might need to create exceptions to this rule for these

purposes:

•

To allow remote computers on the Internet to access a server on your local network.

•

To allow certain applications and games to work correctly when your router does not

recognize their replies.

Your router provides two features for creating these exceptions: port forwarding and port

triggering. The next sections provide background information to help you understand how

port forwarding and port triggering work, and the differences between the two.

Remote Computer Access Basics

When a computer on your network needs to access a computer on the Internet, your

computer sends your router a message containing the source and destination address and

process information. Before forwarding your message to the remote computer, your router

has to modify the source information and create and track the communication session so that

replies can be routed back to your computer.

Here is an example of normal outbound traffic and the resulting inbound responses:

1.

You open a browser, and your operating system assigns port number 5678 to this

browser session.

2.

You type http://www.example.com into the URL field, and your computer creates a web

page request message with the following address and port information. The request

message is sent to your router.

Source address

. Your computer’s IP address.

Source port number

. 5678, which is the browser session.

Destination address

. The IP address of www.example.com, which your computer finds

by asking a DNS server.

Security Settings

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N150 WiFi Router (N150R)

Destination port number

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

process.

3.

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

session between your computer and the web server at www.example.com. Before sending

the web page request message to www.example.com, your router stores the original

information and then modifies the source information in the request message, performing

Network Address Translation (NAT):

•

The source address is replaced with your router’s public IP address. This is

necessary because your computer uses a private IP address that is not globally

unique and cannot be used on the Internet.

•

The source port number is changed to a number assigned by the router, such as

33333. This is necessary because two computers could independently be using the

same session number.

Your router then sends this request message through the Internet to the web server at

www.example.com.

4.

The web server at www.example.com composes a return message with the requested web

page data. The return message contains the following address and port information. The

web server then sends this reply message to your router.

Source address

. The IP address of www.example.com.

Source port number

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

Destination address

. The public IP address of your router.

Destination port number

. 33333.

5.

Upon receiving the incoming message, your router checks its session table to determine

whether there is an active session for port number 33333. Finding an active session, the

router then modifies the message to restore the original address information replaced by

NAT. Your router sends this reply message to your computer, which displays the web

page from www.example.com. The message now contains the following address and port

information.

Source address

. The IP address of www.example.com.

Source port number

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

Destination address

. Your computer’s IP address.

Destination port number

. 5678, which is the browser session that made the initial

request.

6.

When you finish your browser session, your router eventually detects a period of inactivity in

the communications. Your router then removes the session information from its session

table, and incoming traffic is no longer accepted on port number 33333.

Security Settings

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N150 WiFi Router (N150R)

Port Triggering to Open Incoming Ports

In the preceding example, requests are sent to a remote computer by your router from a

particular service port number. Replies from the remote computer to your router are directed

to that port number. If the remote server sends a reply to a different port number, your router

does not recognize it and discards it. However, some application servers (such as FTP and

IRC servers) send replies to multiple port numbers. Using the port triggering function of your

router, you can tell the router to open additional incoming ports when a particular outgoing

port originates 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 router, “When you initiate a session with destination port 6667, you have to also

allow incoming traffic on port 113 to reach the originating computer.” Using steps similar to

the preceding example, the following sequence shows the effects of the port triggering rule

you have defined:

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 router.

3.

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

session between your computer and the IRC server. Your 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 having observed the destination port number of 6667,

your router creates an additional session entry to send any incoming port 113 traffic to your

computer.

5.

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

(as in the previous example, say port 33333) as the destination port. The IRC server also

sends an “identify” message to your router with destination port 113.

6.

Upon receiving the incoming message to destination port 33333, your router checks its

session table to determine whether there is an active session for port number 33333.

Finding an active session, the router restores the original address information replaced by

NAT and sends this reply message to your computer.

7.

Upon receiving the incoming message to destination port 113, your router checks its

session table and learns that there is an active session for port 113, associated with your

computer. The 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 router eventually senses a period of inactivity in the

communications. The router then removes the session information from its session table,

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

To configure port triggering, you need to know which inbound ports the application needs.

Also, you need to know the number of the outbound port that will trigger the opening of the

inbound ports. You can usually determine this information by contacting the publisher of the

application or user groups or newsgroups.