42 | Chapter 3: Protecting Your Network
N300 Wireless Gigabit ADSL2+ Modem Router DGN3500 User Manual
Figure 19.
Considerations for Inbound Rules
• If your external IP address is assigned dynamically by your ISP, the IP address might
change periodically as the DHCP lease expires. Consider using the Dynamic DNS screen
so that external users can always find your network.
• If
the IP address of the local server computer is assigned by DHCP, it might change when
the computer is rebooted. To avoid this, use the Reserved IP address feature in the LAN
IP Setup screen to keep the computer’s IP address constant.
• Lo
cal computers must access the local server using the computer’s local LAN address
(192.168.0.11 in the example in the previous figure). Attempts by local computers to
access the server using the external WAN IP address will fail.
Outbound Rules (Service Blocking)
The wireless modem router allows you to block the use of certain Internet services by
computers on your network. This is called service blocking or port filtering. You can define an
outbound rule to block Internet access from a local computer based on the following:
• IP ad
dress of the local computer (source address)
• IP ad
dress of the Internet site being contacted (destination address)
• T
ime of day
• T
ype of service being requested (service port number)
The following is an application example of outbound rules.
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