Reference Manual for the Model DG824M Wireless ADSL Modem Gateway
Network and Routing Basics B-13

Stateful Packet Inspection

Unlike simple Internet sharing routers, a firewall uses a process called stat eful packe t inspect ion to
ensure secure firewall filtering to protect your network from attacks and intrusions. Since
user-level applications such as FTP and Web browsers can create complex patterns of network
traffic, it is necessary for the firewall to analyze groups of network connection "states." Using
Stateful Packet Inspection, an incoming pa cket is intercepted at the network layer an d t hen
analyzed for state-related information associated with all network connections. A central cache
within the firewall keeps track of the state information associated with all network connections.
All traffic passing through the firewall is analyzed against the state of these connectio ns in order to
determine whether or not it will be allowed to pass through or rejected.

Denial of Service Attack

A hacker may be able to prevent your network from operating or communicating by launching a
Denial of Service (DoS) attack. The method used for such an attack can be as simple as merely
flooding your site with more requests than it can handle. A more sophisticated attack may attempt
to exploit some weakness in the operating system used by your router or gatewa y. Some operating
systems can be disrupted by simply sending a packet with incorrect length information.
Wireless Networking
The DG824M gateway conforms to the Institute of Electrical and Electronics Engineers (IEEE)
802.11b standard for wireless LANs (WLANs). On an 802.11b wirel ess link, da ta is en coded usin g
direct-sequence spread-spectrum (DSSS) technology and is transmitted in the unlicensed radio
spectrum at 2.5GHz. The maximum data rate for the wireless link is 11 Mbps, but it will
automatically back down from 11 Mbps to 5.5, 2, and 1 Mbps when the radio signal is weak or
when interference is detected.
The 802.11b standard is also called Wireless Ethernet or Wi-Fi by the Wireless Ethernet
Compatibility Alliance (WECA, see http://www.wi-fi.net), an industry standard group promoting
interoperability among 802.11b devices.

Wireless Network Configuration

The 802.11b standard offers two methods for configuring a wireless network - ad hoc and
infrastructure.