13-22 Administration Guide

Logical AND function

When a packet is compared (in most cases) a logical AND function is performed. First the IP addresses and subnet masks are converted to binary and then combined with AND. The rules for the logical use of AND are as follows:

0 AND 0 = 0

0 AND 1 = 0

1 AND 0 = 0

1 AND 1 = 1

For example:

Filter rule:

Deny

IP: 163.176.1.15BINARY: 10100011.10110000.00000001.00001111

Mask: 255.255.255.255BINARY:11111111.11111111.11111111.11111111

Incoming Packet:

IP 163.176.1.15BINARY: 10100011.10110000.00000001.00001111

If you put the incoming packet and subnet mask together with AND, the result is:

10100011.10110000.00000001.00001111

which matches the IP address in the filter rule and the packet is denied.

Implied rules

With a given set of filter rules, there is an Implied rule that may or may not be shown to the user. The implied rule tells the filter set what to do with a packet that does not match any of the filter rules. An example of implied rules is as follows:

Implied

Meaning

 

 

Y+Y+Y=N

If all filter rules are YES, the implied rule is NO.

 

 

N+N+N=Y

If all filter rules are NO, the implied rule is YES.

 

 

Y+N+Y=N

If a mix of YES and NO filters, the implied rule is NO.

 

 

Established connections

The TCP header contains one bit called the ACK bit (or TCP Ack bit). This ACK bit appears only with TCP, not UDP. The ACK bit is part of the TCP mechanism that guarantees the delivery of data. The ACK bit is set whenever one side of a connection has received data from the other side. Only the first TCP packet will not have the ACK bit set; once the TCP connection is in place, the remainder of the TCP packets with have the ACK bit set.

The ACK bit is helpful for firewall design and reduces the number of potential filter rules. A filter rule could be created just allowing incoming TCP packets with the ACK bit set, since these packets had to be originated from the local network.

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Netopia 4752 manual Logical and function, Implied rules, Established connections
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4752 specifications

The Netopia 4752 is a versatile networking device that serves as a digital subscriber line (DSL) modem and router, designed to provide high-speed internet connectivity and advanced networking capabilities for home and small office environments. This device is notable for its reliability and ease of use, making it a popular choice among users looking for seamless internet access.

One of the main features of the Netopia 4752 is its support for various DSL technologies, including ADSL and ADSL2+. This compatibility ensures that users can achieve optimal bandwidth and speed, even on legacy DSL lines. The modem’s capability to handle downstream speeds of up to 24 Mbps allows for smooth streaming, gaming, and browsing experiences.

Equipped with a robust built-in router, the Netopia 4752 offers multiple Ethernet ports for direct wired connections, accommodating multiple devices simultaneously. This feature is especially beneficial in environments where multiple users need to access the internet without latency. Additionally, the device supports wireless connectivity, enabling users to connect their laptops, smartphones, and other Wi-Fi-enabled devices effortlessly.

Security is a crucial aspect of the Netopia 4752’s functionality. The device incorporates a built-in firewall and supports various security protocols, including WPA and WPA2, ensuring that users’ data remains protected from unauthorized access. The user-friendly web-based interface facilitates easy configuration of security settings, making it accessible even for those with limited technical knowledge.

The Netopia 4752 also features advanced Quality of Service (QoS) settings that allow users to prioritize bandwidth for specific applications or devices. This capability is crucial for households or offices that demand high performance for video conferencing, streaming services, or online gaming.

In terms of characteristics, the Netopia 4752 boasts a compact form factor, making it easy to integrate into any workspace without occupying much space. Its durable design ensures longevity, providing reliable service over time.

Overall, the Netopia 4752 stands out as a dependable DSL modem and router solution, with its high-speed internet capabilities, security features, and flexible connectivity options suitable for both home and small office users who require efficient and effective internet access.
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