How individual ﬁlters work, ﬁltering rule

13-6 Administration Guide

How individual ﬁlters work

As described above, a ﬁlter applies criteria to an IP packet and then takes one of three actions:

■Forwards the packet to the local or remote network

■Blocks (discards) the packet

■Ignores the packet

A ﬁlter forwards or blocks a packet only if it ﬁnds a match after applying its criteria. When no match occurs, the ﬁlter ignores the packet.

A ﬁltering rule

The criteria are based on information contained in the packets. A ﬁlter is simply a rule that prescribes certain actions based on certain conditions. For example, the following rule qualiﬁes as a ﬁlter:

Block all Telnet attempts that originate from the remote host 199.211.211.17.

This rule applies to Telnet packets that come from a host with the IP address 199.211.211.17. If a match occurs, the packet is blocked.

Here is what this rule looks like when implemented as a ﬁlter on the Netopia 4752:

+-#--	Source IP Addr--	Dest IP Addr-----	Proto-Src.Port-D.Port--	On?-Fwd-+
+--------------------------------------------------------------------				+
1	199.211.211.17	0.0.0.0	TCP 23	Yes No
+--------------------------------------------------------------------				+

To understand this particular ﬁlter, look at the parts of a ﬁlter.

Parts of a ﬁlter

A ﬁlter consists of criteria based on packet attributes. A typical ﬁlter can match a packet on any one of the following attributes:

■The source IP address (where the packet was sent from)

■The destination IP address (where the packet is going)

■The type of higher-layer Internet protocol the packet is carrying, such as TCP or UDP

Port numbers

A ﬁlter can also match a packet’s port number attributes, but only if the ﬁlter’s protocol type is set to TCP or UDP, since only those protocols use port numbers. The ﬁlter can be conﬁgured to match the following:

■The source port number (the port on the sending host that originated the packet)

■The destination port number (the port on the receiving host that the packet is destined for)

By matching on a port number, a ﬁlter can be applied to selected TCP or UDP services, such as Telnet, FTP, and World Wide Web. The following tables show a few common services and their associated port numbers:

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.

Netopia 4752 manual How individual ﬁlters work, ﬁltering rule, Parts of a ﬁlter, Port numbers

Models: 4752