Monthly Archives: August 2010

Why a port mirroring switch is required to monitor my network? How to monitor internet usage without a manageable switch?

What is port mirroring?

Usually, a computer connected to a switch or a router can only receive its own network packets. A switch with port mirroring function allows you to monitor network packets from a mirroring port.

With port mirroring is enabled, the switch sends a copy of all network packets seen on one port (or an entire VLAN) to another port, where the packets can be analyzed.

How to monitor network without a port mirroring switch?

There’re three methods to monitor your network without a manageable switch.

1. Using a broadcasted Hub

A broadcasted hub is a data packet repeater commonly used in broadcast networks.

Most broadcasted hubs provide a uplink port to connect with a up layer device. You shall connect the up layer device to the uplink port of the hub (Note: Do not use the port next to the uplink port).

However, most broadcasted hubs only work in 10Mb speed, and all the computers connected to the hub will share the bandwidth, which is not so fast as a switch. So we recommend you use a manageable switch instead.

2. Windows Gateway, Proxy Server or Bridge

Windows Gateway

If a port mirroring switch is unavailable, you can setup a windows gateway by your network edge. With an internet monitoring/filtering product in this windows gateway,

you will be able to monitor all internet traffic of network computers.

How to configure Windows 2008 Server IP Routing?

Proxy Sever

A Proxy Sever is a computer that offers a network service to allow clients to make indirect network connections to internet.

Like the gateway solution, you also can do monitoring/filtering in the proxy server. To make things simple, some proxy servers have monitoring/filtering modules integrated,

while some monitoring/filtering programs also have a proxy module integrated.

For example, you can easily enable the proxy server service in WFilter enterprise. For more details about WFilter proxy settings, please check:



Bridges (sometimes called “Transparent bridges”) work at OSI model Layer 2. Bridges just forward data depending on the destination address in the data packet.

By deploying a bridge in your internet entrance, you can setup a monitoring product in this bridge to monitor internet activities of your whole network.

3. ARP Spoofing

ARP spoofing, also called ARP Cache poisoning, is one of the hacking methods to spoof the contents of an ARP table on a remote computer on the LAN. With ARP spoofing,

you act as a relay server between client computers and the real gateway, so you will be able to monitor their traffic. However, as a hacking technology, ARP spoofing will make your network unstable.

So I recommend you not to use it unless necessary.

WFilter in comparison to other similar products.

There are a lot of products for you to manage your network: firewall, content filtering, web filtering proxy… Some users might get confused to choose them.
Since more and more customers had requested a comparison of WFilter to other similar products, I wrote this guide to list some important differences.

WFilter is a passby internet monitoring and filtering software program. It monitors network traffic from a mirroring port in your switch. When a TCP connection needs to be blocked, WFilter will send 1-2 RST packets to reset this connection. This is called “Passby Filtering”. More technical details of WFilter can be found at: WFilter Technologies

WFilter VS firewall program/appliance


1. WFilter monitor and archive most internet activities, while firewalls don’t keep internet usage details.

2. WFilter parses protocols at the application layer, it can recognize 100+ common protocols according to their signatures and behaviors. Most firewall program/application filters packets based on ports or ip addresses.

3. WFilter analyse copies of internet packets from a mirroring port of your switch. It is easy to be deployed, without any delay of your network. However, a firewall program/appliance needs to be deployed at the edge of your network. And since each packet goes through the firewall program/appliance, there will be a slight delay.

4. If the WFilter server goes down, the Internet connection stays alive. If the firewall program/appliance hangs, you will not be able to access internet.

5. WFilter is a content filtering product. It is designed to monitor and filter internet usage of employees to raise your productivity. However, a firewall program/appliance is designed to filter network packets and protect your network.


1. WFilter can not block UDP packets. So you also need to block UDP ports in your router/firewall.

2. WFilter consumes more memory and disk space of your computer. If you archive all internet activity, it might consume 2-3M disk space for each monitored computer every day.

WFilter VS open source web filtering projects

Some open source projects, like “SQUID” and “dansguardian”, also provide web filtering solutions. Below I list some major differences:

1. Most open source projects work as a proxy server. It requires you to change your internet access to proxy mode.

2. Most open source projects are web filtering only. Blocking of p2p traffic, internet monitoring/archieving are not supported.

3. Lack of statistics and reports for open source projects.

4. Lack of support for open source projects. Since protocols are changing, live update/support is required to keep your pattern database up to date, while most open source projects don’t have such support. In IMFirewall protocol lab, to keep our pattern database up to date, we have a system to monitor most common internet products/protocols, so when a new version of certain product is released, our team will work on it immediately.

Try “WFilter Enterprise” by yourself:

How to block TeamViewer on my network using WFilter?

TeamViewer is a computer software package for remote control, desktop sharing, and file transfer between computers. The software operates with Microsoft Windows, Mac OS X, iOS, and Linux. It is possible to access a machine running TeamViewer with a web browser.

With TeamViewer, it will be very convenient for employees to access computers in their homes, transfer files to remote computers. So for security purpose, sometimes you may want to block TeamViewer on your network.

This tutorial will guide you to block TeamViewer with “WFilter Enterprise 3.3″.

Because blocking of Teamviewer is not supported by default in WFilter, in this example, we uses “Customize Protocols” feature of WFilter to define TeamViewer protocol.

First, Add “TeamViewer” Protocol.

TeamViewer has two patterns:
1. “teamviewer01″:
  Type — “HTTP SEND”
  Format — “X-IM-URL”
  Content — “s=.*\&(p|id)=.*\&client=.*”

2. “teamviewer02″:
  Type — “TCP ALL”
  Format — “0″
  Content — “^\x17\x24[\x00-\xff]{2}[\x00-\x02]“

Second, Enable blocking of teamViewer in certain blocking levels.

And apply this blocking policy to certain computers.

Now, TeamViewer will be blocked.

WFilter blocking events:

Failure connection of teamViewer.

More information, please check “WFilter Enterprise”.
Other related links:
How to block internet downloading?
How to monitor internet usage on company network?
Internet monitoring software for business
How to filter web surfing?
How to block websites and restrict internet access?