NetCatcher Pro - examples of use

The program allows you to automatically set pre-actions on network interfaces connection/disconnection.

What's new in Pro version:

  • implementation as a Windows Service and management through a single interface
  • autostart when PC reboots
  • single database of network interfaces and commands for all users on PC
  • it requires administrator rights for installing and configuring only, can be used under usual user account

Examples of use

The main purpose of use is automatic routing when network link is going up or down.
However, executing commands can be anything - not routing related only.

Just for an example, you may want to autostart MS Word when your VPN-connection link is goig up - it's also quite possible.

Situation 1: home user or a corporate client

Suppose you have a VPN-connection (or even a few VPN connections). You want the Internet ran through your ISP, and corporate mail through a VPN-connection established with the corporate server.

Or maybe you want to make ICQ and Skype went through a specially purchased encrypted VPN-connection, and the rest of the Internet (including heavy torrent downloads) ran through your ISP.

These desires can easily be implemented. Just set up routes to the necessary resources, and let NetCatcher route your traffic through the appropriate network connection.

In such case NetCatcher Pro might rescue you. With its help you can set up on which events which commands should be executed for any network interface, and everything will be done automatically. In other words, using NetCatcher Pro you can specify the routing for each interface once a time, and everything will work automatically.

So what to do?

  • Bring up the property window of your VPN connection, double click on Internet Protocol Version 4, click "Advanced" button. Untick "Use default gateway on remote network" and save.

how to setup vpn

  • Then start NetCatcher, select your VPN-connection, click "On UP" button, and write command you want to execute when selected network connection is going up. In example: "ROUTE ADD MASK $IP". Click "Apply" button. Connect/reconnect selected interface. That's it! So, now you will going to host through selected connection, and the rest of Internet will be available through your ISP's default gateway.

Situation 2: ISP, home network

If you are a small Internet service provider or administering a city computer network, you may have issues with balancing external channels.

A relatively large company can usually buy autonomous system and provider independent IP-addresses block. Then it can setup a peering with uplink ISP and rise BGP. And that's all - channels are balanced and backed up automatically.

However to buy AS & PI and to rise BGP can be not so good solution in some cases.

What NetCatcher Pro can do for you in this case?

For example, we have two ISP's as uplinks.

Objective: To provide link balancing and link backup

How to solve
Define Internet routes in two parts. It can be divided by the mask. You can get a list of networks and divide by geography. In each case it is decided individually. Now you put "add routes" command of first part on the event onUP for one network interface, and removing these routes from the second interface. At the event onUP of second interface you enter routes to another part of the traffic and removing these routes from the first interface. Then add exactly the same routes but on the opposite interfaces for event onDown to each of the interfaces.

In the end, what you get
  • when network interfaces both are UP, routes for the first part goes to the first interface and the second part to the second - automatically
  • when first interface is going down, the first part of the routes automatically goes to the second interface and all traffic rushes through it
  • when a link to the first interface will rise again, the routes of the first part is automatically deleted from the second interface and added again to the first - and everything will run again in two channels exactly the same way scheme run when the second link goes down.

So, we have kind of load balancing and back-up channels with automatic lifting the right routes at the right interface.


You can use these variables when editing commands:

$IP - IP address of a network connection (can be dynamic)
$GW - gateway IP of a network connection/interface