I have an ADSL line at home with a somehow good speed (1.3 Mbps) and I'm sharing it with three other PCs with a simple ethernet switch. yesterday I started to download simultaneously on every 4 PCs. I noticed that there is no decrease in download speed at all!

So I've just decided to get my hands dirty with C and writing some nasty program that simulates an Ethernet switch with TUN/TAP devices and power up download speed in a single PC by 4 for example.

But before start coding, I just wanted to know that is it even possible? is it possible to achieve this with routine Linux firewall configurations/commands? if yes any hint or resource would be really appreciated.

I've heard about NLB and such, but load balancing needs more than one real connections from ISP, correct me if I'm wrong.

I am familiar with basic principals of networking and I'm using Backtrack 5 right now. so any tips/answers/hints would be really appreciated.

  • Will the question get better answers on the programmer site Stack Overflow? Feb 24, 2012 at 21:28
  • I guess he is asking for server/super user advice in terms of network knowledge not how to code it (i guess that is coming up later eventually).
    – MadBoy
    Feb 24, 2012 at 21:35
  • exactly what MadBoy said. I'm looking for some advice, not coding problems. I know the coding part ;)
    – sepehrl
    Feb 25, 2012 at 14:04

2 Answers 2


I don't know answer to your question but I think it's relevant answer to your question. I suggest to do some hard testing of there is no decrease in download speed at all! before starting to code things.

It's very(!) unlikely your ISP (I guess it has to be a bit bigger isp (offering ADSL) then some home made network) doesn't put limits correctly.

Couple of reasons to do some real testing:

  • It may be that your sources were limiting you per login so using 4 logins on same computer may achieve same thing,
  • maybe you were hitting hardware/software limits
  • the files where small so you may be were hitting the full speed on all because computer 1 was downloading when other computers were switching between files or so. There could be multiple reasons for this (although hard to achieve this on 4 computers at same time, very unlikely but still possible).

So my suggestion is go and try your approach for longer while. Test on very big files with constant transfer rate (some good servers). Then compare and decide if it's really worth the time.

  • Well, My ISP is limiting clients with Username/Password on their modems/routers, so there won't be anything like "multiple login"s. but I'm totally agree with you, I should do some more deep tests. thanks btw.
    – sepehrl
    Feb 25, 2012 at 14:02
  • By multiple logins I meant ftp sites, or other servers where you login and this is where you might be getting throttled.
    – MadBoy
    Feb 25, 2012 at 14:20

You can certainly simulate an Ethernet switch. Just as you can simulate a network.

Simulations tend to run slower than the real thing.

Whatever the bottleneck is that affects your downloads, adding a simulation burden to the computer seems unlikely to help.

  • Interesting wiki link, thanks, I didn't know about it.
    – sepehrl
    Feb 25, 2012 at 14:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.