I have a doubt about my slow internet speed with third party firewall that I am using currently.

Is it true that firewall can limit the internet speed ?


Firewalls slow down the network (a firewall needs to check every packet before it's decided if it is allowed or blocked). Hopefully it will not be significant.

However, a bad firewall software, even if it's properly configured, can limit your network speeds (including the internet) signifcantly, this happended to me a few years ago with a well-known firewall software, called ZA or similar :)

Make sure you have a good firewall software, or, better yet, if possible, no firewall software at all.

  • I've removed the firewall :) – ukanth Oct 21 '09 at 13:28
  • XP, Vista, and possibly W7 have a built-in firewall that block some inbound connections by default (it doesn't have a significant performance impact). Your firewall application may have left the built-in firewall disabled. It's generally a good idea to make sure the built-in firewall is on. – alfplayer Oct 21 '09 at 18:33

It shouldn't have a significant impact.

The firewall should just control whether an application can make the connection or not. Once the connection has been made then it shouldn't intervene with the actual data transfer.

Have you tried disabling the firewall and browsing (to safe sites obviously!)?

  • 1
    It has an impact, at least on latency. It's impossible not to. – alex Oct 15 '09 at 9:24
  • Yes, It does. I can able to see slightly improved performance when I disabled firewall. – ukanth Oct 15 '09 at 9:26
  • It might be worth trying a different firewall. – ChrisF Oct 15 '09 at 9:58

Some firewalls also have options to throttle some types of connection, such as video streaming. Check the advanced options in your router configuration. Also, you should be able to run some tests using some internet benchmarking sites, such as:


It will find the closest testing point to you, and will run some tests. very good one, by the way. I suggest you try this test site with and without a firewall, to see whether it makes a difference. And as I mentionned, if you use the throttling, or QoS, this may affect the performance of some applications, such as video streaming, or Voice-over-IP.


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