So I have a small topology ( 4 AS ), and I tested it on a real environment (College Lab) with Cisco routers (2000 series).

The latency from one point to another was too high when I used GNS3, the latency just spiked (100 ms), while in a real environment was lower (22 ms).

Can someone please explain the reason?

I understand GNS3 emulates routing and switching and depends on my PC especifications. (I have a intel i5 PC with 8GB RAM).

So this is the GNS3 topology, I use my own Windows loopback interface for PC1, and Ubuntu VM on PC2.

In the real environment I use 2 different PCs (and of course, different routers).

I'm testing BGP route propagation and stuff, but when I test latency (using ping and using average value) it spikes in GNS3.

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Thanks in advance for your help.


1 Answer 1


You answered your own question. GNS3 emulates routers and switches, so it can't work as fast as dedicated processors. In this case, you have one processor trying to do the work of eight, and emulate a Linux box. I'm actually impressed it's working as fast as it is.

  • Thanks a lot for answering. I wonder then how packet tracer doesn't present the same issue. So the real question is how heavy is to emulate and IOS rather than simulate it?
    – Daniel
    Commented Nov 23, 2015 at 18:23
  • 2
    Because packet tracer is a simulator the developers can give you any figures they like. They can make it look like your links are running at 10gb if they like. This is because it's purely a software application, it is not running anything which is real. On the other hand, GNS3 is a simulator. It is pretending to be a real router and therefore it has all of the limitations a real router would have. e.g if there is not enough RAM or CPU, things will run from slowly.
    – OzNetNerd
    Commented Nov 23, 2015 at 18:54
  • Additional information: As I mentioned above, GNS3 simulates real equipment. This is why you cannot get switches in it as switches use hardware chips known as ASICs. As PCs do not have these ASICs in them, a switch cannot run on them. On the other hand, older routers do all of their work in software and therefore can be run on a PC.
    – OzNetNerd
    Commented Nov 23, 2015 at 18:56
  • As a GNS3 developer I confirm the anwser. We need to emulate the hardware it's slower but you will have the real IOS processing the packets with real IOS behavior. Commented Dec 8, 2015 at 10:24

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