GNS3 100% CPU Usage – Just hit Enter!

If like thousands of network engineers around the world you use GNS3 you will have come across the 100% CPU Usage problem.

We all know know how to set the idle-pc and most of the time that works, but there is also a few more things to try to get your CPU usage down.

I had created a topology with 10 routers, which on my laptop running 8GB Ram should not have been a problem. I started up one router, let it settle down and then calculated the idle-pc – all good so far.

When I started up the other 9 routers the CPU hit 100% and stayed there.

This is because the routers were simply sat there awaiting an input from me.

GNS3 100% CPU Usage – Fix

Simply console onto each router and hit enter a couple of times.

You will see your CPU drop instantly – I am now running 10 routers with my CPU hovering around 30%

Also ensure you have configured exec-timeout 0 0 on the console line of each router

This can be added to your startup config.

For reference my settings are as below – Click on Edit / IOS Images and Hypervisors

My baseconfig.txt is as below

!
hostname %h
!
no ip domain lookup
ip domain-name lab.local

!
line con 0
 exec-timeout 0 0
 logging synchronous
 privilege level 15
 no login
line aux 0
 exec-timeout 0 0
 logging synchronous
 privilege level 15
 no login
exit

Another helpful tip is I also run this command whenever I get the GNS3 Duplex Mismatch

R4(config)#no cdp log mismatch duplex

Please comment any of your GNS3 tweaks – as once you get this programme running sweet it rocks!

Enjoy your studies

If you are enjoying my CCIE Blog posts and would like to see a post on a specific topic, just comment below and I will try my best to get them into my queue of technical posts. For now I am focussing on topics related to the CCIE in Routing  Switching

Roger