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Jorge Arredondo Dorantes CCIE

Jorge Arredondo Dorantes CCIE

GNS3 "Connection Lost" issue resolution

GNS3 "Connection Lost" issue resolution
I'm posting this in hopes of helping other people that have encountered this frustrating issue in GNS3:


The Issue: When using GNS3, the console connection you have to your devices is suddenly lost/dropped/closed. When using PuTTY you'll get a "Connection Lost" message, and with SecureCRT you'll get a "Connection Refused by Remote Host" message.

The most frustrating part of this issue is that there is no rhyme or reason as to why or when it happens. You will just be sitting there tinkering around in your lab and then WHAM! goodbye configs and topology if you didn't save them. It makes using GNS3 more of an anxiety or panic attack, rather than a sweet time (as it should be), and you start saving your configs and topology every 3 seconds in fear of it crashing.

For those experiencing this issue - put yourself at ease that it is NOT your Computer or your Operating System causing the issue (unless it's plagued with viruses or other nasty stuff of course). I can say this because I tried all of the following while troubleshooting:

  • Capturing the process output of GNS3 and Dynamips with ProcessMonitor. There was nothing that stood out during the captures.
  • Opening ports on the Windows7 Firewall, both inbound and outbound, for all processes related to GNS3.
  • Using Resource Monitor or NetStat to ensure the computer was listening on the configured GNS3 ports
  • Ensured that all processes associated with GNS3 and Dynamips were set to "Run as Administrator"
  • Ensured that GNS3 and it's associated processes ran in XP compatibility mode. (not necessary)
  • Built a VM running Windows XP with SP3 and installed GNS3. The issue still ocurred!

After doing all of this, I sat down and thought.....ok, since nothing that I have tried has solved this issue, what is the one thing that has remained the same during my troubleshooting? Besides GNS3 being installed of course : )

Well - the answer to this question ended up being the solution. It was the IOS (or perhaps the 2621XM emulated hardware) that I was using!

The solution: Instead of running the advanced IP services 12.4 IOS on an emulated 2621XM router, I switched to the 3745 router with the advanced IP services 12.4 IOS, and I have kept my lab running for nearly 24 continuous hours now with no "Connection Lost" messages!!

I really hope that this helps someone, because this had to be one of the most frustrating issues and was a really easy excuse to not study - as in "psshhhh I won't study today! GNS3 will just crash! I'll just play Fallout3 instead! (even though that crashes too sometimes)". Well, it's an easy excuse that I no longer have now : )

Happy Labbing everyone!

1 comment:

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