Viability of GNS3 network simulation for testing features/configurations.

Thu Oct 17 12:12:38 UTC 2019

I've been using network simulation well before GNS3 was around using
dynamips - and even when GNS3 came along it was still not good -since it
just couldn't handle the scale (~40nodes) (not on my compute resources at
that time anyways).

And similarly nowadays in the era of proper HW simulation through VMs
(though I miss the idle-pc), I really like virsh/libvirt along with OVS as
it allows me to programmatically generate the VM files (xmls, images, etc..)
and define the topology in OVS (talking hundreds of links) which would be
otherwise really tedious to draw by hand. 

Also spinning up a big virtual lab from scratch takes several hours (of pure
compute time) so it's better to have some meshing in between the nodes and
just spin up arbitrary L1 topologies on demand rather than spinning up the
VMs every time one needs to load a different topology.

Said that I haven't played with GNS3, EVE-NG, VIRL,. recently so I don't
know if any of these would allow me to create these massive "spreadsheets"
for programmatic generation of labs. 

Best approach is to have at least two virtual environments

1) closely resembling production environment -this is where designers and
Ops people can test day to day operational changes etc..

2) environment where architects can test strategic/evolution changes to the
network infrastructure, new concepts and big migration/integration projects,
etc.   

What is it good for:

Testing design concepts

-this is one of the biggest advantages of virtual testing

Physical labs as we all know cost a small fortune and you can simulate just
a small cross-sections of your overall topology at a time  -but in virtual
lab depending on your computing resources and depending on what you need to
test you can either simulate very large sections or complete network (at
lower resolution) or smaller sections with very high resolution or
combination of both.

This allows you to really see what happens to your traffic patterns and
assess the impact of your design changes from small to large scales.  

What is it not good for:

A) Scale testing 

i.e. how many bgp/bfd/vrrp/etc.. sessions how many routes/VRFs/etc. - you
need the actual HW resources to carry out these tests

B) Performance testing

How much pps I can drive through NPU with these features (QOS,filters,etc.)
what are the failover times, (fast reroute, fabric fail,RE fail, etc.)
-again you need the actual HW that will be used in production to measure
these

But as you can see A) and B) can easily be tested with a single DUT (or some
small topology around it) using actual HW plugged in a loop with
IXIA/Spirent testers. 

adam

From: NANOG <nanog-bounces at nanog.org> On Behalf Of Ryland Kremeier
Sent: Wednesday, October 16, 2019 4:31 PM
To: <nanog at nanog.org> <nanog at nanog.org>
Subject: Viability of GNS3 network simulation for testing
features/configurations.

Hello,

I'm currently in the process of setting up a near identical network to our
own in GNS3 for testing purposes. Has anyone here tried this before to any
success? We need to buy the Cisco IOSv image to continue with the sim so I
figured I would inquire here first before diving in.

All info is appreciated,

-- 

Ryland Kremeier

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