GNS3 is a software for managing virtual networking devices (Cisco IOS, etc)

There is a bug with saving changes from GNS3's GUI to the server config. Changes have to be done manually for now.
Config file is at ~/.config/GNS3/3.0/gns3_server.conf

Dynamips are regular cisco MIPS architecture router images that can be emulated with GNS3.

This helps reduce CPU usage massively. With the correct value you can run dozens of routers/switches on modest hardware without massive CPU spikes.

To find a good Idle PC value:

1. Boot up the node and let it boot fully.
2. Do a 'copy run start'. Restart the device, don't calculate idle value on first boot
3. Only have the target node running, then click 'Idle-PC' and try each one, comparing CPU usage with something like btop.

Source https://community.infosecinstitute.com/discussion/110541/any-solution-to-gns3-dynamips-high-cpu-usage

IOU images are IOS-on-Unix images meant for internal Cisco use.

Currently, it seems that on Arch Linux GNS3 doesn't support IOU images since there is no gns3-iou package.
@research Manually install package from deb file?

GNS3 has support for managing and connecting docker containers to a topology. These are lighter than full blown QEMU VMs but less versatile.

See https://docs.gns3.com/docs/emulators/docker-support-in-gns3 on how to setup docker containers in GNS3.
See https://hub.docker.com/u/gns3/ on gns3 tailored docker images.

ftp://200.93.248.42/pub/windows/routers/cisco/images/router-switch/
ftp://ftp.dan.me.uk/pub/Software/Cisco
ftp://ftp.vasinc.com/Cisco/