GNS3 and especially Dynamips have never been made to get crazy performances.
However, I've recently ran some tests to identify where are the network throughput bottlenecks in GNS3 and I think some of the findings will be useful for some of you.
To measure the throughput, I have used iperf on one client VM or real host and one server VM with the tested device between these 2 elements.
Commands used
VM1 or host: iperf -c <IP_of_VM2> -t 30 -P 10 VM2: iperf -s
Please note that everything has been run on a bare metal server i7-4770 CPU @ 3.40GHz (8 cores) with 32 GB of RAM with Linux Ubuntu and using VirtualBox and Qemu using VT-x when possible. Depending on your machine you may achieve lower or higher throughputs.
Test results
Note that iperf has been run 3 times for each test.
Linux VM1 (VirtualBox) <-> Dynamips c3660 router with Leopard-2FE <-> Linux VM2 (VirtualBox)
18 Mbits/sec 18.1 Mbits/sec 18 Mbits/sec
Linux VM1 (VirtualBox) <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
18 Mbits/sec 18 Mbits/sec 17.9 Mbits/sec
Linux VM1 (VirtualBox) <-> Dynamips c3725 router with GT96100-FE <-> Linux VM2 (VirtualBox)
1.15 Mbits/sec 1.12 Mbits/sec
Using the GT96100-FE network module (default for slot0) resulted in less throughput.
Linux VM1 (VirtualBox) <-> Dynamips c3725 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
18 Mbits/sec 18.1 Mbits/sec 17.9 Mbits/sec
Linux VM1 (VirtualBox) <-> Dynamips c7200 router with PA-2FE-TX <-> Linux VM2 (VirtualBox)
17.6 Mbits/sec 17.5 Mbits/sec 17.6 Mbits/sec
Linux VM1 (VirtualBox) <-> Dynamips c7200 router with PA-FE-TX <-> Linux VM2 (VirtualBox)
112 Kbits/sec 106 Kbits/sec 109 Kbits/sec
Using the PA-FE-TX port adapter resulted in a extremely low throughput. I would advised against using it.
Linux VM1 (VirtualBox) <-> Dynamips c7200 router with PA-4E <-> Linux VM2 (VirtualBox)
18.3 Mbits/sec 18.3 Mbits/sec 18.2 Mbits/sec
Linux VM1 (VirtualBox) <-> Dynamips c7200 router with PA-8E <-> Linux VM2 (VirtualBox)
18.3 Mbits/sec 18.3 Mbits/sec 18.3 Mbits/sec
Linux VM1 (VirtualBox) <-> Linux VM2 (VirtualBox)
831 Mbits/sec 942 Mbits/sec
Without any surprise , VMs back to back resulted is the highest throughput.
Linux VM1 (VirtualBox) <-> Dynamips Ethernet switch <-> Linux VM2 (VirtualBox)
779 Mbits/sec 770 Mbits/sec 832 Mbits/sec
Linux VM1 (VirtualBox) <-> IOU L2 switch <-> Linux VM2 (VirtualBox)
420 Mbits/sec 426 Mbits/sec 424 Mbits/sec
Linux VM1 (VirtualBox) <-> IOU L3 router <-> Linux VM2 (VirtualBox)
649 Mbits/sec 655 Mbits/sec 654 Mbits/sec
IOU performances are higher that I thought.
Linux VM1 (VirtualBox) <-> CSR1000v (VirtualBox) <-> Linux VM2 (VirtualBox)
2.35 Mbits/sec 2.32 Mbits/sec 2.32 Mbits/sec
It is important to note that CSR1000v has 2.5 Mb/s throughput-limited trial license. These results were expected.
Activating the 60-day trial premium license with the "license boot level premium" command will get you a limit of 50Mb/s (you must reboot and this is valid for release Cisco IOS XE 3.12S and earlier).
47 Mbits/sec 47.1 Mbits/sec
Finally, please note that with Cisco IOS XE 3.13S and later, the throughput is limited to 100 Kb/s (comparing to 2.5Mbps that has XE 3.12S and earlier), this is in demo mode - without any license. However with the AppX evaluation license you can get 10 Gb/s. Please see Cisco CSR 1000v Installation on Qemu Virtual Machine for details.
Linux VM1 (VirtualBox) <-> vIOS (Qemu without KVM, e1000 NICs) <-> Linux VM2 (VirtualBox)
2.09 Mbits/sec 2.05 Mbits/sec 2.09 Mbits/sec
It looks like vIOS has also a throughput limitation like in CSR1000v.
Linux VM1 (Qemu with KVM) <-> vIOS (Qemu with KVM, e1000 NICs) <-> Linux VM2 (Qemu with KVM)
2.13 Mbits/sec 2.09 Mbits/sec 2.11 Mbits/sec
It doesn't matter if you have KVM enabled or not.
Local host <-> TAP <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
17.9 Mbits/sec 17.9 Mbits/sec 18.0 Mbits/sec
Local host <-> TAP <-> Dynamips Ethernet switch <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
18.1 Mbits/sec 18.1 Mbits/sec 18 Mbits/sec
Remote host <-> Gigabit Ethernet NIC (nio_gen_eth in the cloud) <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
1.54 Mbits/sec 1.09 Mbits/sec
1.69 Mbits/sec
Interesting finding here, connecting your topology to a cloud using an Ethernet Generic NIO results in a low throughput.
Remote host <-> Gigabit Ethernet NIC <-> TAP (nio_tap in the cloud) <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
17.9 Mbits/sec 17.8 Mbits/sec 17.9 Mbits/sec
No such problem using an TAP NIO. Note that IP forwarding was enabled to allow traffic to pass from the Ethernet NIC to the TAP.
Remote host <-> Gigabit Ethernet NIC <-> Bridge br0 <-> TAP (nio_tap in the cloud) <-> Dynamips c3660 router with NM-1FE-TX <-> Linux VM2 (VirtualBox)
17.9 Mbits/sec 17.9 Mbits/sec 17.8 Mbits/sec
Still good using a bridge which contains the Ethernet NIC and the TAP.
Findings
Low throughputs have been identified when using the following devices: Dynamips c7200 router with PA-FE-TX
Dynamips c3725 router with GT96100-FE
CSR1000v and IOSv are artificially limited to 2.5 Mb/s with their demo license. IOU is faster than expected.
More interestingly throughput is low when using an Ethernet interface directly (nio_gen_eth) in GNS3 on Linux (apparently this doesn't affect Windows). Dynamips uses libpcap to attach to an Ethernet interface on Linux and for an unknown reason it results in a lower throughput than using a TAP interface.
