iperf results

[Chuck Swiger]

Matthew Jakeman wrote:
> Some colleagues and myself have performed some simple tests on various OS's 
> using iperf to simply fire packets from one pc to another over ethernet to 
> test a few characteristics such as packet loss, jitter etc between IPv4 and 
> IPv6. The configuration for all three OS's were 'out of the box' installs. 
> The results we got back from that are strange for FreeBSD with regards to the 
> packet loss iperf reports and I was wondering if anyone has any ideas why 
> they might be as they are. The image at the link below shows the packet loss 
> results for windows, Linux and FreeBSD for comparison! As you can see the 
> packet loss for v6 is substantially less than v4 on FreeBSD, however this is 
> still substantially larger than for the other two OS's, does anyone have any 
> idea why this might be?
> 
> http://www.mjakeman.co.uk/images/4v6tests.jpg

You're probably getting packet loss either because you are filling up the 
network buffer space without pausing until it drains, or are running into ICMP 
response limits.  If you're going to be testing latency around the millisecond 
level, you'll need to increase HZ to at least 1000, if not better.

For example, set "sysctl net.inet.icmp.icmplim=20" on a machine called shot.

# ping -c 1000 -i 0.01 -s 1280 shot
PING shot (199.103.21.228): 1280 data bytes
1288 bytes from 199.103.21.228: icmp_seq=0 ttl=64 time=0.935 ms
[ ... ]
--- shot ping statistics ---
1000 packets transmitted, 220 packets received, 78% packet loss
round-trip min/avg/max/stddev = 0.842/0.877/1.234/0.077 ms

With "sysctl net.inet.icmp.icmplim=2000":

[ ... ]
1288 bytes from 199.103.21.228: icmp_seq=999 ttl=64 time=0.870 ms

--- shot ping statistics ---
1000 packets transmitted, 1000 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.838/0.858/1.068/0.020 ms

...or even:

# ping -c 1000 -i 0.001 -s 1280 shot
[ ... ]
1288 bytes from 199.103.21.228: icmp_seq=999 ttl=64 time=0.849 ms

--- shot ping statistics ---
1000 packets transmitted, 1000 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.839/0.856/1.010/0.015 ms

	-----

You haven't provided a test methodology.  You haven't provided the source code 
for the benchmark program you are using.  You also haven't provided any details 
about the hardware being used, the network topology, or even what some of the 
values in this .jpg image mean.  (For example, what is the first column, 
"duration", measuring?)

-- 
-Chuck