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
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