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Date:      Mon, 13 Oct 2014 17:46:13 -0400
From:      Jack Barber <jack@nyi.net>
To:        freebsd-ipfw@freebsd.org
Subject:   FreeBSD max pipe size?
Message-ID:  <543C4825.6030901@nyi.net>

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I am trying to set up dummynet with FreeBSD 9.3 and a 10 GB Fibre over
ethernet NIC (ix drivers).

Dummynet appears to have a limit of 1.25 gigabits a second, and when I
start setting extremely large pipe values I start running into:

ipfw: bandwidth too large

It doesn't like(in /etc/ipfw.rules)
    $IPFWcmd pipe 10 config bw 8000Mbits
but for some reason it likes
    $IPFWcmd pipe 20 config bw 100000Mbits
and
    $IPFWcmd pipe 10 config bw 10000Mbits

even if there is no notcable performance diffrence betwen them

$ iperf -c load-server2
------------------------------------------------------------
Client connecting to load-server2, TCP port 5001
TCP window size:  434 KByte (default)
------------------------------------------------------------
[  3] local 192.168.20.25 port 56122 connected with 192.168.20.20 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.57 GBytes  1.35 Gbits/sec

$ iperf -c load-server1
------------------------------------------------------------
Client connecting to load-server1, TCP port 5001
TCP window size:  459 KByte (default)
------------------------------------------------------------
[  3] local 192.168.20.20 port 49028 connected with 192.168.20.25 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.36 GBytes  1.17 Gbits/sec


testing is done on a private subnet which houses nothing more than two
loading servers and a FreeBSD bridge in between. All machines have 10
GB/sec ix driver cards.

Now, same set up, but commenting out all dummynet refrences in ipfw.rules:
$ iperf -c load-server1
------------------------------------------------------------
Client connecting to load-server1, TCP port 5001
TCP window size:  459 KByte (default)
------------------------------------------------------------
[  3] local 192.168.20.20 port 49029 connected with 192.168.20.25 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  8.44 GBytes  7.24 Gbits/sec

$ iperf -c load-server2
------------------------------------------------------------
Client connecting to load-server2, TCP port 5001
TCP window size:  434 KByte (default)
------------------------------------------------------------
[  3] local 192.168.20.25 port 56123 connected with 192.168.20.20 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  7.89 GBytes  6.78 Gbits/sec




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