ipfw (Dummynet) cannot configure queue size for pipe

Question

I'm trying to use Dummynet (ipfw pipe) for simulating network switch.

My platform is Linux CentOS 6.4 Final

I have downloaded and compiled the latest version of source code (20130607) from here.

I'm trying to add pipe for relaying ip traffic between two subnets, and everything works fine. But as I try to set the queue size for pipe it fails.

Here is my command:

sudo ipfw pipe 1 config delay 64ms plr 0 bw 1000Mbit/s queue 100Kbytes

Here is the output:

ipfw: queue size must be < 4B

Any help or advice is greatly appreciated.

Answer 1

On FreeBSD where dummynet is built-into the kernel the maximum queue sizes are configurable via sysctl.

For example, to read the maximum queue sizes settings (in slots and bytes):

sysctl net.inet.ip.dummynet.pipe_slot_limit
sysctl net.inet.ip.dummynet.pipe_byte_limit

to set maximum queue sizes:

#these are the defaults on freebsd
sysctl net.inet.ip.dummynet.pipe_slot_limit=100
sysctl net.inet.ip.dummynet.pipe_byte_limit=1048576

While you use CentOS these might not apply directly (and I have never used it on other OS than FreeBSD), but I am pretty sure you need to find where to configure the max queue sizes for dummynet, because the error you get is displayed when you try to set a higher value that is allowed by the settings.