FreeBSD PF and Dummynet

In 14-CURRENT there is now support for dummynet in PF. That means that you can slow down packets based on some criteria. MacOS users probably know how this works as that OS got support for PF+dummynet years ago. For example, you can do the following in /etc/pf.conf:

pass in quick inet from to any dnpipe 1

That way all traffic from will go through dummynet pipe. To create and configure the pipe you use:

dnctl pipe 1 config bw 300KByte/s

I gave it a really low bandwidth because I want it to be really noticeable if packets are going through dummynet or not. You can change the pipe's bandwidth by using the same command just changing the numbers. Note that K and B have to be upper case. You can, of course, use all the usual suffixes like M and G but note that dummynet has a limit on the bandwidth it can configure.

To see what is configured you can use:

dnctl pipe show

With dnctl, show is an alias for list, so you will get the same results using either.

I didn't make it so that packets generated on the machine itself be processed by dummynet, but it might be intentional. What does work is VNET so your jails can have different PF and dummynet configuration than the host.

One annoying thing is that there is no dnctl rc.d service, so you will probably write dnctl commands in something like rc.local or something. I do plan to create rc.d service for myself and when I learn more about dummynet, to publish it hoping it will become part of base so we can easily configure it.


The dnctl service is now available. If enabled it reads /etc/dnctl.conf which has IPFW-like syntax and when only dummynet module is loaded, it will issue an error on non-dummynet IPFW statements.