pf and keep/modulate state on 6.2

JD Bronson jbronson at
Sat Jul 21 12:30:08 UTC 2007

thanks for the update on this. I had forgot about it since I just 
stopped using modulate state (is it really needed anymore?).

Then, the beginning of this month I moved my firewall/router back 
over to OpenBSD 4.1 to stay more current with pf instead of running 
-CURRENT within FreebSD.

This fix really should be incorporated into 6.2-STABLE or even 6.2-STANDARD
I think. I wonder how many people use this and don't even know its messed up?


At 02:14 PM 7/21/2007 +0300, Jordan Gordeev wrote:
>J.D. Bronson wrote:
>>At 02:52 AM 02/26/2007, you wrote:
>>>Wow, this fixed my FTP-over-DSL-to-6.2 problem too. With modulate
>>>state, I was getting ~30K/sec. With just keep state, I'm now getting
>>>more like what my connection is capable of. This is between two 6.2
>>>hosts on opposite sides of the Atlantic.
>>>Ted, I use pf because I like the format of the configuration file, I
>>>like the logging and pftop, and like how it's harder to lock yourself
>>>out of a remote machine by accident :)
>>I use pf since its newer (I think?) and I came from 
>>just works and the config file is nice and sweet.
>>I had thought that modulate state would put a load on my proc, but 
>>sheesh, its a p4-3.06 - thats more than robust for a router.
>>I wonder if we should file a bug on this?
>>I am glad my post helped here. I still use modulate state for any 
>>INCOMING connections though (www/smtp/etc).
>I'm replying to an old and long-forgotten thread to report my recent findings.
>There's a bug in PF with modulate/synproxy state. Modulate/synproxy 
>state modulate sequence numbers, but don't modulate sequence numbers 
>in TCP SACK options. Some firewalls block TCP segments with sequence 
>numbers in the SACK option pointing outside the window, which causes 
>connection stalls. The bug was fixed in OpenBSD with revision 1.509 
>of src/sys/net/pf.c about an year and a half ago. The bug is present 
>in FreeBSD-STABLE. A fix for the bug was imported in FreeBSD-CURRENT 
>with the big import of PF from OpenBSD 4.1.
>I'm CC-ing Max to notify him of the bug present in -STABLE and to 
>ask him to deal with the issue by either porting the fix from 
>OpenBSD, or by documenting that modulate/synproxy state is broken.
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