PF, bridge, states and window scaling problem

Girish Venkatachalam girishvenkatachalam at
Mon Nov 12 18:21:16 PST 2007

On 22:08:03 Nov 12, Alupului Costin wrote:
> I seem to have quite a problem with PF. I have set up a bridge to
> shape my upstream traffic. I use ALTQ with hfsc discipline; but that's
> not really important. My problem comes with the filter rules. I have
> to use keep state because of the speed benefits (really I don't have a
> choice), 

One should always keep state.

> but PF has a problem when the clients passing traffic through
> the bridge use TCP window scaling. Here is an example of four filter
> rules that I thought should work to pass the traffic from one client
> through the bridge and create a state:
> pass in quick on vlan0 from any to anIP/32
> pass out quick on vlan0 from anIP/32 to any keep state queue ul_client
> pass in quick on vlan1 from anIP/32 to any
> pass out quick on vlan1 from any to anIP/32 keep state queue dl_client
> The above rules generate state-mismatches. 

Didn't get you. What sort of mismatch?

> I thought that would be
> because pf doesn't see the SYN packet, although it does (one of the
> out rules) and should create the state then... I tried writing all the
> rules with keep state (even the inbound ones) but then nothing would
> work at all. My intention was to create if-bound states, but I
> switched back to floating states in the hope that pf would associate
> the state created by an outbound rule with the traffic returning on
> another interface of the bridge; still didn't work.

Have you tried adding "flags S/SAFR" to the filter rules?

Try it and let me know.

> I have read the man page for if_bridge and set the following sysctl variables:
> 1
> 0
> 1
> I have also read some posts on the web that said that pf simply
> doesn't have all the hooks necesary to do the filtering inbound and
> outbound, but reading the pfil man page I seem to disaggree with that.

What do you mean? ?

> Has anyone encountered the same problem? And, more important: if i
> give up the bridge setup and switch to routing, would that have any
> effect? I.E: will I then be able to use keep state with the inbound
> rules?

Try it. Routing changes the topology a good deal. But I doubt if that is
the issue here. No harm in testing though.

> Any help at all would be hugely appreciated as I am trying for about a
> week to sort out this problem and can't seem to get any closer. The
> only solution was to kindly ask my clients using TCP window scaling
> (Vista mostly) to turn off this feature... Now I am seriously
> considering bumping my bridge to a router but I am not sure that the
> problem will be solved then.

Try adding the flags switch as mentioned above. That way the states get
established only from a TCP Syn packet.

You should also try flushing the old states using pfctl(8).

> Oh, here is the setup of the bridge from rc.conf, although there
> shouldn't be any problems there (the bridge works fine without pf, or
> with pf stateless):

Stateful filtering is always recommended. Performance is not the only
reason why you should use it.

It also adds to security. Have you tried disabling normalization/scrub?


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