Best way to decrease DDoS with pf.

[Kian Mohageri]

On 5/18/07, Abdullah Ibn Hamad Al-Marri <almarrie at gmail.com> wrote:
> On 5/18/07, Kian Mohageri <kian.mohageri at gmail.com> wrote:
> > On 5/18/07, Abdullah Ibn Hamad Al-Marri <almarrie at gmail.com> wrote:
> > > Thank you for the tip.
> > >
> > > Here what I'm using which fixed the issue.
> > >
> > > pass in on $ext_if proto tcp from any to $ext_if port $tcp_services
> > > flags S/SA synproxy state
> > > pass in on $ext_if proto tcp from any to $ext_if port $tcp_services \
> > >         flags S/SA keep state \
> > >         (max-src-conn 30, max-src-conn-rate 30/3, \
> > >          overload <bruteforce> flush global)
> > > pass out proto tcp to any keep state
> > >
> > > Comments?
> >
> > The first rule won't match anything (same criteria as second rule, and
> > last match wins with pf).  On the third rule, use 'flags S/SA' unless
> > you have a good reason not to.
> >
> > Kian
> >
>
> I thought first rule will defeat syn flood.
>
>  Is the second rule going to do the same job as first rule and will
> prevent syn flood?

The rules are different obviously, but the criteria matches the same
traffic.  Because PF will apply the last matching rule by default
(unless 'quick' is used), your first rule will never be applied.  You
could use synproxy state on the second rule, and remove the first
entirely.

> As for the third rule syntax, Should I make it like this?
>
> "pass out proto tcp to any flags S/SA keep state" and shall I add the
> same for udp?
>
> "pass out proto udp to any flags S/SA keep state" ?

If you only want to pass UDP and TCP, then you can do something like this:

pass out proto tcp to any flags S/SA keep state
pass out proto udp to any keep state

Kian