On Tue, Jun 14, 2016 at 09:29:33PM +0300, atar wrote:
> > atar wrote on 06/14/2016 16:05:
> >>> atar wrote on 06/14/2016 14:52:
> >
> > [...]
> >
> >>>> The hostname "google.com" isn't blocked since its current ip differs
> >>>> from its previous ip when pf has loaded the rule, what can I do in order
> >>>> to be able to block such sites (with many ip addresses)?
> >>>
> >>> I would use tables and populate them periodically from shell script which
> >>> can do FQDN to many IPs resolution.
> >>>
> >>> It can be simple as this
> >>>
> >>> host yahoo.com | awk '$0 ~ /has address/ { print $4 }' >
> >>> /var/run/pf.yahoo_table
> >>> pfctl -t yahoo_table -T replace -f /var/run/pf.yahoo.table
> >>>
> >>> I am sure you will find better solution :)
> >>>
> >>> Miroslav Lachman
> >> Thanks for your answer, it is an interested idea.
> >>
> >> However, is this method of update periodically the pf tables not disturb
> >> or burden the performance of the pf filter engine especially if the script
> >> that update the tables runs too often?
> >
> >
> > How often is "too often"?
> > I think that updating the tables every 5 minutes is enough (no one uses
> > shorter TTL for DNS entries)
> > The nicest thing on PF tables is you don't need to reload PF and tables can
> > live in memory (not need for persistent file on filesystem) so all
> > operations are really quick.
> > Our PF firewalls are using tables with thousands of entries without any
> > issues.
> > I don't see any trouble even if you will update tables each minute.
> >
> > Miroslav Lachman
>
> Thanks again for replying.
>
> I don't know why, but even refresh rate of one minute isn't enough for the
> domains google.com or gmail.com.
>
> Even immediately after I load the table which has the rule to block the above
> mentioned domains I am still able to access those domains. Sometimes it is
> indeed blocked for a half of a minute but finally the chromium browser
> succeed to load them.
If you are looking at blocking HTTP traffic the only way I am aware to
effectively block that without jumping through a lot of hoops is to
use something like squid which can block based on domain, no matter what
the current IP address returned from DNS is. You can use PF to
transparently proxy traffic exiting your gateway to squid so there
is no need to worry about proxy settings in the browser(s)
www.google.com DNS TTLs are 5 minutes so you shouldn't have to worry
about the IP changing in less then a minute UNLESS your PF firewall
and your browser use different DNS servers and could therefore get
different answers
Regards,
Gary
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