Filter connections based on the hostname.

[Miroslav Lachman]

atar wrote on 06/14/2016 20:29:
>> 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.
>
> Do you have any idea?

I am not sure but it can have something with keep-state.

If you have PF disabled, then start it, populate table and then make 
first connection attempt (there should be no states), are you still able 
to connect for a half minute?

You can check tables by: pfctl -vv -s Tables

and check states by: pfctl -vv -s state

Miroslav Lachman