ipfw divert filter for IPv4 geo-blocking

[Dr. Rolf Jansen]

> Am 29.07.2016 um 06:50 schrieb Julian Elischer <julian at freebsd.org>:
> On 29/07/2016 5:22 PM, Julian Elischer wrote:
>> On 29/07/2016 4:53 PM, Dr. Rolf Jansen wrote:
>>>> Am 28.07.2016 um 23:48 schrieb Lee Brown <leeb at ratnaling.org>:
>>>> 
>>>> That makes sense to me.  Your /20 range encompasses 201.222.16.0 -
>>>> 201.222.31.255.
>>>> If you want 201.222.20.0-201.222.31.255, you'll need 3 ranges:
>>>> 
>>>> 201.222.20.0/22 (201.222.20.0-201.222.23.255)
>>>> 201.222.24.0/22 (201.222.24.0-201.222.27.255)
>>>> 201.222.28.0/22 (201.222.28.0-201.222.31.255)
>>> 
>>> Ian, Julian and Lee,
>>> 
>>> Thank you vary much for your responses. In order not bloat the thread, I answer only to one message.
>>> 
>>> I found the problem. As a matter of fact, the respective IP ranges in the LACNIC delegation statistics file are 3 adjacent blocks with 1024 addresses, i.e. those that you listed in your message above:
>>> 
>>> $grep 201.222.2 /usr/local/etc/ipdb/IPRanges/lacnic.dat
>>> lacnic|BR|ipv4|201.222.20.0|1024|20140710|allocated|164725
>>> lacnic|BR|ipv4|201.222.24.0|1024|20140630|allocated|138376
>>> lacnic|BR|ipv4|201.222.28.0|1024|20140701|allocated|129095
>>> 
>>> However, my database compilation combines adjacent blocks with the same country code, and the ranges above turn into one block of 3072 addresses, which obviously doesn't have a valid netmask - log(3072) = 11,5849625.
>>> ...
>>> ..., it is not sufficient to forget about optimization but I need to check also whether, the delegation files contain already some non-CIDR ranges, which need to be broken down.
>> 
>> there is code to take ranges and produce cidr sets.
>> 
>> We used to have exactly that code in the appletalk code before we took it out. Appletalk uses ranges.
>> https://svnweb.freebsd.org/base/release/3.2.0/sys/netatalk/at_control.c?view=annotate#l703 
> 
> though htat uassumes input in the form af an appletak sockaddr..
> there is also this python module
> https://pythonhosted.org/netaddr/tutorial_01.html#support-for-non-standard-address-ranges
> 
>> maybe you can find other versions on the net.
>> however if you fully populate the table, you will get the correct result because more specific entries will
>> override less specific entries. To do that you would have to have a way to describe to your program what
>> value each table entry should output.
>> If you did what you do now, then you would specify the value for the required countries, and give a default falue for "all others".
>> aggregation of adjacent ranges with same value would be an optimisation.

Don't worry, breaking down an arbitrary IP-range into a CIDR conforming set of ranges, doesn't seem too difficult. I quickly hacked into the   for() loop for table generation in geoip.c a nested do while() for if necessary breaking down the given range:

for (i = 0; i < n; i++)
{
   if (!*ccList || findCC(CCTable, sortedIPSets[i][2]))
   {
      ipv4_lo = sortedIPSets[i][0];
      do
      {
         m = intlb(sortedIPSets[i][1] - ipv4_lo  + 1);
         while (ipv4_lo  % (k = (int)lround(exp2(m)))) m--;
         printRange(ipv4_lo, 32 - m, table_number, table_value);		     
      }
      while ((ipv4_lo += k) < sortedIPSets[i][1]);
   }
}

This seems to work as expected, however, I need to check this more carefully (in the course of the weekend) until pushing it to GitHub. At the first glance, the tables become quite large. For example, the table for Brazil of 824 joined entries is bloated to 6621 CIDR records.

Once I came to a conclusion, I will post it to this mailing list.

Best regards

Rolf