ipfw divert filter for IPv4 geo-blocking

[Dr. Rolf Jansen]

> Am 27.07.2016 um 12:31 schrieb Julian Elischer <julian at freebsd.org>:
> On 27/07/2016 9:36 PM, Dr. Rolf Jansen wrote:
>>> Am 26.07.2016 um 23:03 schrieb Julian Elischer <julian at freebsd.org>:
>>> On 27/07/2016 3:06 AM, Dr. Rolf Jansen wrote:
>>>> There is another tool called geoip , that I uploaded to GitHub, and that I use for looking up country codes by IP addresses on the command line.
>>>> 
>>>>     https://github.com/cyclaero/ipdb/blob/master/geoip.c
>>>> 
>>>> This one could easily be extended to produce sorted IP ranges per CC that could be fed into tables of ipfw. I am thinking of adding a command line option for specifying CC's for which the IP ranges should be exported, something like:
>>>> 
>>>>    geoip -e DE:BR:US:IT:FR:ES
>>>> 
>>>> And this could print sorted IP-Ranges belonging to the listed countries. For this purpose, what would be the ideal format for directly feeding the produced output into ipfw tables?
>>> The format for using tables directly is the same as that used for routing tables.
>>> …
>>> table 5 add 1.1.1.0/32 1000
>>> …
>>> your application becomes an application for configuring the firewall.
>>> (which you do by feeding commands down a pipe to ipfw, which is started as 'ipfw -q /dev/stdin')
>> I finished adding a second usage form for the geoip tool, namely generation of ipfw table construction directives filtered by country codes.
> wow, wonderful!
> 
> with that tool, and ipfw tables we have a fully functional geo blocking/munging solution in about 4 lines of shell script.

Unfortunately, I finally discovered that ipfw tables as they are, are unsuitable for the given purpose, because for some reason ipfw mangles about 20 % of the passed IP address/masklen pairs.

For example:

# ipfw table 1 add 201.222.20.0/20
# ipfw table 1 list
-->  201.222.16.0/20 0

$ geoip 201.222.20.1
--> 201.222.20.1 in 201.222.20.0-201.222.31.255 in BR

$ geoip 201.222.16.1
--> 201.222.16.1 in 201.222.16.0-201.222.19.255 in AR

Effectively, I asked ipfw to add an IP-range of Brazil to table 1, but it actually added another one which belongs to Argentina. This doesn't make too much sense, does it?

For the time being I switched my servers back to geo-blocking with the divert filter daemon.

Best regards

Rolf