ipfw divert filter for IPv4 geo-blocking

[Dr. Rolf Jansen]

> 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. My divert filter daemon is agnostic about this, because the exact ranges are stored in the database and for the purpose of country code lookup the address lookup routine doesn't need to work with netmasks. I choose it this way, because I read some RIR documentation stating that delegated address blocks are not necessarily complete CIDR ranges. Even if the above ranges conform to CIDR, future delegations may be different, and I wanted to stay on the safe side.

So far so good. Now, the actual problem with ipfw tables in the given context is that explicit IP ranges are not accepted but ranges must be given in CIDR notation, and I simply forgot about the tiny detail that CIDR is inherently granular, and that this may of course conflict with my CC/IP database optimization strategy. Without combining adjacencies, the complete database has 165815 instead of 83274 records. Perhaps, I add an option to the db tool for CIDR conformity. In this respect, 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 needs to be broken down.

Best regards

Rolf