F2B is OK, but as JP said, it is a real resource hog.
XT Tables/geoip is far more efficient and effective.
Here's the top countries/offenders I have blocked - there are more a lot more but smaller numbers.
Note I have some services like imaps, ssh, sqpsmtpd set as != ie I ONLY permit from a couple of countries.
Everything else gets blocked - so you can see the worst offenders.
I then add any of those bad boys to my qpsmtpd list unless we specifically get mail from them (yes I'd love to entirely block the USA.....) And I periodically have a peek and update as required.
Numbers of IPs banned (xt_geoip) by country during LAST MONTH
( XX means 'country not found' )
--------------------
CN | 89913 | 21.8%
RU | 37209 | 9.0%
KR | 36845 | 8.9%
BG | 35777 | 8.7%
US | 23310 | 5.7%
HK | 23059 | 5.6%
IN | 22646 | 5.5%
SG | 16710 | 4.1%
JP | 16033 | 3.9%
BR | 12498 | 3.0%
TR | 7875 | 1.9%
UA | 5938 | 1.4%
PL | 5294 | 1.3%
TW | 5100 | 1.2%
VN | 4302 | 1.0%
CZ | 3929 | 1.0%
PH | 3799 | 0.9%
MD | 3627 | 0.9%
ID | 3546 | 0.9%
AU | 3625 | 0.9%
IR | 2765 | 0.7%
SE | 2435 | 0.6%
RO | 2476 | 0.6%
MY | 2537 | 0.6%
IL | 2515 | 0.6%
CA | 2472 | 0.6%
AE | 2569 | 0.6%
IT | 2023 | 0.5%
TH | 1619 | 0.4%
NL | 1791 | 0.4%
IQ | 1631 | 0.4%
DE | 1646 | 0.4%
PK | 1257 | 0.3%
MX | 1200 | 0.3%
MA | 1333 | 0.3%
ET | 1164 | 0.3%
BD | 1223 | 0.3%
AR | 1278 | 0.3%
Here's the bans - note that I only permit access to a couple of services from 3 countries - our UK office, me here in Spain, and the server location in France.
If I travel I will add any specific countries temporarily.
Global
Current list of banished country codes : == CN,IN,RU,BR,KR,RO,LT,AR,TW,VN,JP,HK,ID,PH,BD,CZ,BO,TH,MX,MD,IL,CO,BG,SG,RS,PL,IR,UA,EE,AE,BY,NG,TR,AW,AM
Per service
Name PORT STATUS Access Blacklist
ftp 21 disabled private != GB,ES,FR
httpd-e-smith 80 enabled public ==
imap 143 enabled private != GB,ES,FR
imaps 993 enabled public != GB,ES,FR
modSSL 443 enabled public ==
pop3 110 disabled private != GB,ES,FR
pop3s 995 disabled private != GB,ES,FR
qpsmtpd 25 enabled public == CN,IN,RU,BR,KR,RO,LT,AR,TW,VN,JP,HK,ID,PH,BD,CZ,BO,TH,MX,MD,IL,CO,BG,SG,RS,PL,IR,UA,EE,AE,BY,NG,TR,AW,AM
sqpsmtpd 465 enabled public != GB,ES,FR
sshd 2222 enabled public != GB,ES,FR
I have F2B ibstalled on that server but it is it disabled - geoip does all the heavy lifting these days.
HTH.