linux - how to tell if iptables are now blocking a url -

i using ubuntu , have blocked outgoing connections few ips iptables. how can tell if attempt violate rule made (e.g. process trying access ip). there kind of event/callback mechanism (preffered)? there log can track?

iptables -l -v 

will display current iptables configuration, along packet , bytes counters matched each rule.

alternatively, can insert new rule iptables, log packets matching rule: http://www.thegeekstuff.com/2012/08/iptables-log-packets/