And ifconfig -a to see what network cards you have on which IP addresses in the first place. Perhaps route can help you figure out what connections use which routes.

System logging depends a lot on the platform, if dmesg is uninformative then messages.log or syslog.log might be worth looking at, as well as other files in /var/log (or wherever you have the logs). /etc/syslog.conf or some approximation will tell you how logging is set up but again, this is somewhat system-dependent; there are different syslog daemons and different conventions for how they are usually configured.