ZoneAlarm Security Alert - My own ISP?

I often get alerts like this:

ZoneAlarm Security Alert
The firewall has blocked Internet access to your computer (NetBIOS
Session) from
( (TCP Port 3436) [TCP Flags: S].

Since the city name embedded therein is often my own (Miami), and I'm a
dial-up user, I suspect these might be coming from Earthlink, my own ISP.

How can I determine whether they are from Earthlink and whether to let
them through? What about other NetBIOS Session alerts?

If I click on "Don't show this dialog again," will I stop seeing all
security alerts? Should I?

Marshall Price of Miami
Known to Yahoo as d021317c