[oclug] Curiosity / learning question?

[William Case]

Hi;

I am not concerned but just curious.  I have a little gui running that
monitors my network (Internet) usage.  Every now-and-then it shows a
surge of network activity that I can't relate to email usage, browsing,
or cron.

What tools would I use to trace what is causing this activity?  And
generally, (don't need details -- I can use the 'man' page) how would I
go about using them when a surge occurs?  

(I haven't used the word 'surge' in a long time -- I wonder why it
springs to mind just now?)

-- 
Regards Bill