your pc has some sort of sleep mode that activates or so ?
dosbox in its default configuration doesn't do a thing regarding internet or any network at all.

I can't find any setting in Windows XP that makes the connection sleep other than the system itself sleeping with inactivity (but that doesn't happen). Any idea where that is?

Thanks

Probably Device Manager -> Your Adapter Properties -> Power Management.

do you actually get any visible notification when this happens (e.g. network connection icon's status is changed to "disconnected")? or do your apps just lose connectivity and regain it when you close DOSBox?

"connection cuts" and "won't reconnect" are a bit vague...

Sorry. My apps (browsers, chat, etc.) lose connectivity and I can see the connection icon in the corner show that it's disconnected.

And I don't have to close DOSBox for it to reconnect. As soon as I leave DOSBox and make another app active, it reconnects. It only goes down when DOSBox is open and is being used.

do you run DOSBox in a window or full-screen? Please check if this happens in both modes, or just one of them.
(if fullscreen - do any other apps/games cause the same effect if you run them full screen?)

also, some info on your Windows version / hardware?

I'm using Windows 7 Home Premium.

I run it only in window, never in full-screen. I've never noticed any other application do this to the connection.

No one ever encountered this with dosbox yet, and believe me people would have noticed that 😉
What version of Dosbox and where did you download it?

I'm using DOSBox-0.74.
Got it from DOSBox.com.

It's very strange. It's the only program that does this and when I leave it to go to another window, Windows reconnects. But it won't connect as long as I'm in DOSBox.

So did you check out the power management functions? Probably even some 3rd party
application monitors something and wrongly triggers a "nobody is using the PC" event.