Simple Design for a Controllable Ethernet Switch / Router

I want to be able to interrupt an Ethernet link with controllable-length interruptions of perhaps 1msec to a few seconds.  The objective is to get an empirical measure of what interruptions do to various communication links.

I suppose one could do this with a couple of quad 2-input AND gates and a one-shot.  But that seems too clunky and not very flexible should other ideas for applications come to mind.

It occurs to me that an ethernet switch or a router (which includes a switching function of course) might be an ideal platform.  Maybe the interruption control could be from a laptop.  Then the entire implementation might be in software.  

I don't really want to mess with the hardware too much and I probably can't write the code either in any reasonable amount of time.  So, I'm looking for clever ideas that might work and that aren't too demanding of time and energy.  But, of course, a WRT54G with suitably modified DD-WRT does come to mind - but I've never worked on the code even to the point of doing a build.  So, the learning curve seems more demanding than I'd like to invest.

Or maybe a dual NIC PC?  Now, I *can* write batch files.

Ideas?  Maybe a good student project?