Front Differential Leak

I have a 2000, 1500 silverado 4X4.  I have a fluid leaking from my front differentials, which I'm assuming to be differential fluids.  Does anyone know if this normally happens or what it's caused by.  Any help would be awesome, I'm mechanically challenged...

Thanks!

i was getting my oil changed the other day at the local walmart.  im sure u all know how that goes... they always seem to miss sumthin or screw sumthin up, so i was standing out there with them.  one of them told me that i had a front differential leak.  i really shouldnt either because the whole front end was rebuilt 15000 miles ago.  an older mechanic that worked there said there is a hose of some sort that runs up to the top of the motor for sumthin.  they can easily get clogged and make the differential leak.  he said it was pretty easy to fix.  he fixed it on the spot in no time.  maybe thats what it is?