Note:
I've used these shapes only with Dia-win32-v0.88 and really don't know if they'll work with other versions or platforms (I assume they would but haven't tested it).
 network2.tar.gz  
Vague directions:
  1. Save above file to dia directory 
  2. unzip & untar (once completed there should be a new sheet file in the "sheets" directory and a new shape directory under "shapes") 
  3. Restart dia 
Here's a look at the shapes themselves (images in .png format):
  | generic_router: |  | 
  | generic_switch: |  | 
   | generic_switchengine: |  |