Mixing Class A, B and C IP Networks

  I started building a Windows network around access to a Unix box many years ago. The IP address of the Unix box is 10.0.5.1 so I assumed by default is was a Class A network (Subnet 255.0.0.0). As a result I stared static IPing workstations, printers, etc. with Class A IP addresses (Subnet 255.0.0.0). This particular network is on one segement.

   The other day I posted a question about speed issues and the general replies seems to point to getting rid of the Class A network and going to a Class B or even C. That a Class A network might have too many possible devices for routers and switches to handle efficiently.

   Proceeding in that direction I changed the subnet mask on one server, a few printers and a couple workstation from 255.0.0.0 to 255.255.0.0 to see what would happen. Much to my amazement everything still worked.  My next step was to contact the Unix vendor and verify that, indeed, the Unix box was set to a Class A address. The answer shocked me. I was told that the Unxx box was set to a Class C. 10.0.5.1 with a subnet of 255.255.255.0

   All these years I have been setting new additions up with Class A addresses trying to maintain a pure Class A network and today find out it has always been mixed Class A / Class C. To further complicated things the changes I made invoked a mixed Class A/B/C!

   Obviously the subnet masks aren't nearly as important as I thought them to be. I am mixing all three classes and everything still works. Can someone explaine it to me?

Thanks!
   

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