Calculating Subnets

Question

I have just set up my first home LAN, and I want to start playing around with some basic networking concepts. Specifically, I would like to create two subnets. Now although I want these subnets to be meaninful and to serve a real function, I want them more so as to get practice setting up my first subnets.

Since I'm really new to networking, the only use I can think of for subnets on a home LAN might be to have a range of "public" IP addresses that can be reached from outside my private home LAN, and a range of IPs that would be "private" (internal/intranet).

I was thinking that if I gave my network a netmask of 255.255.255.128, that it would split all available IP's into 2 groups: a "public" range in between 192.168.1.[0,127] and a "private" range between 192.168.1.[129,255].

Have my assumptions thus far been correct? If not, please correct me and steer me in the right direction (perhaps my netmask is wrong?).

Answer 1

Your calculations are mostly correct – using 255.255.255.128 would result in two ranges of 128 addresses, 0-127 (network 192.168.1.0/25) and 128-255 (network 192.168.1.128/25).

However, as long as the network is in the 192.168.0.0/16 range, it will not be reachable from outside your LAN; according to RFC 1918 this range is reserved for private networks and will not be routed over the public Internet. (Even if it were, which of the millions of LANs with identical private addresses would the packets go to?)