What is a /32 bit subnet mask & How can it help me?
So what is a /32 bit mask? A /32 bit mask would be 32 one's, leaving just NO zero's that could be used for host network addressing. In other words, you get just a single IP address. What use is that? Why would I want a network that has no other hosts on it and doesn't even have room for a default gateway IP address to get to other networks? Let me show you how useful this can be...
Say that we have a Cisco router. On that router we want to have a few loopback adaptors. These are virtual network adaptors that are created on the router for special purposes like representing the router as a router ID, testing, and update sources for communication. As the loopback adaptor is directly connected to the router, it doesn't need any default gateway to communicate as a PC would with the same IP address. For this reason, a loopback adaptor in a network with only a single useable IP address can still communicate because it is part of the router. Let's look at some configuration...
Say I take the IP address 188.8.131.52 and subnet it with a /30 (as we talked about above). That would give me 4 IP addresses before I subtract the network and broadcast. I could then take 3 of these IP addresses, assign them as loopback adaptors, then take the 4th IP address (the network), summarize these 3 loopback adaptors into a single IP, and advertise all 3 using a routing protocol. Here is the configuration example:
ip address 184.108.40.206 255.255.255.255
ip address 220.127.116.11 255.255.255.255
ip address 18.104.22.168 255.255.255.255
Router(config)# router ospf 1
Router(config-router)# area 1 range 22.214.171.124 255.255.255.252
Router(config-router)# network x.x.x.x
This would create the 3 loopback adaptors, then summarize them into a single IP address, and send them out to our other OSPF networks to allow those networks to communicate with us and for us to communicate with them.