Thirty-one-bit subnets were first proposed in RFC 3021, which was primarily motivated by the potential for public address space conservation. Recall that shrinking a /30 subnet to a /31 effectively doubles the number of point-to-point links you can address from a finite range. Cisco IOS has supported /31 subnets for point-to-point links since release 12.2(2)T. A thorough explanation of the feature is presented here.
We can put this theory into practice by addressing a point-to-point connection between two routers as 10.0.0.0/31. Note that this even applies to Ethernet interfaces, technically a broadcast medium.
Router1(config)# interface f0/0 Router(config-if)# ip address 10.0.0.0 255.255.255.254
% Warning: use /31 mask on non point-to-point interface cautiously
Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/16/20 ms
show ip route
10.0.0.0/31 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/0