Recently i came to know that, we can configure a /31 ip addressess on a point-to-point networks ,when i first learned this i wondered how the /31 is configured on p-to-p so i tried it on GNS3 and found a very interesting results, cisco added this feature in IOS 12.2 and later versions.
Based on the above explanation check this out
R1:
R2:
Reachability bet'n R1 and R2:
Point-to-point links only have two endpoints (hosts) and do not require broadcast support because any packet that is transmitted by one host is always received by the other host. Therefore the all-ones broadcast IP address is not required for a point-to-point interface.
The simplest way to explain RFC 3021 is to say that the use of a 31-bit prefix (created by applying a 31-bit subnet mask to an IP address) allows the all-zeros and all-ones IP addresses to be assigned as host addresses on point-to-point networks. Prior to RFC 3021 the longest prefix in common use on point-to-point links was 30-bits, which meant that the all-zeros and all-ones IP addresses were wasted.
The below table shows an example of the two IP addresses that are created when a 31-bit (otherwise known as 255.255.255.254 or /31) subnet mask is applied to the IP address 192.168.1.16.
Based on the above explanation check this out
R1:
R2:
Reachability bet'n R1 and R2:
