Which of the following would be the MOST efficient subnet mask for a point-to-point link?
A. /2S
B. /29
C. /31
D. /32
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/31 networks are used for point-to-point links. This was standardized in December 2000, when RFC 3021, Using 31-Bit Prefixes on IPv4 Point-to-Point Links was published. The key is that there is no need for broadcast on a point-to-point link because every other host on a point-to-point network will get the traffic, anyway. Ordinarily, using /30 for point-to-point networks wastes half of the network addresses. This can really add up when your business has a lot of point-to-point links. You can cut the number of used addresses in half, doubling the number of point-to-point links with the same number of addresses.
Niks is correct, the question helps by not including /30 as an option.
A /31 is used for point to point communications where only two IP addresses are needed. Previously, a /30 was used, but it is grossly inefficient. A /30 has two usable IP addresses (4 total), a /31 has 2 addresses total (0 usable if we need a bcast and network id) The network and broadcast address is not needed in the point to point link though hence we can use /31.
It can’t be /31, because only one usable IP address you are going to get, for point-to-point you at least required two useable host addresses
/31 gives you two usable IP addresses 🙂
Why C??? what makes it better?
The answer is letter C because a point to point link only needs two IP address. Remember that the bit zero is for the host while the the value of one is for the network.