What method borrows bits from the host field of an IP address to create a subnet?

The correct method that borrows bits from the host field of an IP address to create a subnet is Classless Inter-Domain Routing, commonly referred to as CIDR. This technique allows for a more flexible and efficient allocation of IP addresses compared to traditional classful addressing, which strictly defines classes of networks (A, B, C) with fixed subnet masks.

CIDR enables the division of a network into subnets by allowing the use of variable-length subnet masking (VLSM). This means that the number of bits used to represent the network and the number of bits used for hosts can be customized. By borrowing bits from the host portion, CIDR can accommodate more subnets without wasting IP addresses, effectively increasing the number of available networks and better aligning address assignments with actual needs.

Classful subnet masking, while related, does not allow for such flexibility, as it operates under the rigid constraints of predefined subnet boundaries. Virtual Private Networking and Virtual Local Area Networking pertain to different concepts in networking, such as creating secure virtual networks over public connections or managing local networks, rather than directly addressing the method of subnetting IP addresses.